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Seattle, WA, United States

Galindo H.M.,University of Washington | Loher T.,International Pacific Halibut Commission | Hauser L.,University of Washington
Marine Biotechnology | Year: 2011

The discovery of genetic markers linked to physiological traits in wild populations is increasingly desired for ecological and evolutionary studies, as well as to inform management decisions. However, identifying such markers often requires a large investment of both time and money. Serendipitously, in a recent microsatellite survey, we discovered three out of 16 microsatellite loci that were correlated to the female sex in Pacific halibut (Hippoglossus stenolepis). These three loci were screened in 550 Pacific halibut to determine their accuracy at identifying sex. Genetic assignment successfully identified sex in 92% of individuals from sample collections spanning 3,000 km and 9 years. All but two of 287 females had one copy of a characteristic allele for at least one of the three microsatellite loci, resulting in consistent heterozygote excess in females. This pattern is consistent with the hypothesis that females are the heterogametic sex in Pacific halibut, which thus may have a different sex-determination pattern than the closely related Atlantic halibut (Hippoglossus hippoglossus). A rapid divergence of sex-determining mechanisms could be either a cause or consequence of speciation between Pacific and Atlantic halibut. In either case, the ability to genetically identify sex in individual Pacific halibut provides a new tool for ecological studies, fisheries management, and insight into the evolution of sex determination in flatfish. © 2011 Springer Science+Business Media, LLC.

Hanselman D.H.,National Oceanic and Atmospheric Administration | Clark W.G.,International Pacific Halibut Commission | Heifetz J.,National Oceanic and Atmospheric Administration | Anderl D.M.,National Oceanic and Atmospheric Administration
Fisheries Research | Year: 2012

A mark-recapture experiment provided a collection of 172 known-age sablefish from Alaska waters. Otoliths from each fish were read by three readers. The readings have a positive bias among young fish and a negative bias among older fish. Among otoliths of the same age, some tended to give consistently high or low annulus counts, so that the variance of age readings at each true age was about half due to variance among otoliths and half due to variance among replicate readings of individual otoliths. The statistical distribution of age reading errors is well described by an asymmetrical two-sided geometric distribution with age-varying parameters. For comparison, the error distribution was estimated with naive methods that do not use the known ages and that assume the readings are unbiased. These estimated distributions do not match the actual error distributions very well, but they do a surprisingly good job of predicting the distribution of age readings from a stock assessment model's internal estimate of a true age composition. They also produce estimates of recruitment and biomass close to those obtained with the actual error distributions when used in the present sablefish stock assessment. © 2012.

The fishery for halibut (Hippoglossus stenolepis) in the eastern Pacific is closed during the boreal winter, roughly corresponding to the seasonal spawning of the species. Opening and closing dates for each season are stipulated annually based on economics and biology. Historical surveys and data from electronic tags are analysed to assess the extent to which recent closures have encompassed the annual spawning cycle of the species, as defined by migration to offshore spawning sites, active spawning, and return to feeding areas. These were assessed by calculating mean maximum daily depth profiles for fish exhibiting seasonal migration, calculating the date-specific proportions of the tagged population either migrating to or resident on their feeding or spawning grounds, and examining the temporal distribution of spent and running fish in historical surveys along with evidence of spawning contained in high-resolution tag data. The data indicate that fishery closures over the past 20 years have been consistently too short to protect the entirety of a migration period that begins as early as September and is not substantially completed until May. Additionally, some recent season openings have encroached on the active spawning season. Failure to fully protect spawning migrations may allow seasonal interception fisheries, and the selective removal of early and late spawners could cause changes in stock demographics, restrict effective spawning, and influence long-term stock productivity, especially in the face of environmental variability. © 2011 International Council for the Exploration of the Sea.

Loher T.,International Pacific Halibut Commission | Hobden J.C.,University of Victoria
Fishery Bulletin | Year: 2012

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%. Male-and 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 variable.

Seitz A.C.,University of Alaska Fairbanks | Loher T.,International Pacific Halibut Commission | Norcross B.L.,University of Alaska Fairbanks | Nielsen J.L.,U.S. Geological Survey
Aquatic Biology | Year: 2011

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 independent 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 components may respond to fishing pressure and changing environmental conditions.© Inter-Research 2011.

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