Despite the location and easy accessibility of Berlengas, its seabird populations are still poorly studied and information is still required for the effective conservation of Cory’s shearwater (Calonectris borealis), Band-rumped storm-petrel (Hydrobates castro), European shag (Phalacrocorax aristotelis) and Common murre (Uria aalge). Many information gaps must be filled on the ecology, population dynamics, effect of predation by black rat and Yellow-legged gulls, foraging areas, interactions with boats and fishing gears and impacts caused by other human activities.
The accidental bycatch of seabirds by fishing activities is still largely unknown in Portugal. Pioneering studies in our country found that gillnets, longlines and purse seines have the greatest impact on seabird populations. The most susceptible species are those that dive to feed on small fish or cephalopods, such as the Common murre, the Cory’s shearwater or the European shag. As an example, the population of Common murre in Berlengas has decreased dramatically from 6000 pairs in 1939 to just one breeding pair observed in 2002. It is widely known that the Common murre is very susceptible to drown because they get entangled in gillnets while looking for food. Therefore, it is a priority to identify birds foraging areas in order to understand the real impact of fishing gears on these populations and develop solutions. In the LIFE Berlengas project several mitigation technologies are due to be tested in cooperation with local fishermen.
As in most of the world’s islands, the black rat was accidentally brought to Berlengas and constitutes a serious threat to the conservation of seabirds. The black rat is a known predator of Cory’s shearwater nestlings and adults of other seabirds on several islands around the world, and there is strong evidence of its negative impacts in Berlenga Island. It is very likely that the small Band-rumped storm-petrel is absent from Berlenga Island due to the presence of black rats. Common rabbits were also introduced in Berlengas and they have a considerable impact on the island native flora.