Effects of fishing on population structure and life history of roman Chrysoblephus laticeps (Sparidae)

Abstract

The effects of fishing on the population structure and life history of roman Chrysoblephus laticeps, a protogynous hermaphroditic seabream from South Africa, were investigated by comparing fish from protected and exploited areas. Experimental (controlled) fishing and underwater visual census were used to sample roman and to measure population parameters inside and outside the Goukamma Marine Protected Area. Sites chosen for comparisons were adjacent and physically similar to reduce environmental influences on the comparison. Both methods revealed that roman had a higher density and mean size inside the protected area than outside. Age-at-maturity and ageat-sex-change were lower in the exploited area. The shift in age-at-sex-change maintained a constant sex ratio between the exploited and unexploited areas. The condition factor of roman from the protected area was lower than that of roman from the exploited area.KEY WORDS: Fishing effects · Life history · Population structure · Chrysoblephus laticeps · Sparidae · Marine protected area · Sex change Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 362: [245][246][247][248][249][250][251][252][253][254][255][256][257][258][259] 2008 demographic differences between areas (Robertson et al. 2005). As Hilborn & Ludwig (1993) point out, this makes the research in this area of science more difficult, and progress is largely determined by how many replicates can be performed, the difficulty or impossibility of obtaining controls, and whether environmental treatments can be randomized. Despite these difficulties, we have chosen this approach to study the effects of fishing on reef fish in South Africa for 2 reasons.Temperate reef fish are the most heavily exploited of marine fishes in South Africa, a predicament that is exacerbated by their slow growth, longevity and hermaphroditic life-styles (Buxton 1993). With the collapse of many species (Griffiths 2000, Griffiths & Lamberth 2002) the line fishery has been declared to be in a state of emergency. The absence of suitably archived data or long-term data series on catch-at-age and ageat-maturity prevents us from analyzing temporal changes in reef fish life-history and production traits. The only realistic option, therefore, is contemporary comparison between areas that have been subjected to different rates of fishing.Sex-change in some coral reef fish is known to be density dependent (Collins et al. 1998), yet this characteristic is one of the least well-known agents of density-dependent population regulation (Rose et al. 2001). Sánchez-Lizaso et al. (2000) review studies examining density-dependent changes in life-history traits of exploited populations. They suggest that Marine Protected Areas (MPAs) should be a useful tool for testing the common hypotheses; however, definitive results from comparative studies have been unclear. Two such studies on reef fish that reported some effects that were opposite to what one might expect are of importance here:(1) Lloret ...

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