MESOSCALE FISHING PATTERNS OF FACTORY TRAWLERS IN THE PACIFIC HAKE (MERLUCCIUS-PRODUCTUS) FISHERY

During 1991-95, up to 60% of the annual catch of Pacific hake (Merlucc ius productus) in the U.S. management zone was harvested by a U.S.-bas ed fleet of factory trawlers. Optimal foraging theory was used to moti vate a statistical analysis of movement patterns of these vessels. Thi s study focused on the mesoscale characteristics of the environment (5 -50 km), and vessel movement at these spatial scales. Geostatistical a nalyses of hake densities derived from the 1992 and 1995 National Mari ne Fisheries Service assessment surveys with quantitative echo-soundin g techniques showed that strong spatial correlations of hake density d o not extend beyond similar to 25-35 km. The range of Pacific hake spa tial correlation suggests an association with mesoscale oceanographic features whose characteristic scale in the California Current system i s determined by the Rossby radius of deformation (similar to 25 km in mid-latitudes off the West Coast). The foraging patterns of factory tr awlers can be described as a series of moves between trawling location s. The distance between successive hauls depends on whether the vessel continues fishing within a local area of high fish density, or moves to a different area. Generalized additive models (GAM) were used to ex amine influence of the catch rates of prior hauls on the distance betw een successive hauls. The GAM models suggested that deviations from th e expected catch rate influence the decision to move from a local fora ging area, as expected from optimization models of animal foraging. Th ese decisions appeared to be based on relatively short time frames, su ch that information from only the most recent one or two hauls in the area is used. In addition, results indicated that the presence of othe r fishing vessels operating nearby reduces the probability that a vess el will leave an area.