Rougheye and Blackspotted Rockfish Species Identification Experiment
The rougheye rockfish was recently split into two species, rougheye rockfish (Sebastes aleutianus) and blackspotted rockfish (S. melanostictus). The presence of a second species was established through genetic analysis and formally verified in 2008. However, a series of field identification experiments since 2005 have led scientists to be concerned about their ability to accurately distinguish between the two species during surveys. The high at-sea misidentification rates from these experiments prompted a special project on the 2009 AFSC GOA bottom trawl survey. The goal of the project was to collect relevant biological and genetic data to improve at-sea identification and examine differences in life history characteristics between the two species. Field scientists collected length, weight, and muscle tissue from most rougheye and blackspotted rockfish being sampled for ages.
Genetic samples and age structures (otoliths) were collected from a total of 934 rougheye and blackspotted rockfish during the 2009 GOA bottom trawl survey. Of these, 495 were identified in the field as rougheye, 420 as blackspotted, and 19 as unidentified rougheye/blackspotted. During the summer of 2010, otolith samples from this project were aged by members of the AFSC Age and Growth Program, and the genetic samples were analyzed by scientists at the ABL’s genetics lab. Analysis of these samples indicated that 66% of blackspotted rockfish were correctly identified, and 91% of rougheye rockfish were correctly identified. Combining this genetic information with the age data will allow for estimation of
biological parameters such as growth and distribution by species. In the future, we plan to extend this sampling to commercial fisheries as a special project requested of the Observer Program. When combined with accurate species-specific catch and survey data, such information will help determine whether one species is a weaker stock and may be at greater risk of overfishing.
By S.Kalei Shotwell, Jay Orr, Jon Heifetz,
Mark Wilkins, Tony Gharrett, and Sharon Wildes
Recompression Experiments on Rougheye Rockfish with Barotrauma
Because rockfish (Sebastes spp.) are physoclystic (i.e. their gas bladders are closed off from the gut), they often suffer internal injuries from rapid decompression when caught. If these fish are brought to surface by fishermen and then discarded, many do not survive either because they cannot submerge due to excessive buoyancy or because of internal damage caused by rapid gas expansion during ascent. There is some evidence that recompression may greatly increase the survival of barotrauma-injured rockfish. However, survival can be species-specific, and it is therefore important to gauge the impacts of rapid decompression on each species of interest.
Research completed at ABL in 2010 demonstrated that rougheye rockfish, (Sebastes aleutianus) caught at depths greater than 700 feet and exhibiting severe barotrauma could survive if recompressed immediately after capture with portable pressurized tanks. These 12”x42” tubular tanks were constructed in-house and adapted from a design described by Jeff Smiley at Hubbs SeaWorld. They are small and light enough to be transported by hand when empty and with a crane or on a hand-truck when full of water. This result is noteworthy because it is the deepest known successful capture and recompression of any rockfish species, and it opens the door for future scientific tagging studies to track movements and behavior of deepwater rockfish. Objectives are to tag captured rougheye and shortraker rockfish and rapidly recompress them by dropping them back to depth. Fish will also be recompressed with portable pressure tanks for estimates of survival of tagged fish.
By Cara Rodgveller, Chris Lunsford,
and Pat Malecha
