AGE AND GROWTH OF PACIFIC HAKE, 

 MERLUCCIUS PRODUCTUS 



Thomas A. Dark' 



ABSTRACT 



The age and growth of Pacific hake, Merluccius productus, collected off California, Oregon, and 

 Washington in 1964-69, were studied. 



The age determination procedure was examined and considered to provide valid ages. 



Several sources of variation in the age structure of the population were given cursory examination. 

 Relative size of the year class and sampling area (average age tends to increase with latitude) 

 contribute substantially to the variation of the population age composition while sex and sampling 

 season have lesser effects. 



Growth in length is rapid during the first 3 yr after which it slows and approaches an asymptote in the 

 oldest ages, 10-13 yr. Females have a faster rate of growth than males and tend to survive 2 or 3 yr 

 longer, to age 13. Growth in length can be adequately described by the von Bertalanffy growth 

 equations: /, = 56.29 (l-e"^'^^ ('C2U>) f^^ ^^^^^ ^^^ /^ ^ gj 23 (i_e-0-30 (^-O.Oi)^ j^^. fgj^^les. Year class 

 variation in growth rate was detected by back-calculation, using the body length (F) -otolith radius {X) 

 relationship Y = 18.78957 - 3.79065X -1- 0.67490^^^ - 0.01836Jf'. Growth in weight was determined by use 

 of the length-weight equations: log VF = - 1.45990 + 2.55618 log L for males and \og W = - 1.68944 -I- 

 2.69509 log L for females. Males attain an average weight of about 1,211 g by age 11 and females reach 

 an average weight of 1,374 g by age 13. Annual instantaneous growth rates in weight were computed 

 and were found to decrease most during the fourth year for both sexes and very little growth occurred 

 after the sixth year for males or after the ninth year for females. 



The Pacific hake, Merluccius productus, is a com- 

 mon gadid fish that ranges from the Gulf of 

 CaHfornia to the Gulf of Alaska (Hart 1973) but is 

 most abundant from Baja California to southern 

 British Columbia (Alverson et al. 1964). There is 

 apparently a single population offshore and 

 another in Puget Sound, Wash. (Utter and Hod- 

 gins 1971). The Puget Sound population supports 

 only a small fishery and is not considered in this 

 report. 



Feeding adult hake are usually found over the 

 continental shelf and exhibit pronounced diel 

 movement. During the day they are most com- 

 monly found in compact schools near the seabed, 

 but as darkness approaches the schools rise and 

 become more loosely structured. During their 

 spawning period mature hake are more pelagic in 

 behavior than during the rest of the year. They 

 apparently spawn at intermediate depths in water 

 1,000 m deep or more and demonstrate little diel 

 movement (Nelson 1967). Spawning occurs from 

 January through April off northern Mexico and 

 southern California (Ahlstrom and Counts 1955). 



' Northwest Fisheries Center, National Marine Fisheries Ser- 

 vice, NOAA, 2725 Montlake Blvd. E., Seattle, WA 98112. 



Eggs and larvae are pelagic and are found mostly 

 near the thermocline at depths of about 45 to 100 

 m. It is not clear at what age juvenile hake leave 

 their pelagic phase and become more closely as- 

 sociated with the seabed. One-year-old hake are 

 found in inshore waters off southern California, 

 associated at times with schools of northern 

 anchovy, Engraulis mordax (Dark et al. 1970). 

 Hake, 1 to 3 yr old, are taken in shrimp trawls 

 along the Oregon and California coasts (Morgan 

 and Gates 1961). Pacific hake less than 4 yr old are 

 rarely found north of Oregon. Most 4- to 13-yr- 

 old hake mature and are found feeding off the 

 coasts of Oregon, Washington, and southern Bri- 

 tish Columbia during the spring and summer. By 

 early winter only a small portion of the summer 

 population remains in these areas. 



Temporal and areal distribution of the various 

 life history stages suggest that adult Pacific hake 

 undertake extensive annual migrations along the 

 west coast of North America (Alverson and 

 Larkins 1969). Most adult hake seem to move 

 northward along the coasts of California, Oregon, 

 and Washington in early spring on a feeding 

 migration as far north as central Vancouver 

 Island. In late fall the adults begin a return 



Manuscript accepted August 1974. 

 FISHERY BULLETIN: VOL. 73, NO. 2, 1975. 



336 



