Study of distribution and habit

People at sea see seals often lying in groups along the shore or on tidal flats. For a long time, one used to believe that the seals were strongly bonded to these banks. But when discussions began concerning the establishment of seal reservation boundaries, there was a need for more insight into the actual habit of the seal. With the help of transmitters attached to the seals, our understanding of seals has grown tremendously since the end of the 1990s.

Alterra (now IMARES) studied Dutch seals. The first group of nine seals from 1997 were supplied with transmitters fastened to their heads and released in the Brielse Gat, in the South-Holland delta region. The researchers received lots of new information about the habits of the seals via these transmitters: where they hunt, their primary haul-out places, how far they wander and where to? The transmitters were glued to the skin of the seal and were made to be shed during the following molting period.

Studies have shown that the transmitters and antennae do not disturb the animals.

Within the period that they were followed, all of the seals from the first group swam to the Wadden Sea. Within the second group of released seals, one seal chose the Wadden Sea while the other three remained in the Brielse Gat. After 1998, seals were occasionally released with transmitters to further complete the research data.

The scientists also learned much about the migration habits of seals. The transmitted seals would wander along the entire coast and sometimes cover several hundreds of kilometers within a short period of time. During the study, one seal swam back and forth to England. The results of the study show that seals use a much larger area than what one used to think. Therefore, protecting the seal should not end by the sandbanks were they haul out.

signals from transmitted seals

Even the migration behaviour of seals has become much clearer. The transmitters show that seals can wander along the whole coastline and sometimes travel as much as several hundred kilometres. One seal swam back and forth to England during the study.

In 1998, ten seals from the Wadden Sea where followed through transmitters. These animals provided information concerning their way of life for six months through the transmitters. Although seals are often seen in groups on the sandbanks, it appears that the animals barely attach themselves to a group. Most seals live alone. The study also showed that adult seals need an area measuring a radius of around twenty kilometres for foraging for food. Twenty to thirty kilometres can lie between their rest area and foraging area.