West African coastal nations often lack the necessary legislation or resources to adequately protect their marine resources. These waters have suffered for many years from unsustainable fishing practices, by both foreign and domestic fishers. They experience the highest levels of illegal, unreported and unregulated fishing in the world, which jeopardise West African economies and food security.
Many seabird species are in competition with the fisheries for these diminishing fish stocks, and may be killed by fishing equipment, either accidentally or deliberately. Migratory seabirds connect West African marine ecosystems to distant ecosystems, suggesting that damage to one could affect the health of the other.
The northern gannet (Sula bassana) and Scopoli’s shearwater (Calonectris diomedea) are two such species that migrate to West Africa. Both have populations that live and breed in protected European habitats during the late spring and summer months.
Previous studies of these species’ migration have mainly focused on adult birds, since they are easier to fit with tracking devices. This is the first study to track both adult and juvenile European seabirds as they fly to West Africa in the autumn. Knowledge of juvenile birds is important because they are more vulnerable than adults to food shortages and by-catch.
The researchers tracked the birds by fitting them with miniaturised tags. A total of 37 adult gannets and five juvenile gannets were tagged at their breeding site in France, off the coast of Brittany in June 2010. Forty-three adult and 10 juvenile shearwaters were captured and tagged at various locations in the Mediterranean between July and October 2011.
However, some birds could not be re-caught and some tags did not work. This meant that migratory data were only available for 24 adult and four juvenile gannets and 34 adult and six juvenile shearwaters.
Both gannets and shearwaters used the waters around the west coast of Africa extensively during the winter months (October to March). They were mostly within the Exclusive Economic Zones of Morocco, Western Sahara, Mauritania and Senegal.
The tagging data showed that most gannets actually spent the winter in Europe, but 24 per cent went to Western Africa, including all juveniles. All of the shearwaters travelled through West
Africa with 56 per cent of them staying there all winter. The remaining 44 per cent travelled further south or to the mid-Atlantic.
These findings show that juveniles, not just adults, of these two species depend on threatened marine resources in West African coastal areas.
The study’s authors emphasise that this research does not show that gannets or shear waters are being starved or killed by West African fisheries. However, such threats are real. For example, Mauritanian authorities confiscated eight containers of frozen seabirds (thought to contain tens of thousands of birds, including gannets) destined for shipping to Asia and intended for human consumption in early 2013.
In conclusion, they state that there is an urgent need for improved marine conservation in West African coastal areas. Their findings demonstrate the strong links between European seabirds and African wintering areas, and highlight Europe’s role as a stakeholder in the conservation of African waters, they say.
Source: Gremillet, D., Peron, C., Provost, P. Lescroel, A. (2015). Adult and juvenile European seabirds at risk from marine plundering off West Africa. Biological Conservation 182: 143– 147. DOI:10.1016/j.biocon.201 4.12.001.