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From gannets to seagulls, puffins to penguins, all seabirds suffer the same drop in birth rates when the supply of fish drops to less than a third of maximum capacity. That’s the result from an international study ( 1) on the relationships between predators and prey in seven ecosystems around the world, published in the magazine Science and coordinated by Philippe Cury, an IRD researcher. Based on nearly 450 cumulative years of observation, the research team compared the growth in fish supplies and the reproductive patterns ( 2) of 14 species of coastal birds. These birds mainly feed on sardines, anchovies, herring and prawns, all of which are victims of over fishing. Below the critical level of one third of the fish biomass, the birds — and the stability of the entire ecosystem — come under threat.
These studies also provide a reference level for the sustainable management of fisheries, so as to safeguard the bird population, which is often imperilled, and so as to maintain the healthiness of marine environments.
The jumbo squid can grow up to 4 metres in length from the end of its tentacles to its tail. Known scientifically as Dosidicus gigas , it is a voracious predator in the oceans. It feeds on anything that comes its way, a wide range including shrimps, hake, anchovy or even its own kind. This cephalopod * has been proliferating in the waters off Peru, in spite of a decrease in its prey, especially hake owing to overfishing. A Franco-Peruvian research team( 1) took advantage of an innovatory method to produce the first description of the squid’s remarkable feeding strategy, in the journal PlosOne . These scientists explain the boom of the pota , as the Peruvian fishermen call it, both in biological and economic terms.
Up to now the jumbo squid has not only managed to resist excessive exploitation of fishery resources. It has drawn benefit from this trend. Tuna, sea bream, jack mackerel, also less abundant owing to extension of the oxygen minimum zones( 2) which force them further out from the coasts, are giving way to the squid, enabling it to forage nearer the land. A windfall for Peru, which has become the world’s second largest exporter, after China, thanks to squid and anchovy fishing.
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.