Aspects of the ecology of selected offshore linefish species in the South Eastern Cape

Stocks of a number of linefish species in South Africa have collapsed. Constant overfishing has severe effects on the state and recovery of fish stocks, especially those of territorial reef fish species. Marine reserves have been advocated as the most suitable tool for the management of such species, and their establishment requires information on abundance, distribution, movement patterns and mobility of target species. This project will contribute to work recently done on the movement patterns of Red Roman (Chrysoblephus laticeps, a reef dwelling fish species) in the Goukamma Marine Reserve, Southern Cape, South Africa. Using acoustic telemetry, this project will test the assumption that Red Roman will remain on an isolated reef after being relocated, as a preliminary means to assess the feasibility of relocating reef fishes to newly closed areas to artificially enhance local stocks. Assessing the effectiveness of a reserve requires knowledge of the state of the ecosystem prior to reserve establishment. This project will provide ‘before’ information on the state of the ecosystem in an area in Plettenberg Bay identified for protection, for comparison with results obtained after area closure. This project is partly a continuation of the work recently completed by Kyle Smith (MSc Thesis, formerly of the O.R.C.A. Foundation) in the area, and will serve to initiate a long-term monitoring program to measure ecological indicators, to monitor the marine ecosystem health of Plettenberg Bay. The project will provide information on the use of SCUBA-based underwater visual census surveys and fishery-independent catch-per-unit-effort research angling surveys, as well as tag-recapture and tag-resighting methods for estimating abundance of reef species important to the linefishery.

The first objective of the project will be to estimate abundance, and measure ecological indicators (species diversity, species relative abundance and length-frequency distributions) of fishery important reef fishes at each of the three locations (Tsitsikamma National Park, an area in Plettenberg Bay identified for closure and an area within the Bay to remain unprotected), and to compare these population parameters among the three sites. The second objective is to determine whether Red Roman is able to return to its home range after relocation to a nearby isolated reef. The project will also compare results obtained from tag-recapture and tag-resighting experiments, those from underwater census and fishery surveys, and those from transect and point count underwater census methods, to determine the most suitable methods for estimating abundance of selected suprabenthic reef fishes.

Assessment of the feasibility of stock enhancement of dusky kob Argyrosomus japonicus

At present the spawner biomass of dusky kob is sitting at between 1 and 4.5% of pristine, the fishery has collapsed and the fish is listed as vulnerable in South Africa. The traditional management procedures that are in place do not seem to be working effectively to facilitate the recovery of the species, as the stocks are still declining. Alternative measures need to be investigated to try to restore the dusky kob stocks to original levels so that it may be fished on a productive and sustainable level, before it is too late.

Stock enhancement is a management tool that is being used in several countries on a wide variety of fish including closely related species. It is presently being investigated on the same species in Australia but is also in its very early stages. Stock enhancement of marine fish involves the spawning and rearing of larval fish to their juvenile stage and the release of these juvenile fish into the wild to augment depleted natural populations.

This project will assess the feasibility of stock enhancement of dusky kob in South Africa as well as investigate the possible risks involved in stock enhancement and methods of minimising these dangers. The study involves reviewing current management, as well as modelling the effects of stocking. Suitable estuaries for stocking will be identified based on their current ichthyofaunal composition. Funding options for stock enhancement in South Africa are being investigated and a willingness-to-pay survey is to be conducted among the various user groups based on a user-pays principal.  Tagging studies will be undertaken to assess suitable post release monitoring strategies which are an important aspect of stock enhancement.

This study is the first of its kind in South Africa and will hopefully lead the way to recovering our depleted fish stocks.

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