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

Abstract

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).

Description of diet of pelagic fish in the southwestern Atlantic, Brazil

“…The absence of elasmobranchs in the diet of I. oxyrinchus helps to corroborate results obtained by Maia et al (2006). As Pikitch et al (2005) state, this absence may be credited to the low densities such sharks and other ones present in the oceanic environment, when compared to more complex habitats. Other large predators, such as X. gladius, should also be considered as potential prey for I. oxyrinchus (Stillwell & Kohler 1982, Maia et al 2006, but this fact was not observed in this study.…”

Complexities of coastal shark movements and their implications for management

“…Similarly, young-ofthe-year grey nurse sharks use shallow-water reef habitat as a refuge from larger species (Dicken et al 2006). Pikitch et al (2005) found that small juvenile Caribbean reef sharks were relatively more common inside lagoons, and larger individuals used shallow fore-reef habitats near deeper water to increase foraging opportunities . Small Caribbean reef sharks also move from shallow forereef habitats during the day into the lagoon at night presumably to reduce predation risk (Chapman et al 2007).…”

Spatial and temporal movement patterns of a multi-species coastal reef shark aggregation

“…The spatial and temporal shifts in movement of these predators can affect their prey both directly through ingestion and indirectly through predation risk (Speed et al 2010). The presence of multiple species and size classes of reef sharks on healthy reefs (Nelson & Johnson 1980, Stevens 1984, McKibben & Nelson 1986, Chapman et al 2005, DeAngelis et al 2008 suggests that coexistence arises in part because habitat partitioning occurs at some spatial and temporal scales.…”

“…Intra-specific habitat partitioning is common in some species, with many studies concluding that juveniles and adults partition habitats by depth, temperature, salinity, or benthos type (Chapman et al 2005, Pikitch et al 2005, McAuley et al 2007, Yeiser et al 2008, Speed et al 2010. However, few studies have quantified temporal and spatial habitat partitioning among different species, although there is some evidence to support inter-specific partitioning in relation to the distribution of prey (White & Potter 2004), habitat type and season (White & Potter 2004, DeAngelis et al 2008.…”