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1.
This paper gives an overview of the main living marine resources of Namibia. It focuses on the scientific research conducted during the past decade as input to the management of these resources. The distribution and habitats of the most important harvested species and the main seabird populations are briefly described and discussed. The life histories of the major exploited species are summarized, with emphasis on spatial and temporal spawning patterns, dispersal of early life stages, migration patterns of recruits and adults, and diet, the latter particularly as it relates to potential competition between species. A number of commercially important species, such as the hake Merluccius capensis and M. paradoxus, deep-sea red crab Chaceon maritae, West Coast rock lobster Jasus lalandii, skipjack tuna Katsuwonus pelamis, southern albacore Thunnus alalunga and to a lesser extent Cape horse mackerel Trachurus capensis, southern African sardine Sardinops sagax and Cape anchovy Engraulis capensis, are distributed across national boundaries, requiring regional cooperation in research and management. The history and current status of the major fisheries is discussed. Over the past 30–40 years total annual catches have declined from a peak of around 2 million tons in the late 1960s to less than a million tons in the 1990s. This decline has been due, mainly, to a collapse in the sardine stock in the late 1960s and 1970s, and a reduction in the catches of hake and horse mackerel under a conservative management strategy in the past decade. Changes in the abundance and distribution of commercially important species, as determined by acoustic and trawl surveys and catch-based analytical methods, are presented. The effect of major environmental anomalies on the distribution and abundance of the resources in recent years is discussed. The most dramatic anomaly in recent years was the wide-scale advection of low-oxygen water into the northern Benguela from the Angola Dome in 1994, and the subsequent Benguela Niño of 1995, which appear to have severely impacted the Namibian sardine population and many other resources. The present socio-economic value of the Namibian fishing industry is given together with the broad policy, legislation and formal structures for managing the living marine resources.  相似文献   
2.
An age-structured population model was used to examine the variability of yield created by randomly fluctuating recruitment success in the South African anchovy Engraulis capensis stock. Three different harvesting strategies were examined: (1) constant age-specific pattern of fishing mortality, (2) constant quota with effort limitation and (3) annual quota adjustments by means of an F msy procedure. Variable recruitment was generated by a stochastic stock-recruit relationship, and mean yields, mean spawner biomasses and probability distributions of yield were calculated at each exploitation level after 150 projections from the population structure of anchovy in 1981. Under conditions of constant fishing mortality, the variability of yield increased continuously as the exploitation rate was increased. The maximum average yield (MAY) is the stochastic equivalent of the maximum sustainable yield (MSY) of deterministic models, but an attempt to sustain this MAY by a constant quota resulted in a very high risk of stock collapse. An Fmsy policy based on pre-season adult biomass resulted in more variable yields than were obtained at the equivalent constant fishing mortality at age. Stability of yield therefore demanded the acceptance of lower average yields than could be attained in the long term by quota adjustment. It was considered that the South African purse-seine industry could not cope with the wide fluctuations of yield necessary to attain MAY. Specific management policies sufficiently robust to withstand both fluctuating recruitment success and the uncertainties in the parameters of working population models would be required.  相似文献   
3.
The Ilha dos Tigres of Angola is the only sandy island off the coast of the 2 000km-long Namib Desert and it remains the least known coastal wetland on a desert coast rich in shorebirds. Two surveys of the Baia dos Tigres region in 1999 and 2001 indicated a rich wetland bird diversity consisting of 25 species, with a total of 11 000 birds, at a density of 33 birds km?1 of beach. We established breeding by three species of seabirds — two cormorants and the great white pelican Pelecanus onocrotalus — and confirmed northward range extensions for two of these species. The region supports seven regionally threatened Red Data birds. Several threatened marine turtles occur at the nearby Cunene River mouth, and given the possibility that turtles and other Red Data birds may breed at Ilha dos Tigres, it is recommended that it should become an integral part of the Iona National Park on the adjacent mainland.  相似文献   
4.
This paper considers the scientific achievements of the Benguela Environment, Fisheries, Interaction and Training (BENEFIT) Programme as reflected in 29 internally evaluated BENEFIT research projects carried out between 1998 and 2007 when the programme ended, and draws a number of important lessons relevant to future regional marine research programmes in the Benguela from the manner in which the projects were initiated and executed. The founding of BENEFIT, its organisational structures, and the way in which the projects were planned, formulated and executed through these structures are outlined. The major findings and other achievements of the research on fish resources, the environment and the linkages between them are discussed under these headings, and in the case of projects on resources, in relation to key questions developed from guidelines in the BENEFIT Science Plan. Based largely on a final evaluation by the programme's International Scientific Advisory Panel, it is concluded that BENEFIT added materially to greater knowledge of the dynamics of key resources in the Benguela, markedly increased the extent of environmental monitoring in the region, and the capacity for future such monitoring, and added significant new insights into key physical, chemical and biological processes of relevance to stock dynamics. BENEFIT's most important achievement in a wider sense was the pioneering development, almost from scratch, of a regional marine research community which, inter alia, was crucial in the development of other regional marine research activities in the Benguela, such as the Benguela Current Large Marine Ecosystem (BCLME) Programme whose primary objective was the creation of a Benguela Current Commission. In this sense, the establishment of the Commission in 2007 to deal with transboundary management of the living resources of the Benguela Current and regional biodiversity issues can be regarded as the greatest single legacy of BENEFIT.  相似文献   
5.
In South Africa, kelp gulls Larus dominicanus first breed when 4 years old. At least 50% of 4-year-olds breed; virtually all older birds breed annually. Most chicks leave natal colonies in the austral autumn and winter, when about 6 months old, and 60% of them may not return until aged 2 or 3 years. One 3-year-old showed signs of defending territory, but birds only attain full adult plumage when aged 4. The plumage of 3-year-olds is similar to that of adults, but the white spots on the outer primaries are less well developed and the secondaries and inner primaries have no white trailing edge. Chicks are dark, whereas birds aged 1 and 2 years gain increasing amounts of pale or white plumage on the face, neck, underparts and tail.  相似文献   
6.
The Cape commercial linefishery, established during the first half of the 19th century, currently consists of about 2 500 vessels (±20 000 crew), which land some 15 500 tons of fish each year. In spite of a long history, a lack of a long-term catch and effort data series has severely hindered the management of the fishery. This paper providcs commercial catch and effort data for three periods during the 20th century: 1897–1906, 1927–1931 and 1986–1998. Trends in catch per unit effort (cpue) were verified with additional data from the inshore trawl-fishery, from fishery-independent surveys and, where possible, stock assessment. According to a Linefish Management Protocol developed for the Linefishery, any stock demonstrating a historical reduction in cpue or catch contribution of more than 75% is to be regarded as overexploited. Evaluations based on present datasets support this arbitrarily determined reference point for cpue, but reveal that catch composition is a poor indicator of stock status and should be used with caution. In spite of technological advances such as the advent of combustion engines, nylon lines. echo-sounders, electronic navigational aids, onboard freezer facilities and larger vessels, declines in catch rate indicative of severe overexploitation (i.e. 75–99%) were observed for many important linefish species during the 20th century. Most of these were higher-trophic-Level species from the warm/temperate East Coast, several of which are also endemic. Life-history characteristics of the vulnerable species (i.e those demonstrating declines in cpue of >75%) include predictable location in time and space (either coastal migrant or resident), longevity (>15 years) and late maturity (relative to maximum age). Apart frorreduced productivity associated with stock depletion, other setbacks, such as ecosystem alteration, loss of genetic diversity and shor-term commercial extinction, are also anticipated. In order to rebuild depleted linefish stocks it is deemed essential to create additional marine reserves, dramatically improve enforcement, develop extensive public awareness programmes and substantially reduce commercial effort.  相似文献   
7.
The relationship between mass and length and the landed mass/whole mass conversion factors for Agulhas sole Austroglossus pectoralis were investigated and compared to the results of an earlier study. Earlier length/mass relationships overestimate the mass of small soles but underestimate that of large soles. The mass conversion factor of the present study also differed from the earlier results.  相似文献   
8.
An eight-year research angling dataset collected between February 1998 and December 2005 in the Tsitsikamma National Park marine protected area (MPA), along the south-eastern Cape coast of South Africa, was examined to provide estimates of important fishery and population parameters for eight important shore-angling species. Five different estimates of natural mortality (M), and the coefficients of variation (CVs) of catch per unit effort (CPUE) and size measurements were calculated. There was no consistency in estimates of M between methods, highlighting the difficulty in obtaining reliable estimates of this parameter for per-recruit assessments. The CVs of CPUE measurements were generally higher than those for size measurements. Estimates obtained for the most abundant species, blacktail Diplodus capensis, with a mean CPUE of 0.252 fish h–1, yielded the lowest CVs for CPUE (0.806) and size (0.130) measurements. Therefore, blacktail is considered the preferred indicator species for making comparisons with estimates obtained for shore-angling fish in exploited areas and other MPAs along the South African coastline. The large inter annual variations in mean CPUE and size for all species indicated that a minimum assessment period of four years is required to obtain reliable estimates.  相似文献   
9.
During the period April 1991–March 1996, 10 entangled Antarctic fur seals Arctocephalus gazella, 28 entangled Subantarctic fur seals A. tropicalis and one entangled southern elephant seal Mirounga leonina were observed at Marion Island, Southern Ocean. Entanglement of fur seals was estimated at between 0.01 and 0.15% of the combined population of both species.  相似文献   
10.
Ichthyological literature gives the distribution of M. scolopax as along the whole coast of West Africa. However, analysis of this literature and the results of trawling surveys in the North-East Atlantic suggest only exceptional occurrences in the tropics. Plankton surveys off N.W. Africa, up to and including 1977, rarely yielded M. scolopax larvae off the coast of the southern Sahara and not at all off Mauritania, though a few specimens were collected after having been swept southwards in the open ocean by the Canary Current. Larvae did occur off northern Mauritania in February 1983. Details of distribution, abundance and length composition of early stages caught during the period January–April 1983 are given. It is concluded that the reproductive range of M. scolopax (as well as that of some other temperate species) extends south of that documented and that its spawning season there may be shorter than in the centre of this species' distribution. The findings are discussed in relation to interannual variation of upwelling intensity and the current system off N.W. Africa.  相似文献   
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