Aspects of spatial and temporal cooccurrence in the life history stages of the sibling hakes, <i>Urophycis chuss</i> (Walbaum 1792) and <i>Urophycis tenuis</i> (Mitchill 1815) (Pisces: Gadidae)

Abstract

The amount of coexistence in the sympatric sibling species, Urophycis chuss and U. tenuis, appears to be a function of ontogeny, with each life history stage showing different probabilities of interspecific encounters. Demersal juveniles coexist the least since U. chuss is inquiline with scallops and U. tenuis is in nearshore shallows. In U. tenuis there is also intraspecific segregation, with older juveniles and young adults bathymetrically segregated from the youngest demersal juveniles in summer.Relatively more coexistence is seen between neustonic juveniles. However, they show some seasonal and pronounced diel differences in availability to neuston nets (U. chuss predominates during the day and U. tenuis during night). The greatest coexistence is seen between adult U. chuss and adolescent to adult U. tenuis.Over its life, U. tenuis tends to move into deeper water while U. chuss is relatively stenotopic, its distribution largely a reaction to temperature. The life history strategy of U. tenuis is "get big quick," a goal achieved, in part, through delayed maturation (relative to U. chuss). The strategy of U. chuss seems to be avoid predation, concentrate growth in the juvenile stage, and "get mature quick." We speculate that both species' life histories may be subordinate to getting the demersal juveniles into the right nursery area at the right time.