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Stock structure and movement of tagged sablefish, Anoplopoma fimbria, in offshore northeast Pacific waters and the effects of El Nino Southern Oscillation on migration and growth

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Abstract

Sablefish in the northeast Pacific are found in commercial quantities from the Bering Sea, the Aleutian Islands, throughout the Gulf of Alaska, and south along the west coast of Canada and the U.S. to Baja California. Tag-recovery data support a two-population hypothesis throughout the North American range: an Alaska population ranging from the Bering Sea, including the Aleutian Islands and extending down through the Gulf of Alaska to northwest Vancouver Island, Canada; and a west coast population extending from southwest Vancouver Island to Baja California. Tag recoveries indicate that these two populations mix offsouthwest Vancouver Island and northwest Washington, and to a lesser extent off southern Washington and Oregon. Alaska sablefish, which commonly migrate over 500 n mi, are more mobile than west coast sablefish. Tag recoveries for sablefish tagged in Alaska have shown strong mutual exchanges between nearly all areas. In contrast, west coast sablefish have shown far less migratory behavior. Tagging data with respect to bathymetry are difficult to interpret in both regions owing to the fact that tagging and recovery effort do not cover the full bathymetric range of adults. Results of analysis of tag-recapture growth data were consistent with patterns observed for several other pelagic and demersal species. That is, E1 NinoSouthern Ocean Oscillation events appeared to retard the growth of sablefish along the west coast and to enhance growth of Alaska sablefish. The timing of recoveries from sablefish tagged off Alaska and recovered off southwest Vancouver Island and WashingtonOregon suggests that movement south correlates positively with strong upwelling in this southern area. Although sablefish trap-index surveys show a north to south cline in the percentage of large sablefish (>60 cm, and possibly of Alaska origin) sampled in length frequencies along the west coast, we were unable to correlate annual fluctuations in these percentages with upwelling strength.
... Sablefish have traditionally been treated as two populations based on differences in growth rate, size-atmaturity, and tagging studies (McDevitt 1990, Saunders et al. 1996, Kimura et al. 1998). The northern population inhabits Alaska and northern British Columbia waters and the southern population inhabits southern British Columbia, Washington, Oregon, and California waters, with mixing of the two populations occurring off southwest Vancouver Island and northwest Washington. ...
... However, recent genetic work by Jasonowicz et al. (2017) found no population sub-structure throughout their range along the US West Coast to Alaska, and suggested that observed differences in growth and maturation rates may be due to phenotypic plasticity or are environmentally driven. Significant stock structure among the federal Alaska population is unlikely given extremely high movement rates throughout their lives , Heifetz and Fujioka 1991, Maloney and Heifetz 1997, Kimura et al. 1998. The Alaskan sablefish assessment model assumes a single, homogenous population of sablefish across all Alaskan management areas, including the Bering Sea (BS), Aleutian Islands (AI), western Gulf of Alaska (WGOA), central Gulf of Alaska (CGOA), and eastern Gulf of Alaska (EGOA; including western Yakutat, WY, eastern Yakutat, EY, and the southeast GOA, SE). ...
... Sablefish are long-lived and fish greater than 40 years old have been regularly recorded (Kimura et al. 1993) with the reported maximum age in Alaska being 94 years (Kimura et al. 1998). The current assessment accounts for age-based dynamics until age-31, at which point a plus group is assumed for all ages greater than 31. ...
Technical Report
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https://www.fisheries.noaa.gov/resource/data/2022-assessment-sablefish-stock-alaska
... Juvenile males (those who have not yet developed secondary sexual characteristics) start molting in late March and through April and May, but the older/larger males generally molt later into the spring. Interestingly, in our study, the presence of sub-adult male northern elephant seals along the coast of Vancouver Island overlap with key migration routes of a mix between Alaskan and West coast sablefish stocks during sablefish migrations [e.g., 64,65]. Future studies examining correlations between sablefish and elephant seal migrations might provide insight into elephant seal migration patterns and foraging behavior. ...
Article
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The Ocean Networks Canada (ONC) cabled video-observatory at the Barkley Canyon Node (British Columbia, Canada) was recently the site of a Fish Acoustics and Attraction Experiment (FAAE), from May 21, 2022 to July 16, 2023, combining observations from High-Definition (HD) video, acoustic imaging sonar, and underwater sounds at a depth of 645 m, to examine the effects of light and bait on deep-sea fish and invertebrate behaviors. The unexpected presence of at least eight (six recurrent and two temporary) sub-adult male northern elephant seals (Mirounga angustirostris) was reported in 113 and 210 recordings out of 9737 HD and 2805 sonar videos at the site, respectively. Elephant seals were found at the site during seven distinct periods between June 22, 2022 and May 19, 2023. Ethograms provided insights into the seal’s deep-sea resting and foraging strategies, including prey selection. We hypothesized that the ability of elephant seals to perform repeated visits to the same site over long periods (> 10 days) was due to the noise generated by the sonar, suggesting that they learned to use that anthropogenic source as an indicator of food location, also known as the “dinner bell” effect. One interpretation is that elephant seals are attracted to the FAAE site due to the availability of prey and use the infrastructure as a foraging and resting site, but then take advantage of fish disturbance caused by the camera lights to improve foraging success. Our video observations demonstrated that northern elephant seals primarily focused on actively swimming sablefish (Anoplopoma fimbria), ignoring stationary or drifting prey. Moreover, we found that elephant seals appear to produce (voluntary or involuntary) infrasonic sounds in a foraging context. This study highlights the utility of designing marine observatories with spatially and temporally cross-referenced data collection from instruments representing multiple modalities of observation.
... The disproportionate effect of reduced sampling density on abundance indices for sablefish in comparison to those for the other species analyzed in our study can be attributed to differences in depth distribution. Of the 4 species examined in our study, the sablefish occupies the broadest and deepest range of depths, from less than 100 m to 1500 m (Kimura et al., 1998). In contrast, the Pacific ocean perch, which occupies the next widest depth range, rarely occurs at depths greater than 500 m (von Szalay and Raring, 2016). ...
... Both species are long-lived and large-bodied (A. fimbria, 94 years maximum age and 114 cm total length; S. borealis, 157 years maximum age and 120 cm total length), and they exhibit low recruitment [3,5,6,12,13]. Anoplopoma fimbria and S. borealis support economically valuable fisheries. ...
Article
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Sablefish (Anoplopoma fimbria, Anoplopomatidae) and shortraker rockfish (Sebastes borealis, Sebastidae), co-occur in deepwater marine habitats in the northeast Pacific. Both species are economically valuable, but their ecologies are not well known. We used stable isotope analysis of carbon and nitrogen to explore isotopic niches of A. fimbria and S. borealis in two distinct locations—a deep strait in the inside passage area and an open coastal area of the continental shelf, both in southeast Alaska, USA. Anoplopoma fimbria and S. borealis exhibited similar positions of isotopic niches based on nitrogen and carbon isotopic ratios, suggesting potential interspecific competition, especially in the inside location. In addition, S. borealis had a smaller niche breadth compared to A. fimbria in the coastal location. Both species had enriched nitrogen and carbon isotopic ratios in the inside location compared to the coastal location. Differences in isotopic niches between these two locations suggest the possibility of location-specific variation in isotopic niches of these two species of widespread, abundant deepwater fishes.
... The crest of the Bowie seamount is shallower still at only 65-100 m below the surface (Herzer, 1971). Tagged sablefish released in the Aleutian Islands, the Bering Sea, and the western and central GOA have been recovered on GOA seamounts (Shaw and Parks, 1997) and sablefish tagged on the GOA seamounts have been re-captured on the GOA continental shelf (Kimura et al., 1998;Maloney, 2004). Similarly, tagging evidence suggests migration between the Bowie Seamount and the US west coast (Murie et al., 1995;Beamish and Neville, 2003;Whitaker and McFarlane, 1997). ...
Article
In addition to their prevalence on the continental shelf, adult sablefish have been found over the chain of seamounts far offshore in the Gulf of Alaska (GOA). Many of the females that were observed had recently spawned or were ready to spawn. However, to date, it is not known what role the seamounts play in sablefish life history and there are no observations of sablefish eggs or larvae over the GOA seamounts. Due to their depth and remoteness, there are no suitable shallow nursery areas in the vicinity of the seamounts. For successful recruitment individuals hatching from eggs spawned over seamounts would need to be transported hundreds of miles to suitable areas inshore. Using an individual-based model (IBM) of sablefish, we have demonstrated that if spawning occurs over any of the seamounts in the GOA seamount province it is likely that at least some individuals will be successfully transported to shallow inshore nursery areas in the coastal GOA. As our simulated individuals only exhibit vertical movement behavior this on-shore transport results from the prevailing currents to which they were subjected and not from any geographic or environmental homing capabilities. Our analysis indicates that the strength of the on-shelf velocity is not the primary factor in determining the likelihood of transport to nursery areas. We speculate that the size, strength, location, and direction of the eddies that populate the GOA in any given year could be important in determining transport success. This idea is reinforced by our path analysis which shows that there are markedly different pathways taken by successful individuals among years. Our findings suggest that it may be necessary to expand what is considered suitable habitat for young sablefish. With seamounts being a potentially important spawning site for sablefish, future research priorities should include ground-truthing with fishery or fishery-independent data collected from seamounts. Potential applications of this expanded sablefish IBM include testing for connectivity between seamount and slope spawning areas and the Aleutian Islands and Bering Sea and contributing to the development of spatially explicit assessment models of sablefish.
... The NEPTUNE cabled observatory operated by Ocean Networks Canada (ONC) presently represents one of the best technologically-equipped networks to undertake fish communities monitoring along the Pacific coast of North America (Aguzzi et al., 2020a). One of its nodes, located in Barkley Canyon 2 , consists of several cabled instrumented platforms that span a maximum linear distance of~15 km, and a depth range of 400 to 985 m, overlapping with the habitat range of the greatest sablefish abundance (Goetz et al., 2018;Kimura et al., 2018;Aguzzi et al., 2020a). A total of 5 fixed instrumented platforms and a mobile crawler (with a 70-m radius range) are equipped with a suite of oceanographic and biogeochemical sensors in addition to video cameras mounted on pan and tilt units ( Figure 1). ...
Article
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Ocean observatories collect large volumes of video data, with some data archives now spanning well over a few decades, and bringing the challenges of analytical capacity beyond conventional processing tools. The analysis of such vast and complex datasets can only be achieved with appropriate machine learning and Artificial Intelligence (AI) tools. The implementation of AI monitoring programs for animal tracking and classification becomes necessary in the particular case of deep-sea cabled observatories, as those operated by Ocean Networks Canada (ONC), where Petabytes of data are now collected each and every year since their installation. Here, we present a machine-learning and computer vision automated pipeline to detect and count sablefish (Anoplopoma fimbria), a key commercially exploited species in the N-NE Pacific. We used 651 hours of video footage obtained from three long-term monitoring sites in the NEPTUNE cabled observatory, in Barkley Canyon, on the nearby slope, and at depths ranging from 420 to 985 m. Our proposed AI sablefish detection and classification pipeline was tested and validated for an initial 4.5 month period (Sep 18 2019-Jan 2 2020), and was a first step towards validation for future processing of the now decade-long video archives from Barkley Canyon. For the validation period, we trained a YOLO neural network on 2917 manually annotated frames containing sablefish images to obtain an automatic detector with a 92% Average Precision (AP) on 730 test images, and a 5-fold cross-validation AP of 93% (± 3.7%). We then ran the detector on all video material (i.e., 651 hours from a 4.5 month period), to automatically detect and annotate sablefish. We finally applied a tracking algorithm on detection results, to approximate counts of individual fishes moving on scene and obtain a time series of proxy sablefish abundance. Those proxy abundance estimates are among the first to be made using such a large volume of video data from deep-sea settings. We discuss our AI results for application on a decade-long video monitoring program, and particularly with potential for complementing fisheries management practices of a commercially important species.
... Alaska sablefish or the northern population of sablefish, are assessed as a single population in the federal waters off Alaska from British Columbia to the Bering Sea (McDevitt, 1990;Saunders et al., 1996;Kimura et al., 1998). They have a propensity for large-scale movements (Heifetz and Fujioka, 1991;Hanselman et al., 2015) and adult sablefish are typically encountered between 200 and 1000 m along the continental slope, shelf gullies, and deep-sea canyons (Wolotira et al., 1993). ...
Article
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.
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Objective Our aim was to predict the maturity (will spawn or immature) of Sablefish Anoplopoma fimbria in Alaska for past years during a period when macroscopic data are not of utility and histological observations are not available. Methods In a previous study, female maturity was determined using histology and a model was developed that predicted maturity using maternal length, age, and relative condition. We used this published model to predict the maturity of individual Sablefish collected annually in the same area on the same dates. The maturity predictions were used to create predicted time series of maturity at age for surveys conducted over 22 years. Result A k‐means cluster analysis of annual maturity parameters revealed that data should be split into two clusters. These groups were chronologically sequential (1998–2010 and 2011–2019), with two exceptions: 2015 and 2017 were assigned to the early time period. We created two chronological time blocks by incorporating the two outlier years into the late period post hoc, as we are not aware of mechanisms that may have caused these two outliers, and it is important for stock assessment to capture the signal and not the noise. Sablefish in the later period were predicted to mature later than fish in the earlier period; age at 50% maturity was 5.5 years in the early period and 6.8 years in the later period, and the slope was shallower in the later period. Conclusion There are often gaps in reliable maturity data. This case study illustrates that limited histological data sets can be used to predict maturity in years without ovary samples and illustrates how these data can be grouped based on similarities and chronology for use in stock assessment. We recommend more histological studies in the future to test assumptions of the predictive model, and we recommend evaluations of other factors, such as environmental time series, that may be drivers of annual maturity.
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Sablefish (Anoplopoma fimbria) are a highly mobile species that support important commercial fisheries in the North Pacific Ocean. Information on the genetic stock structure of sablefish is vital for constructing management strategies that ensure the long-term viability of the species. Most previous genetic studies on sablefish have found panmixia throughout the majority of their range, but a recent study suggested that a population structure may exist. Here, we use low-coverage whole genome resequencing to investigate genetic structure in the northern end of the species’ range (from Washington State, USA to the Bering Sea and Aleutian Islands, AK, USA). Additionally, we reanalyzed an existing genomic dataset containing 2661 markers to test specific hypotheses about genetic structure by sex. Genome resequencing data from 119 individuals screened at 7 110 228 markers revealed no evidence of population structure, and reanalysis of the existing genomic dataset supported the same conclusion. Differentiation across the genome was largely driven by variation at two putative inversions located ∼1 megabase apart, which did not display any signals of geographic differentiation. Our study further supports the conclusion of genetic panmixia in sablefish throughout its northern range.
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We used a Markov model to quantify movement rates of tagged sablefish (Anoplopoma fimbria) among regulatory areas of the North Pacific Fishery Management Council during 1979–1987. The model included natural and fishing mortality, tag reporting and shedding rates, and movement probabilities. Maximum likelihood was used to estimate the parameters of the model. Estimated annual movement rates out of an area were in the range 19–69% for small (less than 57 cm fork length (FL)), 25–72% for medium (57–66 cm FL), and 27–71% for large (more than 66 cm FL) sablefish. The predominant direction of movement along the continental slope was eastward for large sablefish and westward for small sablefish. Most estimates of movement rates were precise, unconfounded, and robust to perturbations of input constants (natural and fishing mortality, and tag reporting rates), except for some imprecise estimates of large sablefish. The results indicate that movement plays an important role in determining the amount of sablefish available for harvest in an area. To account for the interactions among fisheries in different areas, the movement dynamics of sablefish should be incorporated into a stock assessment based on size or age-structure.
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