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Differential assemblage responses to non-selective fisheries pressure in Discovery Bay, Jamaica.
Biggers, Andrew*,1, Waltho, Nigel2, 1 Lumbers Building, York University, Toronto, ON, Canada2 Lumbers Building, York University, Toronto, ON, Canada
ABSTRACT- In a non-selective multi-species fishery, changes in species assemblage patterns are thought to occur in non-specific ways. However, hierarchy theory predicts that habitat specialists should change to a greater relative extent than habitat generalists - a counter intuitive expectation when considering a non-selective fishery. We test this hypothesis by collecting fish abundance data from 40 isolated patch reefs on the back reef of Discovery Bay, Jamaica over nine years (in 1993, 1996, 1999, and 2001). For each years data Morisista-Horn assemblage similarities among patches were obtained for species groups containing habitat generalists, intermediate, and habitat specialists. Our null hypothesis states that for each species group changes in assemblage similarities, through time, should be similar. In a factorial design ANOVA we found that the mean Morisita-Horn index (a) does not change for habitat generalists (mean=0.55), suggesting stable assemblage patterns; (b) significantly increases for habitat intermediates (mean=0.18, 0.25, 0.28, 0.44 respectively for each year), suggesting a loss of assemblage diversity; and (c) increases for habitat specialists from 0.07 to 0.18, suggesting similar loss of assemblage diversity but to a lesser degree than in the group of habitat intermediates. These results support predictions derived from the hierarchy theory and indicate that non-selective fishery changes fish assemblages in several ways, from reducing the abundance and richness to simplifying their structure.
KEY WORDS: Coral reef fish, hierarchy theory, assemblage similarity, fishing pressure