Recruitment variability in southeast Bering Sea red king crab (Paralithodes camtschaticus, Tilesius 1815): the roles of early juvenile habitat requirements, spatial population structure, and physical forcing mechanisms

Abstract

Red king crab (Paralithodes camtschaticus) in Bristol Bay once supported the most lucrative fishery in the world, but catches over the last ~20 yrs have been substantially reduced compared to late 1970’s levels.  Since the stock collapse, the fishery has been closely managed and harvests maintained within strict guidelines, but these actions have had little effect on stock rebuilding.  Recruitment levels have remained at relatively constant and modest levels, suggesting that factors outside the fishery may be exert strong influence on population abundance.  I hypothesize that the population is regulated by survivorship of early post-settlement stages, and that presently low recruitment levels are in part the result of climate forcing that has altered larval source-sink dynamics.  Field studies of habitat requirements, conducted in southeast Alaska, indicate that the species is reliant upon complex habitat for settlement and establishment early post-settlement populations.  Such habitat appears to be relatively rare in Bristol Bay, located primarily nearshore along the Alaska Peninsula and in Kvichak and Togiak Bays.  During the early 1980’s a shift occurred in mature female (broodstock) distribution: once found near Unimak Pass, most broodstock is presently located to the northeast and concentrated in the center of Bristol Bay.  At the same time, distributions became more circular and dispersion within the distribution decreased.  These changes in distribution may have represented a response by females to their thermal environment.  During the early and mid-1970’s extensive winter sea-ice generated a “cold tongue” of sub-zero temperature near-bottom water, the signature of which could be seen into summer.  Very low water temperatures likely inhibit egg incubation, and may be avoided by reproductive females.  The northward shift in broodstock distribution was roughly coincident with the recession the cold tongue.  Altered broodstock distributions were also accompanied by changes in spatial recruitment patterns.  Recruitment to southern regions of the Bay, which predominated in the 1970’s, has been rare over the past 20 years, and the stock appears more reliant upon nurseries in Kvichak and Togiak Bays.  These observations are consistent with larval advection modeling that suggests present broodstock may be unable to supply southern nurseries with larvae.