RESOURCE ECOLOGY & FISHERIES MANAGEMENT (REFM) DIVISION (cont.)

STATUS OF STOCKS AND MULTISPECIES ASSESSMENT PROGRAM:

Atka Mackerel Tagging

The fishing vessel Pacific Explorer was chartered from 12-26 July 2003 for tag and release studies of Atka mackerel in the Amchitka Island area of the Aleutian Islands, Alaska. The cruise represents the fourth consecutive year of work by the AFSC on Atka mackerel in the Aleutian Islands and the first year of work in the Amchitka Island area. During the years 1999-2002, Atka mackerel were tagged and released in Seguam Pass; during the year 2002 Atka mackerel were also released in the Tanaga Pass area. The objective of these studies is to determine the efficacy of trawl exclusion zones as a management tool to maintain prey abundance and availability for Steller sea lions at local scales. Trawl exclusion zones were established around sea lion rookeries as a precautionary measure to protect critical sea lion habitat, including local populations of prey such as Atka mackerel. Localized fishing may affect Atka mackerel abundance and distribution near sea lion rookeries. The purpose of the Pacific Explorer cruise in July 2003 was to tag and release Atka mackerel inside and outside the trawl exclusion zones in the Amchitka Island area.

Fish tagged throughout the areas open and closed to the fishery from the years 1999 to 2003 are being recovered by the fishery in the areas outside the trawl exclusion zones. Recoveries of tagged fish in the closed areas are provided by chartered tag recovery cruises. NMFS will estimate movement and abundance of Atka mackerel in areas of Seguam Pass and Amchitka Island open and closed to the fishery.

A feasibility study was conducted in 1999 at Seguam Pass. In the years 2000-2002 approximately 37,000 tagged fish were released in the Seguam Pass area. In 2002 another 14,250 tagged fish were released in the Tanaga Pass area. In addition to T-bar tags, approximately 400 Atka mackerel were released with electronic archival tags (200 in Seguam Pass and 200 in Tanaga Pass). Those tags record depth and time continuously.

During the 2003 tag release cruise aboard the Pacific Explorer 14,596 fish were tagged and released in the Amchitka Island area; 8,906 fish were released inside the trawl exclusion zones, and 5,690 fish were released in the areas open to fishing. Ten tagged fish were randomly selected from every haul and placed in tanks to assess mortality rate following capture and were held for at least 48 hours. Nine experiments were conducted over the course of the cruise. Of the 126 fish participating in the experiments, only 1 died, for a mortality rate of 0.08%.

In addition to tagging and releasing Atka mackerel, AFSC scientists collected length frequency data and took biological samples that will provide information on age, growth, reproductive condition and diet. Otoliths, stomachs and gonads were collected from 5 males and 5 females from every successful haul for a total of 200 fish. Additional to the collection of gonads, maturity stages of fish collected for length frequency data were determined by visual inspection of the gonads. Approximately 1,500 fish were recorded as one of six stages of females or four stages of males.

AFSC scientists also collected physical oceanographic data with the goal of examining the water column characteristics of Atka mackerel habitat. Continuous temperature and salinity data were collected with a Seabird SBE45 plumbed to receive water from the same source as the tanks. Fluorescence was measured continuously with a Turner Designs SCUFA fluorometer, plumbed to receive water from the same source as the tanks. Temperature-depth data were also collected with a microbathythermograph (MBT) mounted on the net.

In previous years AFSC scientists have been exploring Atka mackerel spawning grounds with cameras or divers. For the first time during a tag and release cruise, actual underwater footage of Atka mackerel habitat and spawning males was recorded. A drop camera was deployed off a 16 foot Zodiak and from the vessel to examine Atka mackerel spawning grounds nearshore and in shallow reef areas around the island passes. The camera was deployed mostly in depths ranging from 5 to 50 fathoms in the vicinity of Amchitka, Seguam, Amlia, and Umnak Island and their corresponding passes. Spawning Atka mackerel were found in high current areas in depths from 15 to 50 fathoms. Video footage and corresponding GPS locations of fish were recorded.

Additionally, different types of specimens were collected for special projects at the request of other NOAA scientists. Fin clips from 200 Atka mackerel and from 50 Pacific cod were collected for genetic analysis. Full stomachs from nine Atka mackerel were collected for a study of the feasibility of extracting the DNA of the prey items within. Skate specimens (one male and one female) of a variety of species were collected for taxonomic study. Whole Atka mackerel, walleye pollock and Pacific cod (10 males and 10 females) were frozen for proximate analysis of lipid, protein, water and ash content. A number of Atka mackerel, rockfish and flatfish (10 to 20) were collected to be used as specimens for Observer Program training.

By Susanne McDermott and Libby Logerwell.

AFSC Quarterly
Research Reports
July-Sept 2003