Barotrauma, RAMP, and discard survival

Yelloweye rockfish with barotrauma, OSU

Capture of fishes with physoclist gas (swim) bladders can result in impairment by barotrauma. Symptoms of barotrauma offer additional measures of impairment that can be used as predictors for survival and mortality when combined with reflex impairment to calculate RAMP (Diamond and Campbell 2009, Campbell et al. 2010). 

Calculation of RAMP modified for barotrauma is as follows. A reflex action is scored not impaired (0) when strong or easily observed, and scored impaired (1) when not present, weak, or there is a question about being present. A barotrauma symptom is scored absent (0) when not present or there is a question about presence, and present (1) when easily observed. Barotrauma and reflex impairment scores for an individual animal are then summed and divided by the total observable impairments possible to calculate proportion impairment (RAMP score). 

  

Snapper (Lutjanus sp.) and rockfish (Sebastes sp.) often show many of the barotrauma symptoms listed above in the table. Pressure from an expanded gas bladder results in many forms of swelling, distention, and eversion. Severely impaired discarded fish have difficulty leaving the water surface and returning to depth.  These fish have low survival, which can be improved with recompression devices designed to lower fish to capture depths, where healing and recovery can occur.

NOAA

Behavioral observations of rockfish with barotrauma have shown that fish trapped on the surface have a higher incidence of reflex impairment when caged at depth for recompression. Survival during healing and recovery will be dependent on return to normal behavior, e.g. avoidance of predators, return to feeding, and appropriate habitat choice.

Blue rockfish impairment after barotrauma, Hannah et al. 2008

In a tagging study, rockfish recompressed in a cage and released were shown to recover from barotrauma and resume normal behavior in the sea (Hannah and Rankin 2011).

Copper rockfish movement recovery after barotrauma, Hannah and Rankin 2011

Gadid species such as Pacific cod and Atlantic cod do not show overt symptoms of barotrauma when captured at depth. Instead their gas bladder ruptures and relieves the potential pressure of an expanded gas bladder (Nichol and Chilton 2006, Midling et al. 2012). Discards of these species can more easily descend to depth after release, with healing and recovery occurring within short periods of time.

Pacific cod movement recovery after barotrauma, Nichol and Chilton 2006

Pearl perch is another example of a physoclist species that does not exhibit overt symptoms of barotrauma during capture (Campbell et al. 2014). As angled fish approach the surface, gas is released through rupture.  For this species, hook location and type were found to be important predictors of discard survival.

Pearl perch, Dave Harasti