An age-based demographic analysis of the Caribbean stoplight parrotfish Sparisoma viride

Abstract

The parrotfish Sparisoma viride is an abundant and ecologically important member of the tropical NW Atlantic reef fish fauna. Sagittal otoliths of 417 individuals were analysed to estimate age-based demographic variables at 4 localities (Lee Stocking Island, Barbados, Los Roques Archipelago and the San Blas Archipelago) spanning 14°of latitude. The sampling localities ranged from an area protected from trap-and net-based reef fisheries (Los Roques) to an area supporting a dense human population and sustained trapping and spearing for reef fishes including S. viride (Barbados). Examination of sectioned sagittal otoliths from each locality revealed regular increments in the sagittal matrix. A preliminary validation at San Blas was consistent with these increments being annual check marks. These increments provided estimates of age structure, maximum longevities and mortality rates for the 4 study populations of S. viride. Von Bertalanffy growth functions fitted to each size-at-age plot generated similar growth curves from 3 of these 4 localities. The exception was Lee Stocking, where fish grew faster and reached a substantially larger size than those from the other 3 localities. Further analysis of the growth curves demonstrated that the differences between Lee Stocking and the other localities were attributable to more rapid growth over the first 4 yr of life. Agebased growth curves derived from the Los Roques population were very similar to a size-based curve generated by an independent study on S. viride carried out in Bonaire, adjacent to Los Roques. Maximum longevities for all 4 of our populations varied from 7 to 9 yr. Mortality rates generated from catch curve analysis were also similar among localities and suggest that maximum life spans do not exceed 12 yr. This result differs from that obtained at Bonaire, where repeated censuses of tagged fish suggest 30 yr maximum longevity. Abundances of S. viride varied 3-fold among localities, being highest at Los Roques (protected from reef fishing), lowest at Barbados (high fishing) and Lee Stocking (low fishing). Thus our age-based study suggests that S. viride is a relatively short-lived fish with consistent demographic parameters over a range of localities, latitudes and fishing intensities.

Ocean surgeonfish Acanthurus bahianus. II. Fishing effects on longevity, size and abundance?

“…The human population density in the Bahamas is fairly low (295 000 people on 10 000 km 2 land, 3150 km 2 reef), especially in the general vicinity of Lee Stocking Island (data collection November 1998November , 1999, which is well away from population centers. We saw no evidence of trap-fishing, and predatory reef-fishes were not uncommon there during our work there (Choat et al 2003).…”

“…Our study area was in a part of the reserve where no fishing for reef-fishes is allowed (see Choat et al 2003). At nearby (50 km to the west) Las Aves Archipelago (data collection August 2002) there are no controls on fishing.…”

“…The entire reef system around the island of Bonaire (15 000 people, 285 km 2 land, 26 km 2 reef; data col-lection August 1992) is a reserve, with no organised reef fishery and fishing (by hook-and-line only) mainly for pelagic species (Choat et al 2003, Hawkins & Roberts 2003. At nearby Curaçao (205 000 people, 450 km 2 of land, ~50 km 2 of reef; data collection August 1992) predatory reef fishes are uncommon, due to a long history of overfishing.…”

“…To ensure that we obtained a representative sample at each location, we made collections at at least 5 sites separated by distances of kilometres, and across a range of habitats used by the ocean surgeonfish at the different sites. To estimate the abundance of adult A. bahianus, counts were made of fish other than small juveniles in 30 × 10 m belt transects (see Choat et al 2003) by J. H. Choat at 11 locations in the NW Atlantic. Such transects are suitable for estimating densities of this species because it is relatively small, common and sedentary.…”

“…This presents an opportunity to determine if effects of fishing readily can be disentangled from those of natural influences on the demography and abundance of a species that does not represent a universal, high-value fishing target. To do so we compared the longevity, adult survivorship, size and density of the ocean surgeonfish across a set of geographically widely dispersed reefs exposed to varying patterns of fishing, a method frequently employed in analyses of fishing effects (Jennings & Polunin 1996, Choat et al 2003, Hawkins & Roberts 2003, Dulvy et al 2004, Williamson et al 2004.…”