The divergent effect of capture depth and associated barotrauma on post-recompression survival of canary (Sebastes pinniger) and yelloweye rockfish (S. ruberrimus)

Abstract

We evaluated the external signs of barotrauma and 48-h post-recompression survival for 54 canary and 81 yelloweye rockfish captured at depths of 46–174m, much deeper than a similar prior experiment, but within the depth range of recreational fishery catch and discard. Survival was measured using specialized sea cages for holding individual fish. The external physical signs associated with extreme expansion and retention of swimbladder gas (pronounced barotrauma), including esophageal eversion, exophthalmia and ocular emphysema, were common for both species at these capture depths and were more frequent than in prior studies conducted at shallower depths. Despite similar frequencies of most external barotrauma signs, 48-h post-recompression survival of the two species diverged markedly as capture depth increased. Survival of yelloweye rockfish was above 80% across all capture depths, while survival of canary rockfish was lower, declining sharply to just 25% at capture depths greater than 135m. Fish of both species that were alive after 48h of caging displayed very few of the external signs of pronounced barotrauma and had a high submergence success rate when released at the surface. Logistic regression analysis, using a combined data set from this and an earlier experiment conducted at shallower capture depths, was used to more broadly evaluate factors influencing post-recompression survival. For canary rockfish, depth of capture was negatively related to survival (P<0.0001), but the surface-bottom temperature differential was not (P>0.05). Exophthalmia and ocular emphysema were each negatively associated with survival for canary rockfish (P<0.05). For yelloweye rockfish, no significant associations were found between post-recompression survival and capture depth, the surface-bottom temperature differential or any of the signs of pronounced barotrauma (P>0.05).