FIELD STUDIES ON THE UREOGENIC GULF TOADFISH IN A SUBTROPICAL BAY .1.PATTERNS OF ABUNDANCE, SIZE COMPOSITION AND GROWTH

Opsanus beta abundance in Biscayne Bay, Florida, varied significantly depending on site and season. O. beta catch per unit effort (cpue) was highest in southern study sites which tended to provide the combinati on of shallow mean depth, nocturnally high levels of dissolved oxygen, and Thalassia-dominated substrate. Significant seasonal differences i n abundance were restricted to the three sites where O. beta cpue tend ed to be highest; two of these sites shared the same pattern of increa se during the cool-dry season (November-April), followed by a return t o lower levels during warm-wet season (May-September). Dramatic season al abundance increases could not be ascribed to large influxes of imma ture fish. Rather, size composition data suggested sexually mature ind ividuals moved seasonally among habitats, possibly for reproductive pu rposes. Modal analysis of length-frequency data followed by nonlinear regressions yielded preliminary values for the von Bertalanffy growth parameters K and t(0), given that L-infinity = 300 mm. Possible reason s for O. beta growing slower and attaining a smaller maximal size than its temperate congener, O. tau, are discussed. (C) 1997 The Fisheries Society of the British Isles.