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NOAA Technical Memorandum NMFS-AFSC-359

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Long-term survival and observable healing of two deepwater rockfishes, Sebastes, after barotrauma and subsequent recompression in pressure tanks

Abstract

We evaluated the long-term survival and observable healing over 6–18 months for two species of deepwater rockfishes that experienced barotrauma followed by repressurization in portable pressure tanks and slow depressurization to surface pressure. Blackspotted Sebastes melanostictus and rougheye rockfish Sebastes aleutianus were captured at depths from 123 m to 279 m. Barotrauma was assessed immediately after capture and fish were recompressed to 70 psi in pressure tanks on-board the fishing vessel, gradually acclimated to atmospheric pressure at sea-level over a 2- or 4-day period, then held in the laboratory. Others were released from a weighted cage held at ~75 m and observed with a video camera. Survival in the laboratory was highest when fish were given 4 days (78% in 2013) to acclimate to the pressure change, as opposed to 2 days (54–60% in 2011 and 2012, respectively).

A longer fish length increased the probability of mortality; however, neither the presence of external or internal barotrauma nor the depth of capture were associated with the probability of survival. Videos taken of fish that were released after capture from the weighted cage showed that fish were not positively buoyant, were oriented upright, and 67% were able to swam away. A previously released fish was recaptured in a bottom-longline fishery 6 months later, 58 km from the release site, demonstrating that fish are capable of surviving in the wild post-barotrauma. This study illustrates the utility of pressure tanks for 1) slowly acclimating fish to surface pressure for transport to a holding facility and 2) as an alternative to underwater cages for short-term observations. Our results indicate that short-term observations of recompressed fish may be adequate for studies of survival. However, long-term observations are required to observe the healing of some injuries.

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