AGE-SPECIFIC MORTALITY AND TRANSPORT OF LARVAL WALLEYE POLLOCK THERAGRA-CHALCOGRAMMA IN THE WESTERN GULF OF ALASKA

A field study was conducted in May 1988 to estimate mortality rates of individual cohorts of larval walleye pollock Theragra chalcogramma in Shelikof Strait, Gulf of Alaska. Two surveys of the area of larval di stribution were done 12 d apart and daily mortality rates estimated fr om changes in abundance of each cohort. This study was designed to min imize potential sources of bias to mortality estimates, such as larval extrusion or escapement from sampling gear, advective or diffusive ga in or loss of larvae into or out of the sampling area, the uncertainty incurred by the use of length as a proxy for age, and the often erron eous assumption of constant production and mortality rates. The age-sp ecific mortality rates from this study were low compared to rates prev iously estimated for larval wall-eye pollock. Four significant mortali ty estimates, ranging from 0.041 to 0.076 d-1, came from among the you ngest cohorts. The low larval mortality rates in 1988 coincided with v ery calm ocean conditions. Larval drift rates estimated in this study were coherent with the movement of a satellite-tracked drift buoy and averaged 3.1 to 3.9 cm s-1, which is comparable to rates reported from other studies.