Habitat use and demographic population structure of elasmobranchs at a Caribbean atoll (Glover’s Reef, Belize)

A 5 yr spring and summer survey (July 2000 to May 2004) of the elasmobranch fauna of Glover’s Reef Marine Reserve, Belize, documents the use of this oceanic atoll by at least 12 elasmobranch species, including early life-stages of nurse sharks Ginglymostoma cirratum, Caribbean reef sharks Carcharhinus perezi, lemon sharks Negaprion brevirostris, and southern stingrays Dasyatis americana. Elasmobranch abundance was sampled in 3 atoll macrohabitats (deep lagoon, ocean reef, shallow lagoon) using standardized longlines. Total elasmobranch abundance did not change from year to year, but was significantly higher inside the lagoon than on the ocean reef outside the atoll. G. cirratum dominated both shallow and deep lagoon catches, with smaller individuals more prevalent in the shallow lagoon. C. perezi of all size classes dominated the ocean reef catches, but small juveniles of this species were also common in the deep lagoon. This species rarely utilized the shallow lagoon. A wide range of sizes of C. perezi and G. cirratum occupy Glover’s Reef in spring and summer, with males maturing at 150 to 170 cm and 185 to 200 cm total length, respectively. The sex ratios of these species did not deviate from unity. A large juvenile Galápagos shark, C. galapagensis, was collected on the ocean reef, extending the range of this species into the Western Caribbean. Opportunistic surveys of fish markets on the Belize mainland revealed that inshore areas are utilized by early life-stages of sharks from the families Carcharhinidae (C. limbatus, N. brevirostris, Rhizoprionodon porosus) and Sphyrnidae (Sphyrna tiburo, S. lewini, S. mokarran).