VERTICAL-DISTRIBUTION OF PACIFIC HAKE EGGS IN RELATION TO STAGE OF DEVELOPMENT AND TEMPERATURE

The vertical distribution of eggs of Pacific hake (Merluccius productu s) was determined from 27 MOCNESS samples taken on cruises off souther n and central California in March 1995 and February 1996. In 1995, nin e depth strata (0-25, 25-50, 50-75, 75-100, 100-125, 125-150, 150-200, 200-250, and 250-300 m) were sampled. In 1996, nine 25-m depth strata were sampled down to 225 m. In 1995 Pacific hake eggs were taken in a ll strata down to 250-300 m; most of the eggs were found between 50 an d 150 m, with the highest densities in the 50-75- and 75-100-m strata. Average temperatures for developing Pacific hake eggs were estimated to be 10.2 degrees-11.3 degrees C. Early-stage eggs were generally dee per in the water column than later-stage eggs. Most early-stage eggs w ere found between 75 and 150 m, with highest densities in the 125-150- m stratum. Tn contrast, mid-and late-stage eggs were most dense m the 50-75- and 75-100-m strata. Early-stage eggs were taken primarily in t ows between 2200 and 0600 hrs, suggesting diel periodicity in spawning . On the 1996 cruise hake eggs had a slightly shallower distribution c ompared with 1995, and there was more overlap in vertical distribution between stages. Methods are given for separating Pacific hake eggs fr om similar eggs of other species, and criteria are described for stagi ng Pacific hake eggs.