Early life biology and ecology of king and tanner crabs in the Bering and Chukchi seas

Abstract

Pelagic larvae and early benthic juveniles are believed to be the most vulnerable life stages for crabs. Where and when young crab occur and their response to environmental conditions is poorly understood. I present two case studies that demonstrate the importance of monitoring crab early life stages of economically and ecologically important species in the Bering and Chukchi Seas. First, collapsed fisheries and poor juvenile recruitment are recurring issues for many Alaska king crab stocks. Among the most notable examples, Pribilof Islands blue king crab is a federally overfished stock that has failed to rebuild after decades of conservation. Comparison of field assessments from modern and historical periods suggests a current bottleneck in larval supply, severely limiting blue king crab recruitment. Supplementary assessments showed available nursery habitats and fish predation pressure do not appear to be limiting for juvenile king crabs. Blue king crab are unlikely to recover by natural means, therefore juvenile enhancement may be an appropriate tool for possible restoration. Second, larval crab dispersal during the pelagic life phase is relatively unknown across the Pacific Arctic. A multiyear study of larval crab abundance and distribution during late summer months, and their association with environmental covariates, was completed for the north Bering and Chukchi Seas. Larval community structure varied strongly across regions from south to north and many species and stages had specific associations with coastal or offshore water masses. Snow crab larvae were relatively abundant and ubiquitous across the study region and appear to originate from both Pacific and Arctic spawning stocks. Blue king crab larvae were relatively rare in the Chukchi Sea and likely dispersed away from north Bering Sea natal areas. Larvae likely experience increased growth rates and northward dispersal in warm years, which could impact delivery to and survival of settling crabs in nursery habitats. Across analyses, these results improve our understanding of early life dispersal, settlement processes, and possible recruitment bottlenecks for Arctic crab stocks.