Selecting species specific vitality metrics to predict red king crab (Paralithodes camtschaticus) discard survival

Abstract

Abstract Quantifiable behavior and reflex responses, termed “vitality assessment metrics”, have successfully linked impact from the commercial fishery capture and handling process with post-discard survival. These metrics have been effectively applied to commercially important crab species, including Tanner (Chionoecetes bairdi) and snow crab (C. opilio) bycaught in the Eastern Bering Sea groundfish bottom trawl fishery. When applied to red king crab (RKC; Paralithodes camtschaticus) in the same fishery, those metrics had limited success. We examined a suite of candidate RKC-specific metrics based on prior studies as well as several recommended by commercial fishermen. Provisional testing in a laboratory setting was used to narrow the list of metrics for field testing to include only those to which RKC showed consistent and definitive responses. Ultimately, seven vitality metrics were advanced for at-sea testing on RKC caught during commercial groundfish bottom trawl fishing. A total of 55 RKC were collected, 37 on deck as the codend was emptied and 18 from the below-deck factory at the regulatory point of discard. An initial assessment testing for the presence of the seven metrics was conducted immediately upon collection, generating a vitality score based on the number of absences. Crabs were tagged for individual tracking and held for 72\u202f-hs in seawater tanks for re-assessment at 2, 4, 6, 12, 24, 48 and 72\u202f-hs. Crab collected from the factory had higher initial impairment scores based on the vitality metrics than crab collected from the deck. In total, 6 crab, with higher impairment scores, died and the remaining 49, with lower impairment scores, showed evidence of strong to moderate recovery and were discarded alive after 72\u202f-hs. Results from this study indicate that our species-specific vitality metrics successfully captured impairment, initial recovery and short-term mortality. This work elucidated the relationship between RKC impairment and delayed discard mortality, providing a mechanism to generate quantitative post-discard mortality rates in future studies.