Interactions of Dimorphic Growth, Reproductive Behavior, and a Size-Regulated Fishery: a Case Study Using Spotted Seatrout Cynoscion Nebulosus

Sexual dimorphism occurs in many fishes and is expressed in a range of traits, including growth and reproductive effort. These traits can result in sex-specific fishing mortality in a size-selective fishery. Our goal was to understand the trade-offs between growth, mortality, and reproduction, for a species with sexually dimorphic growth, within a fishery context. We used gill nets and hook-and-line fishing to capture 1957 spotted seatrout Cynoscion nebulosus from Tampa Bay, Florida (USA), between 2001 and 2002. Females were significantly larger-at-age than males. This larger female size corresponded to a greater prevalence of females in the fishery, evidenced by an 8:1 ratio of females to males at harvestable size. Despite this female-biased sex ratio in the fishery, the total instantaneous mortalities (Z) between the sexes were not statistically different (female Z = 0.77 yr(-1); male Z = 0.82 yr(-1)). We developed a conceptual model to explain the tradeoffs between reproduction and growth as seen in spotted seatrout. Male reproductive effort, including greater spawning frequency and the production of courtship sounds, is hypothesized to result in lower somatic growth, as well as higher natural mortality from increased predation risk. The contrasting roles of fishing pressure on females and natural mortality in males may have important implications for population productivity and fishery management of this species.