THE EARLY LIFE HISTORY OF THE PACIFIC HAKE, 

 MERLUCCIUS PRODUCTUS 



Kevin M. Bailey 1 



ABSTRACT 



The early life history of Pacific hake. Merluccius product us, is described from laboratory and field 

 studies. At ambient temperatures (11°-13°C) egg hatching takes about 100-120 hours; complete 

 absorption of the yolk takes about 150-200 hours. Respiration rates for first feeding larvae at 12°C 

 are 4.8-6.8 jul/mg per hour. Growth rates for at least the first 20 days are slow compared with other 

 larvae in the California Current. First-feeding hake larvae require a daily ingestion of about 0.13 

 calories. 



In this study I present information on the early 

 life history of Pacific hake, Merluccius produc- 

 tus, including rates of development, starvation, 

 growth, and metabolism. I have also used sam- 

 ples from Ahlstrom (1959) and others to examine 

 the vertical distribution of eggs and larvae by 

 size class. My objectives in examining these life 

 history processes are to 1) evaluate the hypothe- 

 sis that the availability of food directly after com- 

 plete yolk-sac absorption is the critical factor in 

 survival of larval Pacific hake and 2) to deter- 

 mine the relative length of time Pacific hake are 

 in egg and yolk-sac stages and are most vulner- 

 able to invertebrate predators. 



The early life history of Pacific hake repre- 

 sents an interesting contrast to other fishes that 

 spawn off the coast of California, including the 

 northern anchovy, Engraulis mordax, and the 

 Pacific mackerel, Scomber japonicus. Compared 

 with these other species the early life history of 

 Pacific hake has been little studied. It is known 

 that hake larvae live below the mixed layer in 

 colder water, and that first-feeding larvae have 

 large mouths, so they can feed on a wide spec- 

 trum of food particles (Ciechomski and Weiss 

 1974; Sumida and Moser 1980). Both the anchovy 

 and mackerel have been subject to intensive in- 

 vestigation as models of the causes of egg and 

 larval mortality. Eggs and larvae of both anchovy 

 and mackerel are found within the warm upper 

 mixed layer (Ahlstrom 1959). Compared with 

 hake larvae, anchovy and mackerel have rela- 

 tively small mouths at first feeding; thus, the size 



'College of Fisheries, University of Washington, Seattle. WA 

 98195. 



of ingested food particles is restricted (Hunter 

 1980). At least for first-feeding anchovy larvae, it 

 has been shown that the availability of food of the 

 proper size and in adequate densities is impor- 

 tant to survival (Lasker 1975). The results of the 

 present study, in particular the determination of 

 the food requirements of hake larvae may indi- 

 cate important differences in the survival strate- 

 gies of these three fishes. 



METHODS 



Development and Growth 



All laboratory experiments in this study were 

 conducted using eggs collected at Port Susan, 

 Wash. This stock is reproductively isolated from 

 the Pacific hake spawning off the California 

 coast (Utter 1969), but I am assuming that tem- 

 perature-specific rates of metabolism of larvae 

 hatching from Port Susan eggs are similar to the 

 rates for larvae hatching from eggs spawned in 

 the California Current because 1) egg size is the 

 same, 2) temperature-dependent hatching times 

 are the same (see results this study), and 3) 

 growth to age 2 is the same (Kimura and Milli- 

 kan 1977). 



Eggs were collected with a 500 /urn mesh meter 

 net (equipped with a cod end designed to capture 

 live zooplankton) and returned to the laboratory 

 at 5°-10°C. Eggs and larvae were reared in fil- 

 tered seawater in 1-4 1 jars containing 50 ppm 

 each penicillin G potassium and streptomycin 

 sulfate. Egg hatching experiments were done 

 with 3 replicates of 10-20 eggs/1. Percent hatch- 

 ing was checked every 12 h. The eggs used in 

 these experiments were without visible embryos 



Manuscript accepted January 1982. 

 FISHERY BULLETIN: VOL. 80. NO. 3, 1982. 



589 



