Stock Structure of Dungeness Crab (Metacarcinus magister) in British Columbia

Abstract

To meet the requirements of the Fish Stock Provisions under the Fisheries Act, the Dungeness Crab fishery in British Columbia (BC) requires a stock definition in order to determine the scale at which reference points should be estimated. A template used to delineate Alaskan groundfish and crab stocks was followed to evaluate Dungeness Crab biological stock structure in BC, which included literature reviews of genetic, movement, and oceanographic information, analyses of fisheries data, and a review and new analysis of phenotypic variation. Available genetics information, which was spatially and temporally limited, suggested genetic connectivity of Dungeness crab through BC, with some evidence of genetic structure in some fjords. Analysis of Dungeness Crab catch per unit effort trends in the commercial fishery did not show differences among Crab Management Areas nor between Pacific Fishery Management Areas. Existing oceanographic classifications were reviewed and were found to vary in BC, but shared a common split at the northern end of Vancouver Island where the California Current and the Alaska Current diverge. This break may result in limited larval exchange between northern and southern BC. However, there is a lack of information on larval dispersal to assess this split. Analyses of phenotypic traits showed some variability across BC, likely due to temperature differences. Growth is associated with latitude and softshell timing occurs later in the year in offshore and northern areas. Additionally, frequency of egg extrusion differs between California and Alaska. Most published work indicates limited movement of adult Dungeness crab, with some exceptions. There is potential for widespread larval movement, which is strongly influenced by multiple processes including biological, geographic, and oceanographic factors. Overall, there is evidence of spatial heterogeneity in Dungeness Crab, but there is insufficient information to delineate multiple stocks at this time. However, data are limited spatially and temporally, which leads to uncertainty about the lack of multiple stocks, most notably in fjords where uncertainty is particularly high. At this time, it is recommended that Dungeness Crab in BC be defined as one stock. Additional information on genetic differentiation and connectivity (e.g., from biophysical models, tagging studies) is critical for understanding stock structure over space and time. It is recommended that future work incorporate simulation testing to evaluate/examine the impact of uncertainty in stock structure. Fishery management can occur at finer scales than the scale at which a biological stock is defined. Broad biological stock definitions do not preclude finer scale management or assessment. It is recommended that the stock definition be revisited as new information becomes available.