Report for Jan-Feb-Mar 2001)
Assessment & Conservation Engineering:
Eastern Bering Sea and Bogoslof Island Survey
Scientists from the Midwater Assessment and Conservation Engineering (MACE) Program conducted an echo integration-trawl survey of the Southeastern Bering Sea Shelf and Bogoslof Island region from 19 February to 11 March 2001 (Figure 1 above). The survey was designed to provide data on the abundance and biological composition (size and age) of walleye pollock in the Steller sea lion Conservation Area (SCA) and the portion of the Central Bering Sea Convention Area close to the Aleutian Islands, between Akutan Island and the Islands of Four Mountains. The data will aid in managing and assessing the impact of commercial fisheries on Steller sea lions and their habitat.
Survey operations were conducted 24 h per day. The acoustic systems were calibrated between the shelf and Bogoslof legs of the survey. A total of 32 trawls were made with the standard Aleutian wing trawl and 3 were made with an 83-112 bottom trawl.
Preliminary survey results show that pollock were most abundant at the eastern edge of the SCA (Figure 1 above), an area with high commercial catches. Pollock were on average about 45 cm in length in this area, and very few pollock smaller than 30 cm were observed here. On the northern and western part of the SCA, age-1 pollock with lengths 10-15 cm were abundant. Age-1 pollock were not abundant in the SCA in previous winter surveys. In the Bogoslof area, pollock were concentrated in two locations: between Umnak and Unalaska Islands and in Samalga Pass. The size distribution was as in previous years, with mean lengths about 60 cm, indicating that the population has not been renewed by the appearance of new, strong year classes. Pollock biomass was substantially reduced from that observed in the 2000 survey.
Ancillary research projects conducted during the survey included: pollock ovary collections for fecundity determination, whole fish collection, spawning mature pollock and culture of fertilized eggs, analysis of DNA markers for pollock fin clips, and whole stomach collections. A Korean scientist, Mr. Hyun-Su Jo, was aboard for both legs of the cruise.
By Paul Walline.
Gulf of Alaska Survey
MACE scientists conducted an echo integration-trawl survey of the Shumagin Islands area 12-19 February. Survey operations were conducted 24 hours per day. Ten trawls were made with an Aleutian wing trawl (AWT) and 7 were made with a Poly Nor’eastern (PNE) bottom trawl. Pollock were present in most of the surveyed area, with adults generally distributed near Renshaw and Swedania Points (typically within 50 m of the bottom), and 2-year olds generally distributed in West Nagai Strait and Shumagin Gully. Two-year old pollock also often formed a well-defined layer at depths between about 150-180 m depth. Eulachon (Thaleichthys pacificus) were present in most of the areas surveyed (4% by weight, 30% by number). Nearly 45% of the adult pollock (i.e., greater than 35 cm fork length) were either in a “spawning” or “spent” stage of maturity. This suggests that the time of peak spawning was a little earlier than that observed during the last formal survey of this area, which occurred 14-20 February 1995, when about 6% of the fish were classified as spawning or spent.
MACE scientists conducted echo integration-trawl surveys of the Shelikof Strait area and east Kodiak Island from 13 to 27 March. The Shelikof Strait portion of the survey, which was conducted 13-18 March between Chirikof Island and Cape Chiniak, was the 19th spawning stock survey of pollock in Shelikof Strait since 1980. (No surveys were conducted in 1982 and 1999.) Transect spacing was 7.5 nmi. A total of 15 AWT and 4 PNE hauls were conducted during this portion of the survey. Unlike most previous years, relatively few mature prespawners were found in the Shelikof Strait sea valley on the west side of the strait (Katmai Bay to Cape Nukshak). The pollock distribution was similar to the 1988 survey, when a relatively greater amount of pollock were found on the east side of the strait rather than on the west side. Significant quantities of juvenile pollock (primarily age-2) were observed from about Chirikof Island to Cape Kerkurnoi, including a well-defined midwater layer of primarily age-2 pollock at about 160-180 m depth. Few age-1 pollock were present in the Shelikof Strait. Survey timing was appropriate based on time of peak spawning. For example, maturity comparisons were similar to previous years. For females greater than 40 cm, 73% were mature prespawning, 1% were spawning, and 2% were spent. A second pass of the strait occurred 23-26 March at 15 nmi spacing. Three transects in the southern strait were dropped because of bad weather. Two AWT and 5 PNE hauls were conducted during the second pass. No changes in pollock distribution or length or maturity composition were generally observed between the two passes.
Chiniak and Barnabas Gullies were surveyed 19-23 March to assess the distribution of pollock off the east side of Kodiak Island. Three AWT hauls were conducted in Chiniak Gully, and three AWT and one PNE haul were conducted in Barnabas Gully. Virtually no pollock were detected in either gully. The small amount of pollock echosign that was detected was attributed primarily to either 1- or 2-year olds. Juvenile pollock size compositions varied slightly among the few hauls that were conducted in both gullies (e.g., 1-year olds throughout Barnabas and near the head of Chiniak gully; 2-year olds nearer shelf break in Chiniak and absent in Barnabas). Whether these trends in catch data represent “typical” winter-spring distribution patterns will require further research.
Ancillary research projects for the Gulf of Alaska surveys included pollock ovary collections for fecundity determination, whole fish collections for sea lion and seabird diet studies, whole juvenile pollock collections for studies on the winter check on juvenile pollock otoliths and on seasonal effects on juvenile pollock diet and condition, spawning mature pollock and culture of fertilized eggs, analysis of DNA markers from pollock fin clips to examine genetic population structures, and whole stomach collections for food habits analyses.
By Mike Guttormsen.
Fisheries-Oceanography Coordinated Investigations (FOCI)
Scientists of the RACE Division and visiting scientist Fumihito Muto (Hokkaido University, Laboratory of Marine Biodiversity, Japan) participated on cruise MF01-01 aboard the NOAA ship Miller Freeman from 28 January to 5 February. The primary objective of the cruise was to conduct bottom trawl sampling on the outer continental shelf and upper slope in the Gulf of Alaska to collect ripe adult arrowtooth flounder and deploy deep bongo plankton tows to collect their eggs. This work was needed to establish the appearance of arrowtooth flounder eggs so they can be identified with confidence in plankton samples. Twenty four stations were occupied. Operations included recovery and deployment of an oceanographic mooring for the Center’s Kodiak Laboratory, CTD casts, 60-cm bongo tows, and Nor’eastern bottom trawls. On 2 February, eggs stripped from a ripe female arrowtooth flounder were successfully fertilized with milt collected from three ripe males. After the cruise, the eggs were transported to the AFSC Seattle facilities where they completed development and began hatching 24 February. Yolk-sac larvae are currently being sampled to document development of pigmentation.