Effects of fishing on a temperate reef community in South Africa 1: ichthyofauna

Abstract

Exploitation of temperate reef fish not only affects the target species but potentially changes the composition of reef fish assemblages. This study investigated the effect of fishing on the ichthyofaunal community at protected and exploited sites around the Goukamma Marine Protected Area (MPA) on the South African temperate south coast. Abundance and size frequency data from 273 standardised angling and 44 underwater visual census sites were analysed with generalised linear modelling and multivariate techniques to separate the effects of exploitation, habitat, time of day and season. Ichthyofaunal communities differed significantly between protected and exploited sites, which is likely a result of differential fishing pressure. Abundance and size of roman Chrysoblephus laticeps, the dominant species of the local linefishery, were significantly lower at exploited sites. Non-target species with considerable dietary overlap with roman were significantly less abundant inside the MPA, probably due to interspecific competition, whereas species whose diets differed to that of roman were more abundant at protected sites. The results show that fishing can have an influence on the composition of target and non-target species and that these effects need to be considered in fisheries management and conservation planning.

Effects of fishing on a temperate reef community in South Africa 2: benthic invertebrates and algae

“…The higher abundance of roman at protected sites may account for the lower crinoidea abundance there as they are the main food source for roman (Buxton 1984, AG unpublished data). Götz et al (2009) also found higher abundances of strepie Sarpa salpa, blacktail Diplodus hottentotus and steentjie Spondyliosoma emarginatum at protected sites. It is likely that the lower algae abundance found at those sites is a result of the higher abundances of these species, which are partially herbivorous (i.e.…”

“…Here, we attempted to overcome these limitations by interpreting the results from a larger study by considering the key components of the reef ecosystem, i.e. invertebrates and algae and fish (Götz et al 2009). At Goukamma, fishing was identified as the single-most important factor determining fish abundance (Götz et al 2009).…”

“…invertebrates and algae and fish (Götz et al 2009). At Goukamma, fishing was identified as the single-most important factor determining fish abundance (Götz et al 2009). The dominant sparid, roman Chrysoblephus laticeps, was the main target species of the subtidal-reef fishery in the study area and was found in lower abundances at exploited sites.…”

“…This small MPA (40 km 2 ) harbours a number of endemic commercially exploited reef fish species (Emanuel et al 1992, Turpie et al 2000. Götz et al (2009) evaluated the effects of fishing on the ichthyofaunal community in the Goukamma area. This investigation complements that study by examining the effects of fishing on the abundance of benthic organisms.…”

Reviewing evidence of marine ecosystem change off South Africa

“…Dyer 1995, Punt and and environmental effects (van der Lingen et al 2006a, Watermeyer et al 2008. Near Tsitsikamma, fishing on a temperate reef community was found to affect the size and abundance of roman Chrysoblephus laticeps (Götz et al 2009a), the dominant fish species in catches, allowing their competitors to increase and also affecting benthic communities (Götz et al 2009b). Small marine protected areas have been found to benefit resident fish populations like roman that are heavily exploited (Kerwath et al 2008), whereas seasonal or spatial closures can be used for wide-ranging or migratory species (Grantham et al 2008).…”