Bottom Trawl Surveys Research Articles

The influence of age and cohort on the distribution of walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea

The spatial distributions of marine fish populations are influenced by environmental conditions, intrinsic properties of the populations, and prior distribution. The influence of these factors may not be consistent across age classes. For this study, age composition estimates for walleye pollock ( Gadus chalcogrammus) collected on bottom-trawl surveys in the Bering Sea were used to estimate range correlation indices, population centers of gravity, and effective area occupied. Age-specific density maps suggested a circular ontogenic migration during the summer feeding season, with the youngest and oldest groups most broadly distributed. Range correlation analysis among age groups and year classes provided clear evidence of a population cohort effect in the spatial distribution of the population. Variance decomposition analysis indicated that the variance in the spatial distribution of age groups during summer was influenced by the initial distribution of that cohort as recruits. Model-based analyses showed that extrinsic temperature variables affected the youngest and oldest age classes the most, but provided no indication of age-related effects for intrinsic population factors. This study showed that both cohort and age-specific factors are important drivers of spatial distribution.

Importance of fish species in the bottom and near-bottoml biotopes of the Far-Eastern Seas and Pacific waters of Russia

Importance of fish species in the benthal ichthyocoenoses (up to depths of 2000 m) is discussed for the Russian waters in the Far-Eastern Seas and adjacent North-West Pacific on the data of bottom trawl surveys conducted by Pacific Fish. Res. Inst. (TINRO) in 1977–2010. The inverse Simpson index (or polydominance index) was chosen as a measure of dominance; Sorensen-Chekanovsky similarity index was used for comparative analysis of the dominance structure in ichthyocoenoses. The importance is determined for the top 20 species ranked by biomass (94.9 % of the total biomass of all demersal fish on the shelf and 95.8 % — at the continental slope, on average). Poor evenness under strong domination of 2–4 species is noted in the fish communities within the range of 0–2000 m. Walleye pollock Theragra chalcogramma dominate in all regions whereas the subdominants are pacific herring Clupea pallasii, pacific cod Gadus macrocephalus, atka mackerel Pleurogrammus monopterygius, or okhotsk atka mackerel P. azonus, depending on the region. The pollock domination is interrupted at the continental slope of the Bering Sea, where giant grenadier Albatrossia pectoralis dominate. The subdominants at the continental slope of all regions are greenland halibut Reinhardtius hippoglossoides matsuurae, popeye grenadier Coryphaenoides cinereus, pacific herring, pacific sleeper shark Somniosus pacificus, scale-eye plaice Acanthopsetta nadeshnyi, and blackfin flounder Glyptocephalus stelleri. Generalized graphs of the ichthyocoenoses similarity between the studied regions (Okhotsk Sea, Bering Sea, Japan Sea, and Pacific waters at Kamchatka and Kuril Islands) by species structure and composition of the dominant species are presented, separately for the shelf and continental slope.

Changes in Distribution Patterns for Larimichthys polyactis in Response to Multiple Pressures in the Bohai Sea Over the Past Four Decades

Understanding patterns of change in the distribution of species among their critical habitats is important for analyzing population dynamics and adaptive responses to environmental shifts. We investigated spatio-temporal changes in small yellow croaker (Larimichthys polyactis) using eight alternative models fitted to data from bottom trawl surveys conducted in the Bohai Sea each spring (spawning period) and summer during 1982–2018. These models included different combinations of local sea temperature, fishing pressure, and individual climate index (i.e., North Pacific index, NPI, and West Pacific index, WPI) as explanatory variables. Selection of the most parsimonious model for each season was based on Akaike’s Information Criterion (AIC). The model with NPI as its only explanatory variable was used as a base case for pre-analysis. In spring, a spatio-temporal model with sea temperature as a quadratic effect, plus the spatially varying effects of a climate index and fishing pressure was selected, as the AIC value of this model was reduced by 41.491 compared to the base case model without these effects. In the summer after spawning, the spatio-temporal model with WPI as a climate index covariate lagged by 1-year best explained the spatio-temporal distribution patterns of the stock. The results suggested that small yellow croaker populations significantly decreased in biomass in the Bohai Sea over the study period. A statistically significant northeastward shift in the center of gravity (COG) and a contraction in the distribution range occurred in summer throughout the study period (p<0.05). During the spring sequence (1993–2018), a statistically significant northeastward shift in the COG was also found (p<0.05). Our results showed that biomass-density hotspots of small yellow croaker in both seasons have shrunk or disappeared in recent years. Overall, these findings suggest that the spatio-temporal patterns of the populations in their spawning, feeding and nursery grounds have been influenced over the past 40 years by multiple pressures, and population density in the southwestern areas of the Bohai Sea declined faster and more drastically than in the northeastern areas. This study has important implications for developing targeted spatial conservation measures for small yellow croaker at various stages of its life history under different levels of stress.

Diversity and Structure of Demersal Fish Community Over the Northern Slope in the South China Sea

Three bottom trawl surveys over the northern continental slope in the South China Sea (18°50′–20°40′N, 112°50′–115°10′E) were carried out, in June 2015, March 2017 and September 2018, to investigate species composition, biodiversity and community structure of demersal fish. Surveys in 2015, 2017 and 2018 captured 97 fish species (representing 77 genera, 52 families, 26 orders), 108 fish species (representing 84 genera, 61 families, 19 orders) and 126 fish species (representing 105 genera, 74 families, 25 orders), respectively. Three surveys captured a total of 252 fish species, representing 164 genera, 97 families, 30 orders. Perciformes dominated. Species richness in station linking shallow continental shelf with deep slope was the lowest among stations. In three surveys, 16 species occurred in the catches of three surveys, accounting for 6.35% of all species. Species replacement rate between stations showed a significant linear relationship with the depth difference and latitude difference. Margalef’s species richness index (D), Shannon–Weiner diversity index (H’) and Pielou’s evenness index (J’) among stations ranged 2.65–6.74, 1.02–4.15 and 0.28–1.14, respectively. Differences of D, H’ and J’ were insignificant among seasons. There were significant positive linear relations between H’ and J’ and latitude. D, H’ and J’ decreased with increasing sampling depth, however the relations were not significant. Based on multivariate statistical analysis, fish community at species level was divided into five groups with average dissimilarities of 95.69%–99.96%. In terms of genus and family, average dissimilarities among groups were more than 88.11% and 82.69%. There were significant differences in species composition between depths, but no significant differences between seasons and temperatures, as well as in genus and family composition.

Marmara Denizi’nde bentik deniz çöpü

This study presents the first data on benthic marine litter in the Marmara Sea, Turkey. To obtain the data, bottom trawl surveys were conducted at 34 sites between May 2017 and February 2018. The litter items were sampled and sorted following the MEDITS’ relevant instructions. 660 pieces of litter, weighing 434.9 kg, were sampled. The litter density was found to range between 27.5 n/km2 and 661.2 n/km2, averaging 73.9 n/km2, and the obtained items’ weights ranged between 0.03 kg/km2 and 1597.8 kg/km2, averaging 48.7 kg/km2. The plastic group L1 constituted 71.7% of the trawled litter. The highest mean litter density was detected in the Northeastern Marmara Sea in the spring and summer of 2018. The mean benthic litter density was found to be higher than the nearby areas. It was concluded that more effort should be invested in reducing marine pollution.

Assessing the Stock Dynamics of Elasmobranchii off the Southern Coast of Sicily by Using Trawl Survey Data

Elasmobranchii (sharks and rays), which have peculiar and vulnerable life-history traits, are highly threatened by fishing activities. Indeed, between 53% and 71% of Mediterranean elasmobranch species are at risk of extinction. In this context, using the abundance MSY (AMSY) model, the present study provides an assessment of 20 batoids and 16 shark species in the Strait of Sicily, sampled during a bottom trawl survey from 1995 to 2020. Overall, the outputs underline a progressively improving condition for shark and ray assemblages of both shelf and eurybathic zones. As for slope-dwelling species, a horseshoe-shaped dynamic, characterized by a progressive decrease in relative harvesting pressure and an increase in relative biomass followed by an increase in fishing pressure and decrease in biomass, was detected. The dynamics of the Elasmobranchii living in the Strait of Sicily appear to be affected by changes in the fishing patterns of trawlers, showing a shift from shallow water to bathyal fishing grounds and targeting deep-water red shrimp. In this context, it seems wise to limit the impact of deep-water fisheries on Elasmobranchii by reducing fishing efforts and implementing ad hoc management measures aimed at safeguarding these vulnerable species.

Three‐dimensional ontogenetic shifts of groundfish in the Northeast Pacific

AbstractIt has been more than 100 years since fish were first described to move to deep waters as size increased, termed ‘Heincke's Law’. However, large‐scale studies on ontogenetic shifts are rare compared with increased reports of distributional changes in response to temperature, often confounded with the ontogenetic shifts. We fill this gap by examining the distribution of ten abundant groundfish species in three dimensions, depth, latitude and longitude, at 10‐cm size intervals within nine subregions of NE Pacific. Here, we utilized large, quality‐controlled datasets from random depth‐stratified, bottom trawl surveys consistently conducted during summer along the NE Pacific shelf from 1996 to 2015. Groundfish demonstrated complex ontogenetic movements in three dimensions across species, size class and subregion. In addition to the expected ontogenetic deepening, shoaling also occurred and some species demonstrated major ontogenetic shifts in longitude and/or latitude with limited changes in depth. Based on standardized ontogenetic shifts in three dimensions, our analyses show that there were significant differences in aggregate fish ontogenetic shifts between small (≤30 cm) and large (>30 cm) size groups. Small fish exhibited substantially larger ontogenetic shifts in depth than the large size group while both groups showed relatively small shifts in latitude and longitude. Our analyses strongly suggest that size structure and ontogenetic shifts should be included in the population distribution.

Response of alewife abundance to the bacterial kidney disease outbreak in the Chinook salmon population of Lake Michigan: importance of predation

Prey fish abundance can be influenced by predation (top-down) and food limitation (bottom-up) effects. I characterized temporal trends in yearling and older (YAO) alewife (Alosa pseudoharengus) biomass density, as estimated by a long-term bottom trawl survey, in Lake Michigan during 1973–2019. Special attention was given to the bacterial kidney disease (BKD) outbreak in the population of Chinook salmon (Oncorhynchus tshawytscha), the predominant predator on alewives in the lake. YAO alewife biomass density exhibited a steep and significant decline during 1973–1985, but then partially rebounded with a significant increase between the 1983–1985 and 1986–2003 (BKD years) periods, followed by a significant decrease between the 1986–2003 and 2004–2006 periods. YAO alewife biomass density showed another significant decline during 2004–2019. The BKD outbreak led to a partial relaxation of predation on the YAO alewife population, and YAO alewife biomass density responded by showing a moderate increase in 1986 and then fluctuating about this moderately higher level for more than 15 years. Overall, temporal trends in YAO alewife biomass density were primarily driven by predation.

Delineating yellowfin sole (Limanda aspera) reproduction in the northern Bering Sea provides information across the eastern Bering Sea continental shelf

Yellowfin sole (Limanda aspera) is an abundant, commercially harvested flatfish that ranges across the northern and southeastern Bering Sea continental shelf. In recent years, the summer bottom trawl survey of the southeastern Bering Sea (SEBS) conducted by the National Marine Fisheries Service’s Alaska Fisheries Science Center (AFSC) extended into the northern Bering Sea (NBS) in August. This opportunity allowed for describing yellowfin sole reproductive parameters in the NBS, such as female length and age at maturation, reproductive status, and sex ratio distribution. Estimates of 50% female sexual maturity were 10.11 years (A50; 95% CI: 9.47–10.76 years; n = 209) and 28.47 cm (L50; 95% CI: 27.16–29.68 cm; n = 212). Histology indicated much of the mature population was approaching the end of spawning. Yellowfin sole spawning timing (summer) appears to be synchronous across the NBS and SEBS. There is evidence that part of the yellowfin sole spawning population in the NBS is connected to a recognized spawning migratory group from the SEBS. A higher proportion of females than males was observed, which varied by year and stratum. This was negatively related to warmer bottom temperature and positively related to location (western longitudes and northern latitudes). Yellowfin sole females in the NBS exhibit a similar size and age of maturation, depth of spawning, and sex ratio proportions with those females inhabiting the SEBS. These results provide further information for fisheries managers on the yellowfin sole stock throughout this region. Spatial and temporal aspects of reproduction, however, should be more thoroughly investigated.

Length-Weight Relationships of 52 Species from the South of Sicily (Central Mediterranean Sea)

The Length-Weight relationships (LWRs) of 52 species (14 never reported before) of fishes, crustaceans and cephalopods living on the shelf and upper slope off Southern Sicily are provided. Data were collected in the framework of the International bottom trawl survey in the Mediterranean (MEDITS) in the South of Sicily (Central Mediterranean), covering a time frame ranging from 2012 to 2019. Linear regressions were significant for all species (p < 0.05) with R2 values ranging from 0.86 to 0.99. The intercept (a) of LWRs ranged from 0.0003 to 0.4677, while the slope (b) ranged from 2.1281 to 3.306. The Welch t-test, used to evaluate differences between the obtained LWRs with those reported in the literature, revealed that most of the LWRs (about 55%) reported in this study are in disagreement with those obtained previously by other authors from the Strait of Sicily. It is expected that the results obtained from this study will contribute to filling the knowledge gap of fish populations in this area and also assist fisheries scientists in future stock assessment studies.

Modern state for stocks of Sakhalin-Hokkaido herring Clupea pallasii at the coast of Sakhalin Island and southern Kuril Islands

Data of bottom trawl surveys at southwestern Sakhalin and surveys of the herring spawning grounds at southern Sakhalin and Kuril Islands are summarized, with assessment of the spawning grounds size and the eggs density in clutches. Fishery statistics and media reports are overviewed, as well. The stock of the Sakhalin-Hokkaido population increases since 2015, both off southwestern and southeastern coasts of Sakhalin, in the Aniva Bay, and at southern Kuril Islands. Number of the spawning herring increases everywhere within the Russian waters, as well as the size of spawning grounds and the density of eggs laying. In particular, the biomass of spawning herring was estimated in 2020 as 35.5 . 103 t at southwestern Sakhalin and 62.5 . 103 t at southeastern Sakhalin; it was 21.6 . 103 t in the Aniva Bay in 2021; the total catch of herring in the waters at Sakhalin Island and southern Kuril Islands reached 8.3 . 103 t in 2021. The stock of Sakhalin-Hokkaido herring is restoring after long depression, so this species is capable to return to the list of the major objects for fishery in the Sakhalin- Kuril region of Russia.

Bathymetric trends in the body size, and diet of Astropecten americanus in the northwest Atlantic Ocean

Sea stars are major predators of marine invertebrates, in particular, mollusks. Data on the diet composition and the size structure of sea stars in the N.W. Atlantic Ocean are limited. Samples of sand star (Astropecten americanus) collected from three regions in the N.W. Atlantic Ocean were used to determine spatial and seasonal differences in diet and size structure. Samples were collected from ten stations during the 2009 spring and fall NMFS bottom trawl surveys. Four hundred and eighty-eight (488) prey items belonging to various taxa were identified from stomach contents of 524 sea stars of which 302 contained food. In terms of percentage contribution by number of prey items belonging to each taxon (Cn%), gastropods (40%), bivalves (22%) and crustaceans (21%) were the most important. Gastropods were more important in the diet of Southern New England (SNE) and Mid-Atlantic Bight (MAB) sea stars accounting for ∼50% of the diet in each area, and were consumed by 35–42% of the sea stars, whereas crustaceans were more important in Georges Bank (GB) where they contributed ∼83% of the diet, and were consumed by about 77% of the sea stars. There were more gastropods and foraminiferans in the stomachs of sea stars collected in fall, while crustaceans and bivalves were more common in spring samples. These differences may be due to spatial and seasonal differences in the abundance and composition of macrobenthic invertebrates. The size of sea stars decreased with depth, perhaps due to a reduction in prey abundance and higher sea star densities with depth. Additionally, length-weight relationships suggest that sea stars in GB were heavier at a given size (length) than those from SNE and MAB. This might have resulted from the latitudinal variation in the density and species composition of macrobenthic invertebrates that serve as prey for sea stars, such that densities were low on the continental shelf off Delaware-Virginia-North Carolina and relatively high in the region off southern Massachusetts and Rhode Island.

Multidecadal changes in the demersal community structure in an urban bay: Shift from a bottom- to a top-heavy pyramid

Fish community structures in urban bays have changed over time as a result of anthropogenic activities, leading to changes in species richness, diversity, fish assemblage composition, and abundance. Tokyo Bay is one of the most eutrophic urban bays in Japan, and hypoxia occurs every summer in the bottom water of the bay. Accordingly, the demersal community in the bay has undergone drastic changes in taxonomic composition over the past several decades. We analyzed data from a bottom trawl survey spanning 35 years to characterize multidecadal changes in the slopes of body size spectra of the demersal community in Tokyo Bay, as a reliable index to represent shifts in community structure. We found that the community shifted from bottom-heavy pyramids in the past (1977–1995) to top-heavy pyramids in recent years (2003–2019) due to a decrease in the biomass of small-sized crustaceans and an increase in the biomass of large-sized elasmobranchs. Human-induced hypoxia can promote the formation of top-heavy pyramids, as it decimates the number of small-sized individuals. The existence of energy subsidies to large-sized individuals from the inner-shallow and outer bay areas as well as the pelagic community provides a possible explanation for the persistence of top-heavy pyramids.

TROPHIC RELATIONS OF PACIFIC SAFFRON COD <i>ELEGINUS GRACILIS</i> (TIL.) IN THE ICHTHYOCENES OFF KAMCHATKA AND NORTHERN KURILES

Materials collected during 28 bottom trawl surveys on the shelf and continental slope of Kamchatka and Northern Kuriles from 1996 to 2019 were basicaly used for the research. Analysis of 1980 trawl catches was made, where saffron cod was found. In examined waters off Kamchatka and Northern Kuriles saffron cod coexixted with species from 11 faunistic complexes and 7 ichthyocenes. Maximum similar species compositions of fish communities (>80% similarity) coexisting with saffron cod were obsered among communities in geographically adjacent areas, including Northern Kuriles – Southeastern Kamchatka and Northwestern Kamchatka – Southweatsern Kamchatka. Maximum differences in the fish fauna (<60% similarity) were revealed between districts strongly different in width of their continental shelf: Northwestern Kamchatka – Northern Kuriles and Northwestern Kamchatka – Southeaster Kamchatka. Depending on heat content in different years saffron cod was in the company of different, typical elittoral fish species – Pacific cod, walleye pollock or yellowfin sole. It was found based on the published and observed data, that saffron cod forage competitors and forage objects in most cases belong to elittoral group of the broad-boreal Pacific Ocean faunistic complex.

STARRY FLOUNDER <i>PLATICHTHYS STELLATUS</i> (PLEURONECTIDAE) OF THE PACIFIC WATERS OFF KAMCHATKA: SOME FEATURES OF THE BIOLOGY DISTRIBUTION AND STATE OF THE STOCK

Distribution, size composition of starry flounder Platichthys stellatus was investigated, and data on the biomass and abundance for the research period were demonstrated, based on the materials collected on the shelf of Southeastern Kamchatka in the process of bottom trawl surveys in 1999, 2002 and for the period 2016–2020. It was found that in summer most of the fish were in the northern parts of Avachinsky and Kamchatsky Gulfs and everywhere within Kronotsky Gulf. The trawl catches included large-sized flounder individuals. The maximum for the period of the research abundance and biomass were observed in 2002.

Differences in the size at maturity of female American lobsters (Homarus americanus) from offshore Southern New England and eastern Georges Bank, USA

Female reproductive dynamics of the offshore American lobster fishery are not well understood due to the difficulties associated with biological sampling offshore. This lack of knowledge limits our understanding of population dynamics and the impacts of fishery removals on the offshore lobster resource. Addressing needs identified by stock assessment scientists, we determined the size at which female lobsters reach sexual maturity for two offshore areas (offshore Southern New England and eastern Georges Bank) utilizing data from commercial lobster gear and the Northeast Fisheries Science Center bottom trawl survey. A total of 491 female lobsters were collected and assigned a maturity status based on standard ovarian staging techniques. The size at which 50% of females in the population are mature (L50) occurred at a smaller size (L50 = 79.5 mm) in Southern New England compared to eastern Georges Bank (L50 = 91.9 mm). Comparisons of our results to historical data from nearby regions show only a slight decline in Southern New England, but, depending on the data source, a larger decline in size at maturity for Georges Bank. These maturity estimates for offshore lobsters provide new information for assessment scientists and managers on lobster population demographics in a data-poor region of the fishery, and reinforce the value achieved by working collaboratively with the fishing industry to address data gaps in the offshore lobster fishery.

Something strange in the neighborhood: Diverging signals in stock assessment data for Northeast U.S. fish stocks

AbstractIn the Northeast U.S., many stock assessments have a history of problematic model diagnostics, with multiple age‐based assessments recently being rejected in the peer review process, and are not suitable for management advice. The role in which diverging signals in the coastwide bottom trawl survey may be contributing to assessment problems was explored here for 18 stocks in the region. Specifically, trends in total mortality (Z) estimated from catch curve analysis and a relative measure of the harvest rate (total catch/survey index; called relative F) were evaluated. Across stocks, relative F has declined over time, on average, since the mid‐1990s, yet Z has not for many stocks. Weak positive or even negative correlations between relative F and Z resulted for 13 stocks. This diverging signal appears to be contributing to assessment model performance, as larger retrospective patterns (a measure of assessment uncertainty) occurred for stocks with negative correlations between relative F and Z. While a variety of mechanisms could be involved in these diverging signals, the available evidence suggests that unreported catch and/or increasing natural mortality likely play a role to varying degrees for each stock.

Incorporating spatial heterogeneity and environmental impacts into stock-recruitment relationships for Gulf of Maine lobster

ABSTRACT Functional stock-recruitment relationships (SRRs) are often difficult to quantify and can differ over space. Additionally, climate change adds to the complexity of recruitment dynamics. This paper's aim was to incorporate spatial heterogeneity and environmental effects on productivity in SRRs with American lobster in the Gulf of Maine (GOM) as a case study. GOM lobster recruitment has substantially increased since the mid-2000s, due to improved survival rates of pre-recruits and increased spawning stock biomass (SSB). GOM bottom water temperatures have increased at a rate of 0.2ºC per decade, which caused lobster settlement area to expand and improved survival rates. We first estimated local SSB using bottom trawl survey data and a geostatistical model. Using estimated SSB, recruitment data from a ventless trap survey, and an interpolated bottom water temperature field, we developed modified Ricker stock-recruitment models accounting for spatial heterogeneity and temperature impacts with varying coefficient generalized additive models. Results showed that temperature significantly impacted recruitment. Changes in temperature mediated productivity differed between the eastern and western GOM. Our study demonstrated that the incorporation of spatial heterogeneity and environmental effects impacts our understanding of SRRs. These methods can be applied to other species to understand recruitment dynamics influenced by climate change.

Accounting for a nonlinear functional response when estimating prey dynamics using predator diet data

Abstract Forage fish species are key in the transfer of energy from lower to upper trophic levels in marine ecosystems. Therefore, understanding their population dynamics, including population levels, is crucial for understanding productivity and the regulation of marine food webs. However, many forage fishes are poorly sampled by bottom trawl surveys, leading to poor estimates of their abundance. These estimates can be improved by using predator stomach contents as an additional sampling strategy; however, nonlinear relationships between prey abundance and predator consumption (i.e. the functional response) may bias stomach data as well. Using predator stomach contents and bottom trawl survey data, this study aimed to minimize this bias by developing a model to estimate prey dynamics and account for the predator functional response. This model was tested using a series of simulations and applied to a case study of northern sand lance Ammodytes dubius on the Grand Bank, Newfoundland, Canada. The simulations revealed that when predators consumed prey following a nonlinear functional response, our model outperformed a classical model (the model adopted by most studies) that assumed a linear functional response. In the case study, we estimated the relative abundance of sand lance from 1995 to 2018, which exhibited oscillatory dynamics with a period of approximately 7 years. Our results demonstrate that our model is capable of more accurately estimating the abundance of data‐limited prey populations, which contributes to a better understanding of food web dynamics.

Food habit variability of arrowtooth flounder (Atheresthes stomias) along the U.S. west coast

A diet study of arrowtooth flounder (Atheresthes stomias) was undertaken to provide current information on their food habits and predator-prey relationships in the California Current Ecosystem. Arrowtooth flounder stomachs (n = 573) were collected between 2013 and 2018 from 397 trawls during the Northwest Fisheries Science Center’s West Coast Groundfish Bottom Trawl Survey. A total of 357 stomachs (62.3%) contained prey, which revealed a highly piscivorous diet across all lengths examined (14 – 77 cm) and described a regionalized and opportunistic feeding behavior. Increased predator length correlated both with an increase in percentage of fish prey consumed and an increase in depth of capture. Smaller (< 43 cm) and shallower (≤ 183 m) arrowtooth flounder consumed a relatively high percentage of euphausiids and shrimp, while larger arrowtooth flounder (≥ 43 cm) captured at greater depths (> 183 m) consumed more fish and fewer shrimp and euphausiids. Arrowtooth flounder diet varied by geographic area, likely resulting from regional differences in prey availability. North of the mean latitude of capture (44.45°N), Pacific hake (Merluccius productus) and Pacific herring (Clupea pallasii) were the predominant fish in arrowtooth flounder diets, while arrowtooth flounder caught south of the mean latitude consumed mostly Pacific hake and rockfishes (Scorpaenidae). Unidentified teleost fish contributed much to the diet across all size, depth, and latitude ranges.