Historical changes in the abundance and distribution of ovigerous red king crabs (Paralithodes camtschaticus) in Bristol Bay (Alaska), and potential relationship with bottom temperature
Distribution and abundance of ovigerous female red king crabs (Paralithodes camtschaticus) in the southeast Bering Sea from 1975 to 2001 were investigated using data collected during National Marine Fisheries Service annual trawl surveys. Peak abundance of ∼140 million crabs was observed in 1978, and declined rapidly to a low of just over 6 million in 1986. Abundance fluctuated from ∼6 to 22 million from the late 1980s through 2001, with a single strong recruitment event that resulted in ∼35 million ovigerous females observed in 1998. Changes in abundance were accompanied by changes in distribution. During the late 1970s the population was typified by high abundance to the southwest, along the northern shore of Unimak Island and the Alaska Peninsula. By the mid-1980s the population's average center of abundance shifted substantially to the northeast and was found in central Bristol Bay. The distribution remained similar throughout the 1990s. Changes in distribution during the late 1970s and early 1980s coincided with changes in early summer near-bottom temperature. The 1970s were typified by a pool of very cold water (<1°C) within central Bristol Bay. This retreated in ∼1978, and was not observed in consecutive summers during the remainder of the time series. The northeastward shift in the population, measured as the distance between Unimak Pass and the average center of abundance, showed a negative correlation with the geographic extent the cold-pool. Abundance calculated for smaller spatial strata indicate that changes in distribution were not simply the result of relative abundance phenomena or solely generated by mortality in southwestern Bristol Bay, but also reflected regional increases in absolute abundance. Total broodstock abundance declined after 1978, but abundance in the western and northern areas of the region increased until at least 1982. The fact that distribution patterns change over time may have implications for population dynamics and fishery management. Changes in spatial population structure may affect recruitment patterns via changes in larval dynamics, and management might benefit if the causes of geographic displacement can be identified and predicted.