Why have we seen declines in the populations of many seabirds in recent years?
Most of the declines in seabird populations that we’ve witnessed in the last decades can be attributed to two major causes:
1) the incidental bycatch in longline, gillnet and trawl fisheries (estimated to affect around 40 % of all threatened seabird species, and primarily responsible for the steep decline of many albatross populations)
2) predation by invasive alien species (such as rats, mice and cats in islands), affecting ca. 75% of all threatened seabirds.
However, seabirds face many other threats, both at-sea and in the breeding colonies: overfishing and/or inappropriate spatial management of fisheries (a well-known example is the population decline of the African penguin, after the depletion of sardines and anchovies through commercial exploitation), pollution, hunting and trapping, human disturbance, infrastructural development on breeding areas, energy production, mining and climate change (through sea-level rise, changes in prey distribution and in wind patterns).
How widespread are these declines in seabird populations – are they occurring in just a few species, or are seabirds as a whole under threat?
Seabirds are the most threatened bird group and their status has deteriorated faster over recent decades. Almost one third of all species are currently threatened (i.e., classified as Critically Endangered, Endangered or Vulnerable in the IUCN Red List), and an additional 12% are near threatened. The declines are widespread across regions, but the most threatened groups are the albatrosses (all the 22 species threatened or near-threatened), the penguins (15 out of 18) and the gadfly petrels (30 out of 39).
How important are seabirds to the overall health of the oceans?
As top marine predators, seabirds play a key role in oceanic ecosystems. They consume ca.70 million tonnes of food every year, an amount that is similar to the global fisheries landings. Therefore, seabirds are important regulators of the marine environment via top-down effects. The major consumers are, by far, krill predators such as the macaroni penguin.
read more: blogs.biomedcentral.com/on-biology/2016/10/10/seabird-conservation-qa-maria-dias/
photo: JJ Harrison