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Soft flesh in sablefish, Anoplopoma fimbria, of southeastern Alaska: relationships with depth, season, and biochemistry.

Introduction

The quality of fish flesh is important to both commercial and sport fishermen. Soft flesh in fish may affect the yield, the success of preservation by freezing, the palatability, and the overall quality of the fish for market or consumption.

The condition of "soft" flesh has been noted in several species of marine fish in the North Pacific, Gulf of Alaska, and the North Atlantic. The reasons for the occurrence of soft flesh has been determined for several fish species: parasite infestations (Levsen et al., 2008), spawning and cessation of feeding (Tomlinson et al., 1967), mineral accumulation (Teeny et al., 1984), temperature/exercise (Foy et al., 2006), biochemical adaptation to the deep sea (Siebenaller and Somero, 1989), and depth of occurrence (Norris et al. (1)).

Sablefish or blackcod, Anoplopoma fimbria, a marine species of the shelf and slope of the North Pacific Ocean, are found in commercial quantities from northern Mexico to Alaska and as far west as eastern Siberia (Kimura et al., 1998; Low et al. (2)). United States and Canadian fishermen have fished the North American resource for over a century, but it was not until the Japanese distant-water longline fishery developed in the 1960's that the resource was subject to intense exploitation (Low et al. (2)). The fishery did not fully develop on the U.S. west coast until the advent of the pot (trap) fishery developed by the Bureau of Commercial Fisheries (BCF) Biological Laboratory in Seattle, Wash., in the late 1960's (Hughes et al., 1970). It was then that the issue of sablefish with soft-textured flesh was noted by the commercial fishing industry and relayed to BCF fisheries personnel. Sablefish with "soft" flesh were first documented in deep-water samples taken during exploratory fishing activities in the mid 1960's off the coasts of Washington and Oregon, near the mouth of the Columbia River (Heyamoto and Alton, 1965).

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Chemical analysis of sablefish, caught at depths ranging between 457 and 640 m in November and December of 1969, showed that the edible flesh of fish judged to be soft had an average water content of 81%, 10.1% fat content, and protein content of 6.7% (Patashnik et al. (3)). These data suggested that the increased water content and apparent protein depletion may be similar to a condition found in Dover sole, Microstomus pacificus (Patashnik and Groninger, 1964) and American plaice, Hippoglossoides platessoides (Templeman and Andrews, 1956) and may make these fish less suitable for processing. This condition was thought not to be unusual by Love (1970) who observed "the majority of fish experience severe (food) depletion for a part of every year of their lives and are therefore unusually adapted to mobilizing their body constituents as a fuel for survival."

Follow-up research to the 1969 study was initiated by the National Marine Fisheries Service in 1971 and again in 1979 to further study the soft flesh problem as it concerned the emerging west coast pot fisheries for sablefish. The intent of that research was to examine possible methods for detecting and separating sablefish with soft flesh from "normal" sablefish that could be used by fishermen at sea or by fish processors at dockside. To accomplish this, it was necessary to acquire a better understanding of the nature of the problem. The studies included additional chemical analyses to reconfirm results of the earlier analyses, tests to determine the degree of softness or firmness by finger pressure or by specific gravity in brine, and tests to determine whether skin color was an indicator of softness. The results of these tests were related to depth of capture, which ranged between 457 and 823 m. Results from these studies (unpublished data) essentially confirmed what had been seen previously, that sablefish with high water content and low protein content generally were soft textured, and the incidence of this condition increased with depth of capture. The subjective methods to determine if fish were soft or firm when landed were evaluated during this period. A process using depth of catch and skin color of the fish was used in conjunction with finger pressure as a rapid method for separating soft fish from firm fish at point of landing. It was also observed that sablefish caught deeper than 548 m tended to be larger, blacker or darker gray in color, sometimes with a rose-colored lateral tint, especially if spawned; these fish generally had soft-textured flesh (Fig. 1). Firm sablefish, caught shallower than 548 m and not spawned, were characteristically a green-gray color dorsally with a light gray or white underbelly (Fig. 2). These photos show the extremes of soft and firm sablefish. Soft fish ranged from very black on back and belly to black backs and dark grey bellies to dark grey backs and bellies.

Our study addressed the following questions:

* Does the occurrence of soft sablefish in Alaska waters relate to depth of capture, season, spawning condition, and type of fishing gear used?

* Do the results obtained in sablefish studies off Oregon and Washington apply to Alaska?

* Can the harvest of sablefish with soft-textured flesh be avoided by manipulating fishing seasons and fishing depths?

Specific objectives of our study were to 1) determine the effects of season, depth of capture, sex, sexual maturity, and gear type on flesh quality and 2) determine the relationships of water, protein, lipids, ash, and mineral content of muscle to flesh quality.

Materials and Methods

Collection and Shipboard Processing

Sablefish were collected in southeastern Alaska in the summer (June and August) of 1985 and winter (January and February) of 1986 at four locations in Chatham and Icy Straits and at one location offshore of Cape Cross (Fig. 3). Fish were captured with a 400-mesh otter trawl, longline (LL), and conical pots. Longlines were fished for 3 h, pots for 24 h, and the trawls for 0.5 h at depths ranging between 259 and 913 m. Depths of capture were recorded. Following capture, the fish were immediately sacrificed, weighed, bled, measured (fork length), and subjectively classified as soft or firm using the methods previously described, i.e. finger pressure and skin color. They were then sexed, dressed, and classified as to gonad developmental stage. There are five stages of gonad development for each sex: 1) immature, 2) maturing juvenile, 3) mature, 4) spawning, and 5) post-spawning. Stomach fullness and contents were also noted but are not reported in this study. The cleaned fish were frozen and stored at -29[degrees]C for later objective and subjective testing. A total of 681 sablefish (n = 242 summer; n = 439 winter) were processed for the study. Data from all study sites were pooled.

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Sample Preparation

In preparation for conducting thaw and cooked drip analyses, 25-mm thick steaks were removed by band saw from just posterior to the pectoral fins of each frozen fish. The steaks were skinned and bones removed. Samples of nape meat frozen at the time the fish were caught were prepared for chemical analysis by partially thawing the meats and then homogenizing them by passing them through a 4-mm perforated plate attached to a food grinder.

Chemical Analyses

Samples were stored frozen at -29[degrees]C until analyzed chemically. Analyses for water (moisture), lipids, total protein, and ash were determined according to official AOAC methods (Horowitz, 1980). Protein was determined by the Kjeldhal (4) method and lipids were extracted using a soxhlet apparatus and methylene chloride solvent. Elemental (metal) analyses were made by atomic emission spectrometry as described by Teeny et al. (1984). Analyses were made for Na, K, Mg, Ca, P, Mn, Fe, Co, Cu, Sr, and Zn. Soluble protein was determined by the "salt extractable" nitrogen test or the modified Biuret method described by Snow (1950).

Thaw and Cooked Drip Analyses

To determine thaw and cooked drip loss, a steak sample from each fish was weighed and placed frozen in plastic, cook-in-the bag pouches with perforated bottoms that were in turn placed in slightly larger outer plastic bags. Half of the bags were weighted to ensure submersion of the sample during cooking. Samples were cooked in boiling water for 12 min. After removal from the boiling water, the samples in the inner bag were cooled and reweighed. Samples in the unweighted bags were suspended on racks and placed in a refrigerated cooler at 3[degrees]C and allowed to thaw for 24 h and reweighed after loss of water.

Data Analyses

Flesh condition--soft and firm--was tested for differences in total protein, lipid, gonad stage, pH, and yellow or yellow-green bile by capture depth with separate multiple linear regression models. Yellow or yellow-green bile is indicative of well fed or recently fed fish while progressively darker green shades to dark blue indicates fish not recently fed (Robb, 1992). Flesh condition was treated as a dichotomous predictor (Weisberg, 1985) in the models with soft fish coded as 0 and firm fish coded as 1. For a fixed depth, the estimated regression coefficient for flesh condition can be interpreted as the estimated difference in the dependent variable for the two flesh conditions. Seventeen biochemical and chemical components of flesh samples were tested with one-way ANOVA's for differences between the two flesh conditions.

The components tested for differences between the soft and firm flesh include K, Mg, P, Zn, pH, total protein, Ca, Co Mn, Fe, Na, Cu, Sr, soluble protein, lipid, ash, and water. The a-level of significance (0.05) was adjusted with a Bonferroni correction for performing multiple comparisons. Various length-weight regressions by flesh condition, season, gender, and gonad condition were fit for graphical comparison. Condition factor, computed as K = [10.sup.4] x W(g)/[L.sup.3](cm), was compared for flesh condition and by season with a two-way ANOVA. Only immature or developing fish (maturity stages 1 and 2) were included in the analysis.

The relative weight loss of soft- and firm-flesh fish samples was compared for thawed and cooked processing with one-way ANOVA's. Relative weight loss (%) of processed samples was calculated as (post-weight-pre-weight)/ pre-weight x 100. Analyses were performed separately for the summer and winter seasons. The tests were one-tailed as the soft flesh was hypothesized to lose more weight than firm flesh during thawing and cooking.

Results

Flesh Quality of Catch

By Season and Gender

More sablefish were subjectively classified as firm in the winter than in summer (Table 1). Firm males and females made up 67% of the winter catch (30% and 37%, respectively), but only 40% of the summer catch. The percentage of soft fish in the summer catch (61% males, 59% females) was, respectively, 2.3 and 1.5 times that seen in the winter. Soft females and males were about equally abundant in the summer landings, 59% and 61%, respectively, but soft females exceeded soft males in the winter catch (39% vs. 26%).

By Gear, Depth, and Season

Gear selectivity for flesh condition varied with type of gear and depth (Table 2). At the shallowest depth fished in summer (259-364 m) about three times more fish were designated firm than soft in catches from both longline and pot gear. At depths 365-547 m nearly equal numbers of firm and soft fish were taken by longline gear in the summer. At depths 548-913 m most fish were soft in longline and pot catches.

Catches in the winter with longlines and pots showed a similar trend but started deeper; at 365-547 m and 548-730 m most fish were firm while most fish were soft at 731-913 m. Trawls caught more firm fish than soft fish at all depths. In contrast, flesh quality composition of trawl catches was much different than the composition of combined longline and pot catches at the same depths in winter (Table 2). The proportion of firm fish in trawl catches was, respectively, 25% and 40% lower than pots and longline at depth intervals of 365-547 m and 548-730 m. No trawling was done in summer.

Catches of firm-fleshed sablefish on longlines and in pots declined with increasing depth in winter and summer (Table 2). Most of the fish caught in summer at depths shallower than 365 m were firm, but fish were increasingly soft-textured when caught at depths greater than 547 m. Most winter-caught fish (> 80%) were firm at depths in the shallow interval (365-547 m) and the middle interval (548-730 m). In both summer and winter the percentage of firm fish caught was low (4-16%) in the depth interval 731-913 m.

Sexual Maturation and Flesh Quality

Winter catches by gonad stage and quality of flesh were summed over depths and compared for longline plus pots (LL+POT) and trawl catches (Table 3). Most fish were gonad stage 1 or 2 (immature or developing), but a few were stage 3, 4, or 5 (gravid, ripe, or spent). The percentages of firm and soft fish of both sexes were similar and nearly overlapping for all three gear types. Spent females appear only in the soft category. Also, a greater percentage of maturity stages 3, 4, and 5 occurred among the soft fish compared to firm fish, especially for trawl catches.

Fish Condition by Season

Length-weight regressions for male fish judged to be firm or soft in flesh texture indicate that summer fish were generally heavier than winter fish of the same fork length. Fit for most of these regressions is good with [R.sup.2] values ranging from 0.76 to 0.91 (Table 4). Figure 4 shows the winter and summer maturity regressions for firm males. Firm summer males of 54 to 66 cm fork length (line 2) appear to be heavier than firm winter males of similar length (line 1). Gonad development further explains the differences in weight between firm males (Fig. 5). As gonads develop through stages 1-4, they account for an increasing proportion of weight to the overall mass of the fish. Length-weight regressions for firm and soft, winter and summer females (Fig. 6) show a similar length-weight relationship with respect to maturity stage but the slopes for the various gonad stages (Fig. 7) are different than the males.

To eliminate the inluence of gonad weight on the summer and winter comparison of fish, we calculated the condition factor (K) for all fish that were immature or developing (maturity stages 1 and 2). The formula for the condition factor is K = [10.sup.4] x W(g)/[L.sup.3](cm). Gonad weights in these fish would be less than other maturity stages. A two-way analysis of variance on condition factor (K) classified by season and flesh condition was calculated for these fish.

No evidence of interaction between season and lesh (ANOVA, F = 1.16 ~ [F.sub.1,577], P = 0.28) or a significant difference in flesh condition (ANOVA, F = 0.54 ~ [F.sub.1,577], P = 0.46) was seen but the seasonal difference was significant (ANOVA, F = 1.16 ~ [F.sub.1,577], P = 0.02). The summer fish had a higher mean condition factor (108.5, SE = 1.45) than the winter fish (104.6, SE = 0.70). Assuming that sablefish of all gonad developmental stages would show this difference in condition factor, we could expect fish caught in the summer to be about 3% heavier than fish caught in the winter.

Winter and summer differences in body weight were further examined by comparing the average weight of winter and summer fish (combined males and females) by length intervals (Table 5). These data show that mean weights of winter and summer caught fish differed by size groups. Small fish (< 58 cm) were 15% heavier in summer than in winter, but differences between other size groups varied from -2 to +9%. Overall, fish caught during the summer averaged 6% heavier than fish caught during the winter. We believe that gonad weights inluenced the comparison of larger fish, winter versus summer, and therefore the 6% difference between mean weights of winter and summer fish is a minimum estimate. These data indicate that summer fish are clearly heavier than winter fish of the same length.

Depth of Capture vs. Proximate Analyses, Flesh Condition, and Gonad Stage

The relationships of total protein, lipid, gonad stage, pH, and green bile to depth of capture were complex and inconsistent (Table 6). Total protein, lipid, and green bile were related to flesh condition and depth of capture. Gonad development was related to depth of capture but only marginally related to flesh condition. Conversely, flesh pH was related to flesh condition but not to depth of capture.

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Proximate Composition and Electrolyte Analyses and Flesh Condition

Among 17 variables (including protein, lipid, and pH previously mentioned) that we examined in sablefish flesh, 11 showed significant differences between firm and soft fish (Table 7). Variables for which the means were higher for soft fish compared to firm fish included lipid, water, and the electrolytes sodium (Na) and strontium (Sr). All other means were lower for the soft fish. Higher sodium and lower potassium (K) in white muscle of fish are usually indicative of starvation (Love, 1980). Similar differences in sodium and potassium have also been observed in spawning salmon (Tomlinson et al., 1967). In laboratory studies, Sullivan and Somero (1983) were able to induce physiological changes in starved sablefish that closely resemble the biochemical and physical characteristics of soft fish that we observed in the research reported here.

Differences in mean chemical constituents in soft compared to firm fish were as follows: protein was lower by 14% from 137 mg/g to 118 mg/g, water was higher by 1% from 721 mg/g to 726 mg/g (but not significantly), lipid was higher by 12% from 133 mg/g to 148 mg/g, and ash was lower by 3% (Table 7).

Yield Analysis

Changes in weight of winter and summer samples during the processes of thawing and cooking are shown in Table 8. Soft sablefish lost 45% more thaw drip loss in 24 h and 24% more cooked drip loss than the firm sablefish. Average weight loss in the thaw drip loss test was 6% for the firm fish and 12% for soft fish. In the cooked drip loss test, average losses for firm- and soft-textured fish were 21% and 27%, respectively.

Yield differed in winter and summer by flesh quality, but not consistently. Thaw drip loss for soft fish in winter was more than twice that of summer caught fish (14.6% vs. 6.7%). Thaw drip loss for firm fish averaged 8.3% in summer and 5.6 % in winter.

Differences in cooked drip loss in winter and summer were not great between firm and soft fish. Cooked drip loss for firm fish in winter averaged 21.7%, while soft fish averaged 29.8%. In summer the cooked drip loss was 18.9% for firm fish and 24.0% for soft fish.

The relative weight loss of the soft-flesh samples in winter was significantly higher than the firm-flesh samples for both the thawed (ANOVA, F = 99.0 ~ [F.sub.1,229], P < 0.001) and cooked samples (ANOVA, F = 106.1 ~ [F.sub.1,220], P < 0.001) (Table 8, Fig. 8). The relative weight loss of the summer, thawed samples was not significantly higher for the soft-flesh samples than for the firm-flesh samples (ANOVA, F = 2.0 ~ [F.sub.1,115], P = 0.16) (Fig. 9a); however, the soft-flesh samples lost significantly more relative weight during the cooking process (ANOVA, F = 9.3 ~ [F.sub.1,118], P = 0.003) (Fig. 9b).

Discussion

Biological, Physiological, and Environmental Factors

Several factors may be contributing to the observed incidence of soft flesh in sablefish: reproductive cycle, distribution of fish over a greater depth range as they mature and grow, changes in diet as they move deeper in the water column, and physiological changes induced by increased pressure. We have noted soft flesh in sablefish after spawning but have not determined whether spawning itself or their presence at great depth (> 300 m) contributes to the incidence of soft flesh. Most of the soft fish are dark black in color, and their size range extends from small, recently-maturing fish to very large females that have spawned several times. This suggests that depth of occurrence may have a major influence on the development of soft flesh but the reproductive cycle may exacerbate its development. We need to examine available tag data reports on soft female sablefish to determine if individual fish remain soft following spawning at great depth.

Effects of Time and Depth of Fishing and Gear Type on Catch Composition and Yield

Results of our study indicate that regulating time of fishing, depth of fishing, and gear type may increase the number of firm sablefish in catches. Yield from soft fish is considerably less than from firm fish (this study; Norris et al. (1); Patashnik et al. (3)); therefore, it is important to optimize the catch of firm fish. Yield is also dependent upon the condition factor of the fish or weight per given length. Our study shows that summer fish of all flesh conditions are on average 6% heavier than winter fish; therefore, yield from summer fish would be expected to be higher. Summer catches of sablefish, however, have 27% more soft-fleshed fish, which would reduce their overall yield.

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If fishing were in late summer, would the increased yield from heavier fish offset the loss from soft fish? Probably not, because loss of yield from soft sablefish is considerable: 45% greater thaw drip loss from thawed raw fillets and 24% greater cooked drip loss. Although not measured here, there is also a loss of quality associated with the loss of drip in that nutrients such as protein, nitrogen, essential electrolytes, and other flavor components are removed with the drip (Miyauchi and Spinelli, 1967). Storage temperature could also significantly affect the composition and amount of drip produced in soft-textured sablefish. Storage temperatures of -20[degrees]C, commonly used in commercial cold storage facilities, would be expected to produce a higher thaw and cooked drip loss than storage at -30[degrees]C (Miyauchi, 1963).

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The numbers of sablefish with soft flesh are probably of more importance to overall yield than small differences in physical conditions. A detailed calculation of overall yields from summer and winter catches is beyond the scope of this paper, but based on available information, winter catches would probably produce higher yields. Fishing all depths in winter (Jan.-Feb.) would yield a catch consisting of 67% firm fish, whereas the summer catch (June-Aug.) would yield only 40% firm fish. Presently the season in Chatham Strait is from 15 Aug. to 15 Nov. We have no information on the composition of the catch regarding flesh condition from this area from September to November but expect it would be between 40% and 60% firm fish over all fishing depths. Based on the results of our research, it appears that the commercial season in Chatham Strait may already be at the optimum time.

Regulating the depth of fishing also has the potential for increasing the yield from sablefish landings. Depth distribution of sablefish changes by season; however, all appeared to move deeper in winter. Firm fish were located at shallower depths (< 365 m) in summer but appeared to be located in deeper water (< 548 m) in the winter. Soft fish also appeared to be in deeper water in the winter from 548 to 730 m or more. Limiting fishing to depths where soft fish are less abundant may increase yield from the catch and reduce waste of soft fish. If fishing were limited to less than 731 m in winter, the catch would produce about 82% firm fish.

How much this would affect the overall catch is not clear; 23% of the winter catch in our study was from depths greater than 730 m. If, on the other hand, fishing in the summer were limited to less than 548 m, the catch would yield about 63% firm fish. However, the overall catch may be reduced because 44% of the summer catch in our study came from depths greater than 547 m. Catches from depths greater than 730 m have more large fish in winter and summer; therefore, the average weight of fish would probably be less if the above depth changes were adopted.

How changes in fishing depth and season would affect the offshore fishery is not clear. Presently, the sablefish fisheries in both the Gulf of Alaska and the Bering Sea use fixed gear (longlines and pots) under Individual Fishing Quota (IFQ) programs. The fixed gear seasons open 15 Mar. and close 15 Nov. Only one of our study sites (Cross Sound) was in offshore waters. Distribution of firm- and soft-textured fish by depth at this site was similar to the Chatham Strait sites, so perhaps our study results could be applied.

Whether regulating fishing depth is feasible and beneficial to yield depends upon several factors: 1) the present depth distribution of fishing effort, 2) the area of depth strata available, and 3) the distribution of fish by depth. Clearly more information is needed before one can determine the impact of depth regulations on yield.

The effect of gear selectivity for soft fish seems clear. Longlines and pots took similar proportions of soft fish in both summer and winter. Trawl catches contained a higher proportion of soft fish compared to longlines and pots, perhaps because soft fish may be less attracted to bait and are, therefore, less available to longlines and pots. Trawls would take them regardless of feeding behavior.

Relationship of Biochemistry to Soft Flesh

Biochemistry of sablefish flesh differs from soft to firm. A better understanding of the cause-effect relationship of the soft flesh problem would help us predict its distribution in time and location. Differences in flesh quality may be the result of genetic variability or the prolonged exposure to different environmental factors associated with depth as hypothesized in previous studies (Norris et al. (1)). Food availability, food quality, activity level, temperature, and pressure are all factors associated with depth, which could change the physiology and biochemistry of sablefish. Sablefish (Sullivan and Smith, 1982) and many other mesopelagic and bathypelagic fishes living at great depths (Siebenaller and Somero, 1989; Drazen, 2007) have been shown to have higher water content and lower protein and lipid content than species living at shallow depths. Deepwater species adapt biochemically by lowering metabolic and enzyme rates to conserve energy and change physiological processes by reducing locomotory activity in response to living in an environment where food resources are sparse and meals infrequent (Drazen, 2007). Metabolic rates of vertically migrating mesopelagic fish decreased with increase in depth of occurrence (Karinen, 1965), but the duration of time at depth necessary to initiate biochemical changes has not yet been established. Foy et al. (2006) investigated the roles of temperature, pH, and exercise in the development of "chalkiness" in Pacific halibut, Hippoglossus stenolepis, but were not able to reproduce the effects in halibut held and exercised to exhaustion in a laboratory experiment. Reproductive development may also inluence the biochemical composition of fish flesh as shown by our data.

Results of our study seem contradictory with respect to determining the cause of soft flesh in sablefish. Is it diet, parasites, depth of occurrence, life stage, or genetics? High sodium, low potassium, and yellow to yellow-green bile in soft fish are all indicative of well-fed fish (McCormick and Podoliak, 1984). Parasites can cause soft flesh; myxosporean parasites are known to cause soft flesh in Atlantic mackerel, Scomber scombrus (Levsen et al., 2008). Some species of these parasites are known to be present in the North Pacific but it is unlikely that such parasites were present in our study because cysts (black or white) in the flesh can usually be seen with the naked eye and the flesh liquefies when cooked. Perhaps one way to answer the question of cause and effect would be to determine the genetic types and variability of firm and soft sablefish (Tsuyuki and Roberts, 1969).

Acknowledgments

We wish to thank the following for their help in this study: Alice S. Hall, Adam Moles, Jerome Pella, Joanne Hudson, Nancy Maloney, Tom Rutecki, Mike Sigler, and the crew and fisheries personnel of the NOAA ships John N. Cobb and Miller Freeman.

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(1) Norris, J. G., J. Rowley, and S. B. Mathews. 1987. Analysis of four factors affecting the sablefish soft fish problem. Contr. NA85-ABH00056, FRI-UW 8715, Fish. Res. Inst., Univ. Wash., Seattle, Final Rep. to Saltonstall/Kennedy Program, 55 p.

(2) Low, L. L., G. K. Tanonoka, and H. H. Shippen. 1976. Sablefish of the northeastern Pacific Ocean and Bering Sea. NWAFC Processed Rep., 115 p. Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA. 2725 Montlake Blvd. E., Seattle, Wash.

(3) Patashnik, M., H. Barnett, and J. Conrad. 1980. A preliminary report on soft sablefish from the pot fishery off the Washington Coast. Unpubl. rep., URD, Northw. Alaska Fish. Cent., NMFS, NOAA, 2725 Montlake Blvd. E., Seattle, Wash.

(4) Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.

John F. Karinen is with the Auke Bay Laboratories, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Ted Stevens Marine Research Institute, 17109 Point Lena Loop Road, Juneau, AK 99801 and is the corresponding author (john.karinen@noaa.gov). Harold J. Barnett is with the Resource Enhancement and Utilization Technologies Division (REUT), Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2725 Montlake Boulevard East, Seattle, WA 98112. Michele Masuda is with the Auke Bay Laboratories, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Ted Stevens Marine Research Institute, 17109 Point Lena Loop Road, Juneau, AK 99801.
Table 1.--Numbers of sableftsh classified as firm or soft in
winter catches from Chatham and Icy Straits and Cross Sound,
Southeast Alaska, and in summer catches from Chatham and Icy
Straits, Southeast Alaska.

                       Males     Females
            Flesh
Season    condition   No. (%)    No. (%)

Winter      Firm      131 (74)   161 (61)
            Soft       45 (26)   102 (39)
            Total     176        263

Summer      Firm       45 (39)    52 (41)
            Soft       70 (61)    75 (59)
            Total     115        127

Table 2.--Numbers of firm and soft sablefish captured by longline
(LL) and pots in the summer and winter by depth and by trawl in
the winter only. Percent firm fish by season, gear, and depth are
indicated.

                                           Depth (m)
                   Flesh
Season    Gear     condition   259-364     365-547     548-730

Summer    LL       Firm        45 (76%)    29 (48%)     4 (17%)
                   Soft        14          32          19

          Pot      Firm        11 (73%)    0 (0%)       0 (0%)
                   Soft         4          0           27

Winter    LL       Firm                    68 (89%)    24 (100%)
                   Soft                     8           0

          Pot      Firm                    39 (87%)    50 (100%)
                   Soft                     6           0

          LL+Pot   Firm                    107 (88%)   74 (100%)
                   Soft                     14          0

          Trawl    Firm        22 (100%)    33 (63%)   40 (60%)
                   Soft         0           19         27

                        Depth (m)

Season    Gear     731-913    914-988

Summer    LL        1 (4%)    6 (75%)
                   26         2

          Pot       1 (5%)
                   21

Winter    LL        8 (16%)
                   42

          Pot       8 (15%)
                   45

          LL+Pot   16 (16%)
                   87

          Trawl

Table 3.--Numbers of sablefish with firm and soft flesh condition
by gonad development caught in winter with longlines (LL) and
pots versus trawls. Catches are summed over all depths and
percentages by gonad stage are given in parentheses.

                                  Number of Gonad Stage (1) (%)
                    Flesh
Gear       Gender   condition      1         2        3         4

LL+Pot     Male     Firm        55 (68)   16 (20)   1 (1)    9 (11)
                    Soft        17 (68)   4 (16)    0 (0)    4 (16)

           Female   Firm         8 (7)    92 (79)   5 (4)    11 (9)
                    Soft         0 (0)    48 (63)   6 (8)    11 (14)

Trawl      Male     Firm        14 (28)   33 (66)   3 (6)     0 (0)
                    Soft         2 (10)   12 (60)   2 (10)    4 (20)

           Female   Firm         4 (9)    37 (82)   1 (2)     3 (7)
                    Soft         0 (0)    11 (42)   1 (4)    12 (46)

                    Number of Gonad
                     Stage (1) (%)

Gear       Gender      5      Total

LL+Pot     Male      0 (0)      81
                     0 (0)      25

           Female    0 (0)     116
                    11 (14)     76

Trawl      Male      0 (0)      50
                     0 (0)      20

           Female    0 (0)      45
                     2 (8)      26

(1) Maturity code: 1) immature, 2) maturing juvenile,
3) mature, 4) spawning, and 5) spent or post-spawning.

Table 4.--Fitted regressions of sableflsh weight (Y) on length
(X), associated figures, and summary statistics: residual degrees
of freedom (d.f.), estimated standard error of regression ([??],
multiple correlation coefficient (R2), the F statistic, and the
p-value for the model (P). Gender, season, flesh condition, gonad
stage, and fork length (cm) of samples are provided for each
fitted regression line.

                                                       Fork
                                 Flesh      Gonad     length
Figure        Gender   Season   condition   stage   (cm range)

4, line 1     Male     Winter     Firm      All       37-68
4, line 2     Male     Summer     Firm      All       54-67
4, line 3     Male     Winter     Soft      All       51-70
4, line 4     Male     Summer     Soft      All       54-72
5, line 1     Male     Winter     Firm      1         37-68
5, line 2     Male     Winter     Firm      2         49-64
5, line 4     Male     Winter     Firm      4         55-68
6, line 1     Female   Winter     Firm      All       39-85
6, line 2     Female   Summer     Firm      All       45-70
6, line 3     Female   Winter     Soft      All       48-93
6, line 4     Female   Summer     Soft      All       52-84
7, line 2     Female   Winter     Soft      2         47-78
7, line 4     Female   Winter     Soft      4         68-96
7, line 5     Female   Winter     Soft      5         65-93

Figure             Equation         d.f.   [??]   [R.sup.2]     F

4, line 1     Y = -8.45 + 0.23 X    129    0.52     0.86      778.5
4, line 2     Y = -13.26 + 0.31 X    16    0.47     0.85       88.0
4, line 3     Y = -9.42 + 0.24 X     43    0.35     0.90      389.1
4, line 4     Y = -8.89 + 0.24 X     50    1.04     0.48       46.6
5, line 1     Y = -6.69 + 0.19 X     67    0.37     0.90      580.9
5, line 2     Y = -10.85 + 0.27 X    47    0.61     0.76      151.3
5, line 4     Y = -9.13 + 0.25 X      7    0.43     0.87       48.2
6, line 1     Y = -11.06 + 0.27 X   159    0.70     0.91      1653.0
6, line 2     Y = -10.11 + 0.26 X    15    0.47     0.90      140.5
6, line 3     Y = -17.61 + 0.38 X   100    1.26     0.90      927.8
6, line 4     Y = -10.33 + 0.26 X    53    1.37     0.77      181.1
7, line 2     Y = -12.00 + 0.29 X    57    0.77     0.86      349.4
7, line 4     Y = -29.18 + 0.53 X    21    1.21     0.91      202.7
7, line 5     Y = -22.40 + 0.43 X    11    1.75     0.81       45.7

Figure           P

4, line 1     < 0.001
4, line 2     < 0.001
4, line 3     < 0.001
4, line 4     < 0.001
5, line 1     < 0.001
5, line 2     < 0.001
5, line 4     < 0.001
6, line 1     < 0.001
6, line 2     < 0.001
6, line 3     < 0.001
6, line 4     < 0.001
7, line 2     < 0.001
7, line 4     < 0.001
7, line 5     < 0.001

Table 5.--Average weight (g), sample sizes (n), and percent
difference in weight by length interval for combined male and
female sablefish in winter and summer. Only sablefish of maturity
stages 1 and 2 were included. The average percent difference in
weight was 6%.

                              Length interval (cm)
Weight
                < 58    58-60   60-63   63-66   66-69   69-97

Winter         1,525    2,104   2,444   2,881   3,253   3,979
n                173      38      54      37      30      21
Summer         1,749    2,135   2,636   2,931   3,195   4,354
n                 16      18      34      21      20      33

% difference      15       2       8       2      -2       9

Table 6.--Summary statistics for the multiple linear regressions
of total protein, lipid, gonad stage, pH, and green bile on flesh
condition (soft coded as 0 and firm coded as 1) and depth of
capture. Summary statistics are the estimated regression
coefficients (Coefficient), the standard error of the estimate
(SE), the t-statistic (t), and the marginal p-value (P). Also
reported are the estimated standard error of regression ([??],
multiple correlation coefficient ([R.sup.2]), the F statistic and
associated degrees of freedom, and the p-value (P).

Variable                  Coefficient     SE       f        P

Total Protein
  Intercept                   132.79     4.36    30.4    < 0.001
  Flesh condition              12.75     2.60     4.9    < 0.001
  Depth                        -0.02     0.01    -3.5    < 0.001
  [??] = 12.8; multiple
   [R.sup.2] = 0.36;
   [F.sub.2, 176] =
   49.7; P < 0.001

Lipid
  Intercept                   192.11    15.25    12.6    < 0.001
  Flesh condition             -33.08     9.09    -3.6    < 0.001
  Depth                        -0.06     0.02    -3.0      0.003
  [??] = 44.5; multiple
   [R.sup.2] = 0.07;
   [F.sub.2, 176] =
   7.0; P < 0.001

Gonad
  Intercept                     1.06     0.29     3.7    < 0.001
  Flesh condition               0.25     0.17     1.5      0.14
  Depth                       1.6e-3    3.7e-4    4.2    < 0.001
  [??] = 0.8; multiple
  [R.sup.2] = 0.10;
   [F.sub.2, 176] =
   10.2; P < 0.001

pH
  Intercept                     6.74     0.06    119.1   < 0.001
  Flesh condition               0.18     0.03     5.4    < 0.001
  Depth                      -4.1e-5    7.4e-5   -0.6      0.58
  [??] = 0.2; multiple
   [R.sup.2] = 0.24;
   [F.sub.2, 176] =
   28.1; P < 0.001

Green bile
  Intercept                    -6.25     1.16    -5.4    < 0.001
  Flesh condition               5.71     0.69     8.2    < 0.001
  Depth                         0.01    1.5e-3    8.2    < 0.001
  [??] = 3.4; multiple
   [R.sup.2] = 0.32;
   [F.sub.2, 176] =
   41.1; P < 0.001

Table 7.--Means, standard deviations (S.D.), and probabilities
(P) for the ANOVA models for firm (n = 64) and soft (n = 115)
sablefish tested for differences among 17 biochemical variables.

                              Flesh condition

                         Firm              Soft

Variable (1)          Mean (S.D.)       Mean (S.D.)          P

K                   3669.8 (461.7)    3351.5 (252.4)    < 0.001 (2)
Mg                   260.1 (28.5)      215.1 (23.1)     < 0.001 (2)
P                   1928.9 (150.4)    1700.8 (116.1)    < 0.001 (2)
Zn                     3.1 (0.6)         2.5 (0.4)      < 0.001 (2)
pH                     6.9 (0.1)         6.7 (0.2)      < 0.001 (2)
Protein (Total)      136.8 (12.0)      118.2 (13.8)     < 0.001 (2)
Ca                    60.9 (21.6)       49.1 (17.7)     < 0.001 (2)
Co                     0.02 (0.02)       0.01 (0.007)   < 0.001 (2)
Mn                     0.08 (0.07)       0.05 (0.03)    < 0.001 (2)
Fe                     4.6 (4.2)         3.0 (1.3)      < 0.001 (2)
Na                   494.1 (95.2)      595.9 (206.3)    < 0.001 (2)
Cu                     0.25 (0.09)       0.21 (0.1)     0.01
Sr                     0.22 (0.11)       0.26 (0.1)     0.02
Protein (Soluble)     64.3 (8.9)        60.5 (11.2)     0.02
Lipid                132.6 (53.4)      148.1 (40.6)     0.03
Ash                   10.6 (1.1)        10.3 (0.9)      0.04
Water                720.7 (49.0)      726.1 (48.4)     0.48

(1) Protein, lipid, ash, and water are in units of mg/g; all
others except pH are in units of [micro]g/g.

(2) Significant test with [alpha] = 0.05 and a Bonferroni
correction of 1/17.

Table 8.--Means, standard errors of the means (SE), and sample
sizes (n) for the relative drip and cook drip loss (%) of the
winter and summer samples. Relative weight loss (%) is
calculated as (post-weight-pre-weight) -pre-weight x 100.

                       Winter

               Firm                Soft

        Mean     SE    n    Mean    SE     n

Thaw     5.6    0.41   93   14.6   0.68   138
Cook    21.7    0.70   94   29.8   0.44   128

                       Summer

               Firm                Soft

        Mean     SE    n    Mean    SE     n

Thaw     8.3    0.80   33   6.7    0.64   84
Cook    18.9    1.43   36   24.0   0.89   84
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Author:Karinen, John F.; Barnett, Harold J.; Masuda, Michele
Publication:Marine Fisheries Review
Geographic Code:1USA
Date:Sep 22, 2010
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