FY 1992

Some interactions between young walleye pollock and their environment in the western Gulf of Alaska

Schumacher, J.D., and A.W. Kendall, Jr.

California Cooperative Oceanic Fisheries Investigations (CalCOFI) Report, Vol. 32, 22–40 (1991)

Surveys of Shelikof Strait, Alaska, show that large concentrations of walleye pollock (Theragra chalcogramma) enter the sea valley each March and spawn early in April. Surveys for eggs and larvae have disclosed dense regions of eggs that become patches of larvae. Processes that transport larvae to nursery grounds or to the open ocean seem important to recruitment. Early results suggested that larvae could be rapidly removed (in 14 days) from the shelf by the vigorous, varying flow of the Alaska Coastal Current (ACC). In the upper 100 m, however, most of the volume transport remains on the shelf. Baroclinic instability between the ACC and coastal waters can create eddies (first observed in infrared satellite images) at the exit of Shelikof Strait. Eddies frequently contain the highest concentrations of larvae. The phasing and location of eddies, the ACC, and hatching determine how a given mechanism will affect retention of larvae on the shelf. Year-class size seems largely determined by the end of the larval period, although events during the following summer may also reduce the year class. Storms during the early larval period may be particularly detrimental to survival, although the mechanism is not yet clear. An index of storminess in the Gulf of Alaska may provide a way of predicting year-class size. Studies of physical and biological conditions in larval patches and adjacent shelf waters are being made to determine whether growth and mortality rates differ in these areas.