U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications
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 distribution were done 12 d apart and daily
mortality rates estimated from changes in abundance of each cohort. This study was
designed to minimize potential sources of bias to mortality estimates, such as larval
extrusion or escapement from sampling gear, advective or diffusive gain 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 erroneous assumption of constant production and mortality rates.
The age-specific mortality rates from this study were low compared to rates previously
estimated for larval walleye pollock. Four significant mortality estimates, ranging from
0.041 to 0.076 d
, came from among the youngest
cohorts. The low larval mortality rates in 1988 coincided with very 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, which is comparable to rates reported from other studies.