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Timothy Loher - One of the best experts on this subject based on the ideXlab platform.
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survival outcome patterns revealed by deploying advanced tags in quantity pacific halibut Hippoglossus stenolepis survivals after release from trawl catches through expedited sorting
Canadian Journal of Fisheries and Aquatic Sciences, 2019Co-Authors: Craig S Rose, Julie K Nielsen, John R Gauvin, Timothy Loher, Suresh A Sethi, Andrew C Seitz, Michael B Courtney, Paige DrobnyAbstract:Bycatch of Pacific halibut (Hippoglossus stenolepis) limits many trawl fisheries in Alaska and greatly concerns stakeholders from local communities and fisheries that rely on Pacific halibut. To re...
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connectivity between pacific halibut Hippoglossus stenolepis residing in the salish sea and the offshore population demonstrated by pop up archival tagging
Journal of Sea Research, 2018Co-Authors: Timothy Loher, Eric SoderlundAbstract:Abstract Fisheries for Pacific halibut (Hippoglossus stenolepis) in the US Pacific Northwest support a variety of harvest sectors including some that are restricted to coastal offshore waters and others confined to the inland waters of the Salish Sea. Such restrictions have generated interest in the degree to which the Salish Sea represents an extension of the offshore population versus its potential to support an isolated stock. Here, twelve female Pacific halibut were tagged during boreal summer with pop-up archival transmitting (PAT) tags that were programmed to report during either the subsequent winter spawning period or late-spring feeding period. High-resolution depth data failed to produce evidence of spawning within the Salish Sea, while depth-temperature profiles were consistent with the departure of migrants between October and January. Final positions and at-liberty longitude estimates suggest that ~60% of the tagged fish departed the Salish Sea, with confirmed migrations to Canada and Alaska. The recapture in the southern Salish Sea of one fish whose tag had reported earlier from offshore Canadian waters demonstrated the occurrence of cyclic migrations. Evaluation of likely maturity status suggests that local demographics reflect either the cumulative effects of spawning migrations in which some emigrants remain offshore after departing the system, or some combination of enhanced growth or delayed maturity. These findings confirm that the Salish Sea does not represent a functionally-independent stock, but suggest that inshore waters may play a unique role by receiving recruits, rearing individuals to maturity, and exporting spawners to the offshore stock components, while retaining a proportion of site-faithful individuals with cyclic seasonal connectivity with offshore spawning groups.
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subtle genetic population structure in pacific halibut Hippoglossus stenolepis
Journal of Fish Biology, 2016Co-Authors: Daniel P Drinan, Timothy Loher, Heather M Galindo, Lorenz HauserAbstract:Pacific halibut Hippoglossus stenolepis from 10 sampling locations throughout their range were investigated for signs of population structure. Two genetic data sets were created: (1) all individuals (n = 828) at few anonymous microsatellite markers (number of loci = 16); (2) fewer individuals (n = 435) genotyped at anonymous as well as expressed sequence-tag linked microsatellites (number of loci = 61). A combination of multidimensional scaling plots, discriminant analysis of principal components and pairwise differentiation estimates suggested that samples from the Aleutian Islands, particularly the western Aleutian Islands, were genetically distinct from samples collected in other regions. In addition, outlier analyses found that two markers linked to expressed sequence tags may be under directional selection and could explain the differentiation among samples. These results confirm findings from previous research and suggest that population structure may exist within a current management unit (i.e. International Pacific Halibut Commission Regulatory Area 4B).
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Incorporation of bomb-produced 14C into fish otoliths. An example of basin-specific rates from the North Pacific Ocean
Canadian Journal of Fisheries and Aquatic Sciences, 2015Co-Authors: Stephen Wischniowski, Timothy Loher, Craig R Kastelle, Thomas E. HelserAbstract:Sagittal otoliths from juvenile Pacific halibut (Hippoglossus stenolepis) of known age were used to create a bomb-produced radiocarbon reference chronology for the eastern Bering Sea (EBS) by fitting a coupled-function model to Δ14C values from each specimen’s birth year. The newly created EBS reference chronology was then compared with a reference chronology previously created for Pacific halibut from the Gulf of Alaska (GOA). Adult Pacific halibut age-validation samples from the EBS were also analyzed for 14C and modeled to validate age-estimation accuracy. A Bayesian model was developed and Markov chain Monte Carlo simulation was used to estimate model parameters and adult Pacific halibut ageing bias. Differences in reference chronologies between ocean basins were reflected in a large deviance information criterion (ΔDIC) between models, supporting the hypothesis that two separate coupled-function models were required to adequately describe the data, one each for the EBS and GOA. We determined that reg...
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length and sex effects on the spatial structure of catches of pacific halibut Hippoglossus stenolepis on longline gear
2012Co-Authors: Timothy Loher, Jessica C HobdenAbstract:Field experiments were conducted to test the hypotheses that Pacific halibut (Hippoglossus stenolepis) display small-scale spatial structure within longline catches, relative to other species and empty hooks, or within-species based on sex or length. Sequential hook-by-hook inventories, along with length and sex data, were taken at thirty-one survey stations. Two-dimensional spatial statistics were used to test for 1) aggregation, defined as the clustering of individuals within a given demographic of size or sex over small intervals of distance; and 2) segregation, defined as the sequential occurrence of individuals within a given demographic of size or sex, uninterrupted by other observations, irrespective of the distance between individuals. Statistically significant structure was detected within catches that is more commonly associated with fish length than sex. Significant spatial structuring occurred at 60% of all stations tested. Significant aggregation of halibut of legal length for commercial retention (≥82 cm) was detected at 44% of stations and aggregation of sublegal-size halibut was detected at 11%. Maleand female-based aggregations were observed at 22% and 11% of stations, respectively. Significant segregation of females was observed at 20% of stations, male segregation occurred at 8% of stations, and segregation by size at 16% of stations. Understanding small-scale spatial structure within longline catches may help us interpret changes in survey and commercial catch data. If structure is generated by behavior, then observed size-at-age or relative sex-ratios may be biased relative to underlying distributions. Although physical processes such as gape limitation should remain stable over the time, dynamic processes may be spatially and temporally variabl
Andrew C Seitz - One of the best experts on this subject based on the ideXlab platform.
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survival outcome patterns revealed by deploying advanced tags in quantity pacific halibut Hippoglossus stenolepis survivals after release from trawl catches through expedited sorting
Canadian Journal of Fisheries and Aquatic Sciences, 2019Co-Authors: Craig S Rose, Julie K Nielsen, John R Gauvin, Timothy Loher, Suresh A Sethi, Andrew C Seitz, Michael B Courtney, Paige DrobnyAbstract:Bycatch of Pacific halibut (Hippoglossus stenolepis) limits many trawl fisheries in Alaska and greatly concerns stakeholders from local communities and fisheries that rely on Pacific halibut. To re...
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an approach to describe depth specific periodic behavior in pacific halibut Hippoglossus stenolepis
Journal of Sea Research, 2016Co-Authors: John D Scott, Julie K Nielsen, Michael B Courtney, Thomas J Farrugia, Andrew C SeitzAbstract:Abstract Correspondence between patterns of occupied depth and environmental cycles, called “depth-specific periodic behavior”, has been used to inform management of several flatfishes. However, little is known about depth-specific periodic behavior of Pacific halibut ( Hippoglossus stenolepis ), an important species in recreational, commercial and subsistence fisheries in the eastern North Pacific Ocean. To evaluate depth-specific periodic behavior of Pacific halibut, an approach was developed in which depth data from electronic tags were used to produce four types of complementary plots, including two-dimensional time series of depth, activity level derived from differencing adjacent depth recordings, periodograms, and wavelet transform coefficients. From a visual examination of the plots, daily depth-specific periodic behavior types, including diel, tidal, spawning, semi-lunar and lunar, were assigned to 37 individual Pacific halibut. Overall, the approach used in this study was useful for describing relatively short term depth-specific periodic behavior, but was less informative for understanding relatively long term behavioral patterns. The results suggest that patterns in occupied depth may be related to seasonal activities of Pacific halibut. Specifically, during the summer feeding season, fish most commonly behaved periodically on a diel scale or inactively laid on the seafloor, which was manifested as tidal periodicity as the height of the water column fluctuated above the fish. Both active swimming and inactivity on the seafloor may be related to different foraging strategies. During fall and spring migratory periods and the winter spawning season, no periodicity in depth-specific behavior was most common, which may correspond to directed movement over irregular bathymetry between feeding and spawning locations or to reproductive behaviors. Evidence of an additional reproductive behavior, spawning rises off the seafloor, was also observed during the winter spawning season. This approach for understanding the periodicity of occupied depth of Pacific halibut provides additional insight into the behavior of this iconic species. This knowledge perhaps may be used in the future to inform this species' management, such as refining estimates of susceptibility to capture and examining timing of movement among regulatory areas.
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dispersal and behavior of pacific halibut Hippoglossus stenolepis in the bering sea and aleutian islands region
Aquatic Biology, 2011Co-Authors: Andrew C Seitz, Timothy Loher, Brenda L Norcross, Jennifer L NielsenAbstract:Currently, it is assumed that eastern Pacific halibut Hippoglossus stenolepis belong to a single, fully mixed population extending from California through the Bering Sea, in which adult halibut disperse randomly throughout their range during their lifetime. However, we hypothesize that hali but dispersal is more complex than currently assumed and is not spatially random. To test this hypo thesis, we studied the seasonal dispersal and behavior of Pacific halibut in the Bering Sea and Aleutian Islands (BSAI). Pop-up Archival Transmitting tags attached to halibut (82 to 154 cm fork length) during the summer provided no evidence that individuals moved out of the Bering Sea and Aleutian Islands region into the Gulf of Alaska during the mid-winter spawning season, supporting the concept that this region contains a separate spawning group of adult halibut. There was evidence for geographically localized groups of halibut along the Aleutian Island chain, as all of the individuals tagged there displayed residency, with their movements possibly impeded by tidal currents in the passes between islands. Mid-winter aggregation areas of halibut are assumed to be spawning grounds, of which 2 were previously unidentified and extend the species' presumed spawning range ∼1000 km west and ∼600 km north of the nearest documented spawning area. If there are indeed inde- pendent spawning groups of Pacific halibut in the BSAI, their dynamics may vary sufficiently from those of the Gulf of Alaska, so that specifically accounting for their relative segregation and unique dynamics within the larger population model will be necessary for correctly predicting how these com- ponents may respond to fishing pressure and changing environmental conditions.
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fine scale population genetic structure in alaskan pacific halibut Hippoglossus stenolepis
Conservation Genetics, 2010Co-Authors: Jennifer L Nielsen, Sara L Graziano, Andrew C SeitzAbstract:Pacific halibut collected in the Aleutian Islands, Bering Sea and Gulf of Alaska were used to test the hypothesis of genetic panmixia for this species in Alaskan marine waters. Nine microsatellite loci and sequence data from the mitochondrial (mtDNA) control region were analyzed. Eighteen unique mtDNA haplotypes were found with no evidence of geographic population structure. Using nine microsatellite loci, significant heterogeneity was detected between Aleutian Island Pacific halibut and fish from the other two regions (F ST range = 0.007–0.008). Significant F ST values represent the first genetic evidence of divergent groups of halibut in the central and western Aleutian Archipelago. No significant genetic differences were found between Pacific halibut in the Gulf of Alaska and the Bering Sea leading to questions about factors contributing to separation of Aleutian halibut. Previous studies have reported Aleutian oceanographic conditions at deep inter-island passes leading to ecological discontinuity and unique community structure east and west of Aleutian passes. Aleutian Pacific halibut genetic structure may result from oceanographic transport mechanisms acting as partial barriers to gene flow with fish from other Alaskan waters.
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characterization of active spawning season and depth for eastern pacific halibut Hippoglossus stenolepis and evidence of probable skipped spawning
Journal of Northwest Atlantic Fishery Science, 2008Co-Authors: Timothy Loher, Andrew C SeitzAbstract:The eastern Pacific halibut (Hippoglossus stenolepis ) fishery is prosecuted over a nine-month season with a provision to cease harvests if stock declines to historically-observed minimum spawning biomass. The industry has requested to extend fishing into winter, but little information exists regarding potential impacts on spawning aggregations or effective spawning biomass. A strictly annual spawning cycle is presumed, but some adults fail to undertake the offshore migration associated with continental slope spawning. We examined depth records of halibut tagged with Pop-up Archival Transmitting (PAT) tags for evidence of offshore seasonal migration (n = 72). For tags that were physically recovered (n = 16) we identified the occurrence of abrupt (~100 m) mid-winter ascents, believed to be egg release. The active spawning season, defined by occurrence of these rises, lasted from 27 December–8 March, at bottom depths of 278–594 m. Eighteen percent of tagged halibut remained onshore. Thirty-one percent of fish with detailed archival records did not exhibit spawning rises, including all fish that remained onshore. Correcting for the possibility that some were likely immature, the data suggest that ~10% of the mature fish do not participate in the spawning migration and 10–15% that migrate to deep water may not actively spawn. The data suggest that opening the commercial fishery in early spring would likely subject actively spawning fish to fishing mortality, and could truncate the effective spawning period. Natural rates of skip-spawning and fisheries-induced reduction of the spawning period relative to suitable larval rearing conditions could introduce temporal and regional variance into levels of effective spawning biomass and warrant further investigation.
Waldo W Wakefield - One of the best experts on this subject based on the ideXlab platform.
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Testing of Two Selective Flatfish Sorting-Grid Bycatch Reduction Devices in the U.S. West Coast Groundfish Bottom Trawl Fishery
Marine and Coastal Fisheries: Dynamics Management and Ecosystem Science, 2017Co-Authors: Mark J M Lomeli, Waldo W Wakefield, Bent HerrmannAbstract:AbstractIn the U.S. West Coast limited-entry (LE) groundfish bottom trawl fishery, catches of stocks with restrictive harvest limits (e.g., Darkblotched Rockfish Sebastes crameri, Sablefish Anoplopoma fimbria, and Pacific Halibut Hippoglossus stenolepis) continue to hinder many fishermen’s ability to fully utilize their quota shares of more abundant flatfish stocks (e.g., Dover Sole Microstomus pacificus and Petrale Sole Eopsetta jordani). We used a recapture net to examine the size-selection characteristics of two selective flatfish sorting-grid bycatch reduction devices (BRDs), which were designed to reduce catches of Pacific Halibut and non-flatfish species while retaining target flatfishes. The two devices were identical in materials and design except that the sorting-grid dimensions differed (BRD-1: 6.4- × 25.4-cm grid size; BRD-2: 6.4- × 30.5-cm grid size). The size selectivity for rockfishes, other roundfishes, Pacific Halibut, English Sole Parophrys vetulus, and Rex Sole Glyptocephalus zachirus di...
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a flexible sorting grid to reduce pacific halibut Hippoglossus stenolepis bycatch in the us west coast groundfish bottom trawl fishery
Fisheries Research, 2013Co-Authors: Mark J M Lomeli, Waldo W WakefieldAbstract:Abstract This study examined a flexible sorting grid excluder designed to reduce Pacific halibut ( Hippoglossus stenolepis ) bycatch in the US west coast groundfish bottom trawl fishery. Tests occurred off Washington during 2011 aboard a commercial trawler. A recapture net was used to quantify the retention rates of target and non-target species. Pacific halibut bycatch was reduced 61.6% by weight and 57.0% by numbers. Exclusion was greatest for Pacific halibut weighing more than 4.5 kg. A significant difference in the mean total length was also noted between Pacific halibut caught in the codend and the recapture net, with larger fish occurring in the recapture net. The retention of primary target groundfishes of marketable-size ranged from 76.7 to 89.3%. We demonstrated the capability of a flexible sorting grid excluder to reduce Pacific halibut bycatch in the groundfish bottom trawl fishery while retaining a relatively high proportion of the targeted species.
Steven R Hare - One of the best experts on this subject based on the ideXlab platform.
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distribution patterns of pacific halibut Hippoglossus stenolepis in relation to environmental variables along the continental shelf waters of the us west coast and southern british columbia
Fisheries Oceanography, 2014Co-Authors: Steven R Hare, Lauri L Sadorus, Nathan J Mantua, Timothy E Essington, Barbara M HickeyAbstract:Knowing how Pacific halibut (Hippoglossus stenolepis) distribute in relation to ocean conditions is of primary importance to halibut managers, as they are tasked with estimating stock size and designing effective monitoring programs amidst a changing climate. This research examined near-bottom environmental data alongside halibut survey catch data for the years 2006–2009 on the continental shelf of Oregon, Washington, and southern British Columbia. The objectives of the research were to: (1) characterize summer environmental conditions and halibut distribution; (2) explore ranges and possible tolerance thresholds for halibut in relation to temperature, dissolved oxygen (DO), salinity, and pH; and (3) identify the primary environmental factors affecting distribution of halibut and model the observed relationships. Seasonal hypoxia is an annual feature of the study area and results suggest halibut exhibited an apparent DO minimum threshold of 0.9 mL L−1. Ordinary least squares multiple regression analysis indicated that depth, temperature, and DO were significant variables in predicting halibut distribution, whereas salinity and bottom type were not. Ambiguity in model results led to the use of two additional analytical methods, geographically weighted regression (GWR) and tree regression, to examine regional variation and the overarching structure of halibut distribution. The three models yielded similar results indicating the importance of DO and temperature as variables describing structure. The GWR model yielded the best fit of the three when using DO as a predictor variable, indicating that regional variation is a factor. These results suggest that low, but above-threshold, DO may be contributing to catchability differences in the survey.
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A Conditional Constant Catch Policy for Managing the Pacific Halibut Fishery
North American Journal of Fisheries Management, 2004Co-Authors: William G Clark, Steven R HareAbstract:Abstract Since 1985, the staff of the International Pacific Halibut Commission (IPHC) has used a constant harvest rate policy—currently 20% of exploitable biomass—to estimate the yield currently available from Pacific halibut Hippoglossus stenolepis stock. This paper outlines a more stable alternative policy in which yield is held constant at some ceiling level so long as taking that yield would not result in a total exploitation rate exceeding a specified ceiling rate. During any periods of low abundance, the policy would revert to a constant harvest rate policy at the ceiling rate. The ceiling harvest rate would be chosen so as to assure that spawning biomass remained above a specified minimum. A policy of this kind could produce a yield similar to the present 20% constant harvest rate policy but with much less year-to-year variation attributable to changes in stock abundance, assessment methods, and estimated removals by other fisheries.
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Effects of Climate and Stock Size on Recruitment and Growth of Pacific Halibut
North American Journal of Fisheries Management, 2002Co-Authors: William G Clark, Steven R HareAbstract:Abstract This paper compares long-term changes in the recruitment and growth of Pacific halibut Hippoglossus stenolepis with long-term changes in climate and stock size. It appears that environmental variability—both interdecadal and interannual—is responsible for most of the observed variation in Pacific halibut recruitment. The large changes in growth rates that occurred during the 20th century appear to have been density-dependent responses to changes in stock size, with virtually no environmental influence.
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decadal changes in growth and recruitment of pacific halibut Hippoglossus stenolepis
Canadian Journal of Fisheries and Aquatic Sciences, 1999Co-Authors: William G Clark, Steven R Hare, Ana M Parma, Patrick J Sullivan, Robert J TrumbleAbstract:Since the climate regime shift of 1976-1977 in the North Pacific, the individual growth of Pacific halibut (Hippoglossus stenolepis) has decreased dramatically in Alaska but not in British Columbia. Recruitment has increased dramatically in both areas. The decrease in age-specific vulnerability to commercial longline gear resulted in a persistent underestimation of incoming recruitment by the age-structured assessment method (CAGEAN) that was used to assess the stock. This problem has been corrected by adding temporal trends in growth and fishery selectivity to the assessment model. The recent sustained high level of recruitment at high levels of spawning biomass has erased the previous appearance of strong density dependence in the stock-recruitment relationship and prompted a reduction in the target full-recruitment harvest rate from 30-35 to 20-25%. The climate regime shift affected a number of other stocks of vertebrates and invertebrates in the North Pacific. While the general oceanographic changes h...
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Accounting for Bycatch in Management of the Pacific Halibut Fishery
North American Journal of Fisheries Management, 1998Co-Authors: William G Clark, Steven R HareAbstract:Abstract Since the 1960s, fisheries for groundfish other than Pacific halibut Hippoglossus stenolepis have caused an average of about 9,000 metric tons (mt, round weight) of halibut bycatch mortality every year, whereas annual directed catches of Pacific halibut have varied from 13,000 to almost 50,000 mt. About half of the bycatch consists of juvenile Pacific halibut caught in Alaska, some of which would otherwise migrate south and contribute to the fishery in British Columbia. These interceptions have long been a difficult issue for the United States and Canada. At recent levels of high juvenile abundance, the juvenile bycatch reduces coastwide recruitment by about 10%. The resulting yield loss, plus bycatch of adult fish, reduces yield to the directed fishery by about 11,000 mt per year. Migration modeling indicates that the yield loss due to bycatch occurs almost entirely in the area where the bycatch is taken. In particular, bycatch in Alaska reduces Pacific halibut yields in British Columbia by, at ...
Mark J M Lomeli - One of the best experts on this subject based on the ideXlab platform.
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Testing of Two Selective Flatfish Sorting-Grid Bycatch Reduction Devices in the U.S. West Coast Groundfish Bottom Trawl Fishery
Marine and Coastal Fisheries: Dynamics Management and Ecosystem Science, 2017Co-Authors: Mark J M Lomeli, Waldo W Wakefield, Bent HerrmannAbstract:AbstractIn the U.S. West Coast limited-entry (LE) groundfish bottom trawl fishery, catches of stocks with restrictive harvest limits (e.g., Darkblotched Rockfish Sebastes crameri, Sablefish Anoplopoma fimbria, and Pacific Halibut Hippoglossus stenolepis) continue to hinder many fishermen’s ability to fully utilize their quota shares of more abundant flatfish stocks (e.g., Dover Sole Microstomus pacificus and Petrale Sole Eopsetta jordani). We used a recapture net to examine the size-selection characteristics of two selective flatfish sorting-grid bycatch reduction devices (BRDs), which were designed to reduce catches of Pacific Halibut and non-flatfish species while retaining target flatfishes. The two devices were identical in materials and design except that the sorting-grid dimensions differed (BRD-1: 6.4- × 25.4-cm grid size; BRD-2: 6.4- × 30.5-cm grid size). The size selectivity for rockfishes, other roundfishes, Pacific Halibut, English Sole Parophrys vetulus, and Rex Sole Glyptocephalus zachirus di...
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a flexible sorting grid to reduce pacific halibut Hippoglossus stenolepis bycatch in the us west coast groundfish bottom trawl fishery
Fisheries Research, 2013Co-Authors: Mark J M Lomeli, Waldo W WakefieldAbstract:Abstract This study examined a flexible sorting grid excluder designed to reduce Pacific halibut ( Hippoglossus stenolepis ) bycatch in the US west coast groundfish bottom trawl fishery. Tests occurred off Washington during 2011 aboard a commercial trawler. A recapture net was used to quantify the retention rates of target and non-target species. Pacific halibut bycatch was reduced 61.6% by weight and 57.0% by numbers. Exclusion was greatest for Pacific halibut weighing more than 4.5 kg. A significant difference in the mean total length was also noted between Pacific halibut caught in the codend and the recapture net, with larger fish occurring in the recapture net. The retention of primary target groundfishes of marketable-size ranged from 76.7 to 89.3%. We demonstrated the capability of a flexible sorting grid excluder to reduce Pacific halibut bycatch in the groundfish bottom trawl fishery while retaining a relatively high proportion of the targeted species.