Aarhus University Seal / Aarhus Universitets segl

What does the seals eat ?

Investigations of harbour seals in Limfjorden and Karup Å,

and their impact on the Karup Å trout stock 

The seals choice of food in Limfjorden and Karup Å

It is essential to look at the seals’ preferred prey species and their level of consumption in order to estimate the seals’ impact on the trout stock. Seal scats are collected from the haul-out sites in the area close to Karup Å (Skive, Sundsøre og Løgstør Bredning). The scats are used to identify species-specific otoliths from fish and for DNA-analysis to ensure that all ingested fish species are detected. For otoliths to be present in the scats, seals need to eat the head of the fish, and this is not always the case. Furthermore, the seal tissue is used for stable amino acid analysis. With this technique, we identify species specific combinations of amino acid composition and compare these signatures from potential prey to estimate how much they each contribute to the seals’ diet. Three regulated seals from Karup Å have been retrieved, all adult males, two of the age of 10 and one being 25 years old. The stomach contents were analyzed and one otolith from eel and one from trout was found, together with the remains of a signal crayfish and two trout.

Analyzing stomach content

Photo by Emilie Nicoline Stepien

A fishy fingerprint

An otolith is found in the inner ear, and each species of fish has its own unique shape of otolith, just like the human fingerprint. It is therefore possible to determine which species a seal has eaten, by looking at what kind of otoliths are found in the stomach of the seal. Here we have found two different kind of otoliths in a regulated seal from Karup Å: trout (left) and eel (right), and the remains of a signal crayfish (bottom right). Photo by Emilie Nicoline Stepien.