posted on October 01, 1989 04:19
Ralph K. Mayo, Jacqueline M. McGlade and Stephen H. Clark
National Marine Fisheries Service, Northeast Fisheries Center
Woods Hole Laboratory, Massachusetts 02543, USA
Source - Journal of Northwest Atlantic Fishery Science, Volume 9(1): 13-36
Commercial exploitation of pollock in NAFO Divisions 4VWX and Subareas 5 and 6 has increased considerably over the past two decades as abundance of traditional groundfish species has declined. Total pollock landings from this area increased from less than 30 000 (metric) tons per year during the late-1960s to over 60 000 tons since 1985; USA recreational catches have contributed between 1 000 and 2 000 tons to the annual totals. Since 1977, when both the USA and Canada extended uni-lateral jurisdiction over their fishery resources to 200 miles, domestic management programs for pollock have been either non-existent or ineffective in restricting total landings.
Assessment and management advice for pollock has traditionally been predicated on the assumption of a single unit stock within the region. Tagging studies and morphometric and meristic measurements, however, suggest a possible separation of Gulf of Maine pollock from those on Browns Bank and Emerald Basin on the Scotian Shelf. The distribution of pollock eggs and larvae also indicates the presence of several spawning sites on the Scotian Shelf in addition to previously documented locations in the western Gulf of Maine. Sexual maturation and growth rates for pollock are similar throughout the region. Growth rates of males and females do not differ significantly, although the median size at maturity is slightly larger for males. The majority of pollock of both sexes become sexually mature during their third year.
Recruitment has been consistent since the late-1960s with one or more relatively strong year-classes appearing throughout the region every 3-4 years. Pollock become fully recruited to the fishery between ages 6 and 7, although partial recruitment declines again after age 7. Estimates of total stock size (age 2+), derived from virtual population analysis (VPA), increased from 102 million fish in 1974 to 145 million in 1977, but declined to 97 million in 1980. Following recruitment of the 1979 year-class at age 2 in 1981, stock size increased to 168 million before declining to 113 million in 1988. Instantaneous fishing mortality (F) has exceeded F0.1 (0.29) but remained at or below Fmax (0.57) throughout the 1970s. Fishing mortality has been close to Fmax, however, in 4 of the 6 years since 1982.
Analyses of research vessel survey data generally agree with results obtained from the VPA, indicating a recent decline in stock abundance and biomass, and an increase in instantaneous total mortality. Equilibrium calculations suggest that fishing at F0.1 would provide a long-term yield of 53 600 tons from a stock biomass of 317 700 tons, while fishing at Fmax would provide a yield of 58 100 tons from a stock biomass of 204 600 tons. Corresponding spawning stock biomass levels at F0.1 and Fmax are 260 400 and 149 800 tons respectively. Although long-term yields are approximately 8% greater at the Fmax level, fishing at F0.1 provides for a 55% increase in total stock and 74% increase in spawning stock biomass over those allowed under Fmax.
Language - English
Publisher - Northwest Atlantic Fisheries Organization (NAFO), Dartmouth, N.S., Canada
Publication Date - September 1989
Publication Type - Journal Article