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Every year between May and July enormous shoals of the sardine Sardinops sagax give a splendid show as they migrate off the coasts of South Africa, performing their Sardine Run. They are subjected to relentless attack by predators of all kinds –sharks, dolphins, sea lions, whales, birds, fishermen. Although well known to the general public, this wholesale migration is still not well understood scientifically. IRD specialists and their research partners( 1) examined the different hypotheses put forward to explain the event. Is it a relict inherited behaviour, stemming from the Last Ice Age, when the sardine lived further to the North? This would represent an annual return of the fish to the site where they themselves were hatched to spawn, by a long journey that continues to the present day. Or, as another hypothesis suggests, did a shoal once stray from its habitual seasonal migration route? Its descendants would have proliferated year by year and built up the present Sardine Run. The research opens ways towards improved understanding of this extraordinary mass behaviour.
The loss of biodiversity will continue in the 21st Century. Global-scale extinctions will increase strongly, the average species abundance( 1) will decline and their distribution will be disturbed. Scientists thought until recently that the complexity of biodiversity made it unfeasible to predict future trends. Now, however, like the climatologists, life science specialists are able to predict future situations. A group of international experts( 2), including several IRD researchers, have just published a compilation of global-scale quantitative scenarios depicting possible changes in biodiversity. In spite of a degree of uncertainty in the models elaborated, the possible trends converge. If the processes of human and economic development do not change radically, the Earth is heading for disaster. With changes in land use, in climate and overexploitation of natural resources, humans activities are central to the major threats to biodiversity. The scenarios developed nevertheless point to possible lines of action.
The once splendid colours are dulled, algae growing everywhere and the biodiversity is impoverished Who would believe that this forlorn picture depicts Réunion Island’s coral reef, known for its beauty and rich living communities? Since the 1980s, these corals have lost much of their splendour, victims of high visitor pressure, waste water outflow and runoff, coastline development and deforestation which provokes ground erosion. Ten years’ monitoring of the coral reef has led to a report for the Réunion Marine Nature Reserve authority, co-published by an IRD research scientist( 1). It gives a stark warning. Water quality in the lagoon is deteriorating and the corals are dying. The authors recommend restricted-access measures for the reef, with the aid for example of waymarked pathways, special wildlife refuge areas and intensified surveillance of fishing and leisure activities. Such an approach is vital if human activities and ecosystem conservation, all essential for the island’s economic development, are to be reconciled.
The Peruvian seine fishery 1, the world’s largest fleet deployed for one particular species, anchovy, has a capacity three times that needed for optimal exploitation of the stock. Research scientists from IMARPE 2 and the IRD point to this imbalance, a real “time bomb” for the Peruvian fishing industry. Anchovy naturally undergo periods of high and low abundance, pseudo-cycles, probably caused by climate oscillations in the Pacific. Peruvian waters are currently producing exceptional quantities. However, fisheries scientists 3 warn that this resource could diminish drastically in only a matter of years. To avoid stock collapse, as happened during the 1970s crisis, the Peruvian government followed scientists’ recommendations and established an individual fishing quota. This is already proving its worth.
There is not enough oxygen in the ocean. Over 50 years, climate change and human activities have been causing the expansion of oxygen minimum zones (OMZ). These now cover almost 10 % of the world’s ocean and exert a strong constraint on the vertical habitat for marine pelagic organisms. To monitor how these zones change, IRD and their partners 1 have developed an innovatory acoustic method. It is straightforward to put into operation and yields data on the upper limit of these anoxic zones 2 every second. Applying the technique off Peru, the team established maps about 100 000 times more detailed than those obtained with standard hydrological profiles. Scientists can thus produce very high-resolution estimates of the available surface habitat for fish. This research opens great prospects especially for fisheries management.