Recruitment Limitation in Alaskan Red King Crab....
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GRANT NUMBER:  NA76FD0036           NMFS NUMBER: 96-AKR-025

REPORT TITLE:  Recruitment Limitation in Alaskan Red King Crab (Paralithodes camtschaticus): The Importance of Early Life History Stages

AUTHOR:  Timothy Loher and David A. Armstrong

PUBLISH DATE:  February 10, 2000

AVAILABLE FROM:  National Marine Fisheries Service, Alaska Region, P.O. Box 21668, Juneau, AK 99802-1668.  TELEPHONE:  (907) 586-7273


The primary objective of this project was to examine how the unique habitat requirements of early post-settlement states (or the "early benthic phase [EBP]) of Alaskan red king crab (RKC) (Paralithodes camtschaticus) are responsible for structuring commercial crab stocks by examining the linkages between larval supply, larval settlement, and early post-settlement survivorship that govern the distribution, abundance, and recruitment patterns of juvenile crab. In order to quantitatively establish the early habitat needs of the species, the investigators conducted in situ abundance sampling of EBP crab, settlement experiments, and simultaneous assessments of larval supply in the shallow coastal waters of Auke Bay in southeast Alaska. These studies established that EPB RKC rely heavily, if not exclusively, upon complex shallow-water habitat for settlement and early recruitment. Settlement and post-settlement survivorship were high within rocky nursery habitat and lower in shell-hash. No settlement or survivorship could be detected in homogenous muddy-silt habitat despite high levels of larval supply. These habitat requirements suggest that recruitment to fishable stocks is likely to be governed by the spatial structure of the stock in relation to suitable EBP nursery habitat. In particular, the delivery of larvae to suitable settlement sites will be critical to ensure future recruitment, and this process can only be ensured if larvae are spawned and hatched in areas that are oceanographically "upstream" of nursery habitats. In order to assess the likelihood of these events within the Bristol Bay population, the investigators have begun an oceanographic modeling effort that will predict larval delivery patterns given present knowledge of regional oceanography and spatial stock structure. This model will enhance our ability to predict the impact of environmental factors on large-scale recruitment trends and help us to identify spatially explicit management options for the stock. The investigators also analyzed historic shifts in centers of adult breeding distribution to study how subsequent larval dispersion may affect survival relative to final settlement in nursery habitat. To fully realize their goals of developing spatially explicit stock management models, the investigators recommended that future research should include assessments of local habitat structure and distribution, as well as field research examining larval distribution and behavior in relation to important oceanographic features and conditions.

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