Atka Mackerel Research Articles

Diets of Steller sea lions off the coast of Hokkaido, Japan: An inter‐decadal and geographic comparison

AbstractInter‐decadal and geographic variations in the diets of Steller sea lion, Eumetopias jubatus, were examined based on the contents of 408 stomachs collected from coastal areas around Hokkaido Island during the periods 1994–1998 and 2005–2012. The most important prey species in the 1990s were gadid fishes (walleye pollock [Gadus chalcogrammus], Pacific cod [Gadus microcephalus] and saffron cod [Eleginus gracilis]). The frequency of occurrence and gravimetric contribution of gadids decreased in the 2000s latter period at three study sites (Rausu, Shakotan and Rebun) and were replaced by Okhotsk Atka mackerel (Pleurogrammus azonus) and smooth lumpsucker (Aptocyclus ventricosus). However, analysis based on gravimetric composition indicated that the dietary diversity of prey showed only a slight inter‐decadal difference, reflecting the wide diversity of prey ingested during both study periods. These results indicate that Steller sea lions along the Hokkaido coast are opportunistic feeders that utilize a wide variety of prey, and appear to feed mainly upon prey that is easily obtained.

Diet of endangered Steller sea lions (Eumetopias jubatus) in the Aleutian Islands: new insights from DNA detections and bioenergetic reconstructions

The endangered western stock of Steller sea lion (Eumetopias jubatus (Schreber, 1776)) still declines in the western Aleutian Islands and accurate diet information is vital to test leading hypotheses. We undertook the first bioenergetic diet reconstruction using both molecular and hard part prey identifications from >600 scats collected in March–April 2008 and 2012. Atka mackerel (Pleurogrammus monopterygius (Pallas, 1810)) remained a primary prey (17%–27% by energy), but large (mean 60 cm) Pacific cod (Gadus macrocephalus Tilesius, 1810) also emerged as important prey (20%–24%) in a more diverse diet than previously reported, with Cottidae and smooth lumpsucker (Aptocyclus ventricosus (Pallas, 1769)) also contributing ∼10%. DNA detections highlighted a potentially important and previously underestimated prey, giant Pacific octopus (Enteroctopus dofleini (Wülker, 1910) (diet contribution 2%–15%, dependent on prey size assumptions). Although 504 unique DNA identifications resulted in significant increases for cephalopods, Pacific cod, and smooth lumpsucker, hard part alone species rankings were similar to composite ones and bioenergetic species rankings similar to occurrence-based ones. Retention or regurgitation of large cephalopod beaks, the removal of large cod heads, and skeletal fragility of lumpsuckers may explain these differences. DNA identifications provide valuable comparative and complementary prey occurrence data for pinnipeds, but composite diet estimates are optimal.

Historical research on Chinese characters and folk tales of Atka Mackerel, Sandfish, Alaska Pollack

Historical research on Chinese characters and folk tales of Atka Mackerel, Sandfish, Alaska Pollack

Morphological and molecular genetic characterization of two Kudoa spp., K. musculoliquefaciens, and K. pleurogrammi n. sp. (Myxosporea: Multivalvulida), causing myoliquefaction of commercial marine fish.

Genetic characterization of myxosporean species, including members of the genus Kudoa, has advanced dramatically throughout the last decade. This is in stark contrast to those species described further back in time. Kudoa musculoliquefaciens described from the jellied muscle of swordfish, Xiphias gladius, in the western Pacific Ocean off the Sanriku Coast, northern Japan, is one such species. In the present study, multiple pseudocysts (0.66-1.35mm average length and 0.06-0.10mm average width) containing K. musculoliquefaciens spores were collected from three host groups: muscle blocks of swordfish caught in the western Pacific Ocean off the Sanriku Coast, or the northern Indian Ocean, and Indo-Pacific sailfish, Istiophorus platypterus, in the western Pacific Ocean off Kochi, western Japan. Subspherical K. musculoliquefaciens spores, 8.0-10.3μm in width, 7.3-10.0μm in thickness, 6.4-7.9μm in sutural thickness, and 5.5-8.1μm in length, had four subspherical polar capsules, 2.8-4.0μm in length by 2.2-3.2μm in width. The kudoid spores found in the different host groups showed morphometric variations to some extent but had essentially identical nucleotide sequences of the ribosomal RNA gene (rDNA), closest to those of Kudoa hemiscylli or Kudoa carcharhini recorded from elasmobranchs in the Indo-Pacific Ocean. Another kudoid species, Kudoa pleurogrammi n. sp., was recorded from the jellied and normal muscles of Atka mackerel, Pleurogrammus monopterygius and Pleurogrammus azonus, fished in the northern Pacific Ocean or northern Sea of Japan. Subquadrate spores found in round-ended pseudocysts (1.15-3.85mm in length and 0.11-0.26mm in width) in myofibers were 8.2-9.1μm in width, 7.1-8.2μm in thickness, 5.4-7.7μm in sutural thickness, and 5.6-6.8μm in length, with four ovoid polar capsules, 2.7-2.9μm in length by 1.4-2.0μm in width. Kudoid spores from both jellied and normal muscles or different host fish species had identical 18S or 28S rDNA nucleotide sequences. Thus, molecular genetic characterization of kudoid species with the potential to induce post-mortem myoliquefaction will facilitate the reliable and specific identification of myxosporeans found in either jellied or normal muscles of important commercial fish.

Evaluating the Efficacy of Trawl Exclusion Zones by Estimating Local Atka Mackerel Abundance and Movement Patterns in the Central and Eastern Aleutian Islands

AbstractAtka Mackerel Pleurogrammus monopterygius is the most abundant commercially exploited groundfish in the Aleutian Islands, Alaska. It is also the predominant prey of the endangered Steller sea lion Eumetopias jubatus in the Aleutians Islands range. In 1992, trawl exclusion zones (TEZs) that ranged from 10 to 20 nautical miles were established around rookeries to protect Steller sea lion prey abundance. This study examined the efficacy of the TEZs by estimating the movement and local abundance (10–20 nautical miles) of Atka Mackerel inside and outside of these zones using an integrated tagging model that incorporated independent data for tagging survival, recruitment, and tag reporting rates. Atka Mackerel were tagged, released, and recovered from 2000 to 2006 at four Aleutian Island locales, from both inside and outside of the TEZs. Atka Mackerel local abundance and their movement patterns across these harvest boundaries were estimated for all the study areas inside and outside the TEZs, and local exploitation rate by the fishery was calculated for each area open to fishing outside the TEZ boundary. In areas with high Atka Mackerel abundance and little movement from inside to outside the protection zones (e.g., Seguam Pass and Kiska Island), the TEZs were expected to work well to preserve the prey field for Steller sea lions. In areas of low Atka Mackerel abundance and frequent movement from the inside to the outside of the protection zone (e.g., Amchitka Island), the TEZs were expected to be less effective. Our study indicated that TEZs can be effective for preserving prey fields of Atka Mackerel for Steller sea lions, but each study area needs to be carefully evaluated in order to understand area‐specific variations in abundance and movement patterns.Received October 21, 2014; accepted December 16, 2015

Long-term dynamics of biomass and modern fishery of atka mackerel <i>Pleurogrammus monopterygius</i> in the Pacific waters of Kamchatka and Kuril Islands

Long-term dynamics of biomass and modern fishery of atka mackerel <i>Pleurogrammus monopterygius</i> in the Pacific waters of Kamchatka and Kuril Islands

Feeding and food supply of juvenile fishes in the eastern Bering Sea in 2003-2012

Feeding of fish juveniles in the eastern Bering Sea is investigated for the periods of 2003-2006 considered as relatively «warm» and 2007-2012 considered as relatively «cold». Small- and medium-sized zooplankton was the dominant prey in the 2003-2006, in particular copepods prevailed in the food of walleye pollock (41.5 %), pacific herring (48.3 %), and sand lance (71.7 %) juveniles, which in turn were the prey for pollock, herring and cod yearlings and other predators. On the contrary, large-sized zooplankton was more abundant in the 2007-2012, so arrowwarms ( Sagitta sp.), large-sized copepods (in particular Calanus marshallae ), euphausiids (mainly Thysanoessa raschii ), hyperiids, and pteropods were the prey for young fish: C. marshallae - for juveniles of pollock (40-45 % by weight) and capelin (32-34 %), Th. raschii - for yearlings of pollock (51 %) and herring (36-46 %), cold-water hyperiid T. libellula - for adult pollock (24 %), juvenile cod (9-18 %) and juvenile herring (9-11 %), whereas portion of fish in the diets was insignificant. In the warm period (2003-2006), juvenile pollock, herring, sand lance and capelin were zooplankton-eaters with the diets similarity 67 %, while yearlings of pollock and juveniles of cod, herring, sandfish, and atka mackerel were fish-eaters preying upon pollock juveniles. In the cold period (2007-2012), the diets of juvenile pollock, juvenile and adult capelin, and juvenile sand lance were also similar at 85-70 % but they preferred large-sized copepods and euphausiids ( C. marshallae and Th. raschii ), while yearlings of pollock, yearlings and adults of herring, and juveniles of sand fish and cod had the diets of 70 % similarity with Th. raschii prevalence. Feeding intensity was high for all species: the mean stomach fullness was 150-200 ‱ for pollock juveniles and yearlings, 200-250 ‱ for cod juveniles, 200-258 ‱ for sand lance juveniles, 302 ‱ for herring juveniles, and 178-250 ‱ for juvenile atka mackerel. The fullness had diurnal rhythm with three peaks: at noon - up to 179 ‱, in evening - up to 213 ‱, and at night - up to 204 ‱ (the data for walleye pollock juveniles in «cold» years only). Daily food ration of juvenile pollock is estimated as 6.7 % of its body weight in the «warm» years and 7.0 % in the «cold» years.

Assessment of Competition between Fisheries and Steller Sea Lions in Alaska Based on Estimated Prey Biomass, Fisheries Removals and Predator Foraging Behaviour.

A leading hypothesis to explain the dramatic decline of Steller sea lions (Eumetopias jubatus) in western Alaska during the latter part of the 20th century is a change in prey availability due to commercial fisheries. We tested this hypothesis by exploring the relationships between sea lion population trends, fishery catches, and the prey biomass accessible to sea lions around 33 rookeries between 2000 and 2008. We focused on three commercially important species that have dominated the sea lion diet during the population decline: walleye pollock, Pacific cod and Atka mackerel. We estimated available prey biomass by removing fishery catches from predicted prey biomass distributions in the Aleutian Islands, Bering Sea and Gulf of Alaska; and modelled the likelihood of sea lions foraging at different distances from rookeries (accessibility) using satellite telemetry locations of tracked animals. We combined this accessibility model with the prey distributions to estimate the prey biomass accessible to sea lions by rookery. For each rookery, we compared sea lion population change to accessible prey biomass. Of 304 comparisons, we found 3 statistically significant relationships, all suggesting that sea lion populations increased with increasing prey accessibility. Given that the majority of comparisons showed no significant effect, it seems unlikely that the availability of pollock, cod or Atka mackerel was limiting sea lion populations in the 2000s.

Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 527:261-274 (2015) - DOI: https://doi.org/10.3354/meps11255 Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus Rick D. Scherer1,8, Andrew C. Doll1,*, Lorrie D. Rea2,3, Aaron M. Christ2, Craig A. Stricker4, Briana Witteveen5, Thomas C. Kline6, Carolyn M. Kurle7, Michael B. Wunder1 1Department of Integrative Biology, University of Colorado Denver, Denver, CO 80204, USA 2Alaska Department of Fish and Game, Division of Wildlife Conservation, Anchorage, AK 99518, USA 3Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK 99775, USA 4US Geological Survey, Fort Collins Science Center, Denver, CO 80225, USA 5Kodiak Seafood and Marine Science Center, University of Alaska Fairbanks, Kodiak, AK 99615, USA 6Prince William Sound Science Center, Cordova, AK 99574, USA 7Division of Biological Sciences, Ecology, Evolution, and Behavior Section, University of California San Diego, La Jolla, CA 92093, USA 8Present address: Conservation Science Partners, Fort Collins, CO 80524, USA *Corresponding author: acdoll@gmail.com ABSTRACT: Multiple factors, including limitation in food resources, have been proposed as possible causes for the lack of recovery of the endangered western segment of the Steller sea lion population in the United States. Because maternal body condition has important consequences on fetal development and neonatal survival, the diets of pregnant females may be particularly important in regulating population sizes. We used the stable carbon and nitrogen isotope values of vibrissae from Steller sea lion pups as an indirect indicator of maternal diets during gestation. Combining these data with isotope data from potential prey species in a Bayesian mixing model, we generated proportional estimates of dietary consumption for key prey. Our analysis indicated that females in the most westerly metapopulations relied heavily on Atka mackerel and squid, whereas females inhabiting the Gulf of Alaska region had a fairly mixed diet, and the metapopulation of Southeast Alaska showed a strong reliance on forage fish. These results are similar to previous data from scat collections; however, they indicate a possible under-representation of soft-bodied prey (squid) or prey with fragile skeletons (forage fish) from analyses of data from scats. This study supports the utility of stable isotope modeling in predicting diet composition in gestating adult female Steller sea lions during winter, using pup vibrissae. KEY WORDS: Stable isotopes · Vibrissae · Steller sea lion · Carbon · Nitrogen · Mixing model · Diet composition Full text in pdf format Supplementary material PreviousNextCite this article as: Scherer RD, Doll AC, Rea LD, Christ AM and others (2015) Stable isotope values in pup vibrissae reveal geographic variation in diets of gestating Steller sea lions Eumetopias jubatus. Mar Ecol Prog Ser 527:261-274. https://doi.org/10.3354/meps11255 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 527. Online publication date: May 07, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Life cycles and somatic production of hyperiids in the Okhotsk and Bering Seas

Hyperiid species Themisto pacifica , T. libellula , and Primno macropa are widespread in the Far-Eastern Seas. They are an important element of trophic web in pelagic communities of these seas. Their food spectra are very broad and include copepods, euphausiids, arrowworms, and fish larvae. On the other hand, the hyperiids play an important role in the diet of large-sized marine organisms as walleye pollock Theragra chalcogramma , mackerels Scomber japonicus , Pleurogrammus monopterygius , and Pleurogrammus azonus , and japanese squid Todarodes pacificus . Life cycles and production of these hyperiid species are described on the base of samples collected in complex surveys conducted by Pacific Fish. Res. Center (TINRO) in the Okhotsk Sea and the western Bering Sea in 1984-2011. All three species have similar life history though the maximal life span is 2 years for T. pacifica and T. libellula but 3 years for Primno macropa . They spawn twice in their life in the period from May to October with the peak in July. Their weight increments also increase twice, usually when their size is 7-10 and 10-12 mm for T. pacifica and P. macropa and 10-15 and 20-30 mm for T. libellula . The average specific daily production of hyperiids in the Okhotsk Sea is estimated as 0.0410 for T. pacifica , 0.0273 for T. libellula , and 0.0101 for P. macropa ; but in the western Bering Sea - as 0.0492 for T. pacifica , 0.0361 for T. libellula , and 0.0094 for P. macropa . The most favorable feeding grounds for hyperiids are located at Kuril Islands, at West Kamchatka, and in the Anadyr Bay. Their summary annual production is estimated as 30.235 mln t in the Okhotsk Sea and 21.370 mln t in the western Bering Sea.

Occurrence of hexagrammidae fish at early stages of ontogenesis in open waters of the northwestern part of the Pacific ocean

Hexagrammidae are endemics of the northern Pacific widely spread in marginal seas and coastal parts of the Pacific Ocean from the East China Sea in the west and California in the east to the Bering Strait in the north (Rass, 1962; Rutenberg, 1962; Shinohara, 1994). Almost all greenlings are nearbottom fish inhabiting coastal areas, and only lingood Ophiodon elongatus and Atka mackerels of the genus Pleuro� grammus lead a semipelagic mode of life and perform migrations to considerable distances into open waters (Gorbunova, 1962; Rutenberg, 1962). Hexagrammi� dae spawn in coastal areas in shallow water where incubation of bottom eggs takes place. The hatched out larvae are carried out by currents into open waters, sometimes to considerable distances from the coast, and they pass the first several months of life in the pelagial. Despite rather considerable number of publi� cations on the biology and ecology of greenling, the early stages of ontogenesis of these fish have not been adequately covered in literature, and were most com� prehensively considered in the paper of Gorbunova (1962) according to material of the 1950s. The distri� bution of juveniles of arabesque greenling Pleurogram� mus azonus and Atka mackerel P. monopterygius in the epipelagial of far eastern seas and the northern part of the Pacific Ocean is described in papers of Mel'nikov et al. (1996a, 1996b); Mel'nikov and Efimkin (2003); Mel'nikov and Loboda (2003). In the suggested paper, the occurrence in ichthy� oplankton and distribution of Hexagrammidae at early stages of ontogenesis in the northwestern part of the Pacific Ocean are considered.

Finding of aggregation of Atka mackerel Pleurogrammus monopterygius in waters off Iturup Island

Finding of aggregation of Atka mackerel Pleurogrammus monopterygius in waters off Iturup Island

Measurement of Diet Preference and its Variability in Captive Northern Fur Seals (Callorhinus ursinus)

Diet preferences of three captive northern fur seals for seven prey items (Okhotsk atka mackerel, rainbow trout, common mackerel, walleye pollock, Pacific sand lance, horse mackerel, and Japanese common squid) were measured through repeated two-choice tests. Preference indices estimated from the paired consumption data using the normal Bradley-Terry model revealed the existence of diet preferences and their individual variation. The three seals generally preferred Okhotsk atka mackerel, rainbow trout, and common mackerel, but showed individual differences for less preferred food items. The preferred items had moderate food size and high energy content per one item. Once diet preferences were determined, animals were given rainbow trout laced with lithium chloride (LiCl) to induce conditioned taste aversion (CTA). Four to five LiCl treatments were required for CTA, but could only induce temporary aversion of rainbow trout in favor of horse mackerel. Choice tests after CTA demonstrated a decrease in preference indices for rainbow trout in the three animals, but the ranking and preference indices of rainbow trout did not fall below those for horse mackerel. These results suggest that preference and aversion are relative phenomena, and the success of CTA is dependent on the reduction of preference relative to other food items.

First finding of the Okhotsk Atka mackerel Pleurogrammus azonus (Scorpaeniformes: Hexagrammidae) in Tauy bay (northern Sea of Okhotsk): Description of the specimen and the justification of its species definition

The first finding of an adult specimen (TL = 385 mm) of the Okhotsk atka mackerel Pleurogrammus azonus (Scorpaeniformes: Hexagrammidae) is reported for the northern coast of the Sea of Okhotsk (mouth of western Tauy Bay). This is the northernmost finding of this species in the Sea of Okhotsk. The detailed description of the external morphology of the specimen is given. The mtDNA COI gene fragment is compared to GenBank data, and the molecular genetic analysis justifies the species definition significantly.

Calculating impacts of exogenous output changes: application of a social accounting matrix (SAM) model to Alaska fisheries

Some previous studies calculated backward linkage and forward linkage effects of exogenous change in output capacity using mixed endogenous–exogenous models within an input–output (IO) or social accounting matrix (SAM) framework. For calculating forward linkage effects, these studies used the supply-drive(Ghosh in Economica 25(1):58–64, 1958) approach. However, the Ghosh approach has been criticized based on its problematic theoretical interpretation. This study uses an Alaska SAM model to estimate the regional economic impacts of restricting catch of Pacific cod and Atka mackerel in the Aleutian Islands in order to protect Steller sea lions. This study overcomes the problem of calculating forward linkage effects in the previous studies by running the SAM model with (1) changes in output converted to final demand shocks and (2) regional purchase coefficients for all the directly impacted industries (fish harvesting and processing industries) set equal to zero. The impacts of the shift in harvest opportunities in response to the Steller sea lion protection measures are displayed in terms of changes in output, employment, value added, household income, and state and local government revenue.

Temporal variation in chum salmon, Oncorhynchus keta, diets in the central Bering Sea in summer and early autumn

Seasonal, ontogenetic, and diel variations in the diets of chum salmon, Oncorhynchus keta, were examined by analyzing the stomach contents of 1398 fish (300–755 mm fork length) collected in the Bering Sea during summer and early autumn of 2002. Whereas mesozooplankton, including euphausiids, hyperiids, and gastropods, constituted the greatest portion of the stomach contents during the summer, forage fishes (Stenobrachius leucopsarus and Atka mackerel, Pleurogrammus monopterygius) were the most important items during early autumn. Although no apparent diel trend was found in feeding intensity, distinct diel differences in prey composition were observed. Chum salmon caught in the morning contained Stenobrachius leucopsarus, whereas those caught in the afternoon had mainly fed on euphausiids. Thus, chum salmon diets change temporally because of changes in prey availability that result from differences in the annual life cycles and diurnal vertical migrations of prey species.

Prey competition between sympatric Steller sea lions (Eumetopias jubatus) and northern fur seals (Callorhinus ursinus) on Lovushki Island, Russia

Approximately 1 000 Steller sea lions ( Eumetopias jubatus (Schreber, 1776); SSL) and 14 000 northern fur seals ( Callorhinus ursinus (L., 1758); NFS) breed sympatrically on Lovushki Island in the Russian Far East, creating the potential for interspecific competition for prey. An additional 13 000 – 14 000 juvenile NFS are present during the breeding season. The diets of breeding SSL and both breeding and juvenile NFS were examined through analysis of scats and spews collected during the breeding seasons of 2003, 2005, and 2007–2008. There were significant overlaps in the prey species and size selection of SSL and juvenile NFS. There were significant differences between the diets of SSL and breeding NFS. SSL and juvenile NFS fed primarily on Atka mackerel ( Pleurogrammus monopterygius (Pallas, 1810)), while breeding NFS fed on cephalopods, salmon (genus Oncorhynchus Suckley, 1861), Atka mackerel, and northern smoothtongue ( Leuroglossus schmidti Rass, 1955). The partitioning of resources between breeding animals has allowed both species to coexist within the same region and likely reflected differences in foraging abilities and provisioning strategies of the adults and the fasting abilities of their pups. However, continued growth of the NFS population may lead to the exclusion of SSL owing to interspecific competition for prey.

Some issues related to catches of northern Atka mackerel Pleurogrammus monopterygius (Scorpaeniformes: Hexagrammidae) in the near-surface water layer of the northern Kuril Islands

Studies performed in Pacific waters of the northern Kuril Islands from May to August 2003–2007 demonstrated that not only juveniles of Pleurogrammus monopterygius but also its adult specimens are found in the near-surface layer. Some adult fish migrate to the near-surface layer for feeding, while occurrence in this layer for other specimens is related to the change of spawning grounds. Among specimens with a length of 36–48 cm, females comprise 86.2%; among specimens with a length of 22–28 cm, females comprise 56%. Migrations in the near-surface layer have no mass pattern.

Effects of Maternal Growth on Fecundity and Egg Quality of Wild and Captive Atka Mackerel

AbstractTrade‐offs in energy allocation between growth and reproduction can result in variations in reproductive potential in fish with differing growth patterns. Spawning biomass is often used as a proxy for reproductive potential on the assumption that fecundity is directly proportional to body weight. We examined variations in the reproductive potential of Atka mackerel Pleurogrammus monopterygius by studying the effect of differential growth and condition patterns on fecundity, atresia, and egg energy. Fecundity and egg energy were determined for fish from two geographic areas, Seguam Pass and Amchitka Island, Alaska, and compared with those of fish held in captivity. These Atka mackerel showed distinct differences in growth and condition, with weight at length and length at age being the highest among captive fish, intermediate among fish from Seguam Pass, and lowest among fish from Amchitka Island. Realized fecundity showed that on average captive fish spawned seven batches, fish from Seguam Pass six batches, and fish from Amchitka Island five batches. For wild fish, potential and realized fecundity at length or age was significantly higher at Seguam Pass than at Amchitka Island, whereas the fecundity‐at‐weight relationship did not differ by area, suggesting that weight is a better predictor of fecundity than length or age. Atresia and batch fecundity by length or weight did not differ by area, suggesting that the variation in fecundity is better explained by the variation in batch number than by batch size. Oocyte dry weight was higher for captive fish than for wild fish, whereas batch order did not significantly affect oocyte dry weight. Increased potential fecundity, realized fecundity, and oocyte quality in Atka mackerel females were strongly related to body size, indicating that growth differences and maternal feeding success impact the fecundity and oocyte quality of Atka mackerel. Therefore, changes in growth and condition patterns need to be taken into account to accurately estimate the reproductive potential of this species.Received August 21, 2010; accepted March 2, 2011

Seasonal, Small‐Scale Distribution of Atka Mackerel in the Aleutian Islands, Alaska, with Respect to Reproduction

AbstractWe investigated the spatial distribution of Atka mackerel Pleurogrammus monopterygius with respect to maturity stage at Seguam Pass in the Aleutian Islands as well as their spawning locations within trawlable areas at three small‐scale (10–20‐nautical mile or 18.5–37.0‐km) sites. Histological methods were used to determine maturity stages, and male maturity stages are described for the first time. Spawning areas were identified by catch per unit effort of demersal egg masses. At Seguam Pass, spawning was concentrated in the area adjacent to the east side of Amlia Island and between Amlia and Seguam islands. The observed spatial segregation of Atka mackerel by sex and maturity stage appears to interact with the boundaries of the trawl exclusion zone (TEZ) at Seguam Pass. During spawning, mature fish aggregate inside the closed area and immature fish and nonreproductively active mature males aggregate outside the TEZ in the area open to fishing. This increased the commercial catch selectivity of nonreproductively active males and immature fish during the September fishery. The spawning areas observed at Seguam and Tanaga passes and near Amchitka Island were within TEZs, which may serve as de facto marine protected areas for spawning Atka mackerel.