Available at: https://digitalcommons.calpoly.edu/theses/2007
Date of Award
MS in Biological Sciences
Physoclistic fish, such as Pacific rockfishes (genus Sebastes), have closed swim bladders that help them regulate their buoyancy. When anglers catch these fish and reel them to the surface, gases within their swim bladder expand due to the decrease in pressure. This can cause their swim bladder to over inflate––a condition known as barotrauma. Overly buoyant fish experiencing barotrauma often struggle to swim back to dwelling depth if released at the ocean’s surface. These fish may experience high rates of mortality by thermal shock caused by the warmer surface temperatures, starvation, predation, or vision problems caused by barotrauma. Assisted release methods that recompress fish by returning them to depth prior to release may thus greatly improve survival of fish suffering from barotrauma.
In this study, I characterized species-specific responses of four species of nearshore Pacific rockfishes (Canary Rockfish, Sebastes pinniger; Gopher Rockfish, S. carnatus; Deacon Rockfish, S. diaconus; and Blue Rockfish, S. mystinus) to rapid ascent by hook-and-line fishing from shallow depths (<40 m). I videotaped their immediate responses upon recompression using a weighted inverted milk crate to transport fish back to their initial capture depth. Fish were videotaped during their descent, as well as their release from the crate. In some individuals, barotrauma symptoms were reversed and did not show behavioral impairment upon release, indicating that even a simple, inexpensive device can be effective in relieving barotrauma symptoms. Species differences were also observed in the severity of barotrauma observed following the collection of fish from depth. Capture depth was positively correlated with the occurrence of barotrauma for Blue Rockfish and Gopher Rockfish, but not for Canary Rockfish or Deacon Rockfishes.
I utilized data over an eight-year period from the California Collaborative Fisheries Research Project (CCFRP) to assess survivorship of rockfish experiencing barotrauma. A total of 20 rockfish (1 Black Rockfish, S. melanops; 2 Blue Rockfish; 12 Gopher Rockfish; 3 Copper Rockfish, S. caurinus; and 2 Kelp Rockfish, S. atrovirens) initially displaying barotrauma signs upon capture were tagged using a T-bar tag and released. It is unknown if these fish were recompressed because the CCFRP did not record this information. These 20 rockfish were recaptured days to 3 years later––indicating rockfish can survive long term after experiencing barotrauma. To minimize mortality of discarded fish in the fishery, fish recompression is recommended.