. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 528 Fisheries oceanography. Figure 33-1. The worldwide distribution of walleye pollock, Theragra chalcogramma (shaded area). In the eastern Bering Sea, T. chalcogramma is by far the most abundant of the four common gadid species. These other species include Gadus macro- cephalus (Pacific cod), Boreogadus saida (Arctic cod), and Eleginus gracilis (saffron cod). Genetic structure Although pollock are distributed (and perhaps spawn essentially continuously) along th
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering 528 Fisheries oceanography. Figure 33-1. The worldwide distribution of walleye pollock, Theragra chalcogramma (shaded area). In the eastern Bering Sea, T. chalcogramma is by far the most abundant of the four common gadid species. These other species include Gadus macro- cephalus (Pacific cod), Boreogadus saida (Arctic cod), and Eleginus gracilis (saffron cod). Genetic structure Although pollock are distributed (and perhaps spawn essentially continuously) along the northern rim of the Pacific Ocean and Bering Sea, genetic differentiation might reasonably be expected due to the isolating effects of both geographical distance and barriers (Kimura and Ohta 1971). This is because individual migrations will nearly always be consider- ably less than the total distributional range of the species, and instead, effectively form regional breed- ing populations. Similarly, diffusive exchange of eggs and larvae due to advective transport may be expect- ed to be higher within regional current systems than between, although progressive transport of successive generations may be significant. Consistent with these hypotheses, recent studies of biochemical genetic variation have found relatively large genetic differences between pollock sampled from extremes of the species range, but relatively small genetic differentiation within regions (Iwata 1973, 1975, 1977; Johnson 1977). Based upon differences in allelic frequencies for the protein locus tetrazolium oxidase. Grant et al. (1978) con- cluded that the widely separated populations of the western and eastern Pacific are relatively genetically isolated and distinct. Only weak regional differentia- tion was observed, however, among pollock collected from north and south areas of the eastern Bering Sea and from the Gulf of Alaska. Other investigators have proposed a more complex population structure in t
Size: 2126px × 1175px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1900, bookcollectionamericana, bookleafnumber552
