Rockfish Barotrauma and Recompression

Rockfishes (Sebastes spp.) experience high discard mortality rates from a condition called barotrauma, which is caused by the change in pressure during capture. Excessive buoyancy from barotrauma makes it difficult for many rockfish species to submerge under their own power and these discarded rockfish are often left floating on the surface where they can succumb to their injuries or to predation. In recent years, field-based recompression devices have been shown as a way to greatly reduce bycatch of unwanted or protected species by assisting fish back to their depth of capture (California Sea Grant - Bring That Rockfish Down). Researchers from the Southwest Fisheries Science Center recently examined the effectiveness of the different commercially-available descending devices during use in recreational fishing on commercial passenger fishing vessels. This work found that all devices were largely effective at releasing rockfish back toward their depth of capture (Bellquist et al 2019).

In addition, researchers from NOAA's Southwest Fisheries Science Center have recently completed a multi-year study examining the long-term survival rates of rockfishes released using descending devices in Post-release survival and prolonged sub-lethal effects of capture and barotrauma on deep-dwelling rockfishes (genus Sebastes): Implications for fish management and conservation. From December 2011 through March 2015, researchers captured and tagged a total of 113 rockfish from four species on an offshore bank west of San Diego, California within the Cowcod Conservation Area. The goal of this study was to determine the long-term survival rates and post-release behavior of deep-dwelling rockfish species following capture and barotrauma. These fish were monitored post-release using electronic tags for up to one year to develop estimates of mortality and evaluate changes in behavior over time.

Researchers tagged four different species of rockfish (cowcod, S. levis; bocaccio, S. paucispinis; sunset rockfish, S. crocotulus;  and bank rockfish, S. rufus) captured from 75 to 180 meters depth. After assessing overall barotrauma injury, these fish were externally tagged with Vemco V9 or V13 accelerometer and pressure acoustic transmitters. The rockfish were released to depths between 32 to 92 meters using a weighted cage or a SeaQualizer descending device equipped with an underwater video camera. With this underwater camera, researchers were able to monitor rockfish as they were recompressed and noted the condition and behavior of the fish upon release. 

Acoustic receivers attached to temporary moorings were deployed in the vicinity of the fishing/tagging site in an array to continuously monitor the tagged fish. The receivers monitored movement patterns and activity of tagged fish (depth and acceleration) in order to assess post-release survival and potential long-term sublethal effects following capture and barotrauma.  In particular, this work focused on the survival rates of cowcod and bocaccio, two historically overfished species, that heavily influence groundfish management decisions. Researchers found that bocaccio survive capture and barotrauma approximately 90 percent of the time while cowcod survived about 50 percent of the time. Monitoring post-release behavior showed that surviving fish were affected by capture and barotrauma for about 30 to 60 days.

Purchase Recompression Devices

Anglers can use homemade recompression devices such as an inverted milk crate connected to a length of rope or purchase one of several commercially made products from the following websites:

• Ecoleeser
• Shelton Products
• The Seaqualizer

Contact

Please direct all questions to Nick Wegner or John Hyde.