Cd Buxton

Global conservation outcomes depend on marine protected areas with five key features

In line with global targets agreed under the Convention on Biological Diversity, the number of marine protected areas (MPAs) is increasing rapidly, yet socio-economic benefits generated by MPAs remain difficult to predict and under debate. MPAs often fail to reach their full potential as a consequence of factors such as illegal harvesting, regulations that legally allow detrimental harvesting, or emigration of animals outside boundaries because of continuous habitat or inadequate size of reserve. Here we show that the conservation benefits of 87 MPAs investigated worldwide increase exponentially with the accumulation of five key features: no take, well enforced, old (>10 years), large (>100 km2), and isolated by deep water or sand. Using effective MPAs with four or five key features as an unfished standard, comparisons of underwater survey data from effective MPAs with predictions based on survey data from fished coasts indicate that total fish biomass has declined about two-thirds from historical baselines as a result of fishing. Effective MPAs also had twice as many large (>250 mm total length) fish species per transect, five times more large fish biomass, and fourteen times more shark biomass than fished areas. Most (59%) of the MPAs studied had only one or two key features and were not ecologically distinguishable from fished sites. Our results show that global conservation targets based on area alone will not optimize protection of marine biodiversity. More emphasis is needed on better MPA design, durable management and compliance to ensure that MPAs achieve their desired conservation value.

Life-history changes in exploited reef fishes on the east coast of South Africa

SynopsisThe impact of exploitation on various life-history characteristics of two sex changing, reef-dwelling sparid species was examined by comparing populations protected in a large marine reserve with those adjacent to the reserve. Like other sparids, Chrysoblephus laticeps and C. cristiceps grow slowly and are long lived, reaching ages of 17 and 21 years, respectively. No significant differences in the growth rate of C. laticeps were measured, but growth in C. cristiceps was significantly slower in the exploited population. Observed data showed that sex ratios outside the marine reserve were skewed towards the females, a result of size selective exploitation. Size at sex change was also significantly smaller for C. cristiceps in the exploited area, but not so for C. laticeps. This difference between the species was explained as a function of the size at recruitment into the fishery and the degree of protection afforded both large females and male fish. Considering the possibility that reproduction could be impaired as a result of changes in population structure, the tactic of protection through marine reserves is supported as a hedge against recruitment failure.

Abundance and distribution patterns of three temperate reef fishes (Teleostei:Sparidae) in exploited and unexploited areas off the southern Cape coast

(1) Visual underwater census was used to determine the abundance and size structure of three conspicuous marine reef fish species, on the south-east Cape coast in 1984-86. Sites inside the Tsitsikamma Coastal National Park and outside the reserve at Cape Recife were compared to evaluate the effectiveness of the reserve as a management option for the fish. (2) Three sparids were studied: Chrysoblephus laticeps Cuvier, C. cristiceps Cuvier and Petrus rupestris Valenciennes. (3) Transect techniques suggested that point counts were best suited for mobile species and line counts best suited for more sedentary species that could hide within the reef. (4) Distribution within an area was correlated with depth and substratum relief, both factors reflecting feeding and habitat preferences of the fish. Fewer fish were found in shallow water and on flat reefs. (5) During cold upwelling, fish moved away from the study area, presumably following warmer water. Seasonal differences were observed in the abundance of C. laticeps; abundance was greatest in summer. (6) Sampling showed that the fish were significantly more abundant within the reserve, that there were more of the larger size-classes offish and that the maximum size offish was greater than outside the reserve. (7) The data suggested that the reserve is providing effective protection for species vulnerable to line-fishing.

The application of yield-per-recruit models to two South African sparid reef species, with special consideration to sex change

Abstract Yield-per-recruit models were applied to Chrysoblephus laticeps and Chrysoblephus cristiceps , both of which are important to the line-fishery industry in South Africa. Sex change and slow growth were investigated, particularly with respect to the ratio of males to the total number of mature fish in the population. Predictions based on the yield-per-recruit and spawner biomass-per-recruit models were viewed with caution owing to the rapid decline in the number of survivors past the age of recruitment, and their failure to take into account the effects of sex change on the reproductive potential of the population. Model predictions correlated well with observations that indicated a relationship between population structure and the level of exploitation. Considering the options for the management of these and similar reef fishes, the tactic of protection through marine reserves is supported.

The growth ofOreochromis andersonii (Pisces: Cichlidae) from the Okavango Delta, Botswana, and a comparison of the scale and otolith methods of ageing

SynopsisOtoliths and scales were used for age and growth determination ofOreochromis andersonii from the Okavango Delta, Botswana. Marginal increment analysis showed that an annulus was formed in both the scales and otoliths during the dry summer period. Using scales, the growth ofO. andersonii was described by Lt = 285.27(1-e-0.26(t+2.02)) mm SL and using otoliths by the equation Lt = 267.48(1-e-0.25(t+2.18)) mm SL. Maximum age estimates of 10 years using scales and 13 years using otoliths were obtained and the growth curves were significantly different (p < 0.01). Age estimation using scales tended to over-emphasise growth inO. andersonii resulting in larger predicted lengths-at-age. For this reason, otoliths are considered to be more reliable and suitable than scales in determining the age and growth of this species.

Ichthyoplankton distribution and dispersal in the Tsitsikamma National Park marine reserve, South Africa

The nature of ichthyoplankton distribution within the Tsitsikamma National Park marine reserve was investigated in an attempt to evaluate the potential for export of larvae of commercially and recreationally important reef species to adjacent, exploited areas. Monthly, inshore ichthyoplankton samples were taken using Bongo nets over an 18-month period. Sampling sites were located over areas of high-profile reef and sand, Current-meter measurements of the area were used to determine current velocity, direction and reversal periodicity. Statistical analysis of the data was performed independently for larvae from four families: Blenniidae, Gobiesocidae, Sparidae and Engraulidae. Results suggested that blenniid and gobiesocid larvae practised active position retention throughout their pelagic phase, while this feature was less defined in sparid and engraulid larval distribution. Using larval distribution and current-meter information, projected dispersal distances for spa rid larvae, the family containing the...

Aspects of the recreational ski boat fishery off the Eastern Cape, South Africa

The number of anglers and boats participating in the Eastern Cape ski-boat line fishery is high, and at the Port Elizabeth Deep-Sea Angling Club effort increased by a factor of 1,6 between 1975 and 1982. Ski-boat fishing is principally a weekend recreational activity, and estimated annual landings are only 37 per cent of commercial line-fish catches in the study area. It is, however, considered to be economically important in terms of equipment outlay (± R17 million) and running expenses (± Rl,65 million). Sampling of catches in 1979 and 1980 showed that of 79 recorded species only 17 were important. Ski-boaters compete with commercial line fishermen for target species, but there is little overlap with the trawl fishery. The paucity of historical line-fish catch records, the multispecies nature and the seasonality of the fishery make management problematical.

Catch and effort of the shore and skiboat linefisheries along the South African Eastern Cape coast

An assessment of catch and effort in the Eastern Cape shore and skiboat linefisheries was undertaken between 1994 and 1996 by means of roving creel and access point surveys. Catch-and-effort data were obtained from direct observation of 3 273 shore-fishers, 172 recreational and 223 commercial skiboat outings. Total effort in the region was high at 903 186 fisher-days year−1 in the shore fishery and 64 266 and 24 357 fisher-days year−1 in the commercial and recreational skiboat sectors respectively. The fisheries are multispecies in nature. The shore fishery consisted of 66 species, the recreational skiboat fishery 44 species and the commercial skiboat fishery 48 species. Just 10 species accounted for 75, 83 and 90% of the catch of the shore, recreational and commercial skiboat fishery respectively. The average catch per unit effort (cpue) was low in all sectors, 1.15 kg fisher−1 day−1 in the shorefishery, 9.4 kg fisher−1 day−1 in the recreational skiboat fishery and 21.5 kg fisher−1 day−1 in the commercial skiboat fishery. Catch data showed that professional and club anglers are more successful fishers. Comparisons with historic records for Port Elizabeth revealed that the cpue in the shore fishery had declined markedly, whereas the total effort increase was negligible (0.1%). In addition, the species composition of the fishery has changed.

When is spillover from marine reserves likely to benefit fisheries

The net movement of individuals from marine reserves (also known as no-take marine protected areas) to the remaining fishing grounds is known as spillover and is frequently used to promote reserves to fishers on the grounds that it will benefit fisheries. Here we consider how mismanaged a fishery must be before spillover from a reserve is able to provide a net benefit for a fishery. For our model fishery, density of the species being harvested becomes higher in the reserve than in the fished area but the reduction in the density and yield of the fished area was such that the net effect of the closure was negative, except when the fishery was mismanaged. The extent to which effort had to exceed traditional management targets before reserves led to a spillover benefit varied with rates of growth and movement of the model species. In general, for well-managed fisheries, the loss of yield from the use of reserves was less for species with greater movement and slower growth. The spillover benefit became more pronounced with increasing mis-management of the stocks remaining available to the fishery. This model-based result is consistent with the literature of field-based research where a spillover benefit from reserves has only been detected when the fishery is highly depleted, often where traditional fisheries management controls are absent. We conclude that reserves in jurisdictions with well-managed fisheries are unlikely to provide a net spillover benefit.

The subtidal gully fish community of the Eastern Cape and the role of this habitat as a nursery area

The fish fauna of rocky subtidal gullies between Chelsea Point and Skoenmakerskop (South Africa) was sampled between October 1985 and September 1986 using rotenone to investigate the species composition and the importance of this habitat as a nursery area for marine linefish species, A total of 59 species belonging to 28 families were collected. The majority of these were cryptiC fishes such as Clinidae and Cheilodactylidae. Sparldae and Serranidae were represented by juveniles of inshore species. The findings are discussed in relation to previous studies of intertidal pools in the eastern and western Cape, and it is concluded that shallow rocky inter- and infratidal areas are important nursery areas for numerous inshore fishes, including some species caught by recreational line fishermen. The results from this study suggest that previous intertidal studies have over-emphasized the importance of rock pools as nursery areas.