Southward extension of the reproductive range of Macroramphosus scolopax in the upwelling area off North-West Africa

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.     

Changes in the trophic structure of the southern Benguela before and after the onset of industrial fishing

Despite a human presence in the Benguela region for at least one million years, exploitation of marine resources by European seafarers only began in earnest in the 1400s. Ecopath with Ecosim was used to construct and compare mass-balanced foodweb models of the southern Benguela ecosystem, representing the following eras of human influence: aboriginal (10 000 BP–1651), pre-industrial (1652–1909), industrial (1910–1974) and post-industrial (1975–present). Biomass at higher trophic levels (TLs) decreased over the periods examined, whereas that of sardine and anchovy increased in the early 2000s, reflected by the decline in weighted TL of the community (excluding plankton). Fishing became an important predatory impact, taking over consumption of small pelagics and horse mackerel from declined natural predators such as hake. Harvesting of apex predators such as seals and seabirds during the pre-industrial era meant that the mean TL of the catch declined markedly between the pre-industrial (1900) and industrial (1960) models. Biomass removals by fishing have increased substantially over time. Total biomass, consumption, respiration, production and throughput decreased from the pristine model to 1960 and then increased again in the 2000s, probably influenced by the abnormally high small pelagic biomass in the early 2000s. Three additional alternate scenarios were examined for each of the retrospective models, in particular to explore the effects of removing large fish and forage fish from the system. Although biomasses and consumption of various groups in these scenarios differed from base models, indicators such as TL of the community and piscivore groups, and the diversity indices, were not altered much, suggesting that outputs from such retrospective models in the form of derived, relative indicators, may be more robust than comparisons of absolute flows, although the latter provide supplementary inferences. Although South African fisheries have certainly impacted ecosystem structure since their commencement, these effects are in addition to natural (specifically environmental) forcing that has always been influencing the system. Fishing stress at the ecosystem level and the collapse of small pelagic stocks may lead to a shift toward a bottom-up trophic control mechanism becoming the dominant driver of ecosystem dynamics, increasing the impact of environmental events including climate change. It is thus possible that pristine systems were not as severely affected by environmental anomalies as are modern systems.