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Trends in biomass of coral reef fishes, derived from shore-based creel surveys in Guam.

Abstract--Coral reef fisheries have a cultural, economic, and ecological importance and sustain the societal well-being of many coastal communities. However, the complexities of the multigear, multispecies fisheries that target coral reef species pose challenges for fisheries management. We focus on the Guam shore-based coral reef fishery 1) to evaluate the characteristics of the past and recent fishery in terms of catch composition and effort per gear type and 2) to reconstruct the reef-fish population in shallow (depths [less than or equal to] 30 m) water during 1985-2012. To accomplish this, we used the results from a detailed creel survey conducted by the Guam Division of Aquatic and Wildlife Resources. The total estimated effort has stayed more or less stable; however, the estimated total catch has dropped from an annual mean of 100 metric tons (t) during the period 1985-1990 to 37 t during the period 2007-2012. Catch per unit of effort (CPUE) declined for most gear types between the 2 time periods. Reconstruction of historical targeted fish biomass, based on CPUE, showed a general decrease in biomass from 1985 to 2012. Biomass quickly dropped to about half of the 1985 values, then leveled off for a decade before declining again beginning in 2003 and continuing through 2012.


Coral reef fishing is an important activity for the social and economic welfare of many coastal communities (Dalzell et al., 1996; Moberg and Folke, 1999). Both commercial and recreational fishing provides jobs, and fishing expenditures generate millions of dollars in sales revenues and value-added benefits to the states and territories of the United States that have coral reefs (Craig, 2008). Healthy fish stocks also support marine recreational activities, such as scuba diving (Parsons and Thur, 2008). Furthermore, in many Pacific islands, coral reef fisheries serve vital nonmarket functions, such as building social and community networks, perpetuating fishing traditions, and providing food for local communities (Dalzell et al., 1996; Plaganyi et al., 2013; Zeller et al., 2015).

Despite their socio-economic importance, reef-associated fisheries have received relatively little attention, especially when compared with pelagic fisheries (Sadovy, 2005), and comprehensive data for reef fisheries are often lacking (Warren-Rhodes et al., 2003; Houk et al., 2012). Furthermore, reef fisheries are particularly challenging to assess because they typically are more complex than pelagic fisheries (Dalzell, 1996). Generally, multiple gear types are used in reef fisheries, and each gear type has its own selectivity and targets multiple species, resulting in overlaps in the composition of the landings of reef fisheries (Dalzell, 1996; McClanahan and Cinner, 2008). A global comparative study of reef-fish landings and their ecological footprint concluded that 55% of coral reef fisheries in 49 island countries were unsustainable, on the basis of the difference between actual reef-fish landings and an annual coral reef maximum sustainable yield value of 5 metric tons (t)/[km.sup.2] (Newton et al., 2007). A more recent study in just the western Pacific Ocean found a decline in catches of artisanal fisheries in most Pacific countries (Zeller et al., 2015). The potential, and evidently current, widespread overexploitation of reef fisheries highlights the need for proper management of these resources.

We focused our study on trends in catch and effort of the reef-fish fishery of Guam, which is the largest island in Micronesia and the most southerly island of the Mariana Archipelago in the western Pacific Ocean. As in many other Pacific islands, fish have been important sources of food since the first human settlements (Hensley and Sherwood, 1993). From prehistoric to recent times, there have been at least 52 different fishing methods used on Guam (Kerr (1)), and some of these traditional practices, such as the seasonal harvest of bigeye scad (Selar crumenopthalmus), fishing with surround nets, and throw- or cast-net fishing, are all still in use (Hensley and Sherwood, 1993). Modern fishing of reef fishes on Guam is best considered a recreational or subsistence fishery, and pelagic fisheries dominate the commercial landings there (Allen and Bartram (2)). A study of households (van Beukering et al. (3)) conducted in 2007 reported that 35-45% of respondents were active fishermen and that 28% of the fish consumed were caught by family members or friends (the 400 respondents in this study included the main ethnic and socioeconomic groups in Guam). Fish make up an especially important source of food for large cultural events, such as baptisms, weddings, and village fiestas (Pinhey et al., 2006).

Apart from their cultural and socioeconomic significance, reef-fish populations can play an important role in enhancing the resilience of reef ecosystems (i.e., the capacity of reef ecosystems to sustain and recover from a human-induced disturbance). For example, abundant and diverse assemblages of herbivorous fishes are effective at reducing algal biomass and at opening up space for settlement of coral recruits (McClanahan, 1997; Mumby et al., 2007a; Mumby and Harborne, 2010; Graham et al., 2011, 2013; Mumby et al., 2013).

Unlike many other countries and territories with coral reefs, Guam has long-term (>50 years) data for its coral reef fishery that have been obtained from creel surveys conducted by the Division of Aquatic and Wildlife Resources (DAWR), Guam Department of Agriculture. This creel survey program provides information on overall harvest and catch per unit of effort (CPUE). In the mid-1980s, DAWR adapted their existing creel survey program to better reflect changes in fishing practices. This survey program now encompasses an offshore boat-based fishery and an inshore shore-based fishery. The boat-based fishery focuses mainly on trolling for pelagic species and bottom fishing for species of commercial value in deepwater (depths >30 m), and the shore-based fishery targets reef fish in shallow-water (depths [less than or equal to] 30 m) primarily for recreational, subsistence, and cultural reasons (Appendix 1).

Previous analysis of these creel survey data indicated that Guam has a low fishery yield compared with other Pacific islands (Dalzell, 1996). A more recent study concluded that there had been an 86-94% decline in recreational fish catches over the previous 50 years (Zeller et al., 2007, 2015). Other studies in Guam have documented a similar decreasing trend in both the numbers of fish landed and the mean size at capture (Myers, 1993; Mcllwain and Taylor (4); Lindfield et al., 2014). Hensley and Sherwood (1993) conducted a comprehensive analysis of just the shore-based fishery in Guam from 1982 through 1991. Their main conclusions were that the fishery had changed because of the implementation of more modern fishing techniques and a switch from a traditional economic system (barter, catch what you eat) to a more western one (dollar based, sell for profit) and that these changes led to more pressure on reef resources and to overharvesting the most frequently targeted species.

The perception that reef-fish stocks in Guam are depleted has been corroborated by a recent large-scale study based on visual-survey data; this study concluded that reef-fish biomass around Guam was 66% below what would be expected in the absence of human perturbations (Williams et al., 2015). Other studies with visual-survey data have noted the relative scarcity of large-bodied fishes around Guam and other populated islands in the Mariana Archipelago, compared with the lightly or unpopulated islands in this archipelago (Richards et al., 2011; Williams et al., 2011). A paucity of large fishes often is indicative of overfishing (Friedlander and DeMartini, 2002; Fenner, 2014).

Although these studies reflect the declining trend in catch and a depletion of the reef-fish biomass at Guam and provide evidence of the effects of fishing on the life history of some taxa (e.g., parrotfishes [Chlorurus spp., Scarus spp.]; Taylor and Choat, 2014), time series for the total biomass of reef-fish populations and changes in the composition of reef-fish catches have not been quantified. These potential declines in fish populations reduce overall biomass, reproductive potential, and ecosystem function (Taylor et al., 2012; Mumby et al, 2013; Williams et al., 2015). We aimed to improve our understanding of the effects of this socially and culturally important fishery, using the shore-based creel data 1) to compare catch composition in the early years (1985-2000) with the composition in the recent years (2007-2012) and 2) to reconstruct trends in the population biomass of functional groups of reef-fish species over the period 1985-2012 by using recent visual-survey data as a relative index.

Materials and methods

Fishery data source: creel surveys

The creel surveys conducted around Guam by the DAWR included 2 distinct fisheries: the shore-based fishery and the boat-based fishery. This division of the data and the terms used to describe its 2 parts are widely used in Guam, including among fishery management agencies; therefore, we used them in our study. It is important to note that the shore-based fishery includes fishing from boats when boats are launched from shore (Appendix 1). The shore-based fishery differs from the boat-based fishery in several key aspects. In general, larger boats are used in the boat-based fishery, which primarily targets pelagic or bottomfish species, and predominantly is a commercial fishery. However, the boat-based fishery landings also include a substantial amount of reef fishes (Appendix 1). We chose not to include boat-based fishery results in our study for 2 reasons. First, boat-based fishing effort is recorded in trip hours, and shore-based fishing effort is recorded in gear hours; therefore, it was difficult to generate CPUE for just the fishing of reef fishes with the boat-based fishery to include in our analysis (Appendix 1 Figure 1). Second, trends in the catch from spearfishing in the boat- and shore-based fisheries are very consistent, indicating that, at least for reef-fish species, these trends reflect changes that are common among the targeted stocks (Appendix 1 Figure 2).

Categorization of species into functional groups

We analyzed records in the catch database of the shore-based component of the creel survey program for Guam (DAWR data obtained from a database maintained by the Western Pacific Fisheries Information Network [WPacFIN (5)], NOAA Pacific Islands Fisheries Science Center [PIFSC]). A total of 580 species or families appeared in the records. For some taxa, there were very little data; therefore, we grouped data of all taxa on the basis of their taxonomy, ecological function, and importance to fisheries, as shown in Table 1.

Collection of catch and effort data

The shore-based surveys of the DAWR creel survey program are designed to collect information on effort and catch for all shore-based fishing activities (Hensley and Sherwood, 1993; Zeller et al., 2007). There are 2 parts in the shore-based fishery: 1) visual surveys to establish the number of people participating in fishing activities (which are called participation surveys) and to collect data on the type of fishing activities observed (effort data) and 2) interviews of a sample of fishermen to collect data on the duration of fishing activities and numbers and sizes of fish caught (catch and effort data). Effort was recorded as hours fished per gear type (gear hour) and catch was recorded as the number and weights of fish caught per hour fished per gear type (Oram et al. (6)). Data from restricted areas (Appendix 2) were collected during aerial surveys conducted on the same 2 days that the participation surveys took place (Oram et al. (6)).

Catch values for the shore-based fishery are provided on a voluntary basis by fishermen to creel surveyors. Effort primarily is based on the visual surveys of fisherman participating in fishing activities, with details about the actual hours of fishing coming from interviews. When conducting surveys, DAWR staff attempt to interview fishermen for each type of gear observed during the participation surveys (Appendix 3 Table 1). However, interviewers are not always able to collect information on all types of gear. For example, since 2005, many spear fishermen have refused to participate in the creel surveys (Lindfield et al., 2014). Consequently, the number of snorkel-spear interviews has declined from an average of 30 per year in 1985-90 to an average below 8 interviews per year during 2007-2012 (Appendix 3 Table 1), and this decline is unfortunate because counts of observations made during participation surveys indicate that spearfishing represents one of the most used fishing method of the shore-based fishery in terms of effort (Bak (7)). Because collecting data on CPUE for most of the taxa and for most of the gears was difficult and infrequent, results dependent on the CPUE statistics were grouped at the family taxon level and are best considered as relative measures.

Estimates of total catch, total effort, and catch per unit of effort

The staff of the PIFSC program WPacFIN who collaborates with the DAWR, use an expansion algorithm to extrapolate results of the interviews of a sample of fishermen from shore-based surveys to estimates of island-wide catch and effort (Bak (7)). For comparisons of the fishery characteristics of the late 1980s with those of recent years, we used these WPacFIN estimates of aggregate effort and catch to examine possible shifts in fishing activities and catch composition. We somewhat arbitrarily chose to pool across 6-year periods to represent the early and recent periods of fishery data. It was important to pool across multiple years to increase the amount of data available, especially for the recent period (2007-2012); data were pooled also because of large interannual variability.

Fishery-independent surveys: calculation of biomass

In 2011, scientists of the Coral Reef Ecosystem Program of the NOAA Pacific Islands Fisheries Science Center conducted an intensive, short-term stationary-pointcount survey (133 sample sites) of shallow (depths [less than or equal to] 30 m), hard-bottom coral reef areas around Guam. The methods used in this survey are described in detail in Williams et al. (2012) and briefly outlined here. Data of fish abundance and size distribution came from random visual surveys stratified into 3 depth ranges (<6 m, 6-18 m, and 18-30 m). Because roving apex predators, such as sharks (Carcharhinidae) and jacks (Carangidae), are generally not well sampled by divers in small-area surveys, information on abundance and size distribution of species of roving apex predators came from broad-scale towed-diver surveys conducted around Guam in 2007, 2009, and 2011 by the Coral Reef Ecosystem Program (Richards et al., 2011).

Length estimates of fishes from visual censuses were converted to weight by using allometric length-weight conversion:

W = [a.sup.*][TL.sup.b], (1)

where a and b = constants;

TL = total length in millimeters; and

W = wet weight in grams.

Length-weight parameters came from Taylor, (8) Taylor et al. (2012), Taylor and Choat (2014), FishBase (Froese and Pauly (9)), and Nadon et al. (2015). In cases where length-weight information did not exist for a given species, parameters from congeners were used.

For each taxon, trophic classification was based on diet information, largely from FishBase. Using biomass density from the diver surveys and known areas of habitat from GIS maps, which were adapted within the Coral Reef Ecosystem Program from other GIS products (NCCOS (10)), we estimated biomass per functional group and for all fishes combined; these estimates were minimum values because cryptic and nocturnal fishes generally are undercounted by daytime visual surveys.

Estimation of catchability and reconstruction of historical fish biomass

A reconstructed time series of reef-fish biomass can be estimated from a CPUE time series and gear-specific catchability coefficients (Haddon, 2001). Generally, it is assumed that catch rates are linearly related to stock biomass and that the catchability coefficient is constant (Haddon, 2001). For the reconstruction in our study, we estimated the relationship between CPUE (as a proxy for relative biomass) and fish population biomass by incorporating a fishery-independent estimate of biomass in 2011, as described in the previous section. This approach requires that the CPUE data come from a representative sample, where the catch was taken in a consistent way by one or more fishing methods. The CPUE data used in this study had limitations, namely that the CPUE data for taxa infrequently encountered by any gear type in the DAWR creel surveys were not reliable; infrequently encountered taxa included many reef fishes, although the CPUE data have been shown to be reliable for some of the jacks (Bak Hospital (11)). Because of these limitations, in addressing federal management by means of annual catch limits, the CPUE time series available from the creel surveys were rejected for reef-fish stock assessments (Sabater and Kleiber, 2014). However, in this study, we were interested not in absolute abundance or stock size but in temporal trends of fish populations and relative differences between the late 1980s and recent years, and these data are suitable for that purpose.

In the shore-based surveys, 9 gear types were differentiated (Table 2). The gear type hooks-and-gaffs was used almost entirely to catch octopus (98% of hook-and-gaff landings for the period 1985-2012), and the type other methods included gears used in gleaning for invertebrates and algae (60% and 16% of total landings per respective gear type; WPacFIN (5)) (Hensley and Sherwood, 1993). Therefore, for the historical reconstruction of reef-fish biomass, we excluded catch and effort data for the gear types hooks-and-gaffs and other methods from analyses. We also excluded catch and effort data for the gear type cast nets from estimation of reconstructed reef-fish biomass because cast nets were used primarily to catch juvenile fishes (i.e., rabbitfishes [Siganus spp.], goatfishes [Mullidae], and jacks) that can be hyper-abundant in shallow, sandy bays that were not part of the sampling domain for the fishery-independent visual surveys from which we took data. Appendix 4 shows the number of times each of the exploited fish groups defined in Table 1 were caught by fishermen interviewed for the creel survey program; data were broken out by gear type and pooled into 3-year time periods.

During the interviews for the creel surveys, fishing is reported per region per day type (i.e., weekday or weekend days; for a map of the regions used for creel surveys, see Appendix 2 Figure). Therefore, we first compared annual average CPUE by region and day type, using a Welch 2-sample i-test for cases in which we had at least 6 years of CPUE data with at least 3 observations per year (Appendix 3 Table 2). On the basis of the results of these tests (Appendix 5), we decided to aggregate CPUE data over regions and day types for subsequent analyses. Even with such treatment, for some gear types, interview data were sparse, especially for surround net fishing, scuba spearfishing, and drag-net fishing (Appendix 3 Figure). Moreover, for drag-net fishing and scuba spearfishing, some values were missing. We calculated CPUE for missing data as the average of the 3 previous years (Appendix 3 Table 2).

We based our reconstruction of historical relative fish biomass on the assumption that CPUE (I), itself expressed as catch (C) divided by effort (E), is linearly related to biomass (B) in year t:

[C.sub.t]/[E.sub.t] = [I.sub.t] = q x [B.sub.t]. (2)

We further assumed that the gear-specific catchability coefficient (q) was constant. Therefore, although catchability varies depending on the experience of the fisherman and other factors, we assumed that there is no overall change in catchability through time. We also assumed that the observational errors of CPUE were lognormal, were multiplicative, and had constant variance. Although these conditions are unlikely--given the small extent of actual interview data for many taxa and strata, with the resulting high incidence of zeros and Poisson-like distributions with outliers--these assumptions were adopted to allow a simple approximation. If there are n years in an analysis, the best estimate of the constant q is the geometric average of the time series of ratios of CPUE and biomass ([I.sub.t]/[B.sub.t]), and it can be calculated with the following equation (Haddon, 2001):


This method is well established for pelagic fisheries (Haddon, 2001), and we further assumed that it is applicable for the complex reef fishery when we parsed out catches and effort by gear type. We used the fishery-dependent statistics to estimate CPUE per gear type per year and fishery-independent data to estimate biomass (as detailed previously). However, we had reliable biomass estimates only for 2011. Because we required an n of at least 3, we assumed that the mean biomass was the same between 2010 and 2012 and equivalent to that derived from the stationary-point-count surveys conducted in 2011. For each gear type, we derived smoothed estimates of q in accordance with Equation 3, with an n of 3, I equal to the gear-specific annual CPUE values for 2010-2012, and B equal to the summed biomass of functional groups exploited by the gear type. Information on which functional groups to include in the summed biomass was derived from the catch composition of total landings for 1985-2012. Functional groups that composed more than 10% of the catch per gear type were included: for example, over this time span, 23% of the targeted browsers (e.g., unicornfishes [Naso spp.]), 12% of the target grazers (most surgeonfishes [Acanthurus spp.]), and 37% of the roving piscivores (e.g., jacks) were caught by gill-net fishing; therefore, we added the estimates of biomass from the visual surveys for those 3 groups for the calculation of q for gill-net fishing.

To reconstruct the annual total biomass for the period 1985-2012, we divided the gear-specific CPUE for each year by the estimated gear-specific catchability q, using Equation 2 rewritten as [B.sub.t] = [I.sub.t]/q. Within each year, we then calculated the reconstructed biomass for each functional group by multiplying the annual total biomass estimate by the species composition observed in 2011. For example, in 1985, the total biomass was estimated at 10,025 t, and excavators (large-bodied parrotfishes [e.g. Chlorurus spp.]) composed 1.3% of the species composition in 2011; given those values, the biomass of excavators in 1985 was estimated at 130 t (10,025x0.013). Therefore, the results of this analysis indicate trends in relative fish stock size over time, with the assumption of constant catchabilities and species composition.


Past and recent periods: comparing total catch, effort, and catch per unit of effort

Hook-and-line was the most commonly used gear type, accounting for 59% of total estimated annual effort in 1985-1990 (past) and 71% of total estimated annual effort in 2007-2012 (recent) (Table 2). Cast nets were the second most often used gear type, accounting for ~14% of total annual estimated effort in both time periods. Effort for all other gear types was reported less frequently in recent years than during the earlier time period, and declines in effort between the time periods ranged from 16% for drag net fishing to 87% for hook-and-gaff fishing (Table 2). The decline in effort for those other gears was balanced by a 14% increase in effort for hook-and-line fishing, resulting in an estimated total fishing effort that was similar in the 2 time periods: an annual mean of 217,420 gear hours for 1985-1990 in contrast to an annual mean of 205,850 gear hours for 2007-2012.

Reported catch was considerably higher during the period 1985-1990, with an estimated mean annual total catch of 100 t, compared with an average of 37 t in the period 2007-2012 (Fig. 1, Table 2). The most noteworthy difference between the 2 time periods was a 74% decrease in the catch for cast net fishing despite little change in effort and a 21% decrease in the catch from hook-and-line fishing despite a 14% increase in effort. The largest decline in catch was for spearfishing: reported catch of snorkel spearfishing and scuba spearfishing dropped by 87% and 94%, respectively (with reported effort declining by 36% and 90%, respectively). However, the observed decline in estimated spearfishing effort and landings is certainly related to the refusal of some spear fishermen to participate in creel surveys since around 2005 (Lindfield et al., 2014).

Based on the total landings for the shore-based fishery and the use of 95 [km.sup.2] as the reef area at depths of 0-30 m around Guam (determined with the adapted habitat maps of hard- and soft-bottom habitats), annual yields dropped from 1.30 t/[km.sup.2] during 1985-1990 to 0.58 t/[km.sup.2] during 2007-2012. For reef-associated fishes (i.e., excluding pelagic fishes, invertebrates, and non-reef-associated species), annual yield was 1.59 t/[km.sup.2] and 0.74 t/[km.sup.2], respectively, and 71 [km.sup.2] were used as the reef area for hard-bottom habitat at depths of 0-30 m around Guam (determined with one of the adapted habitat maps).

Hook-and-line fishing was assumed to be the most reliable data source because hook and line gear was the dominant gear type in the catch and effort records. On the basis of the fishery data for this gear type only, landings showed no clear trend over time, albeit with large annual fluctuations (Fig. 2A). However, landings of species other than bait fishes (e.g., bigeye scad [Selar crumenophthalmus]) showed a downward trend (Fig. 2A). The mean annual CPUE, based on the unexpanded interview data, for hook-and-line fishing varied because of the interannual fluctuation in bait fish landings, but the overall mean CPUE decreased 49% between the 2 time periods, from an annual mean of 0.15 kg/gear hour (standard error [SE] 0.02) for 1985-1990 to 0.08 kg/ gear hour (SE 0.02) for 2007-2012 (Table 2, Fig. 2B).

CPUE was also significantly lower in the recent time period for gill net fishing and snorkel spearfishing, compared with levels in the past. The only gear type for which CPUE did not significantly decrease (P=0.1) was the gear type other methods (i.e., reef gleaning), although CPUE for that type trended downward (Table 2). For the remaining gear types, there was not enough information to statistically compare differences between the time periods (annual number of interviews was less than 3); however, for all gear types, except hooks-and-gaffs, mean CPUE was lower in the recent time period and the overall trend showed a decline in CPUE (Appendix 3 Figure).

Species composition of landings

In most years, combined landings of browsers (predominantly unicornfishes and rabbitfishes) and invertebrate feeders (predominantly goatfishes and emperors [Lethrinus spp.]) made up >40% of the total catch (Table 3). In comparison with catch data from the late 1980s, data for 2007-2012 showed a shift from the largest group being target browsers to the largest group being pelagic bait fishes. In general, the relative contribution of bait fishes increased over time, with bait fishes making up as much as 72.6% of the total catch (in 2012). The humphead parrotfish (Bolbometopon muricatum) was reported only in catches in 1985, and the humphead wrasse (Cheilinus undulatus) was reported in, on average, 0.4% of the catches during the period 1985-1990 but dropped to <0.1% of catches during the period 2007-2012. Roving piscivores, on the other hand, increased on average from 5.6% to 17.1% of the catch over the same time periods. The available data do not include information on fish size; therefore, it is not clear whether this increase was a result of increases in the seasonal fishery for juvenile jacks or in catches of mature jacks. However, because the gear types that target juveniles--hook-and-line and cast net--had increased catches and because catches by gill net, which does not target juvenile jacks, dropped by half, it appears that the increase in catch of roving piscivores was likely due to an increased catch of juveniles.

Reconstruction of fish biomass by functional group

Results from initial analysis of unexpanded data, from the interviews as part of the shore-based surveys, indicate that only for the CPUE for hook-and-line fishing in regions 1 and 2 on the eastern coast of Guam (for a map of the regions used in creel surveys, see Appendix 2 Figure) was there a difference (P<0.05) between day types (weekdays and weekend days), and there was no significant difference in CPUE between regions (Appendix 5). Therefore, to simplify analysis, we pooled the data up to the island level by combining both day types and all regions. With the estimated catchability coefficient of each gear type (Table 4), we reconstructed a time series for relative biomass (Fig. 3). There was a steep (almost 50%) downward trend in fish biomass from 1985 to around 1990. In the following decade, fish biomass leveled off but then declined again by about 2003 (Fig. 3).

On the basis of the reconstructed time series for total fish biomass (Fig. 3), we were able to estimate relative biomass of the functional groups targeted in the shore-based fisheries for reef fishes (Fig. 4). For the reconstructed biomass per functional group, species composition was assumed to have remained similar to the species composition observed during the visual surveys conducted in 2011 and, therefore, is an estimate of the true value.


The fishery data used in this study show an overall reduction in catches in Guam that in turn indicates a general decline in reconstructed stock biomass from the late 1980s to recent years (Fig. 3)--a finding that is consistent with the results of fishery-independent surveys that show significant depletion of shallow-water reef-fish populations and large fishes around Guam (Richards et al., 2011; Williams et al., 2011, 2015). Parrotfishes were caught by hook-and-line fishing (33%) and by spearfishing (40%), and lower landings were reported in recent years. Assuming there have been no increases in recruitment and that the size composition of the catch reflects the size structure of the population, this decline in catches indicates a reduction in adult biomass and reproductive potential of the stock (Birkeland and Dayton, 2005). The decline in reconstructed biomass of parrotfishes and other herbivores (Fig. 4) observed in our study is also of some ecological concern. Herbivorous fishes play a critical role in maintaining benthic algal communities in states that are conducive for coral growth and recruitment (Mumby et al., 2007a; McClanahan, 1997), and herbivory is particularly important in promoting coral recovery after disturbances, such as hurricanes and bleaching events (Mumby et ah, 2007b; Edwards et al., 2011; Graham et ah, 2013). Therefore, declines in local parrotfish biomass may indicate that reefs surrounding Guam are less resilient to such events.

Estimated CPUE and catches for all gear types were substantially lower during the recent period (2007-2012) than they were during the period 1985-1990 (Table 2). Because CPUE estimates for the hook-and-line fishery in our earliest period (0.15 kg/gear hour for 1985-1990; Table 2) are considerably lower than the estimates recorded in Guam during the early 1980s (0.55 kg/gear hour; Katnik, 1982, cited in Dalzell et al., 1996), it seems likely that the evident downward trends in CPUE and catch began before the first period for which we have creel data (before 1985). Fishery yields of reef fishes around Guam also have been low compared with previously published global yields for coral reef fisheries--annual levels that ranged from 0.2 to 44.0 t/[km.sup.2] (Dalzell, 1996). These global values are, however, confounded by differences in species groupings and effort reported for different locations around the world, as well as by the different assumptions about habitats included in area calculations. Still, our results clearly show that the downward trend in catch and CPUE, a pattern that earlier studies already noted (Hensley and Sherwood, 1993; Myers, 1993), has continued, and another study has reported that declines in catch started at least 50 years ago (Zeller et al., 2015).

Declines in catch are not restricted to Guam. A recent synthesis of domestic catch reconstruction for 25 Pacific island countries and territories from 1950 to 2010 showed that, at 60% of those localities, peak catch occurred before 2000 and that in only one location did the peak catch occur after 2010 (Zeller et al., 2015). Also noteworthy is the shift in catch composition, where the majority of the landings in recent years comprises lower-valued species, such as the bigeye scad (Selar crumenophthalmus). This change in catch composition could be a result of the large pulses in bait fish populations, but it could also indicate a change in composition of the fish community. A similar change in catch composition was found in an analysis of landings by spear fishermen (Lindfield et al., 2014). Scuba spearfishing around Guam was associated not only with a decline in the size of parrotfishes caught but also with a shift from a dominance of large parrotfishes to a mixed assemblage with increasing proportions of surgeonfishes. This shift in community structure and a possible loss in biodiversity could lead to altered ecosystem functioning. Shifts in community structure and an altered ecosystem functioning have been observed in Kiritimati, where, in comparison with an unfished location (Palmyra Atoll), apex predators were relatively smaller, had a shorter life span, and were less abundant and prey fishes were larger but not more abundant (Ruttenberg et al., 2011). In a global analysis of reef fish surveys, Mora et al. (2011) found a strong link between ecosystem functioning and biodiversity, the latter of which is negatively influenced by human populations through overexploitation or the loss or degradation of habitats. Effective efforts to con serve biodiversity should, therefore, include the preservation of the functional roles that species perform (Brown and Mumby, 2014).

Although we are confident that our results provide a good indication of trends in CPUE and in the derived relative fish biomass, our study has several limitations. Calculating the CPUE for a multispecies, multigear reef fishery is not straight forward. Among other issues, many factors influence the decisions that fishermen make about when and where to fish and which gear to use. Consequently, there are undocumented changes in selectivity or catchability of specific gear types over different temporal and spatial scales. Accounting for all of these dependent decisions of fishermen was beyond the scope of our study; however, there was no quantitative or anecdotal information that documented any systematic changes in those decisions over the time period for which we have data. Also, too little creel data are available for some gear types, such as cast nets, and for spearfishing, and that lack of data clearly limits the scope by which the WPacFIN-expanded data can fully represent the total catch and effort.

Additionally, the assumption that the species composition has stayed the same between 1985 and 2012 is also unlikely to be true because the catch composition did change. Fishing affects the species composition of piscivores (e.g., sharks and jacks), and large fishes are often the first ones to disappear from catch records (Friedlander and DeMartini, 2002; Fenner, 2014). We recognize that it is important to be cautious in interpreting the results of our analysis of data from the creel survey program for Guam. However, the lack of alternative survey or fishery information over extended time periods makes it important that these data are used to their fullest extent.

The findings from our analysis of the data from shore-based creel surveys, given the above caveats, indicate a decline in relative biomass of reef-fish populations and a shift in community structure since the start (1985) of our study period. Our results are broadly in agreement with the findings of a number of previous studies that have focused on catches from boat- and shore-based fisheries in Guam (Hensley and Sherwood, 1993; Myers, 1993; Dalzell, 1996; Zeller et al., 2007, 2015), as well as with results of studies of local fish abundance and size distributions (Richards et al., 2011; Houk et al., 2012; Lindfield et al., 2014). Because fishing for reef fishes is an important social and cultural activity for fishermen and their families in Guam, the decline over recent decades in the biomass of stocks of shallow-water coral reef fishes is a cause for concern.


Funding for the senior author and S. Grafeld was obtained from the NOAA Coral Reef Conservation Program. We would like to acknowledge the staff at the Division of Aquatic and Wildlife Resources, Guam Department of Agriculture, for data collection and the following people at the NOAA Pacific Islands Fisheries Science Center: K. Low, M. Quack, and P. Tao for extracting and helping to interpret data, M. Nadon for advice on data analyses, and C. Boggs and J. Wetherall for their valuable comments on the draft manuscript.

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Appendix 1

Boat-based and shore-based creel survey data

Data on both boat- and shore-based fisheries are collected during creel surveys conducted by staff of the Guam Division of Aquatic and Wildlife Resources (DAWR). Boat-based fisheries are focused mainly on trolling for pelagic species and bottom fishing for deepwater (depths >30 m) species for commercial reasons, and shore-based fisheries target shallow-water reef fishes for recreational or cultural reasons. Landings of fishes associated with shallow (depths <30 m) reefs--the focus of this study--accounted for 26% of the total catch of fishes for the boat-based fishery from 1985 through 2012 (based on data from the DAWR boat-based creel surveys). In the last 3 years for which complete data are available (2010-2012), average annual catches of reef fishes from shore-based fisheries were 63 metric tons (t), of which reef fish composed 43.5% and bigeye scad (Selar crumenopthalmus) made up 50.2% (Appendix 1 Table). During the same time period, average annual catches from boat-based fisheries were 359 t, pelagic fishes accounted for 76.4% of the catch composition, and reef fishes accounted for 13.1%.

Although landings of reef fishes from shore-based fishing activities accounted for just 37% of the total (boat-based and shore-based combined) reef-fish landings, the shallow-reef fish populations exploited in the shore-based fishery potentially are very important for subsistence or cultural reasons. Data from interviews from the shore-based fishery of the DAWR creel survey program revealed that only one fisherman sold the catch, on one occasion, during the period from 1985 through 2012. Because boat-based fisheries account for a large amount of reef fish catches, we first determined whether the trend in catches of just the shore-based fisheries was comparable with the trend in catches from the boat-based fisheries of reef fishes and, if so, whether the trend would be representative of the catches of coral reef fish.

The majority of the reef fishes captured in the boat-based fisheries were caught by spearfishing with snorkel and scuba (Appendix 1 Fig. 1), gear types used in both boat-based and shore-based fisheries. We visually compared the difference in trends of the standardized values of catches between boat-based and shore-based spearfishing (Appendix 1 Fig. 2). A Comparison of these trends from both fisheries indicates that only in about the first 4 years did values differ by 2-4 units but, beginning in 1988, values were very similar between the fisheries, leading us to conclude that the trends in catches reflect common changes in the target stocks as well.

Appendix 1 Table
Composition of catches from the boat-based and shore-
based components of the creel survey conducted in
Guam during 2010-2012. Other=invertebrates and un-
known species. Data came from the Guam Division of
Aquatic and Wildlife Resources and the Western Pacific
Fisheries Information Network of the NOAA Pacific Is-
lands Fisheries Science Center.

                   Boat-based fishery       Shore-based fishery

                  Portion      Average     Portion      Average
                     of        annual         of        annual
Species           catch (%)   catch (kg)   catch (%)   catch (kg)

Reef fishes           13.1       47,021        43.5       27,465
Pelagic fishes        76.4      274,129         0.6          395
Bottom fishes          3.3       11,729         0.0            5
Bigeye scad            6.9       24,754        50.2       31,714
Other                  0.3          947         5.7         3614
Total                100.0      358,579       100.0       63,193

Appendix 1 Figure 1
Composition of the 5 gear types used most
in boat-based fisheries to catch reef fishes
(representing 98% of reef fish catches) during
2000-2005, based on data from the Guam
Division of Aquatic and Wildlife Resources
and the Western Pacific Fisheries Information
Network of the NOAA Pacific Islands Fisheries
Science Center.

SPEAR/SCUBA      31%
GILL NET          9%
TROLLING         11%

Note: Table made from pie chart.

Appendix 2

Shore-based creel surveys

For reporting purposes of the shore-based fishery of the creel survey program of the Guam Division of Aquatic and Wildlife Resources, Guam has been divided into 93 fishing sites that are grouped into 4 coastal regions (Appendix 2 Figure):

* Region 1 consists of the northwestern portion of Guam from Gun Beach to Adelup (sites 1-11)

* Region 2 consists of the southwestern portion of Guam from Adelup to Agat (sites 12-34, excluding inaccessible sites 35-41)

* Region 3 consists of the central-eastern to southern portion of Guam from Pago Bay to Merizo (sites 42-71, excluding inaccessible sites 57-60)

* Region 4 consists of the northern part of Guam, and access is restricted there because of a military base (sites 72-93)

The staff of the Western Pacific Fisheries Information Network (WPacFIN), NOAA Pacific Islands Fisheries Science Center, provides assistance with fishery statistics to partners at the Guam Division of Aquatic and Wildlife Resources and has developed an expansion algorithm to extrapolate results of the shore-based creel surveys into estimates of island-wide catch and effort. The shore-based creel surveys have 2 parts, interviews of a sample of fishermen and surveys where fishing activities were observed and recorded (participation surveys). Staff of the WPacFIN estimated annual fishing effort (measured in gear hours) per gear type per region by multiplying the total number of gear hours fished, from observations in the participation survey, by 2 correction factors 1) the ratio of the number of days in a year to the total number of scheduled survey days and 2) the number of available fishing hours in the morning and in the evening (Bak, footnote 1 in the main text). Staff of the WPacFIN estimated total annual catch per gear per region as the product of total annual effort and the gear- and region-specific average catch per unit effort (CPUE), the latter derived within each stratum as total sampled catch divided by total sampled effort. The estimated total catch per species within each stratum was calculated by multiplying aggregate annual catch by the ratio of that particular species in the catch from the interviews (Bak (12)). Missing CPUE data was substituted with a moving average of the previous 10 years of CPUE data.

Appendix 3

Interviews and catch per unit of effort

Appendix 3 Table 1
Number of interviews conducted as part of shore-based creel
surveys conducted around Guam, per gear type per year. For
some gear types in some years, the total number of
interviews was between 1 and 4 or <5.

                 1985   1986   1987   1988   1989   1990   1991

Hook and line     53     46     32     38     45     59     63
Gill net          38     34     28     28     25     41     35
Surround net       7     <5     <5      5      0     <5      0
Snorkel spear     35     20     21     18     14     14     15
Scuba spear       <5     <5      0     <5     <5     <5     <5
Drag net           8      9      8     <5     <5      5      7

                 1992   1993   1994   1995   1996   1997   1998

Hook and line     66     61     83     78     76     87     84
Gill net          40     33     36     49     31     50     48
Surround net      <5      0     <5     <5      0      0      0
Snorkel spear     16     14     36     21     20     25     34
Scuba spear       <5     <5     <5      9     <5     <5     <5
Drag net           7      6     <5      5     <5     <5     <5

                 1999   2000   2001   2002   2003   2004   2005

Hook and line     85     86     86     60     78     61     60
Gill net          51     41     31     28     16     15     13
Surround net       0      0      0      0     <5     <5      0
Snorkel spear     49     28     27     19     14     10      8
Scuba spear       <5     <5     <5     <5     <5      0      0
Drag net          10      4     <5      0      0      0     <5

                 2006   2007   2008   2009   2010   2011   2012

Hook and line     65     61     64     62     57     48     45
Gill net          13     11     12      6     13     12      9
Surround net      <5     <5     <5      0     <5     <5      0
Snorkel spear      9      5      6      5      7     <5     11
Scuba spear        0      0      0      0     <5      0      0
Drag net          <5      0      0      0      0      0      0

Appendix 3 Table 2
Annual values of catch per unit of effort around Guam, by
gear type and year, calculated by the Western Pacific
Fisheries Information Network, NOAA Pacific Islands
Fisheries Science Center, from data collected during shore-
based creel surveys. Values in bold are the mean of the 3
previous years for values that were missing in the survey-

                 1985   1986   1987   1988   1989   1990   1991

Hook and line    0.18   0.21   0.20   0.09   0.11   0.14   0.16
Gill net         1.19   1.16   1.11   1.76   1.08   1.18   0.94
Surround net     1.79   3.07   0.48   1.19   0.72   0.93   0.93
Snorkel spear    1.50   0.87   0.71   0.58   0.49   0.43   0.53
Scuba spear      1.25   1.25#  1.25   0.53   0.89   0.34   0.40
Drag net         1.11   1.23   0.95   0.20   2.66   0.91   2.06

                 1992   1993   1994   1995   1996   1997   1998

Hook and line    0.09   0.06   0.09   0.14   0.08   0.10   0.10
Gill net         0.85   0.45   0.64   0.61   0.48   0.49   0.29
Surround net     0.93   0.37   2.14   0.65   0.65   0.51   0.51
Snorkel spear    0.72   0.92   0.88   0.82   0.49   0.73   1.73
Scuba spear      0.32   0.34   0.34   2.04   0.32   0.34   0.64
Drag net         2.96   0.91   2.11   1.54   1.52#  1.42   1.83

                 1999   2000   2001   2002   2003   2004   2005

Hook and line    0.11   0.08   0.08   0.07   0.09   0.08   0.05
Gill net         0.51   0.62   0.50   0.46   0.35   0.25   0.66
Surround net     0.93   0.65   0.93   0.65   0.37   0.93   0.93
Snorkel spear    0.87   0.64   0.91   0.91   1.49   0.74   0.29
Scuba spear      0.29   0.32   0.40   0.40   0.24   0.40   0.34
Drag net         1.66   0.31   1.21   0.91   0.81#  2.11   0.31

                 2006   2007   2008   2009   2010   2011   2012

Hook and line    0.08   0.09   0.06   0.07   0.03   0.09   0.14
Gill net         0.18   0.45   0.63   0.15   1.26   0.09   0.77
Surround net     0.65   0.65   0.51   0.93   0.51   0.93   0.51
Snorkel spear    0.47   0.40   0.12   0.12   0.06   0.06   0.38
Scuba spear      0.32   0.40   0.35#  0.35#  0.37#  0.40   0.24
Drag net         1.08#  0.31   0.56#  2.11   0.99#  0.91   0.31

Note: Values are the mean of the 3 previous years for values
that were missing in the survey-data are indicated with #.

Appendix 4

Number of times landings included each functional group

The tables in this appendix provide the number of times that a functional group, as defined in Table 1 in the main text, was recorded from landings data for 3-year periods from interviews of shore-based creel surveys conducted around Guam from 1985 through 2012. Data are provided over 3-year periods to preserve the confidentiality of the identities of fishermen. Blank cells indicate that no interview took place in that period.

Appendix 4 Table

             Drag   Gill     Hook     Scuba   Snorkel   Surround
             net    net    and line   spear    spear      net

Scrapers (small-bodied parrotfishes)

1985-1987     0     10        2         4       61         2
1988-1990     0      7        0         0       18         0
1991-1993     0     39        3         1       18         0
1994-1996     0     34        5         6       53         5
1997-1999     1     54        8         5      120
2000-2002     0     16        7         6       39         0
2003-2005     0      7        1         3       20         0
2006-2008     0      4        2                 14         0
2009-2011            3        0         2        5         0
2012-2013            3        0                  8         0

Excavators (large-bodied parrotfishes)

1985-1987     0      3        0         0       24         0
1988-1990     0      2        0         0        7         0
1991-1993     0      8        2         4        8         0
1994-1996     0      4        3         7       21         0
1997-1999     0      6        6         5       39
2000-2002     0      1        2         2       25         0
2003-2005     0      1        4         1        4         0
2006-2008     0      1        2                  1         0
2009-2011            0        2         0        3         0
2012-2013            0        0                  3         0

Target browsers (e.g., unicornfishes, rabbitfishes)

1985-1987    11     92       68        10      198        24
1988-1990     6    112       85         1      137         2
1991-1993     2    104      116         4       46         4
1994-1996     3     80      114        20      129         4
1997-1999    10    145      138        12      229
2000-2002     5    102      127         6      145         0
2003-2005     0     28       47         7       51         2
2006-2008     1     28       39                 30         1
2009-2011           23       24         1       20         2
2012-2013            8        9                 19         0

Target grazers (e.g., surgeonfishes)

1985-1987     1     67       18         2       80         5
1988-1990     2     90       14         0       72         2
1991-1993     0     76       34         3       36         2
1994-1996     0     76       28         9       84         2
1997-1999     2    119       19         6      133
2000-2002     0     64       21         4       77         0
2003-2005     0     25       26         1       29         1
2006-2008     0     17       17                 16         1
2009-2011           10        9         0        8         3
2012-2013            4        5                  9         0

Target invertebrate-consuming fishes (e.g., emperors,
goatfishes, snappers)

1985-1987    60    258       46         2      151        32
1988-1990    23    274       85         1       79         3
1991-1993    44    337      203         6       62         2
1994-1996    18    329      259        12      181         7
1997-1999    64    469      329         3      307
2000-2002    14    305      255        13      163         0
2003-2005     1     77      136         8       47         4
2006-2008     1     29      117                 28         0
2009-2011           48       71         1       16         3
2012-2013           33       29                 29         0

Target benthic piscivores (e.g., groupers)

1985-1987     1     10        8         1       31         1
1988-1990     0     39       33         1       32         0
1991-1993     0     55       93         2       26         1
1994-1996     0     22       61         3       47         2
1997-1999     0     32       68         1       71
2000-2002     0     24       72         2       40         0
2003-2005     0      4       66         2       13         0
2006-2008     0      4       46                 10         0
2009-2011            2       17         0        2         1
2012-2013            2        6                  6         0

Mid-water piscivores (e.g., needlefishes, Heller's barracuda
[Sphyraena helleri])

1985-1987    13     16       17        i        4         7
1988-1990     6      9       25        0        1         0
1991-1993     6     22       25        0        4         0
1994-1996     4     20       29        0        6         1
1997-1999    12     25       25        0       19
2000-2002     2      5       25        0       10         0
2003-2005     2      4       23        0        4         0
2006-2008     2      4        7                 2         0
2009-2011            5       14        0        1         1
2012-2013            3        0                 3         0

Roving piscivores (e.g., jacks)

1985-1987    27     76       71        1        9         5
1988-1990    13     84       78        1        3         5
1991-1993     9     63      139        0        5         0
1994-1996    11     73      234        0        3         1
1997-1999    14     98      303        0        3
2000-2002     6     66      236        0        5         0
2003-2005     0     20      189        1        3         1
2006-2008     0     10      190                 1         2
2009-2011           19      132        0        1         0
2012-2013           13       89                 1         0

Appendix 5

Comparison of catch per unit of effort between day types

Results from analysis in this study revealed a significant difference between weekday and weekend hook-and-line fishing in regions 1 and 2 (for location of these regions, see Appendix 1, Fig. 1). Comparisons of catch per unit of effort (CPUE) per day type for all regions combined and the gear types cast net, gill net, and snorkel spear did not show a significant difference (P [greater than or equal to] 0.05) between weekday and weekend fishing. There were not enough data to compare weekday and weekend CPUE for the remaining gear types.

Appendix 5 Table
Comparison of catch per unit of effort (CPUE) per gear type
between day types (weekday and weekend) with a Welch 2-
sample t-test (which allows for unequal variances) and
between regions with analysis of variance (ANOVA) for the
hook-and-line fishery around Guam. Values are means (and
standard deviations [SD]) during 1985-2012. Region 0 is the
combination of regions 1, 2, 3 and 4. Values of CPUE are
given in kilograms per gear hour.

                                                     Welch 2-sample
                                Mean CPUE (SD)           t-test

Gear type        Region     Weekday       Weekend       P     n

Hook and line      1      0.12 (0.09)   0.07 (0.05)   0.02    28
                   2      0.10 (0.07)   0.07 (0.04)   0.04    28
                   3      0.12 (0.08)   0.09 (0.05)   0.10    28
Cast net           0      0.25 (0.18)   0.22 (0.14)   0.45    28
Gill net           0      0.65 (0.47)   0.71 (0.47)   0.62    28
Snorkel spear      0      0.75 (0.57)   0.59 (0.37)   0.23    28


Gear type         Mean CPUE      P     n

Hook and line    0.09 (0.06)   0.37    28
                 0.09 (0.05)
                 0.11 (0.05)
Cast net
Gill net
Snorkel spear

(1) Kerr, A. M. 2011. Fishing methods of the Mariana Islands, Micronesia. Univ. Guam Mar. Lab. Tech. Rep. 132, 44 p. [Available at website.]

(2) Allen, S., and P. Bartram. 2008. Guam as a fishing community. NOAA Pacific Islands Fish. Sci. Cent. Admin. Rep. H-08-01, 61 p. [Available at website.]

(3) van Beukering, P. (ed.), W. Haider, M. Longland, H. Cesar, J. Sabian, S. Shjegstad, B. Beardmore, Y. Liu, G. O. Garces. 2007. The economic value of Guam's coral reefs. Univ. Guam Mar. Lab. Tech. Rep. 116, 102 p. [Available at website.]

(4) McIlwain, J. L., and B. M. Taylor. 2009. Parrotfish population dynamics from the Marianas Islands, with a description of the demographic and reproductive characteristics of Chlorurus sordidus: final report to the Western Pacific Regional Fishery Management Council, 61 p. Univ. Guam Mar. Lab., Mangilao, Guam. [Available at website]

(5) WPacFIN (Western Pacific Fishery Information Network). 2013. Guam shore-based creel survey. NOAA Pacific Islands Fish. Sci. Cent., Honolulu, HI. [Metadata available at website.]

(6) Oram, R., T. Flores Jr., B. Tibbatts, J. Gutierrez, J. P. Gesner, S. Wusstig, A. Regis, D. Hamm, M. Quach, and P. Tao. In press. Guam shore-based creel survey. NOAA Pac. Islands Fish. Sci. Cent. Admin. Rep., 25 p.

(7) Bak, S. 2012. Evaluation of creel survey program in the western Pacific region (Guam, CNMI, and American Samoa), 58 p. Unpubl. report prepared for the Western Pacific Regional Fishery Management Council, Honolulu, HI 96813.

(8) Taylor, B. 2012. Personal commun. James Cook University, Townsville, Queensland 4811, Australia.

(9) Froese, R., and D. Pauly (eds.). 2015. FishBase, vers. 10/2015. [World Wide Web electronic publication; available at website, accessed March 2015.]

(10) NCCOS (National Centers for Coastal Ocean Science). 2005. National Centers for Coastal Ocean Science, Shallow Water Benthic Habitats of American Samoa, Guam, and the Commonwealth of the Northern Mariana Islands (CD-ROM). Silver Spring, MD. [Metadata available at website]

(11) Bak Hospital, S. 2015. Western Pacific creel survey program data summary and analysis: Guam, the Commonwealth of the Northern Mariana Islands, and American Samoa. NOAA Pac. Islands Fish. Sci. Cent. Admin. Rep. H15-06C, 194 p. [Available from Pac. Islands Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 1845 Wasp Blvd., Bldg. 176, Honolulu, HI 96818.]

Mariska Weijerman (contact author) [1,2]

Ivor Williams [3]

Jay Gutierrez [4]

Shanna Grafeld [5]

Brent Tibbatts [4]

Gerry Davis [6]

Email address for contact author:

[1] Joint Institute for Marine and Atmospheric Research School for Ocean and Earth Science and Technology University of Hawaii at Manoa Marine Science Building 312 1000 Pope Road Honolulu, Hawaii 96822

[2] Environmental System Analysis Group Wageningen University P.O. Box 47 6700 AA Wageningen, Netherlands

[3] Coral Reef Ecosystem Program Ecosystem Sciences Division Pacific Islands Fisheries Science Center National Mariner Fisheries Service, NOAA 1845 Wasp Boulevard, Building 176 Honolulu, Hawaii 96818

[4] Division of Aquatic and Wildlife Resources Guam Department of Agriculture 163 Dairy Road Mangilao, Guam 96913

[5] Department of Natural Resources and Environmental Management University of Hawaii at Manoa 1910 East-West Road Sherman Laboratory 101 Honolulu, Hawaii 96822

[6] Habitat Conservation Division Pacific Islands Regional Office National Marine Fisheries Service, NOAA 1845 Wasp Boulevard, Building 176 Honolulu, Hawaii 96818

Manuscript submitted: 30 April 2015.

Manuscript accepted: 2 March 2016.

Online publication date: 18 March 2016.

doi: 10.7755/FB.114.2.9

Table 1
Categorization of functional groups, based on taxonomy,
ecological function, or importance to fisheries, used in our
study of trends of fish biomass in data from shore-based
creel surveys conducted around Guam during 1985-2012

group name       Description and notes       Example species

Bait fishes      Sardine-like species that   Selar crumenophthalmus,
                 periodically come to        Ellochelon vaigien-sis,
                 nearshore waters in large   Gerres longirostris,
                 numbers                     Crenimugil crenilabis

Invertebrates    The top shell (Tectus       Crabs, lobsters, sea
                 niloticus) was the          cucumbers, mollusks,
                 dominant component in the   octopuses, urchins, and
                 total catch of              clams
                 invertebrates as a result
                 of very high landings of
                 this single species of 30
                 t in 1985 and 16 t in

Nonreef-fish     Species that are pelagic,   Tuna, deepwater snappers
species          deepwater, freshwater, or   (e.g., Etelis corus-
                 associated with sandy       cans), Kuhlia rupestris

Macroalgae       Fish species that feed on   Soldierfishes
Planktivores     particles from water        (Holocentridae), some
                 column                      uni-cornfishes (e.g.,
                                             Naso annulatus),
                                             chromises (Chromis spp.),
                                             cardinalfishes (Apogon

Coral-           Fish species that feed      Mostly butterflyfishes
consuming        primarily on corals         (Chaetodon spp.)

Detritivores     Fish species that feed      Surgeonfishes
                 primarily on detritus       (Ctenochaetus spp.)

Invertebrate-    Fish species that feed on   Exploited: emperors
consuming        invertebrates, separated    (Lethrinus spp.),
fishes           into exploited species      snappers (Lutjanus spp.),
                 and lightly or non-         goatfishes (Mullidae),
                 exploited species           wrasses (Cheilinus spp.);
                                             lightly or non-
                                             porcupinefishes (Diodon
                                             spp.), file-fishes
                                             (Aluterus spp.)

Herbivore-       Fish species that browse    Exploited: sea chubs
browsers         on plants, separated into   (Kyphosus spp.),
                 exploited species and       rabbitfishes (Siganus
                 lightly or nonex-ploited    spp.), unicornfishes
                 species                     (e.g., Naso unicornis);
                                             lightly or nonexploited:
                                             milkfish (Chanos chanos)

Herbivore-       Fish species that graze     Exploited: surgeonfishes
grazers          on plants, separated into   (Acanthurus spp.);
                 exploited species and       lightly or nonexploited:
                 lightly or non-exploit-     sergeants (Abudefduf
                 ed species                  spp.)

Herbivore-       Fish species that feed on   Small-bodied parrotfishes
scrapers         plants and scrape hard      (e.g., most species of
                 substrate (including        Scarus, Chlorurus
                 corals); all exploited      sordidus)

Herbivore-       Fish species that feed on   Large-bodied parrotfishes
excavators       plants and excavate hard    (e.g., most species of
                 substrate (including        Chlorurus, Scarus
                 corals); all exploited      rubroviolaceus)

Humphead         An exploited species        Bolbometopon muricatum

Humphead         An exploited species        Cheilinus undulates

Benthic          Fish species that feed      Exploited: groupers
piscivores       primarily on other fishes   (Epinephelus spp.);
                 and are mostly resident     lightly or nonexploited:
                 to a reef area separated    morays (Gymnothorax spp.)
                 into exploited species
                 and lightly or nonex-
                 ploited species

Mid-water        Fish species that feed      Leatherjacket
piscivores       primarily on other fishes   (Scomberoides sp.),
                 and are benthopelagic,      needlefishes (Belonidae),
                 all exploited species       reef cornetfish
                                             (Fistularia commersonii)

Roving           Fish that feed primarily    Jacks (Carangidae),
piscivores       on other fishes and rove    barracudas (Sphyraena
                 on reefs; all exploited     spp.)

Rays             All exploited species       Stingrays

Sharks           All exploited species       Reef-associated sharks
                                             (e.g., blacktip reef
                                             shark [Carcharhinus
                                             melanopterus], grey reef
                                             shark [C. amblyrhynchos],
                                             and whitetip reef shark
                                             [Triaenodon obesus])

Table 2
Annual mean fishing effort, catch, and catch per unit of
effort (CPUE), by gear type, in Guam during the 2 periods
1985-1990 and 2007-2012. Data were collected during shore-
based creel surveys conducted by the Guam Division of
Aquatic and Wildlife Resources and expanded by the Western
Pacific Fisheries Information Network of the NOAA Pacific
Islands Fisheries Science Center. Catch and effort values
are based on expanded data and exclude nonreef-associated
fishes (e.g., pelagic, freshwater, and intertidal fish
species). Values of CPUE (with standard errors [SEs] in
parentheses) are based on unexpanded interview data (not on
a ratio of tabled catch and effort). P-values are from the
Welch's 2-sample t-test (which allowed unequal variances),
in which CPUE was compared between the 2 time periods. NA
represents cases when less than 3 interviews per year per
gear type were available (see Appendix 3 Table 1). Effort is
given in gear hours (gh), and catch is given in kilograms.


                   Mean effort      Mean catch    CPUE (SE)
Gear type       (gh) (% of total)      (kg)        (kg/gh)

Hook and        127,219 (58.5%)      22,464      0.15 (0.02)
Cast net         31,913 (14.7%)       15,88     00.36 (0.04)
Gill net         22,647 (10.4%)      28,259      1.25 (0.11)
Surround net       1470 (0.7%)         4128      1.36 (0.67)
Snorkel          18,453 (2.9%)       16,507      0.76 (0.15)
  spear (1)
Scuba              1553 (0.7%)          988      0.75 (0.10)
  spear (1)
Hooks and          6396 (2.9%)         2228      0.30 (0.05)
Drag net            901 (0.4%)         1377      1.18 (0.53)
Other gear         6868 (3.2%)         8454      0.55 (0.29)
  Total          217,420         100,285


                   Mean effort      Mean catch    CPUE (SE)
Gear type       (gh) (% of total)      (kg)        (kg/gh)     P-value

Hook and         145,309 (70.6%)      17,828     0.08 (0.02)    0.015
Cast net          29,555 (14.4%)       4,108     0.10 (0.02)   <0.001
Gill net          10,918 (5.3%)        9,807     0.56 (0.18)    0.01
Surround net         552 (0.3%)          555     0.67 (0.08)     NA
Snorkel           11,736 (5.7%)        2,137     0.19 (0.06)    0.013
  spear (1)
Scuba                155 (0.1%)           58     0.34 (0.04)     NA
  spear (1)
Hooks and           5554 (2.7%)        2,139     0.36 (0.16)     NA
Drag net             141 (0.1%)          133      0.97 (0.35)     NA
Other gear          1930 (0.9%)          181      0.07 (0.01)    0.10
  Total           205,850             36,945

Table 3
Relative contributions of functional groups to the total
catch per year, based on data collected during shore-based
creel surveys conducted by the Guam Division of Aquatic and
Wildlife Resources and expanded by the Western Pacific
Fisheries Information Network of the NOAA Pacific Islands
Fisheries Science Center. All values are percentages.
Numbers in italic type indicate a contribution >15% to the
annual total catch. The functional groups are described in
Table 1.

Functional group                  1985   1986   1987   1988   1989

Bait fishes                      16.4    6.8    7.2    9.1    9.8
Invertebrates                    22.0    4.4    3.1    3.6    6.8
Nonreef-associated fishes         1.8    5.2    7.9    2.1    0.8
Macroalgae                        3.2    3.2    0.1    0.1    0.0
Invertebrate-consuming fishes    15.1   20.3   19.7   24.1   27.4
Planktivorous fishes              1.9    0.7    1.1    0.7    2.2
Coral-consuming fishes            0.0    0.0    0.0    0.0    0.0
Detritivorous fishes              0.1    0.2    0.0    0.0    0.0
Browsers                         22.4   30.8   39.0   40.4   34.5
Grazers                           3.9    3.9    9.3    8.8    7.7
Scrapers                          1.3    1.2    0.5    1.1    0.2
Excavators                        1.8    0.0    0.0    0.2    0.0
Humphead parrotfish               0.2    0.0    0.0    0.0    0.0
Humphead wrasse                   0.3    0.1    0.2    0.6    1.1
Benthic piscivores                1.7    2.5    5.2    2.2    1.1
Mid-water piscivores              3.0    3.0    0.0    1.6    3.0
Roving piscivores                 4.7    3.3    6.8    5.2    4.8
Rays                              0.0    0.1    0.0    0.2    0.4
Sharks                            0.0   14.2    0.0    0.0    0.0

Functional group                  1990   1991   1992   1993   1994

Bait fishes                      15.8   42.2   12.0    9.9   10.1
Invertebrates                     5.1   12.2    6.0    8.9    9.2
Nonreef-associated fishes         1.8    0.5    1.8    2.8    2.5
Macroalgae                        0.0    0.5    0.1    0.3    0.8
Invertebrate-consuming fishes    19.0    9.5   21.8   23.8   18.4
Planktivorous fishes              1.5    0.6    1.2    5.2    1.8
Coral-consuming fishes            0.0    0.0    0.0    0.0    0.0
Detritivorous fishes              0.0    0.0    0.1    0.2    0.4
Browsers                         26.3   16.0   35.8   17.0   29.4
Grazers                          12.3    3.9    9.6    7.4    6.3
Scrapers                          0.5    2.5    1.7    2.2    2.2
Excavators                        0.5    0.9    0.9    0.8    0.7
Humphead parrotfish               0.0    0.0    0.0    0.0    0.0
Humphead wrasse                   0.1    0.0    0.0    0.0    0.0
Benthic piscivores                5.4    2.6    3.2    8.1    4.5
Mid-water piscivores              2.8    1.6    1.1    2.2    3.2
Roving piscivores                 8.9    7.1    4.3    9.6    3.6
Rays                              0.0    0.0    0.0    0.0    0.0
Sharks                            0.0    0.0    0.4    1.6    7.0

Functional group                  1995   1996   1997   1998   1999

Bait fishes                      13.9   10.7   23.6    3.7    6.5
Invertebrates                     4.8    2.8   12.8   15.4    9.2
Nonreef-associated fishes         1.6    0.8    2.5    5.3    2.4
Macroalgae                        0.3    0.0   11.6    3.4    6.6
Invertebrate-consuming fishes    19.8   22.6   13.8   18.9   12.5
Planktivorous fishes              2.2    2.5    1.4    3.0    1.1
Coral-consuming fishes            0.0    0.0    0.0    0.0    0.1
Detritivorous fishes              0.3    0.1    0.1    0.2    0.1
Browsers                         35.0   36.2   19.6   30.7   29.0
Grazers                           7.6   10.6    4.4    4.4    4.4
Scrapers                          1.7    1.7    1.6    1.5    4.3
Excavators                        1.6    1.0    0.4    2.7    1.2
Humphead parrotfish               0.0    0.0    0.0    0.0    0.0
Humphead wrasse                   0.0    0.5    0.0    0.0    0.0
Benthic piscivores                4.5    2.3    2.4    4.0    4.4
Mid-water piscivores              2.1    2.2    0.2    0.5    3.4
Roving piscivores                 3.3    5.9    5.4    6.0   10.5
Rays                              0.0    0.0    0.0    0.1    0.0
Sharks                            1.4    0.1    0.4    0.2    4.2

Functional group                  2000   2001   2002   2003   2004

Bait fishes                      16.5    8.3    5.5    5.9    6.0
Invertebrates                     6.1   17.4    3.8   14.4    6.9
Nonreef-associated fishes         2.0    1.9    1.2    5.5   13.1
Macroalgae                        0.1   10.3    0.3    0.2    0.1
Invertebrate-consuming fishes    19.5   19.7   20.8   17.8   10.0
Planktivorous fishes              2.0    0.8    1.0    0.9    3.2
Coral-consuming fishes            0.6    0.2    0.0    0.0    0.0
Detritivorous fishes              0.3    2.2    0.0    0.0    0.0
Browsers                         30.5   16.8   35.0   26.1   22.4
Grazers                           7.8    5.1    5.6   10.3    9.8
Scrapers                          1.6    0.6    1.1    3.4    0.9
Excavators                        0.8    0.7    1.0    3.5    1.4
Humphead parrotfish               0.0    0.0    0.0    0.0    0.0
Humphead wrasse                   0.1    0.0    0.0    0.2    0.0
Benthic piscivores                5.4    2.3    6.1    3.1    4.0
Mid-water piscivores              1.3    2.9    1.3    1.0    2.8
Roving piscivores                 5.4   10.1   13.6    6.0   19.4
Rays                              0.0    0.0    0.0    0.0    0.0
Sharks                            0.1    0.7    3.5    1.8    0.0

Functional group                  2005   2006   2007   2008   2009

Bait fishes                      10.7   11.2   10.4   21.1   47.5
Invertebrates                    20.1    5.5    7.8    2.2   13.7
Nonreef-associated fishes         3.5    2.2    0.4    2.3    2.6
Macroalgae                        0.0    0.1    0.1    0.1    0.1
Invertebrate-consuming fishes    20.5   10.8   16.2    7.9    6.5
Planktivorous fishes              0.5    0.7    0.3    0.6    1.4
Coral-consuming fishes            0.0    0.0    0.0    0.1    0.0
Detritivorous fishes              0.1    0.3    2.7    0.0    0.0
Browsers                         12.1   35.9   25.7   21.1    7.4
Grazers                           8.2    8.4    5.5    8.7    6.9
Scrapers                          2.1    2.6    0.9    4.8    0.6
Excavators                        0.5    0.3    0.1    0.4    0.2
Humphead parrotfish               0.0    0.0    0.0    0.0    0.0
Humphead wrasse                   0.0    0.1    0.4    0.0    0.0
Benthic piscivores                3.5    5.4    6.4    2.2    1.2
Mid-water piscivores              0.8    0.9    0.2    1.8    0.6
Roving piscivores                17.2    9.2   22.9   24.2   11.3
Rays                              0.0    2.0    0.0    0.0    0.0
Sharks                            0.3    4.3    0.1    2.4    0.0

Functional group                  2010   2011   2012

Bait fishes                       3.4   30.1   72.6
Invertebrates                     2.9    1.0    4.8
Nonreef-associated fishes         5.0    0.6    2.8
Macroalgae                        0.3    0.1    0.0
Invertebrate-consuming fishes    10.2   15.3    6.1
Planktivorous fishes              1.0    0.2    0.2
Coral-consuming fishes            0.0    0.0    3.9
Detritivorous fishes              0.0    0.0    0.0
Browsers                         46.1   10.3    2.9
Grazers                          20.3    6.8    0.3
Scrapers                          1.3    1.7    0.5
Excavators                        0.1    0.6    0.0
Humphead parrotfish               0.0    0.0    0.0
Humphead wrasse                   0.0    0.0    0.1
Benthic piscivores                0.5    0.8    0.5
Mid-water piscivores              0.9    1.6    0.0
Roving piscivores                 8.1   30.9    5.2
Rays                              0.0    0.0    0.0
Sharks                            0.0    0.0    0.0

Table 4
Mean catch per unit of effort (CPUE), by gear type, determined
from shore-based creel surveys conducted by the Guam Division
of Aquatic and Wildlife Resources in 2010-2012 and estimated
biomass of targeted species, by gear type, from visual surveys
conducted by the Coral Reef Ecosystem Program of the NOAA
Pacific Islands Fisheries Science Center in 2011. These values
were used to calculate the catchability coefficient (q) for each
gear type. Data for cast-net fishing were excluded from this anal-
ysis (see the Materials and methods section). gh=gear hour.

                        CPUE (kg/gh)
                                      Biomass       q
Gear type        2010   2011   2012     (t)     (/1000 gh)

Drag net         0.99   0.91   0.31     157       0.0042
Gill net         1.26   0.09   0.77     386       0.0012
Hook and line    0.03   0.09   0.14     324       0.0002
Scuba spear      0.37   0.40   0.24     544       0.0006
Snorkel spear    0.06   0.06   0.38     386       0.0003
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Author:Weijerman, Mariska; Williams, Ivor; Gutierrez, Jay; Grafeld, Shanna; Tibbatts, Brent; Davis, Gerry
Publication:Fishery Bulletin
Article Type:Report
Geographic Code:1U0GU
Date:Apr 1, 2016
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