Timothy Loher

Use of Veterinary Ultrasound to Identify Sex and Assess Female Maturity of Pacific Halibut in Nonspawning Condition

Abstract Ultrasound was used for sex identification and female maturity assessment of Pacific halibut Hippoglossus stenolepis ranging from 64- to 144-cm fork length collected during their nonspawning period (boreal summer) in the central and eastern Gulf of Alaska. Ultrasonic sex identification employed inspection of gross morphology and gonadal morphometrics, the latter involving determination of gonad length (maximum posterior gonad extent [MPGE]) and testing for difference between sexes. Morphometric analysis was refined further for females by removing ovaries, macroscopically determining maturity status, and comparing MPGE and proportional ovarian length (POL) among maturity stages. Ultrasonically determined gross morphology was sufficient to achieve accurate sex identification in even the smallest individuals examined. Ovaries were rounded anteriorly with no apparent internal structure, whereas testes were sickle-shaped with characteristic internal structure formed by the junctures between testicular...

Migration patterns and putative spawning habitats of Atlantic halibut (Hippoglossus hippoglossus) in the Gulf of St. Lawrence revealed by geolocation of pop-up satellite archival tags

Arnault Le Bris,* Jonathan A. D. Fisher, Hannah M. Murphy, Peter S. Galbraith, Martin Castonguay, Timothy Loher, and Dominique Robert Centre for Fisheries Ecosystems Research, Fisheries and Marine Institute, Memorial University of Newfoundland, P.O. Box 4920, St. John’s, NL A1C 5R3, Canada Institut Maurice-Lamontagne, Pêches et Océans Canada, CP 1000, Mont-Joli, QC G5H 3Z4, Canada International Pacific Halibut Commission, 2320 West Commodore Way, Suite 300, Seattle, WA 98199-1287, USA *Corresponding author: tel: þ1 709 778 0482; fax þ1 709 778 0669; e-mail: arnault.lebris@mi.mun.ca. Present address: Northwest Atlantic Fisheries Centre, Fisheries and Oceans Canada, 80 East White Hills Road, PO Box 5667, St. John’s, NL A1C 5X1, Canada. Present address: Canada Research Chair in Fisheries Ecology, Institut des Sciences de la mer, Université du Québec a Rimouski, 310 allée des Ursulines, P.O. Box 3300, Rimouski, QC G5L 3A1, Canada.

Subtle genetic population structure in Pacific halibut Hippoglossus stenolepis

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).

Characterization of Depth Distributions, Temperature Associations, and Seasonal Migrations of Atlantic Halibut in the Gulf of St. Lawrence using Pop-Up Satellite Archival Tags

AbstractThe fishery for Atlantic Halibut Hippoglossus hippoglossus in the Gulf of St. Lawrence (Gulf) is currently experiencing its highest landings since the 1950s. However, the absence of information on adult habitat use has limited the development of new survey methodologies. The aim of this study was to use pop-up satellite archival tags on large (≥108-cm) halibut in the Gulf to provide data on seasonal temperature associations, depth distributions, and migrations. Twenty Atlantic Halibut were tagged in 2013 and 15 were tagged in 2015 at two different locations in the northern Gulf. Atlantic Halibut overwintered in the central and northern Gulf based on six tag pop-offs. In the winter in both studies, halibut were distributed at 160–440 m depth with a narrow temperature association of 5.5–6.5°C, which corresponded with the bathymetry and hydrography of the Gulf rather than the deeper and colder waters of the continental shelf where the southern stock occurs. Spawning rises were identified from the dep...

Identification of genomic regions associated with sex in Pacific halibut

Understanding and identifying the genetic mechanisms responsible for sex-determination are important for species management, particularly in exploited fishes where sex biased harvest could have implications on population dynamics and long-term persistence. The Pacific halibut (Hippoglossus stenolepis) supports important fisheries in the North Pacific Ocean. The proportion of each sex in the annual harvest is currently estimated using growth curves, but genetic techniques may provide a more accurate method. We used restriction-site associated DNA (RAD) sequencing to identify RAD-tags that were linked to genetic sex, based on differentiation (FST) between the sexes. Identified RAD-tags were aligned to the Atlantic halibut (Hippoglossus hippoglossus) linkage map, the turbot (Scophthalmus maximus) genome, and the half-smooth tongue sole (Cynoglossus semilaevis) genome to identify genomic regions that may be involved in sex determination. In total, 56 RAD-tags (70 single nucleotide polymorphisms) were linked to sex, and 3 RAD-tags were identified in only females. Sex-linked loci aligned to 3 linkage groups in the Atlantic halibut (LG07: 7 loci, LG15: 1 locus, and LG24: 1 locus), 3 chromosomes in the turbot (LG12: 13 loci, LG01: 1 locus, and LG05: 1 locus), and 1 chromosome in the half-smooth tongue sole (ChrZ: 9 loci). Results add support to the hypothesis that Pacific halibut genetic sex is determined in a ZW system. Two sex-linked loci were further developed into sex identification assays, and their efficacy was tested on individuals that had been morphologically sexed. The accuracy of each assay on its own was 97.5% compared to morphological sex.