The population structure of roundnose grenadier (Coryphaenoides rupestris) in southwestern Norway

Abstract

Ocean circulation, bathymetric barriers, and ecological processes can hinder the dispersal of marine fishes and thus generate sub-populations. The present study investigated the population structure of a benthopelagic fish, Coryphaenoides rupestris, from three Norwegian fjords and two coastal sites using eight microsatellite DNA markers. Genetic analyses revealed significant population genetic structure across the study area (FST = 0.0297, P < 0.001) and temporal stability in the Skagerrak. There was evidence of highly isolated sub-populations, as shown by significant pairwise differences in tests of genic differentiation and analysis of molecular variance (AMOVA), high inbreeding coefficients (FIS), high homozygosity, and low genetic diversity. Small-scale, within-fjord population structuring was also found in Lustrafjord. Mantel tests revealed a strong effect of isolation by distance and isolation by depth (bottom depth) and a possible effect of bottom temperature. Significant differences in fish condition were found between sites and included length-weight relationships (Analysis of Covariance (ANCOVA): F = 8.249, df = 7, P < 0.001), Hepatosomatic Index (HSI; GLM: F = 252.48, df = 3, P < 0.001) and Gonadosomatic Index (GSI; GLM: F = 15.91, df = 3, P < 0.001). In conclusion, population structuring in C. rupestris along the Norwegian coast seems to be influenced by distance, bathymetric barriers like bottom depth and fjord sills, and differences in fish condition indicate possible differences in environmental conditions between sites. Coryphaenoides rupestris is an overfished species that has been redlisted as critically endangered. Based on the present findings, stock management should consider each of the sub-populations independently, and not depend on recovery through recruitment from neighbouring sub-populations.