Fishes with closed swim bladders regulate buoyancy during depth changes by secreting and resorbing swim bladder gases. Forced ascent during fishery capture results in barotrauma caused by rapid expansion and exsolution of gases from body fluids. Pressure changes in hyperbaric chambers were used to examine changes in swim bladder integrity and acclimation rates in two ecologically different, yet congeneric, species: black rockfish Sebastes melanops and China rockfish S. nebulosus. We also conducted simulatedcapture experiments to investigate the relationship between capture in a fishery, barotrauma from pressure change, and survival after release. Black rockfish acclimated faster than China rockfish to both increases and decreases in pressure, but both species were much slower to acclimate than other physoclists, such as Atlantic cod Gadus morhua. Black rockfish required up to 48 h to acclimate from 4 atmospheres absolute (ATA; depth equivalent of 30 m) to surface pressure and required up to 168 h to become neutrally buoyant at 4 ATA after starting from surface pressure. In contrast, China rockfish required over 250 h to become neutrally buoyant at 4 ATA after starting from surface pressure. All black rockfish exposed to a 3-ATA decrease in pressure during simulated capture had ruptured swim bladders. However, mortality from simulated capture and subsequent recompression was low; only 3.3 6 1.7% (mean 6SE) mortality was observed after 21 d. In experiments with black rockfish, rapid recompression reversed visible barotrauma, suggesting that a quick return to depth could be used to minimize mortality of discarded black rockfish in nearshore fisheries.

We evaluated the effect of capture depth and fish size on the ability of several Pacific rockfishes Sebastes spp. to resubmerge after hook‐and‐line capture and surface release. We observed fish as they were released into a bottomless floating enclosure, and we recorded submergence success within a 5‐min time limit. Submergence success was greater than 80% for all rockfish captured in depths less than 30 m. Yellowtail rockfish S. flavidus (N = 51) were 100% successful at submerging in less than 49 s at all depths sampled (10–51 m). At capture depths of 40–51 m, submergence success was 89% for quillback rockfish S. maliger (N = 9), 65% for black rockfish S. melanops (N = 46), and 30% for canary rockfish S. pinniger (N = 40). At depths of 30–51 m, submergence success was 32% for blue rockfish S. mystinus (N = 31). The external signs of barotrauma (e.g., exopthalmia, eversion of the esophagus) increased with depth of capture and were least prevalent in yellowtail rockfish and quillback rockfish. The presence of severe esophageal eversion (beyond the buccal cavity) was strongly negatively associated with submergence success for several species (P < 0.01). At 40–51‐m capture depths, the frequency of severe esophageal eversion by species was correlated with the frequency of submergence failure (P < 0.05). Logistic regression showed a negative relationship between depth of capture and submergence success for black rockfish (P < 0.001), blue rockfish (P < 0.001), and canary rockfish (P < 0.05). Larger body length negatively influenced submergence success only in blue rockfish (P < 0.05).

We evaluated the effect of barotrauma on the behavior of nine species of Pacific rockfish Sebastes spp. after hook‐and‐line capture and release using a video‐equipped underwater release cage. Sampling was conducted across a range of bottom depths (12–194 m), mostly where barotrauma resulting from an expanded swim bladder and gaseous release of dissolved blood gases would be expected. Behavioral impairment from barotrauma was depth related but highly species specific. Increased depth of capture was associated with lower behavioral scores for black rockfish S. melanops, blue rockfish S. mystinus, and yelloweye rockfish S. ruberrimus, but not for canary rockfish S. pinniger. Behaviorally impaired fish showed a decreased ability to maintain vertical orientation and were slower in exiting the release cage. Species differed in the degree of behavioral impairment resulting from barotrauma and in how rapidly behavioral impairment increased with depth of capture. When captured at depths between 40 and 99 m, blue rockfish showed the most serious behavioral impairment, 8 of 18 (44%) failing to swim away at the time of release and simply drifting off in a sideways or upside‐down posture. In the same depth range all of the other species sampled showed only moderate behavioral impairment, which is indicative of some potential for survival after discard by the fishery. Surface observations of the external signs of barotrauma were variable among species and were poor indicators of which species would show behavioral impairment upon release at depth. Within individual species, however, the external signs of barotrauma were associated with an increased probability of behavioral impairment at time of release.

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Four species of Sebastes (Pacific rockfish) showed evidence of a wide array of internal injuries from capture-induced barotrauma, including liver and swimbladder damage, organ displacement related to esophageal eversion, and hemorrhage in the pericardium and abdominal cavity. However, clear evidence of swimbladder rupture was not observed in all fish with external signs of barotrauma. Injection of air through the body wall into the swimbladders of rockfish carcasses generated all of the common external signs of barotrauma documented in wild-captured fish, suggesting that the physical effects of swimbladder gas expansion can create these gross external signs without embolism from dissolved blood gases. Dissections of injected black rockfish S. melanops carcasses showed that, typically, injected air escaped the swimbladder without obvious rupture, moving in an anterio-dorsal direction, generating bulges and air bubbles that were externally visible through the branchiostegal membrane. Injected air also collected dorsally to the esophagus, posterior to the pharyngeal teeth, causing the esophagus to roll outwards into the buccal cavity (esophageal eversion). Injected air also frequently traveled further forward, collecting medially to the eyeball, leading to exophthalmia, and then moved distally along the fascia, invading the corneal stroma from the edges, resulting in corneal emphysemas. Air injected into the swimbladders of quillback rockfish S. maliger carcasses generated similar eye effects, but also escaped through ruptures in the branchiostegal membrane and did not generate esophageal eversion, which is also infrequent in wild-caught specimens. These results demonstrate that the major external signs of barotrauma in Pacific rockfish can develop as result of escaping swimbladder gases following an internal 'path of least resistance'.