SPACE AND TIME SCALES IN PACIFIC HAKE RECRUITMENT PROCESSES - LATITUDINAL VARIATION OVER ANNUAL CYCLES

Habitat of North Pacific hake (Merluccius productus) can be partitione d into three life-history zones: an adult feeding area along the coast al shelf and slope from California to British Columbia, a spawning are a off central California south to Baja California, and a brood area ex tending along the coastal shelf and slopes of California and, at times , into Oregon. Recruitment is potentially influenced by a complex mixt ure of physical and biological processes that operate over a wide rang e of spatial and temporal scales. We quantify the relative importance of demographic (natality, mortality), growth (physical influences, foo d supply), and kinematic (passive motion with now structures, active l ocomotion) processes that can influence recruitment of Pacific hake in scale diagrams of dimensionless ratios. We found that changes in larv al hake biomass are dominated by mortality and drift with prevailing c urrents. Location of adult spawning is therefore important to survival . Changes in juvenile biomass are influenced more by changes caused by somatic growth and active locomotion. Annual survey data show multiye ar trends in the latitudinal placement of spawn toward the equator (19 51-55, 1959-64, 1980-83) or toward the pole (1955-59, 1964-69), but st rong recruitment only in single years (1961, 1970, 1977, 1980, 1984, 1 987, 1990, 1993). We surmise that sharp adjacent year changes in recru itment may not be induced by slow trends in spawning location. The cen ter of adult spawning shifts toward the pole during warm years (>10 de grees C at 100-m depth off Point Conception) and toward the equator du ring cold years. There has been an overall shift in the mid-spawning l ocation of 444 km toward the pole during the 34-year period from 1951 to 1984. On average, three times as many recruits survive from warm ye ars than from cold years. Unfortunately, a warm-water year does not gu arantee higher than usual recruitment.