Abstract:
Tanner crab (Chionoecetes bairdi) is a large-bodied species of crab harvested in commercial, personal use, and subsistence fisheries across Alaska. The commercial fisheries were highly productive until the 1980s, when most stocks faced major declines and were closed to harvest. The recovery success of stocks throughout the state has been variable throughout the subsequent decades, leading managers to question whether there are aspects of the population dynamics that are not accounted for. There is limited information on the genetic population structure of C. bairdi in Alaskan waters, which has caused uncertainty about whether established management areas align well with distribution and migration patterns for this species. I applied novel high throughput sequencing methods to measure genetic diversity and investigate the genetic population structure of C. bairdi in Alaskan waters. Genomic DNA was isolated from samples collected from Southeast Alaska, Prince William Sound, and the Eastern Bering Sea, both east and west of 166°W longitude, and processed according to a Double-Digest Restriction-Associated DNA Sequencing protocol. The final genotype assembly included 89 individuals that were genotyped at 2,740 independent, neutral single-nucleotide polymorphism (SNP) sites, and contained 3.06% missing data. The average observed heterozygosity across SNP sites within regions was significantly lower than the average heterozygosity expected for populations in Hardy-Weinberg equilibrium. An analysis of molecular variance indicated that genetic variability was mostly found within individuals (90%), 10% of variability was observed between individuals within sampling regions, and no significant amount of variation was detected between sampling regions. Furthermore, pairwise FST estimates between sampling regions were low, and thus the null model of panmixia could not be rejected. Principal components analysis was also congruent with a model of no differentiation among regions. Bayesian analysis implemented in the program STRUCTURE did not support any population partitioning above K = 1 clusters, again indicating that there is not substantial genetic differentiation among the regions sampled from across the state of Alaska. These results indicate high gene flow throughout the distribution of Tanner crab across the Alaska continental shelf. Recognized stocks are genetically indistinguishable from each other. This may indicate that stocks exchange a substantial number of migrants, and may not operate independently. This new information can provide insights as management plans are evaluated and refined.
