Resource Assessment & Conservation Engineering (cont.)

Midwater Assessment: Bering Sea

Scientists from the Midwater Assessment and Conservation Engineering (MACE) Program conducted an echo integration-trawl (EIT) survey of the southeastern Bering Sea shelf and Bogoslof Island region from 18 February  to 10 March 2002.  The survey was designed to provide data on the abundance and biological composition of walleye pollock in the Steller sea lion Conservation Area (SCA) and the portion of the Central Bering Sea Convention “Specific Area” close to the Aleutian Islands, between Unalaska Island and the Islands of Four Mountains.

Survey operations were conducted 24 hours a  day.  The acoustic systems were calibrated at the start and end of the survey.  A total of 27 trawls hauls were made with a midwater trawl (Aleutian wing trawl) and 11 were made with a poly Nor-eastern bottom trawl.

Preliminary survey results show that pollock were most abundant inside the eastern portion of the SCA (Figure 5 above ), an area with high commercial catches.  Pollock modal lengths were about 49 cm near Amak Island and decreased gradually towards the west and north.  On the northern and western part of the SCA along the 200 m isobath, age-2 pollock with modal lengths 22-24 cm were abundant.  This year class had been observed as age-1 pollock during the 2001 winter survey.  In the Bogoslof area, pollock were concentrated in two main locations:  between Umnak and Unalaska Islands and in Samalga Pass adjacent to the Islands of Four Mountains.  The size distribution was generally bimodal, with 47 cm fish predominating in the Umnak area, and about 57-60 cm pollock predominating in the Samalga Pass area.  Presence of the 47 cm pollock size class in the Bogoslof area suggests that a younger year class (1995 or 1996) may have recruited to the Bogoslof pre-spawning population.  Pollock biomass in the Bogoslof area was about the same as that observed during the 2001 survey.

Ancillary research projects conducted during the survey included: pollock ovary collections to determine  fecundity , whole fish collection, spawning mature pollock and culture of fertilized eggs, collection of pollock fin clips for analysis of DNA markers, and whole stomach collections.  At the start of the cruise, the NOAA ship Miller Freeman and the Japan Fisheries Agency ship Kaiyo Maru conducted an intership calibration in the Islands of Four Mountains area.  After the intership calibration, scientists aboard the Kaiyo Maru conducted an EIT survey of shelf/basin waters near the Aleutian Island Chain between 170°W and 176°W longitude.

By Taina Honkalehto.

 
Fisheries Oceanography Coordinated Investigations (FOCI):
Arrowtooth Flounder Survey

Morgan Busby, Debbie Blood, Rachael Cartwright, Bill Floering, Ann Matarese, Jim Stark, and Duane Stevenson participated in the 2002 arrowtooth flounder spawning survey aboard the NOAA ship Miller Freeman 3-9 February  in the Gulf of Alaska.  As was observed in last year’s survey, males and females were segregated by depth indicating that  peak spawning  had not yet begun.  Bottom trawls conducted at 200 and 400 m depths on the outer shelf and upper slope west of Kodiak Island were dominated by females with most mature and running ripe individuals occurring at 400 m.  Tows conducted at 500 and 600 m depths contained nearly all males with numerous ripe individuals found at 500 m.  Toward the end of the cruise in the area off the Shumagin Islands, eggs stripped from two ripe females collected at 400 m and held in a live well were successfully fertilized with milt from males collected at 500 m.  On the last trawl of the cruise, eggs stripped from a single ripe female collected at 500 m were fertilized with milt from several males from the same haul.

The ripe female was the only female collected in the tow.  The fertilized eggs were brought back to Seattle for incubation in the FOCI Rearing Laboratory at Sand Point

By Morgan Busby.

AFSC Quarterly
Research Reports
Jan-March 2002