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Groundfish Assessment Program

Habitat-Specific Production of Pacific Ocean Perch in the Aleutian Islands

Figure 2, click to enlarge
Figure 2.  Click image to enlarge.

Figure 3, click to enlarge
Figure 3.  Click image to enlarge.

Figure 4, click to enlarge
Figure 4.  Click image to enlarge.

Figure 5, click to enlarge
Figure 5.  Click image to enlarge.

Research is currently under way to examine the habitat-specific production of rockfish in Alaska. In early June 2008, scientists from the RACE Division completed the first part of a project that examines habitat-specific production of juvenile Pacific ocean perch (POP) (Sebastes alutus) at a nursery location in the Islands of Four Mountains area in the Aleutian Islands (Fig. 2).

Two sites (Semalga Island north and south) were sampled over 2 days using an AFSC bottom trawl and plankton net to collect both juvenile POP and their zooplankton prey. Juvenile POP were found at both locations in high abundances, with more than 650 individuals captured during four tows of less than 5 minutes each. This is the fourth year since 2003 that juvenile POP sampling has occurred at these sites, and rockfish density was higher in 2008 at the nursery sites than in June of preceding years (Fig. 3). Both of these sites will also be sampled in August 2008.

In conjunction with this and another project (to be carried out in July 2008 examining rockfish populations in the Zhemchug Canyon area) an underwater drop camera was developed and tested. The drop camera utilizes two video sources, enabling stereo vision of objects and fish along the seafloor. The stereo video allows researchers to measure fish lengths using pairs of still frames captured from the video. The camera system was developed and built by RACE Division scientists in April and May 2008, calibrated in the NOAA facility dive tank in Seattle in May 2008, and shipped to Alaska in time to be deployed at the juvenile POP nursery sites in June. It is intended that this stereo camera system will be used for assessing groundfish populations in areas too rough or rugged for the established bottom trawl survey to be carried out.

Six successful deployments (three at each study site) of the drop camera system were conducted over the 2 days. The video captured during the Islands of Four Mountains study shows many juvenile POP and other rockfish inhabiting boulder fields at the study site. There were significant amounts of coral and sponge observed in the study areas (Fig. 4). Additionally, adult dusky rockfish (S. variabilis) and northern rockfish (S. polyspinis) schools were observed at one site (Fig. 5). Analysis of the 6 hours of video collected at the study sites is expected to be completed sometime this fall.

By Chris Rooper

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