Effect of an artisanal fishery on the fish and urchin populations of a Kenyan coral reef

Abstract

An investigation of the effects of artisanal fishing on coral reef fish assemblage structure was undertaken through a comparison of fish stocks on 2 apparently identical sets of reefs, one (within the Kisite Marine National Park) on w h c h all fishing is prohibited, and one (within the Mpunguti Marine National Reserve) on which artisanal fishing only is allowed. Replicate visual censuses of fish along 250 X 10 m band transects at 6 intensive study sites demonstrated that there were large differences in population density and biomass of the principal families of conunercial reef fish (Lethrinidae, Lutjanidae and Serranidae) between the unfished marine park area and the adjacent intensively fished marine reserve area, with abundances of commercial species within the park (unfished) being up to 10 or more times those in the reserve (fished). In addition, 6 species of butterflyfish (Chaetodontidae) and 2 species of triggerfish (Balistidae) were significantly more abundant on shallow and/or deep transects within the park. For most species of commercial fish, larger individuals were observed in the park than in the reserve, an effect expected from greater fishing pressure within the reserve. In contrast. smaller Cephalopholis spp. (Serranidae), 1 species of butterflyfish, and sea urchins (mostly Echinornetra mathaej) were significantly more abundant on transects in the reserve. It is suggested that these increased abundances may be second order effects (mediated by reduced competition or predation) of increased fishing pressure. In particular, opposing differences in abundance of predatory triggerfishes (Balistidae) and emperors (Lethrinidae) and of sea urchins are compatible with the view that higher populations of sea urchins may sometimes occur where the densities of their predators are reduced. Overall results allow an assessment of the effect of the artisanal fishery on the fish stocks, and provide a measure of the effectiveness of protection afforded by the marine park.

Rapid Effects of Marine Reserves via Larval Dispersal

“…Fishing can also have indirect effects on predatory fish communities. For example, removal of large-bodied predators may have allowed smaller ones to increase in abundance due to release from competition or predation [30,61,62]. Indeed, the relatively unfished trumpetfish, and the two smallest species of both grouper (i.e., graysby and coney) and snapper (i.e., lane and mahogany snappers) were found to increase in presence with decreasing presence of large predators (Table 3, Figs.…”

Recovery trajectories of coral reef fish assemblages within Kenyan marine protected areas

“…As maximum size is correlated with many other life-history traits, resulting in larger fish being more vulnerable to exploitation (Jennings et al 1999, Denny et al 2002 and because larger fish are generally targeted before smaller fish (Pauly et al 1998), size is proving to be a useful way to assess multispecies fisheries (Bianchi et al 2000, Dulvy et al 2004, Graham et al 2005. Increasing evidence of species-level (Watson and Ormond 1994, Graham et al 2003) and aggregated size-based (Dulvy et al 2004) indirect interactions within coral reef fish assemblages further suggest that recovery trajectories in these ecosystems should be assessed at the assemblage level.…”

“…As maximum size is correlated with many other life-history traits, resulting in larger fish being more vulnerable to exploitation (Jennings et al 1999, Denny et al 2002 and because larger fish are generally targeted before smaller fish (Pauly et al 1998), size is proving to be a useful way to assess multispecies fisheries (Bianchi et al 2000, Dulvy et al 2004, Graham et al 2005. Increasing evidence of species-level (Watson and Ormond 1994, Graham et al 2003) and aggregated size-based (Dulvy et al 2004) indirect interactions within coral reef fish assemblages further suggest that recovery trajectories in these ecosystems should be assessed at the assemblage level.This study examines the size structure and biomass of coral reef fishes in Kenyan coral reefs by examining 4 fully closed MPAs that vary in their time of establishment (from 1968 to 1991) with data that are available from 4 yr prior to and 36 yr after closed-area management (see Table 1). The study sites were examined between 1987 and 2004, and repeatedly sampled so that a 40 yr chronosequence of management can be patched together from this sampling and differences in the starting dates for closed-area management.…”

Evaluating the biological effectiveness of fully and partially protected marine areas

“…[45,56,66,105]) or coral reefs (e.g. [65,91,[106][107][108][109][110]), there was a general lack of data quantifying the relationship between biota and habitat structure inside and outside the MPA (but see [45,91,101,[108][109][110][111][112]). We could only identify 'habitat-confounded' studies with confidence when the authors explicitly reported significant differences in habitat among the sites studied inside and outside the MPA.…”