Auke Bay Laboratory (ABL)

Groundfish Assessment Program

Manned Submersible Studies in the Gulf of Alaska

Figure 4.  School of rougheye rockfish (Sebastes aleutianus) in boulder/cobble habitat. Photo from Albatross Bank survey.

ABL researchers completed two surveys in the Gulf of Alaska during summer 2005 using the two-person submersible Delta, which was launched from the support vessel Velero IV. The first survey was located on Albatross Bank southeast of Kodiak Island during 22 June to 2 July, and the second survey was in the Cape Ommaney and Hazy Islands vicinity off southeastern Alaska from 20 July to 1 August.

The purpose of the Albatross Bank survey was to perform a rockfish catchability experiment and to sample geologically-based habitats on previously mapped areas in this vicinity. The primary objectives were to 1) sample a glacial outwash habitat type to estimate survey gear catchability, and 2) groundtruth multibeam-derived habitat types on three sites along Albatross Bank. Survey participants were Kalei Shotwell (chief scientist from ABL), Dana Hanselman (research biologist from ABL), and Sean Rooney (graduate student from the University of Alaska Fairbanks).

A total of 24 dives were completed during the cruise, most of which were in the “Snakehead” area of the bank. Eight of these dives were on outwash habitat to estimate catchability, and 11 were on other habitat types for groundtruthing. Dives were also completed on two of the bank’s pinnacles: two dives on “49 Fathom” pinnacle and one on “8 Fathom” pinnacle. Finally, two dives were inshore dives during poor weather near Two-headed Island near the southwest end of Kodiak Island. Transect lengths were usually about 1,800 m. For each dive, researchers recorded audio and video from two camera angles and collected conductivity-temperature-depth (CTD) data (usually from start to finish). Twenty-nine additional CTD casts were completed as time allowed.

For the catchability experiment, researchers coordinated with the chartered vessel Sea Storm, which was conducting a biennial trawl survey for the AFSC Resource Assessent and Conservation Engineering (RACE) Division. Scientists aboard the Sea Storm conducted four trawl hauls in areas that were surveyed with the Delta.

Video was recorded of juvenile rockfish on several habitats, particularly moraines, bedrock-like exposures, and bedrock ridges. Gravid sharpchin (Sebastes zacentrus) and yelloweye rockfish (S. ruberrimus) were observed as well as rougheye rockfish (S. aleutianus) schooling behavior and multiple color morphs (Fig. 4 above). Several large schools of rockfish were noted by the submersible observer (e.g., dusky rockfish, S. variabilis) and a particularly active and large Pacific ocean perch (S. alutus) school was recorded on video in sandy mud habitat with occasional sea whips.

The purpose of the Cape Ommaney and Hazy Islands survey was to sample geologically-based habitats that had been previously mapped in this area by multibeam technology. The primary objectives were to characterize benthic habitat for juvenile rockfish and to groundtruth the multibeam-derived habitat types. In addition, a few dives were conducted to gain further information on trawl survey catchability. Survey participants were Jon Heifetz (chief scientist from ABL) and Kalei Shotwell (research biologist from ABL).

A total of 33 dives were completed during the survey. Twelve of these were on the Hazy Islands mapped site, one of which was for estimating catchability ability. Nine dives were completed on the Cape Ommaney mapped site, and two of these were for estimating catchability. The remaining 12 dives were conducted during a period when sea conditions were unfavorable for sampling the mapped areas, which were all located in offshore waters. These remaining dives were completed inshore in the vicinity of the mapped sites off the southern end of Baranof Island and outside of Craig, on Prince of Wales Island. Two of the inshore dives were completed off Coronation Island, four in the Gulf of Esquibel, four in Whale Bay, and two in Big Branch/Little Branch Bay.

Researchers coordinated with the Sea Storm for the catchability dives. Scientists from the Sea Storm completed two hauls off Cape Ommaney near the dives sites (where they caught a large number of Pacific ocean perch) and attempted one unsuccessful haul off the Hazy Islands.

Juvenile rockfish were recorded on several habitats, particularly granite rock exposures and highly-fractured glaciated rock. Researchers observed large schools of juveniles in high relief habitats (e.g., boulder, rock outcrops) and fewer solitary individuals hiding in sponges and under rocks in the low relief habitats (e.g., flat pavement, hummocky sediments). Many gravid females occurred on rocky habitats; these fish included sharpchin, redstripe (S. proriger), redbanded (S. babcocki), greenstriped (S. elongatus), and pygmy (S. wilsoni) rockfish. Inshore habitats had a large diversity of rockfish, and many juveniles were seen mixed with adults.

By Kalei Shotwell


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AFSC Quarterly
Research Reports July-Sept 2005