The effects of embeddedness on the seasonal feeding of mottled sculpin.
Sedimentation occurs in stream channels when excess fine particulate matter is added to the stream channel (Waters, 1995). There is a natural flow of sediments through a stream channel which can originate from the banks along the stream. Major pulses of sediment can be natural, e.g., landslides but often these large pulses are the result of human activity within the watershed (Wood and Armitage, 1997).
Sediment can alter the physical habitat of the stream by filling in interstitial spaces (Lenat et al., 1981). The distinction among riffle, run, and pool habitats becomes reduced and the habitat becomes homogenized (Berkman and Rabeni, 1987). The increase in sediment not only poses a risk as a physical barrier, but the sediment can reduce the flow of water and in turn reduce the dissolved oxygen present (Gordon et al., 2004) while acting as a scouring mechanism to remove benthic organisms (Schofield et al., 2004).
Alterations in stream structure can in turn change the macroinvertebrate taxa present within a stream. Certain taxa may be extirpated from the stream, most notably individuals of the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT; Kaller and Hartman, 2004). Members of these orders often use the underside of the rocky substrate (Novak and Estes, 1974) and will become smothered as sediment increases (Kemp et al., 2011). Additional sediment effects on macroinvertebrates have been decreases in overall density (Wagener et al., 1985), taxa richness (Rabeni et al., 2005), and changes in chironomid abundances (Wagener et al., 1985; Angradi, 1996). Once the macroinvertebrate community has been altered significantly, the stream is classified as impaired (USEPA, 1995a).
One headwater stream fish likely to be impacted by increasing sediment loads is the mottled sculpin (Cottus bairdii. These fish prefer cool (<22 C), clear, and moderate- to high-gradient streams. Large juveniles and adults usually occupy runs and riffles of gravel, rubble, and boulders (Jenkins and Burkhead, 1994). In headwater streams in Maryland, sculpin are often the dominant member of the fish assemblage numerically even when sediment levels increase (Maryland Biological Stream Survey, 2005).
Research on the effects of sedimentation on sculpin usually focuses on the extirpation of sculpin from the stream channel as sediment loads increase (Berkman and Rabeni, 1987; Mebane, 2001; Gray et al., 2005). There has been less research on the effect of sedimentation on diets
of sculpin (Haro and Brusven, 1994; Schofield et al., 2004). Higher levels of sediment can increase the turbidity, which lowers the feeding rates of visual predators, i.e., bluegills (Gardner, 1981) and salmon (Sigler et al., 1984; Sweka and Hartman, 2001; Stuart-Smith et al., 2004). Feeding behaviors of fishes such as mottled sculpin are unlikely to be affected by turbidity because they are nocturnal and rely on their lateral line for feeding and not visual cues (Hoekstra and Janssen, 1985). Because sculpin are not affected by moderate levels of turbidity, the effects of sediment can be used to determine if macroinvertebrate communities are altered, and how this in turn affects mottled sculpin.
The goal of this study was to determine if and how mottled sculpin diets change in two different sediment regimes. Our first objective was to quantify the macroinvertebrate community throughout the year to establish what was available for mottled sculpin. Our second objective was to determine if the dry mass and energy consumption of sculpin was different between the two levels of sedimentation throughout the year.
Four first-order streams were selected from the Youghiogheny River watershed in Garrett County, Maryland. The sites, Two-Mile Run (39[degrees]67'85", -79[degrees]05'87"), Mill Run (39[degrees]71'98", -79[degrees]29'81"), Casselman River (39[degrees]59'85", -79[degrees]20'71"), and Little Bear Creek (39[degrees]65'60", -79[degrees]26'11") were selected based upon the following criteria: (1) mottled sculpin as the only cottid species present, (2) sculpin populations greater than 60 sculpin per 100 m of stream in order for the population to be considered large enough for removal offish samples, and (3) the appropriate level of embeddedness (15% or 35%) as measured by the Maryland Biological Stream Survey (2005). Percent embeddedness is the amount of fine material such as silt and sand that surrounds larger particles such as cobbles and boulders (Roth et al., 1999). These data, provided annually, estimate the amount of sediment in a stream by visual estimation. Three observers make estimations, and the value is averaged among the three. This value of percent embeddedness was used in this experiment as the measure of sediment that is present within a stream. Two sites, an unnamed tributary of Mill Run (MR) and Two Mile Run (TMR) had a level of 35% embeddedness (Fig. 1). The MR site had two houses located within 50 m of the stream. Two additional sites, Little Bear Creek (LBC) and the South Branch of the Casselman River (SB) had a level of 15% embeddedness, were in forested areas, and had no houses within 50 m of the stream (Fig. 1). This resulted in a sample size of two for each embeddedness category (MBSS 2005).
Sediment loads in a stream were measured as percent embeddedness, which is the amount of fine material such as silt and sand that surrounds larger particles such as cobbles and boulders (Roth et al., 1999). These data provided annually by the Maryland Biological Stream Survey (2005) estimate the amount of sediment in a stream by averaged the visual estimation of three separate observers.
A population study was conducted in Jun. 2006 on each site to verify the number of mottled sculpin present. The 100 m section was double pass electroshocked and all sculpin collected were measured to the nearest millimeter and weighed to the nearest 0.1 g.
A peak feeding pilot study was conducted on Little Bear Creek and from 28-29 Mar., 2006 to determine the peak feeding times of mottled sculpin. Ten sculpin were collected every 4 h by electrofishing (Smith-Root 12-B electrofisher) and placed in 10% formalin. These fish were dissected in the lab, their stomachs were removed, and gut contents analyzed to determine peak feeding times. Contents were then placed in 50% isopropanol after analysis. Based upon number of identifiable prey items in the stomach, it was apparent that there were two distinct feeding periods for mottled sculpin. These times were determined to be 2000 and 0400 based upon the number of full stomachs. Other studies (Hoekstra and Jannsen, 1985; Greenberg and Holtzman, 1987) have found sculpin are nocturnal feeders, consuming prey primarily .at night or in the early morning. Although these times may shift through the year, having two time periods allows us to capture feeding in warmer months, where stomach residence time is shorter, hut so are the hours during which feeding can occur. During the colder winter months, digestion will slow down; therefore having two peak feeding sampling times will allow the capture of sculpins with undigested prey items. These times were then related to sunrise and sunset and peak feeding times used throughout the remainder of this study were 1.5 h after sunset and 1.5 h before sunrise.
For macroinvertebrates, three Surber samples (hereafter riffle sample) were taken in the same riffle in which sculpin were collected. The riffle was divided into square foot sections based upon length and width of the riffle. A random numbers table was used to select the area of the riffle to be sampled for macroinvertebrates. Riffle samples consisted of a 30.5 x 30.5 cm metal frame with a 500 [micro]m mesh collecting bag placed upon the substrate. The contents within the frame were agitated and all rocks were scraped. Stream flow carried macroinvertebrates downstream into the mesh bag. All material from a mesh bag was immediately transferred to a container with 70% isopropanol. The same riffle was sample throughout the year in order to determine how the macroinvertebrate community changed in that riffle.
Study reaches were 50 m in length, had at least one pool and riffle habitat unit, no manmade structures, i.e., bridges, and were marked to allow subsequent sampling to be repeated in the same area. Sculpin and benthic macroinvertehrates were collected one night per stream over four seasons from 2006-2007: autumn (9-12 Oct. 2006), winter (8-15 Dec. 2006), spring (27-30 Apr. 2007), and summer (10-13 Jul. 2007). Electrofishing began at the downstream end of the stream reach and continued until 10 sculpin were captured and placed into a 10% formalin solution.
Macroinvertebrates from riffle samples were removed, analyzed under a dissecting microscope, and identified to family (Merritt and Cummins, 1995). Collembolans, amphipods, decapods, and oligochaetes were identified as such and grouped together. Densities of macroinvertebrate families were scaled to 1 m for each riffle sample and the average of the three samples was taken.
After remaining in 10% formalin solution for 2 w, sculpins were rinsed thoroughly in tap water and then stored in a 50% isopropanol solution until the gut contents were analyzed. The stomach and esophagus were dissected and contents were removed and analyzed under a dissecting microscope. The percent of empty stomachs was 5% in spring, 9% in summer, 40% in autumn, and 59% in winter. Identifiable macroinvertebrates were separated from digested material was placed in a separate vial with 50% isopropanol. Stomach contents that could be identified were done so to genus or the lowest practical level (Schofield et al., 2004). In addition, head width and body length of each prey item were measured.
The macroinvertebrate community in the riffle samples was analyzed with several different approaches. Diversity (Simpson's index), taxa richness, density, percent Ephemeroptera, Plecoptera, and Trichoptera (EPT), percent Chironomidae, and percent of decapods, Collembolans, oligochaetes in the riffle samples were calculated for each site and season. Multi-response permutation procedures (MRPP) were performed in R using package vegan (R Development Core Team, 2008) to determine if the riffle samples-differed based upon overall community structure (999 permutations) within a season. This test was not done among seasons because community structure would differ naturally due to emergence of macroinvertebrate larvae as adults.
Nonmetric-multidimensional scaling (NMDS) was used to graphically determine if there were differences in macroinvertebrate species composition of mottled sculpin diets and streams. This technique uses Bray-Curtis dissimilarities to ordinate sculpin and macroinvertebrates based on how dissimilar they are, with points farther away from each other being the most dissimilar. Fifty permutations were performed in order to determine the best possible configuration based upon the stress level. The benthic macroinvertebrates responsible for the differences were overlaid on the ordination using the envfit function in R (R Development Core Team, 2008). A p-value is generated using 1000 permutations and a significance level of 0.05 was used as criteria for selecting the overlays.
Length weight regressions were constructed for the mottled sculpin collected during the population study. The slopes were compared using analysis of covariance (ANCOVA, R Development Core Team, 2008), with an alpha = 0.05. Petty and Grossman (2004) divided sculpin from North Carolina streams into juveniles (<48 mm SL), small adults (48-65 mm SL) and large adults (>65 mm SL) and a similar classification scheme was used in this study. However, since these estimates were from North Carolina, they were adjusted to account for the cooler water in Maryland streams. Therefore, the size classes compared in this study were juveniles (<42 mm SL), small adults (42-64 mm SL) and large adults (>65 mm SL). Fulton's condition factor was computed for the fish in each size class. The following equation was used:
Weight * 100,000/[Length.sup.3]
The condition factor is a method for determining if fish of similar size have a different weight among the streams. The literature suggests that this metric could introduce bias when comparing among size classes within a species, therefore, we were only interested in comparing similar sized fish among the streams. ANOVA and Tukey's HSD post hoc test were used.
The dry mass of prey items consumed was calculated based upon body length or head width measurements (Benke et al., 1999). The average dry mass in mg of all taxa within an individual sculpin stomach was calculated. These values occurred over a range of several orders of magnitude, therefore the dry, weight was logl0 transformed. Many of the values were <1 mg; therefore a constant of one was added to all dry weights before they were log transformed [log10(x+1)]. The dry mass of prey consumed was compared to sculpin standard length in each season graphically.
Dry mass of each prey taxa was converted to calories (Cummins and Wycheck, 1971). These values occurred over a range of several orders of magnitude. Dry weight was log10(x+1) transformed. Many of the averages were <1 mg; therefore a constant of one was added to all dry weights before they were log transformed. The energy value of prey consumed was compared to sculpin standard length in each season graphically. Both dry mass and energy consumed were measured to determine if there was a similar pattern between these variables. This information would help determine if larger organisms were energetically more valuable.
NMDS was performed on the maeroinvertebrate taxa recorded in the diets of mottled sculpin and overlays were produced to determine which taxa were responsible for the ordination. Fifty permutations were performed in order to determine the best possible configuration based upon the stress level. The benthic macroinvertebrates responsible for the differences were overlaid on the ordination using the envfit function in R (R Development Core Team, 2008). A p-value is generated using 1000 permutations and a significance level of 0.05 was used as criteria for selecting the overlays.
Compositional analysis was performed to determine if mottled sculpin preferentially selected or avoided prey. This technique ranks the consumed prey items based upon diet and what is available in the environment and provides a significance value that determines if sculpin are feeding in a random pattern or if sculpin are selecting prey in a matter different than their availability would suggest. Taxonontic groups were collapsed to the order level in order to have fewer prey groups than mottled sculpin sampled. Proportions of the relative abundance of macroinvertebrates in the stomachs and the environment were calculated and scaled to 100% and for compositional analysis (R Development Core Team, 2008).
Benthic macroinvertebrates collected in riffle samples showed variation throughout the year and between the two embeddedness levels (Table 1). Diversity and taxa richness were highest in the 15% embedded streams in spring and summer but these seasons also had the lowest densities of macroinvertebrates. Summer and autumn had the lowest proportion of EPT. The low numbers in summer coincided with the highest proportion of Chironomidae. Collembolans, crayfish, and oligochaetes had the highest proportions in autumn and winter. The 35% embedded streams showed similar patterns of variation but not within the same seasons as the 15% embedded streams. Diversity was similar within 35% embedded streams in all seasons except for summer. The taxa richness also was similar throughout all seasons. Densities were highest in summer and autumn, while the proportion of Ephemeroptera, Plecoptera, and Trichoptera were highest in spring and autumn. As with the 15% embedded streams, the low proportion of EPT coincided with a high proportion of Chironomidae in summer. Collembolans, crayfish, and oligochaetes were highest in autumn and winter.
Although the MRPP revealed that there were no differences in community structure between the embeddedness level (P > 0.05), the NMDS ordination demonstrated that the riffle samples did exhibit differences (Fig. 2; stress = 0.16). The orders Ephemeroptera, Diptera, and Odonata, along with the family Chironomidae, were the most important macroinvertebrate groups in distinguishing the sites based upon the envfit thnction in program R (R Development Core Team, 2008; P < 0.01). Ephemeroptera, Diptera, and Chironomidae varied in their relative contribution throughout the year (Table 2) but often made a large contribution to the community composition. Odonates were consistently among the lowest groups represented.
The 15% embedded sites (LBC and SB) were distinguished by a mixture of Chironomidae and Ephemeroptera. This same composition also distinguished the MR sites in spring and winter. Chironomidae distinguished TMR in spring, summer, and winter along with MR in summer. Odonata separated the 15% embedded sites in autumn and Diptera separated LBC in winter and the 35% embedded sites in autumn (MR and TMR). The sites SB winter and MR autumn did not closely group with any macroinvertebrate taxa.
LENGTH WEIGHT REGRESSION AND DENSITIES
The results of the ANCOVA indicated that there was a significant difference among the streams in regards to the weight at length for mottled sculpin (Fig. 3, P < 0.001). Fish collected from MR weighed less at a similar length than fish from the other three study sites. This trend only became evident at the small and large adult size classes. The densities were as follows: LBC: 0.775 sculpin x [m.sup.2], SB: 0.225 sculpin x [m.sup.2], TMR: 1.28 sculpha x [m.sup.2] and UT MR 1.26 sculpin x [m.sup.2].
Fish in the three size classes exhibited significant differences in condition factor, juveniles from SB had a higher condition factor than juveniles from the 35% embedded streams (TMR and MR, Table 3, P < 0.05). Despite the lower condition, there were more juveniles in both TMR and MR than the other two streams. Small adults from MR had a significantly lower condition factor than the other three streams (P < 0.001). Again, there were more fish in this size category from 35% embedded streams than the 15% embedded streams. Large adults from MR had a significantly lower condition factor than the other three streams (P < 0.001). The number of large adults collected from MR (n = 43) was the second highest only to LBC (n = 48) and much higher than SB (n = 3) and TMR (n = 11).
AVERAGE DRY MASS AND ENERGY CONSUMED
Sculpin showed a weak pattern of consuming larger prey items as the standard length increased (Fig. 4). This pattern was similar for the energy intake of sculpin throughout the sample period. The pattern was random for sculpin in 15% embedded streams in spring (Fig. 4a, [R.sup.2] = 0.01) but stronger for sculpin in 35% embedded streams ([R.sup.2] = 0.15). During the summer, sculpin from 15% embedded streams had a positive pattern (Fig. 4b, [R.sup.2] = 0.26) indicating larger fish consumed larger prey. There was no pattern present for sculpin in 35% embedded streams ([R.sup.2] = 0.05). In the autumn, sculpin from both embeddedness levels showed a positive relationship (Fig. 4c). The pattern for sculpin in 15% embedded streams was exponential rather than linear. Sculpin from 15% embedded streams in winter again showed a positive pattern (Fig. 4d, [R.sup.2] = 0.27), while sculpin from 35% embedded streams showed no pattern.
The NMDS ordination for sculpin diets (stress = 0.22) determined that embeddedness level and season had some influence on the grouping (Fig. 5). The most important macroinvertebrate groups in distinguishing these differences based upon the envfit function in R (R Development Core Team, 2008) were the orders Diptera, Lepidoptera, Coleoptera larvae, Plecoptera, and Hemiptera (P < 0.01). Sculpin in TMR were defined by Coleoptera larvae, while fish from TMR in spring and winter along with fish from LBC in spring and winter and SB spring were all defined by Plecoptera. Fish from MR in all seasons and TMR in the summer were grouped by the absence of Plecoptera prey.
Compositional analysis showed distinct patterns in feeding between the different embeddedness levels (Table 2) and feeding was different than chance (P < 0.05). Within both embeddedness levels, sculpin showed diet patterns that did not always include the most abundant prey present in the stream. Sculpin from 15% embedded streams in spring preferred EPT prey while sculpin from the 35% embedded streams preferred chironomids. The relative rank of Chironomidae was equal in both embeddedness levels but did not translate to equal representation in the diet. During the summer, the same pattern was evident. Sculpin from 15% embedded streams consumed ephemeropterans and megalopterans. Megaloptera were one of the least abundant groups present. Sculpin from 35% embedded streams consumed chironomids, lepidopterans, and coleopteran adults. Lepidoptera and Coleoptera adults again were two of the least abundant groups. Sculpin in the autumn showed patterns similar to the other seasons. Sculpin from 15% embedded streams consumed ephemeropterans, trichopterans, and lepidopterans while sculpin from 35% embedded streams consumed trichopterans and chironomids. In the winter, sculpin from 15% embedded streams had diets consisting of ephemeropterans and trichopterans. Fish from the 35% embedded streams consumed chironomids, ephemeropterans, and trichopterans.
The results from this study document differences in seasonal feeding of mottled sculpin between two different levels of embeddedness. Although community metrics indicate that embeddedness of 35% in the stream may not shift the macroinvertebrate community towards impairment, the pattern of mottled sculpin feeding was different at these levels. Access to preferred prey may be altered forcing sculpin to compensate by consuming smaller prey.
Seasonal variation in the macroinvertebrate community was present within an embeddedness level. As abiofic factors of the stream change, the macroinvertebrate community will also change (Joshi et al., 2007). These factors can include water levels, water temperature, floods, pH, and food availability (Hussaln and Pandit, 2012). Different organisms will use different environmental cues to trigger metamorphosis and emergence from the stream, and these cues usually center on water temperature and water flow (Harper and Peckarsky, 2006). Riffle samples were taken throughout the year, therefore, season was most likely the cause of the differences observed in community structure.
Variation was also present in the macroinvertebrate community between the two embeddedness levels. Excess sediment within a stream channel can cause decreases in macroinvertebrate diversity (Mebane, 2001), density (Lenat et al., 1981), and EPT taxa richness, along with increases in certain Chironomidae genera (Angradi, 1996). However, shifts in these metrics may be less than the natural variation among streams, even as sediment levels approach 30% in the stream (Angradi, 1996). The results from the MRPP indicated that the riffle samples from the two different embeddedness levels were not statistically different. This demonstrates that the embeddedness levels selected in this study may not have been high enough to overcome the variation among streams and cause a shift in the community structure. It was necessary to choose these levels though, as mottled sculpin were not present in streams with higher than 35% embeddedness in the stream channel.
Densities of mottled sculpin were highest in the 35% embedded streams; however, the weight of fish and Fulton's condition factor of fish from one of these streams (MR) were lower than the other streams. As the sediment load increases in the stream channel, interstitial spaces begin to be filled, limiting habitat for benthic fish (Kemp et al., 2011). The removal of these spaces often leads to the extirpation of riffle dwelling fish. These fish may still be present in streams with large levels of sediment, e.g., 60-85% embeddedness but the abundance tends to decrease (Sutherland et al., 2002). Sediment levels in this study may not have been high enough to remove fish but may lead to a decrease in condition Factor. This decrease in condition factor ultimately may lead to the extirpation of mottled sculpin.
Fish tend to be gape limited and can only consume prey items within a certain size range (Schlosser, 1988). There was some indication that mottled sculpin in our study consumed larger prey items as they grew and in turn prey with a higher caloric content. In certain seasons, e.g., summer and winter, fish from the 15% embedded streams showed this pattern while fish the 35% embedded streams did not. The ability for larger fish to select larger prey will ultimately provide more energy for the fish. These data agree with findings that sculpin partition the habitat according to size. Slimy sculpins (Cottus cognatus) inhabit shallower areas in Lake Ontario as juveniles move to deeper and more protected habitats as they grow (Brandt, 1986); while Petty and Grossman (2004, 2007) found that mottled sculpin force smaller conspecifics to less optimal feeding patches in streams.
Energy consumption becomes increasingly important as the water temperature increases and metabolic costs rise (Buckel et al., 1995). These metabolic costs are also coupled with increase in stream macroinvertebrate production (Georgian and Wallace, 1983). The average energy content of chironomids was 0.56 calories compared to 1.93 calories for ephemeropterans in the summer, indicating four times as many chironomids will need to be consumed to equal one ephemeropteran. Data in this study that demonstrate sculpin are feeding in stream riffles is consistent with the literature (Petty and Grossman, 2007). Feeding is occurring in all four seasons (the percent of empty stomachs was 5% in spring, 9% in summer, 40% in autumn, and 59% in winter) but not necessarily on large prey. Overall, a relationship of increasing prey size consumption as sculpins obtain larger sizes is seen in three seasons for 15% embedded streams vs. only two seasons for 35% embedded streams, and the pattern is mirrored between dry mass and energy content. The lack of a strong relationship, especially in summer, could be responsible for sculpin from MR exhibiting a lower body condition for small and large adults compared to the other streams.
The ordination of mottled sculpin diets revealed seasonal and embeddedness level effects on feeding ecology, however, these effects were not able to completely explain the grouping pattern present. Mottled sculpin are thought to select habitat patches based upon prey abundances (Petty and Grossman, 1996) with larger adults able to displace smaller conspecifics for optimal habitat patches (Petty and Grossman, 2004). Small headwater streams have a high degree of habitat heterogeneity and macroinvertebrate abundances are likely different even at small scales within these streams (Longing et al., 2010). Multiple samples were taken at each site and an effort was made to collect sculpin near where the riffle samples were taken to reduce variability.
Results from compositional analysis showed that different feeding patterns were occurring between the two embeddedness levels. Sculpin often fed on the most abundant food item in the stream; however, this was not always the case. In general, ephemeropterans were often the most important food item for the lower embeddedness levels, while chironomids were the most important item for the higher embeddedness level, no matter how abundant or rare these taxa were. Zimmerman and Vondraceck (2007) found that slimy sculpin fed in a similar manner. Other studies have found sculpin seek one specific taxa of macroinvertebrate (Gilson, 1978). The results suggest that sculpin may choose certain prey items but there also appears to be a random component in the diet evidenced by the consumption of rare prey items.
The selection or avoidance of macroinvertebrate prey by mottled sculpin may have been related to the behavior of these insects. Certain macroinvertebrates may be free swimming and more susceptible to predation while others remain hidden on the underside of rocks (Novak and Estes, 1974). Some species will change their habitat in response to the predator (Bo et al., 2010), using interstitial spaces for cover. As stated earlier, sediment begins to fill in the interstitial spaces at higher levels. It may be possible that sediment in the 35% embedded streams has prevented access to these interstitial spaces by sculpin but not macroinvertebrates. This would not manifest itself in a change of the macroinvertebrate community but in the feeding history of mottled sculpin. Sculpin are prevented from consuming larger EPT prey due to lack of access and must consume other prey like chironomids.
While it is difficult to assign causality due to low sample size in this study, possible patterns of sediment effects of feeding may have been present. Our study shows that sediment may not directly affect a stream by changing the macroinvertebrate community. The embeddedness of a stream may, however, result in restricting sculpin access to energetically valuable prey sources. These fish must compensate by consuming other prey, e.g., chironomids, which requires a larger number to be consumed to equal that of EPT taxa. Future studies designed to assess the health of streams affected by sediment should take care to determine what prey benthic fish are selecting and avoiding. This information may provide insight as to whether benthic fish communities are being affected by sediment loads in the stream. A threshold may be present in the stream in regards to sediment, after which the condition of fish begins to decrease.
Acknowledgments.--The authors are extremely grateful to G. Strain, E. Just, and A. Hnatkovich for extensive field help. R. Utz provided valuable guidance with statistics and data analysis.
SUBMITTED 31 MAY 2011
ACCEPTED 10 APRIL 2013
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EDWARD J. MCGINLEY (1)
Wildlife and Fisheries Resource Program, Division of Forestry, P.O. Box 6125, West Virginia University, Morgantown 26506
RICHARD L. RAESLY AND WILLIAM L. SEDDON
Biology Department, Frostburg State University, 101 Braddock Road, Frostburg, Maryland 21532
(1) Corresponding author: e-mail: firstname.lastname@example.org
TABLE 1.--Benthic macroinvertebrate metrics for the study streams. Average values of the two streams in each embeddedness category are presented for each season. Standard error around the mean is presented in parentheses. Diversity is measured as Simpson's index of diversity. Percent EPT refers to percent of the benthic organisms comprised of the orders Ephemeroptera, Plecoptera, and Trichoptera. Percent other refers to a group of Collembola, crayfish, and oligochaetes. Collembola are terrestrial insects and crayfish and oligochaetes represent non-insect invertebrates found within the stream Density Taxa (indiv/ Diversity richness [m.sup.2]) 15% embedded Spring 0.92 (0.008) 44 (5.06) 2958 (744.2) Summer 0.90 (0.002) 43 (0.39) 3018 (361.3) Autumn 0.88 (0.04) 38 (3.36) 5172 (1863.9) Winter 0.89 (0.02) 38 (0.35) 3632 (107.8) 35% embedded Spring 0.87 (0.04) 41 (1.69) 3600 (128.7) Summer 0.83 (0.02) 40 (0.21) 5922 (327.0) Autumn 0.87 (0.06) 43 (2.44) 4389 (107.8) Winter 0.89 (0.04) 44 (1.56) 3625 (817.8) %n % EPT Chironomidae % Other 15% embedded Spring 57.8 (1.34) 20.9 (3.50) 1.33 (0.58) Summer 37.1 (0.67) 42.2 (2.26) 1.96 (0.20) Autumn 37.1 (2.76) 20.8 (2.76) 3.67 (0.71) Winter 62.9 (2.33) 16.5 (2.58) 4.59 (0.90) 35% embedded Spring 51.4 (2.69) 24.6 (4.67) 0.20 (0.09) Summer 18.6 (1.66) 70.3 (2.69) 1.95 (0.02) Autumn 55.9 (8.31) 25.5 (4.10) 4.54 (2.91) Winter 33.4 (1.94) 22.2 (0.95) 5.47 (4.27) TABLE 2.--Ranks of prey items found in the diet and in the stream in all four seasons. The ranks of prey items in the diet are based upon compositional analysis and take into account the relative abundance of prey items in the stomach and in the environment Ranks in the stream are based upon average relative proportions of each group. Other denotes a combination of Collembola, crayfish, oligochaetes, and amphipods. Dashed lines represent the absence of that group. Numbers in parentheses are the respective sample sizes of sculpin Spring 15% (34) 35% (35) Prey group Diet Stream Diet Stream Chironomidae 4 2.5 1.5 2.5 Coleoptera adults 7 5.5 9.5 7.5 Coleoptera larvae 8 3 8 4 Diptera 5.5 5.5 6 5 Ephemeroptera 1 1 5.5 3 Hemiptera -- -- -- -- Lepidoptera -- -- -- -- Megaloptera -- -- 3 7.5 Other 4.5 7 7 9 Odonata 10 8 5.5 10 Plecoptera 3 3.5 5 2.5 Trichoptera 3 7 5.5 4 Summer 15% (28) 35% (35) Prey group Diet Stream Diet Stream Chironomidae 4.5 1 2 1 Coleoptera adults 5.5 7.5 2 11 Coleoptera larvae 7 3.5 10 5.5 Diptera 5.5 6 8.5 5 Ephemeroptera 2 3 5.5 2 Hemiptera 6 9.5 10 9 Lepidoptera -- -- 2 12 Megaloptera 3 9 6 8 Other 4.5 7.5 6 7 Odonata 11 11 8.5 10 Plecoptera 8.5 2.5 11 3.5 Trichoptera 5.5 5 7 4 autumn 15% (23) 35% (24) Prey group Diet Stream Diet Stream Chironomidae 6.5 6 2.5 4.5 Coleoptera adults 12 9.5 8.5 3 Coleoptera larvae 7 7.5 9 6.5 Diptera 5.5 1 6 2.5 Ephemeroptera 2.5 5.5 4.5 6 Hemiptera 12 10.5 9 9 Lepidoptera 3 12 7 11.5 Megaloptera 10.5 6.5 8 8 Other 12 6 10 6 Odonata 9.5 7.5 6.5 9.5 Plecoptera 6 4 8.5 3.5 Trichoptera 3.5 2 2 5 Winter 15% (32) 35% (18) Prey group Diet Stream Diet Stream Chironomidae 7 8 1.5 2.5 Coleoptera adults 9.5 5 6 5.5 Coleoptera larvae 8.5 6.5 7 3.5 Diptera 7 1.5 7.5 4.5 Ephemeroptera 1.5 3.5 3 7.5 Hemiptera -- -- -- -- Lepidoptera -- -- -- -- Megaloptera 5 9 10 9.5 Other 9 4 5.5 6 Odonata 6 8 10 9.5 Plecoptera 1.5 3.5 4.5 2 Trichoptera 3 5 3.5 4.5 TABLE 3.--Condition factor of the three size classes for each stream. Sculpin were sampled during a population study in Jun. 2006. The 15% embedded streams are LBC and SB; the 35% embedded streams are TMR and MR Sample size in each group is denoted by n and Fulton's condition factor is denoted by F. Condition factors were compared within a size group, with different letters from left to right indicating a significant difference at the 0.05 level LBC SB n F n F Juveniles 61 2.19 (ab) 34 2.44 (b) Small adults 47 2.21 (a) 30 2.12 (a) Large adults 48 2.28 (a) 3 2.26 (a) TMR MR n F n F Juveniles 72 2.05 (a) 160 1.94 (a) Small adults 94 2.08 (a) 100 1.46 (b) Large adults 11 2.15 (a) 43 1.14 (b)
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|Author:||McGinley, Edward J.; Raesly, Richard L.; Seddon, William L.|
|Publication:||The American Midland Naturalist|
|Date:||Oct 1, 2013|
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