Pacific Ocean Perch Research Articles

Fishery and notes on the biology of Pacific ocean perch Sebastes alutus (Sebastidae) off the Commander Islands

The fishery and some aspects of the biology of the Pacific ocean perch Sebastes alutus off the Commander Islands. It has been established that the harvest of this species is episodic in nature, is not subject to seasonal dynamics and is carried out in a local area located west of the Bering Island. The contribution of this water area to the total catch of rockfishes in the Petropavlovsk-Commander subzone in 2001–2022 did not exceed 26.5%. Near the Commander Islands, S. alutus was observed at depths of 138–370 m at a water temperature near-bottom of 3.1–3.9°C, and in catches it was represented by individuals 17–45 cm length. Presumably the formation of accumulations in the upper part of the continental slope to the west of the Bering Island is due to the presence of an anticyclonic circulation, which contributes to the formation of high concentrations of zooplankton as the main food source and favorable conditions for the development of spawned larvae.

The design of a camera-based fisheries-independent survey for untrawlable habitat in the Gulf of Alaska

Biomass and size composition estimates from the fishery independent biennial Alaska Fisheries Science Center Resource Assessment and Conservation Engineering Division’s Groundfish Assessment Program Gulf of Alaska bottom trawl survey are an integral component of stock assessments and management of fishes in the region. A substantial proportion of the seafloor in the Gulf of Alaska survey area consists of rocky, high-relief habitat that is not accessible to trawl survey gear and is important habitat for many harvested fish species, especially rockfishes (Sebastes spp.). Survey estimates of groundfish abundance from trawlable grounds are expanded across the entire region. Therefore, survey abundance estimates could potentially be biased as a result of sampling that does not spatially represent all of the available habitat circumscribed by the Gulf of Alaska study area. Mapping the extent of the untrawlable habitat is a critical step toward understanding the scale of these potential biases and would benefit the design of a future untrawlable habitat survey. Several previous efforts have provided trawlability maps for part or all of the Gulf of Alaska based on different data inputs. In the present work, we compile two previously published untrawlable habitat maps with three other relevant data sources to create a new untrawlable habitat map, and use this map in conjunction with density estimates from existing underwater camera studies to investigate the feasibility of an untrawlable habitat rockfish survey in the Gulf of Alaska. An analysis of 1 km2 grids sampled more than once with a lowered camera system suggested that a single-stage sampling design (one camera transect per grid) would be most effective. Post-stratification analysis showed that either a simple depth stratification or stratification based on species distribution models provided lower coefficient of variation (CV) values at a given sample size compared to random sampling. Furthermore, a target CV of 25 % could be reached for a camera survey of dusky rockfish, northern rockfish, or Pacific ocean perch with less than 200 lowered camera transects if a stratification scheme based on species distribution models was used.

Incorporating non-stationary spatial variability into dynamic species distribution models

Abstract Ecologists and fisheries scientists are faced with forecasting the ecological responses of non-stationary processes resulting from climate change and other drivers. While much is known about temporal change, and resulting responses vis-à-vis species distributional shifts, less is known about how spatial variability in population structure changes through time in response to temporal trends in drivers. A population experiencing decreasing spatial variability would be expected to be more evenly spatially distributed over time, and an increasing trend would correspond to greater extremes or patchiness. We implement a new approach for modelling this spatiotemporal variability in the R package sdmTMB. As a real-world application, we focus on a long-term groundfish monitoring dataset, from the west coast of the USA. Focusing on the 36 species with the highest population densities, we compare our model with dynamic spatiotemporal variance to a model with constant spatiotemporal variance. Of the 36 species examined, 13 had evidence to support increasing patchiness, including darkblotched rockfish, lingcod, and petrale sole. Species appearing to be more uniformly spatially distributed over time included: Dover sole, Pacific ocean perch, and Dungeness crab. Letting spatiotemporal variation change through time generally results in small differences in population trend estimates, but larger estimated differences in precision.

The estimated impact of changes to otolith field-sampling and ageing effort on stock assessment inputs, outputs, and catch advice

Generating accurate data for stock assessments is resource-demanding, necessitating periodic evaluation of survey sampling designs and potential impacts on stock assessments. We developed a framework for bootstrapped resampling of survey age data and calculation of input sample sizes as a function of among-bootstrap variance in age compositions. Data from this bootstrap estimator were then used to evaluate the influence of alternative sampling rates and methods on uncertainty in estimates of the overfishing limit (OFL) calculated using stock assessment models. For dusky rockfish ( Sebastes variabilis) and Pacific ocean perch ( Sebastes alutus), a 10% decrease in the number of tows sampled upon led to a predicted 5%–6% increase in the CV of OFL (log–log slope = −0.576 to −0.486), which was greater than the 0%–2% increase from a 10% decrease in otoliths-per-tow (log–log slope = −0.238 to −0.029). Application of this approach across all stocks monitored in the survey of interest is required to identify which stocks ( i) benefit the most from increased sampling of ageing structures or ( ii) cost the least in terms of OFL uncertainty owing to reduced sampling.

Sustainable fisheries: Towards operationalization of decision making accounting for biodiversity

Overexploitation of biotic resources constitutes a major threat on marine biodiversity while demand for seafood will rise in the next decades. Application of Life Cycle Assessment to marine ecosystems needs further focus. This study applies two existing methods (Langlois et al., 2014 and Emanuelsson et al., 2014) of fishing impact assessment on biodiversity to 125 common fish stocks fished in the 14 marine areas drawn by FAO and proposes operational guidelines for sustainable production and efficient conservation policies. We show that unsustainable fishing is responsible for a loss of up to 30 times the potential yield of major fish stocks such as Atlantic cod, red snapper and bluefin tuna. We identify depleted fish stocks for which biomass is up to 15 times lower than it should be (yellownose skate fished in South America) and stocks facing fishing mortality up to 1.9 × 107 times higher than required to allow sustainable recovery (Pacific Ocean perch fished on the US West Coast). Regarding intrinsic biodiversity, our study shows that we are not able to understand the consequences of overfishing through a cause-effect chain due to lack of science knowledge. However, we display how to limit the impacts on biodiversity by using complementary indicators at species and ecosystem level. The complexity of marine ecosystems and the remaining limits of studied methods are discussed, showing the compelling need for further data collection and analysis, and opening ways for targeted research.

Synthesizing integrated ecosystem research to create informed stock-specific indicators for next generation stock assessments

Over the past two decades, numerous ecosystem surveys and process studies have emerged to monitor and assess the large marine ecosystems of Alaska. Several regional collaborative integrated ecosystem research projects (IERPs) were conducted to gain understanding of fish population fluctuations in relation to the surrounding environment. The Gulf of Alaska (GOA) IERP is one example of such an effort. Products of this program include a suite of in situ observations from fully integrated ecosystem surveys, laboratory experiments of physical thresholds for fish condition, and high-resolution oceanographic, planktonic, and habitat distribution models. When coupled, the synthesis products of this program can be utilized to understand system connectivity and highlight the primary ecosystem drivers of the GOA. Much of this information was included in annual GOA ecosystem status reports through individual indicator contributions. However, assimilation of these data into single-species stock assessments has remained limited. We provide a clear and direct avenue for including the products of these IERPs through the new ecosystem and socioeconomic profile (ESP) framework that identifies mechanistic relationships and tests ecosystem linkages within the stock assessment process. We present a case study using a data synthesis of the five commercially and ecologically valuable focal species of the GOAIERP (sablefish, pollock, Pacific cod, arrowtooth flounder, and Pacific ocean perch). Information was organized along the categories of distribution, phenology, and condition by life history stage to develop life history narratives for each species. These narratives identified critical ecosystem processes that could impact survival of each species. We then used habitat distribution models, seasonal phenology, and energy allocation strategies to sequentially reduce two gridded temperature datasets to reflect the life experience of the stock. This method essentially aligns ecosystem information at a spatial and temporal scale relevant to a stock and creates informed indicators that could then be related to a stock assessment parameter of interest, such as recruitment. Informed temperature indicators differed in magnitude and variability when compared to non-informed indicators and demonstrating species and stage-specific thermal preferences. The difference between the informed indicators and the non-informed indicators can also highlight thresholds and trends in habitat preference that could be further investigated with targeted process studies or laboratory experiments. The coordinated nature of the IERP allowed for the creation of these informed indicators that would not be possible with the results of any one process study. Both the stock-specific narratives and the informed indicators can be included into the ESPs for further monitoring and development. This integration ensures that the identified ecosystem linkages are evaluated concurrently with the stock assessment and ultimately transferred to fishery managers in an efficient and effective format for informing management decisions.

Cautious considerations for using multiple covariate distance sampling and seafloor terrain for improved estimates of rockfish density

Distance sampling is one of the most widely used methods for adjusting fish counts for detectability, which allows the estimation of absolute density. Further, abundance can be estimated spatially beyond the transect width with density surface models. The present study used a density surface modelling approach with survey data from line transects and terrain metrics from multibeam acoustic bathymetry data, integrated with a Geographic Information System, to estimate the population density of Pacific Ocean perchSebastes alutus(POP) within 6 sampling areas in the Gulf of Alaska (GOA) at 2 sampling scales: local and landscape. For adult POP, the final density model included depth as a significant predictor for density estimation at both the local and landscape scale. Additional factors included sponge coverage (local scale), aspect eastness and seafloor slope (landscape scale). Predicted densities of adult POP are highest on low (<5°) eastern-facing slopes with high sponge coverage (>75%), at depths of 100 to 200 m. By using habitat-based density models with data collected from line transect distance sampling and multibeam acoustic seafloor mapping surveys, we provide an alternative method for estimating rockfish abundance in untrawlable areas, which may help improve rockfish stock assessments and essential fish habitat descriptions and maps.

A resource saving technology for industrial processing of deep-sea and demersal fishes

This article shows the results of testing the technology of producing combined fish farce from deep-sea and demersal fishes. The object of our research is frozen fish, such as Giant grenadier (Albatrossia pectoralis), Alaska plaice (Pleuronectes quadritubercula-tus), Pacific halibut (Hippoglossus stenolepis) and Pacific ocean perch (Sebastes alutus). We found out that a combination of Giant grenadier (Albatrossia pectoralis) and demersal fishes, such as Alaska plaice (Pleuronectes quadrituberculatus), Pacific halibut (Hippoglossus stenolepis) and Pacific ocean perch (Sebastes alutus) in the proportion of 50:50 and a certain salt curing method make it possible to produce high-quality farce systems. We provide a scientific basis for the certain technological parameters defining the formation process of farce system texture depending on the quantity of sodium chloride, temperature of salt curing and length of curing. We found out that sodium chloride at a rate of 1.5-2.0% increases rheological properties of combined fish farce. We outlined conditions and parameters of technological treatment affecting the quality characteristics of ground fish muscle of giant grenadier (Albatrossia pectoralis) with preliminary salt curing. We found out that the highest values of adhesiveness, viscosity, water retention capacity and yield strength belong to experimental samples with 1.5-2.0% of sodium chloride to the raw mass with the temperature of curing plus 20±2°C and reasonable curing time of about 15-20 minutes. Based on the data obtained, it seems promising to produce combined fish farce from deep-sea and demersal fishes, since this method makes it possible to improve their functional and technological properties and to increase consumption of deep-sea and demersal fishes for food.

The Fishery Technology Complex: From Mapping to Depletion of Pacific Ocean Perch, 1880s-1970s.

The rapid collapse of the valuable Pacific Ocean perch fishery in the Gulf of Alaska around the mid-twentieth century is a vivid example of how the development, adoption, and transfer of technology between scientific cultures contributed to a conservation crisis. Technology adopted to support trawl fishery in the Gulf suggests that knowledge of bottom topography, deployment of a full suite of navigational instruments, specialized fishing gear, fleet communications, and positioning systems were key to exploiting and sampling this species of fish. The technologies were transferred to fishers and fishery researchers from a spectrum of sources ranging from academic researchers to natural historians to military agencies. Soviet and Japanese trawl fleets quickly brought about overfishing levels by moving into the region, targeting key fish habitats, and accessing and refining information on the Alaskan continental shelf garnered by American agencies. Technology was applied perversely; it was used to support development of recommendations for reducing exploitation but was also used to assist fishers in fish stock location. In the end, production goals set by managers resulted in over-exploitation.

Estimates of availability and catchability for select rockfish species based on acoustic-optic surveys in the Gulf of Alaska

Fishery-independent surveys, such as bottom trawl surveys, provide time-series abundance estimates, which inform many modern stock assessments. Area-swept biomass estimates from trawl surveys assume that fish densities do not differ between trawlable (T) and untrawlable (UT) areas. Bias and imprecision in the biomass estimates can occur when this assumption is not met. Thus, reliable estimates are needed for both the extent of T and UT habitat types in the surveyed area, and the relative densities of the fish species in the two habitat types to accurately assess groundfish populations. Acoustics and stereo-camera survey tools were used in the present study to determine the extent of T and UT habitat within 25-km2 bottom trawl survey grid cells historically designated as T/UT. Splitbeam acoustics were used to compare the abundance of rockfishes (Sebastes spp.) between the T/UT grid cell areas. Acoustic data were collected along uniformly spaced transects within 52 T and 43 UT grid cells throughout the Gulf of Alaska during summers 2013, 2015, and 2017. The acoustic backscatter attributed to rockfishes in UT grid cells was approximately three times that in T cells, and the percentages available to the bottom trawl survey were 40 % for harlequin rockfish, 43 % for northern rockfish, 51 % for dusky rockfish, and 98 % for Pacific ocean perch (POP). These findings allowed for estimation of the trawl catchability coefficient (q; a scaler between estimates of the area-swept survey abundance and actual abundance) of 0.46 for harlequin rockfish, 0.50 for northern rockfish, and 0.64 for dusky rockfish, and 1.15 for POP. These values could be used to inform the relationship between trawl survey estimated and actual abundances of rockfishes to improve the accuracy of stock assessments for these species.

Characterizing uncertainty in climate impact projections: a case study with seven marine species on the North American continental shelf

AbstractProjections of climate change impacts on living resources are being conducted frequently, and the goal is often to inform policy. Species projections will be more useful if uncertainty is effectively quantified. However, few studies have comprehensively characterized the projection uncertainty arising from greenhouse gas scenarios, Earth system models (ESMs), and both structural and parameter uncertainty in species distribution modelling. Here, we conducted 8964 unique 21st century projections for shifts in suitable habitat for seven economically important marine species including American lobster, Pacific halibut, Pacific ocean perch, and summer flounder. For all species, both the ESM used to simulate future temperatures and the niche modelling approach used to represent species distributions were important sources of uncertainty, while variation associated with parameter values in niche models was minor. Greenhouse gas emissions scenario contributed to uncertainty for projections at the century scale. The characteristics of projection uncertainty differed among species and also varied spatially, which underscores the need for improved multi-model approaches with a suite of ESMs and niche models forming the basis for uncertainty around projected impacts. Ensemble projections show the potential for major shifts in future distributions. Therefore, rigorous future projections are important for informing climate adaptation efforts.

Long-lived marine species may be resilient to environmental variability through a temporal portfolio effect.

Maintenance of genetic variation may provide resilience of populations to natural environmental variability. We used Pacific ocean perch (POP; Sebastes alutus) to test for the maintenance of adaptive variation across overlapping generations. POP are a long‐lived species characterized by widespread larval dispersal in their first year and a longevity of over 100 years. In order to understand how early marine dispersal affects POP survival and population structure, we used restriction site‐associated DNA sequencing (RADseq) to obtain 11,146 single‐nucleotide polymorphisms (SNPs) from 401 young‐of‐the‐year (YOY) POP collected during surveys conducted in 2014 (19 stations) and 2015 (4 stations) in the eastern Gulf of Alaska. Population clustering analysis showed that the POP samples represented four distinct ancestral populations mixed throughout the sampling area. Based on prior work on larval dispersal of POP, these larvae are most likely from distinct parturition locations that are mixing during their pelagic dispersal life stage. Latent factor mixed models revealed that POP larvae face significant selection during their first year at sea, which is specific to the year of their birth. Thus each adult cohort's genetic composition is heavily influenced by the environmental conditions experienced during their first year at sea. Long‐lived species relying on broadcast spawning strategies may therefore be uniquely resilient to environmental variability by maintaining a portfolio of cohort‐specific adaptive genotypes, and age truncation due to overfishing of older cohorts may have detrimental effect on the population viability.

Bycatch Quotas, Risk Pools, and Cooperation in the Pacific Whiting Fishery

The US Pacific whiting fishery uses mid-water trawl gear to target Pacific whiting off the US West Coast. The fishery is subject to sector-specific bycatch caps for Chinook salmon and several rockfish species (widow rockfish, canary rockfish, darkblotched rockfish, Pacific Ocean Perch (POP)). Chinook bycatch can include fish from endangered populations and rockfish stocks were recovering from severe depletion though most are now rebuilt. Catch of these species is rare and uncertain, making it difficult for vessels to meet strict individual performance standards. Consequently the industry has developed risk pools in which bycatch quota for a group of vessels is pooled, but vessels are required to follow practices that minimize bycatch risk including temporal and spatial fishing restrictions. The risk pools also require vessels to share information about bycatch hotspots enabling a cooperative approach to avoid bycatch based on real-time information. In this article we discuss the formation and structure of these risk pools, the bycatch reduction strategies they apply, and outcomes in the fishery in terms of observed bycatch avoidance behavior and utilization of target species. The analysis demonstrates the ability of these fishers to keep bycatch within aggregate limits and keep individual vessels from being tied up due to quota overages.

Seasonal habitat use and community structure of rockfishes in the Gulf of Alaska

Research is needed to determine the seasonal importance of high-relief habitats, particularly those containing biotic structures to rockfishes within the Gulf of Alaska. We examined the density and community structure of commercially important rockfishes in low-relief, high-relief, and biotic habitats in the spring, summer, and winter seasons at three sites in the central Gulf of Alaska using stereo drop cameras and bottom trawls. The fish community structure within all three sites was dominated by dusky rockfish (Sebastes variabilis), northern rockfish (S. polyspinis), Pacific ocean perch (S. alutus), and harlequin rockfish (S. variegatus). There was no effect of season on community structure and density of rockfish in the study area. While there were local differences in fish density and community structure, rockfish densities throughout the study areas were higher in complex than bare habitats. Significant differences in densities between high-relief and biotic habitats were not found and the additional value of structure- forming invertebrates was not proven. Juvenile rockfish were also associated with high-relief habitat, particularly complex boulder habitat. This study advances our knowledge of seasonal habitat preferences of commercially important rockfish species with the Gulf of Alaska and emphasizes the need to consider these preferences in surveying and managing these species.

SOME DATA ON BIOLOGY AND DISTRIBUTION FOR LARVAE OF ROCKFISHES FROM GENUS SEBASTES IN THE WATERS OF THE AVACHINSKY BAY (KAMCHATKA PENINSULA)

Results of ichthyoplankton surveys conducted in the Avachinsky Bay in the springs of 2003–2018 are presented. The larvae of 3 species of genus Sebastes occurred in the bay, starting in March, as shortraker rockfish Sebastes borealis, pacific ocean perch Sebastes alutus, and rougheye rockfish Sebastes aleutianus. The maximal catches of the larvae were obtained at the depth ≤ 500 m, mostly over the deep-water canyons. Problems of the rockfish larvae identifying to species are discussed, as absence of the detailed identifier for these species. Photo-images of the larvae are presented for Sebastes alutus and Sebastes aleutianus collected in spring of 2018, their typical differences are considered. Size composition is presented for the larvae of Sebastes.

How “The Blob” affected groundfish distributions in the Gulf of Alaska

AbstractWe investigated the distributional shifts of groundfish in response to anomalous ocean conditions, particularly the recent anomalously warm period (2014–2016; “The Blob”), based on data from ten Gulf of Alaska bottom trawl surveys conducted by the Alaska Fisheries Science Center during 1996–2015. Six groundfish species were considered: Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), walleye pollock (Gadus chalcogrammus), Pacific ocean perch (Sebastes alutus), northern rock sole (Lepidopsetta polyxystra), and southern rock sole (Lepidopsetta bilineata). Ontogenetic differences were examined by dividing data for each fish species into size classes. Our study demonstrated that after accounting for size‐specific depth preferences, the spatial responses of groundfish to anomalous ocean conditions differed by species and foraging guild in the central Gulf of Alaska. Pacific cod and arrowtooth flounder showed similar responses to ocean warming, but different responses to cooling. In general, Pacific cod moved to deeper depths in warmer years and moved to shallower depths in colder years. Arrowtooth flounder also moved deeper in warmer years. However, in colder years, large arrowtooth flounder (>40 cm) shifted toward shallower depths while smaller‐sized fish shifted toward deeper depths. In warmer years, large pollock (>30 cm) moved to deeper waters while smaller pollock (10–20 cm) moved to shallower waters. Pacific ocean perch exhibited an opposite response to thermal changes in habitat compared with Pacific cod and arrowtooth flounder. They moved deeper in colder years, but there was no clear change in depth as a function of size in response to warmer habitat.

Temporal records of diet diversity dynamics in individual adult female Steller sea lion (Eumetopias jubatus) vibrissae

Detailed information on the nutrition of free-ranging mammals contributes to the understanding of life history requirements, yet is often quite limited temporally for most species. Reliable dietary inferences can be made by analyzing the stable carbon (C) and nitrogen (N) isotopic values (δ13C and δ15N) of some consumer tissues; exactly which tissue is utilized dictates the inferential scope. Steller sea lion (SSL) vibrissae are grown continuously without shedding and thus provide a continuous multi-year record of dietary consumption. We applied a novel kernel density approach to compare the δ13C and δ15N values along the length of SSL vibrissae with δ13C and δ15N distributions of potential prey species. This resulted in time-series of proportion estimates of dietary consumption for individual SSL. Substantial overlap in δ13C and δ15N distributions for prey species prevented a discrete species-scale assessment of SSL diets; however, a post hoc correlational analysis of dietproportion estimates revealed grouping by trophic level. Our findings suggest that adult female SSL diets in the western and central Aleutian Islands shift significantly according to season: diets contain a higher proportion of lower trophic level species (Pacific Ocean perch, northern rockfish, Atka mackerel and walleye pollock) in the summer, whereas in the winter SSL consume a much more diverse diet which includes a greater proportion of higher trophic level species (arrowtooth flounder, Kamchatka flounder, darkfin sculpin, Pacific cod, Pacific octopus, rock sole, snailfish, and yellow Irish lord).

Running the gauntlet: Connectivity between natal and nursery areas for Pacific ocean perch (Sebastes alutus) in the Gulf of Alaska, as inferred from a biophysical individual-based model

Little is known regarding the importance of early-life transport and dispersion mechanisms in determining recruitment variability for Pacific ocean perch (POP) in the Gulf of Alaska (GOA). These mechanisms influence the degree of, and variability in, connectivity between offshore natal areas (parturition sites) and inshore demersal nursery habitats for young-of-the year juveniles, and may thus play an important role in the “gauntlet” that individuals must survive from parturition to recruitment. As a first attempt to assess interannual variability in connectivity between natal and nursery areas for POP in the GOA in a synthetic manner, we developed a coupled biophysical individual-based model (IBM) for POP early life history and dispersal with simple representations of active vertical movement, passive horizontal movement, growth, and settlement in appropriate nursery habitat to integrate known early-life traits with variability in environmental forcing. We used an oceanographic model for the GOA based on the Regional Ocean Modeling system (ROMS) to provide the underlying daily physical environment to force the IBM for 1996–2011 and simulated hundreds of thousands of individual POP from parturition along the shelf break to settlement in inshore demersal nursery habitats as young-of-the-year. We used the IBM results to assess spatial patterns of annual “maximum potential” connectivity between presumed natal and nursery areas at alongshore scales of ~ 150 km, as well as the interannual variability in these patterns.Results showed that, even in the absence of mortality, most (> 70%) individuals were unsuccessful in dispersing from presumed natal areas along the continental shelf break to inshore nursery areas. For those that were successful, connectivity was directed in a counterclockwise fashion (southeast to northwest) around the GOA following prevailing current patterns. Typical dispersion distances were on the order of 100's of km alongshore, much larger than those inferred from genetic sampling. Natal areas from which the highest fractions of successful individuals originated were in the southeast GOA, while the nursery areas most frequently reached by those successful individuals were in the central GOA. POP from natal areas in the western GOA were consistently exported from the system and likely contribute little to the GOA population, although they may contribute to populations in the Aleutian Islands and eastern Bering Sea. We also found that annual indices derived from the connectivity matrices were not very strongly related to any of a suite of basin- and regional-scale environmental indices, reflecting the overall complexity and scale of the pathways POP in the GOA may undertake during their early life stages and suggesting that multiple drivers operating at different spatial and temporal scales influence connectivity patterns. Finally, while our results indicate that interannual variability in physical transport may have a substantial impact on connectivity, we found little support for the hypothesis that this alone drives variability in POP recruitment.

Habitat suitability models for groundfish in the Gulf of Alaska

Identifying and quantifying the major ecosystem processes that regulate recruitment strength of commercially and ecologically important fish species is a central goal of fisheries management research. In the Gulf of Alaska (GOA) five groundfish species are of particular interest: sablefish (Anoplopoma fimbria), Pacific cod (Gadus macrocephalus), walleye pollock (Gadus chalcogrammus), arrowtooth flounder (Atheresthes stomias), and Pacific ocean perch (Sebastes alutus). Habitat suitability models (HSM) were developed for the demersal early juvenile stage to inform survival to recruitment for these species, using catch data and seafloor habitat metrics with presence-only models. Regional-scale maps were produced that predict the probability of suitable habitat available in the GOA from settlement through residency in nursery areas. For example, the HSM for sablefish (150–399 mm) described suitable habitat as bathymetrically low-lying areas with low rocky structure within 25–300 m depth. In contrast, the HSM for Pacific ocean perch (50–200 mm) described suitable habitat as bathymetry rises with rocky structure present on north-south facing slopes within 85–270 m depth. These habitat covariates are useful to refine population estimates for North Pacific groundfish species and to inform life stage-specific definitions of Essential Fish Habitat. This application of MaxEnt models should be applicable for species with low occurrence of spatial data in other marine ecosystems globally.

Long-term Bering Sea environmental variability revealed by a centennial-length biochronology of Pacific ocean perch Sebastes alutus

The productivity and functioning of Bering Sea marine ecosystems are tightly coupled to decadal-scale environmental variability, as exemplified by the profound changes in community composition that followed the 1976-1977 shift from a cool to a warm climate regime. Longer-term ecosystem dynamics, including the extent to which this regime shift was exceptional in the context of the past century, remain poorly described due to a lack of multi-decadal biological time series. To explore the impact of decadal regime shifts on higher trophic levels, we applied dendrochronology (tree-ring science) techniques to the otolith growth-increment widths of Pacific ocean perch Sebastes alutus (POP) collected from the continental slope of the eastern Bering Sea. After crossdating, 2 chronology development techniques were applied: (1) a regional curve standardization (RCS) approach designed to retain as much low-frequency variability as possible, and (2) an individual-detrending approach that maximized interannual synchrony among samples. Both chronologies spanned the years 1919-2006 and were significantly (p < 0.001) and positively correlated with sea surface temperature (March-December). The RCS chronology showed a transition from relatively slow to fast growth after 1976-1977. In both chronologies, the highest observed growth values immediately followed the regime shift, suggesting that this event had a critical and lasting impact on growth of POP. This growth pulse was, however, not shared by a previously published yellowfin sole Limanda aspera chronology (1969-2006) from the eastern Bering Sea shelf, indicating species- or site-specific responses. Ultimately, these chronologies provide a long-term perspective and underscore the susceptibility of fish growth to extreme low-frequency events.