Human activity in the coastal zone is increasing worldwide, including Norway. Aquaculture, kelp harvesting, fisheries, increasing boat and ship traffic present sources of disturbance and pose a variety of potential threats to seabirds.

The importance of seabird habitat

The habitat that seabirds use for foraging during the breeding season is particularly important and worthy of protection, because any deterioration can affect breeding success. International conservation efforts therefore often focus on protection of not only the colonies, but also the nearby foraging habitats at sea. However, in order to protect this at-sea habitat, one first needs to know where it is. GPS-tracking of birds seeking food can help with this task – but it is not possible to track birds from all colonies. A new, but so far rarely used approach is to use tracking data from one or several colonies to predict the foraging areas for another colony. This so-called model transferability could thus help to identify important foraging areas around colonies where tracking is not feasible.

Shags collected data using GPS

European shags (Phalacrocorax aristotelis) breed in many scattered colonies along the entire Norwegian coastline. Hosting more than 35 % of the NE Atlantic population, which is currently declining in other European countries, Norway has a special responsibility for the protection and management of this species. Using 2-10 years of GPS tracking data from five colonies spread along the Norwegian coast, the at-sea habitat breeding shags were using when searching for food around each of the colonies was identified. The data from 1-4 colonies were used to predict the foraging locations around the fifth colony. Model results were then compared with actual tracking data from the fifth colony to test how well the predictions fitted with reality.

Modelling important habitat

European shags from all five colonies used shallow coastal areas (shallower than 50 m) within about 20 km around the colony as their main foraging habitat. In four of the five colonies, foraging locations were strongly associated with the presence of kelp forests. Model transferability was very high when using data from four colonies to predict the habitat around the fifth colony. The study shows that based on a sufficiently large tracking dataset, it is possible to identify important foraging habitat around shag colonies on a fine spatial scale with reasonable precision. These findings help to facilitate much needed management actions for the coastal marine ecosystem that sustains the European shag.

Read the article:

European shags on cliff. Photo © Nina Dehnhard
European shags feed mainly on young age classes of cod fish, especially saithe, which they catch diving down to 60 meters, often in kelp forests. Sand eels (sand lances) ar also part of their diet.
Photo © Nina Dehnhard
Adult European shag. Foto © Nina Dehnhard
An adult European shag weighs between 1,8 and 2,5 kg and can grow up to 78 cm in length.
Photo © Nina Dehnhard

Contact person: Nina Dehnhard, NINA