Characteristics and value of the Thukela Banks crustacean and linefish fisheries,and the potential impacts of changes in river flow

This study describes the Thukela Banks crustacean and linefish fisheries and investigates the potential impacts of reduced flow from the Thukela River on the value of these fisheries. Data were obtained from published and unpublished material, key informants and government records. The crustacean fishery employs about 300 people, and comprises an inshore and offshore fishery. Inshore catches and effort are strongly seasonal, peaking in April to June. The probability of fishing in any particular month is positively correlated with catch per unit effort. Average overall annual catch (inshore and offshore) was estimated to be in the region of 700 tonnes for 1992–2002 with a gross output of about R36.7 million per annum, and a gross value added (net output) of R13.8 million (1 US$ = R6.40; 2003). Inshore prawns were estimated to contribute R8.5 million of the gross output. The Thukela Banks was estimated to contribute R4.5 million and R35 million (rand value in 2003) to the gross output of the commercial linefishery and boat-based recreational angling fishery respectively. Freshwater reduction scenarios yielded 0.7–11% reductions in prawn catches, which translated into only a 1–2% drop in the annual value of the fishery. The latter was attributed to the fishery's diversity (predominantly the buffering effect of bycatch) and the fact that the stocks of the species targeted by the offshore component are largely independent of flow. Catches and value of the recreational boat-based linefishery were predicted to remain fairly constant irrespective of any changes in flow. The commercial linefishery was the most responsive, with a 20% decline in total catch and 17% value predicted for the most extreme flow reduction scenario.     

Seasonal fluctuations in occurrence of inshore Bryde's whales in Plettenberg Bay,South Africa,with notes on feeding and multispecies associations

Seasonal fluctuations in the occurrence of inshore South African Bryde's whales Balaenoptera edeni were investigated between November 2005 and June 2008. Sighting data were collected in Plettenberg Bay on the south-east coast of South Africa. Bryde's whale occurrence was modelled in relation to the following environmental covariates: sea surface temperature, chlorophyll a concentrations and wind speed. Seasonal increases in encounter rates (sightings per day) were observed during summer and autumn, with a peak in April that corresponded to increased feeding activity and above average aggregation sizes. All three environmental covariates were significant factors in terms of explaining variability in the occurrence of whales. Multispecies associations with common dolphins Delphinus capensis and Cape gannets Morus capensis were most common in summer and autumn, when feeding activity was highest.     

Prioritising species for research,conservation and management: a case study of exploited fish species

Studies that categorise species according to their conservation status often fall short in their implementation by not having taken into account the impacts on, or the response from, those that either benefit from, or exploit, the resource under consideration. This is especially true in multispecies fisheries where personnel and funding limitations often create the dilemma over which species should be the first to receive management and research attention. This study uses a multicriteria decision analysis approach to prioritise 176 South African linefish species on the basis of a number of criteria indicating conservation and socio-economic, including fishery sector, importance. For each species, conservation criteria were: abundance trend, level of knowledge, vulnerability, range, and relative exploitation throughout that range. Sectoral criteria were: total catch, degree of targeting, the number of participants and the economic value of each species. The scores given to each species on the basis of each of these criteria were summed to allow an examination of each fish's importance from the points of view of (i) conservation, (ii) each fishery sector separately and combined, and (iii) the overall combined conservation and sectoral importance. Different weight sets were used in the weighted summation of the scores, and results were examined for sensitivity. The results were reasonably insensitive to these changes in weights. Relative scores within each of the fishery sectors were dominated by two or three species. Consequently, the scores separating the remaining species from each other were small. This meant that, in many cases, even when the rank of species changed by a number of places with a different weight set, the differences in score were slight. On the whole, the top fish included the most important species in each sector and biogeographical region and in terms of conservation. The separate and overall rankings should assist in the development of broadly acceptable management strategies for different fish species.