Harbour Porpoises at last!

This year the Harbour Porpoise Scan 2012 of Stichting Rugvin, my First, was scheduled on Sunday September 9^th. The weather was outstanding and we (one of nine groups) boarded on the luxurious yacht FRIEND-SHIP in the harbour of Marina Roompot  Zeeland, at the National Park of the Oosterschelde. We were heading for the Zeeland Bridge when the first Harbour Porpoise showed just outside of the harbour. Two other porpoises followed quite soon after the first encounter. It seemed to become a spectacular day for counting these cetaceans. The mammals didn’t breach the surface close to us, but near enough to spot the triangle fin rolling through an almost flat water surface.

Harbour Porpoise near the Harbour of Marina Roompot

The next picture shows the route we’ve been taking by ship, though my GPS had problems in tracking a nearby satellite. So the map starts by the flag which is thereby not accurate in pinpointing our starting location. We started more to the left in the harbour at Kamperland.

GPS-log of the route of the FRIEND-SHIP

To ensure the reasons why porpoises are counted, I should tell something about the history of the Harbour Porpoise in the Dutch waters. Counting them is essential to learn about distribution patterns, and the history of the porpoise isn’t all too clear about it.

Sure enough is that it seems that the Harbour Porpoise is making its comeback. Before World War II Harbour Porpoises were abundant and no one really took any ‘real’ interest in them, except for Jan Verwey, a biologist from Den Helder. He described the behaviour of porpoises and their calves, in particular  hunting strategies in shallow water and even sunbathing on the water surface.

The period there after, 1950-1969, is mainly characterized by a lack of information about distribution patterns of these cetaceans. Only rare incidental sightings are reported. Researchers do know that after 1958 Harbour Porpoises were very rare across the Dutch and Belgian coasts.

Ever since the late 1980’s Harbour Porpoises were seen along the Dutch coasts again. Fishermen, bird observers, sailors and tourists started to see more porpoises every year since 1985 - especially in the Southern North Sea area, porpoises were spotted increasingly in numbers. According to scientists there even seems to be a shift in seasonal patterns, whereby Harbour Porpoises migrated from the Northern Wadden Sea area to the Southern North Sea area.

Zeeland Bridge Oosterschelde

It’s not yet clear why this shift from North to South happened, but the main cause could be better foraging grounds in the South than in the North. Food is always a very good motivator to search for new grounds! 

An explosion of porpoise observations in the South of the Netherlands since the 1990’s seems to indicate that the Harbour Porpoise is making its comeback. Nevertheless, we do need to take into account that (1) the birth rate seems to have increased as well, while not as rapid as the shift took place, (2) Shetland populations have decreased in the same period that the Southern populations of porpoises have increased in the Dutch North Sea, (3) it’s still not clear if the food availability in the South is enough to sustain a growing population of cetaceans, and (4) sadly enough, strandings of porpoises are not unusual and even increasing. So are they really making a comeback or is it just keeping up appearances?

Scanning the area in search for Harbour Porpoises
Photograph: Frank Zanderink Stichting Rugvin

We do know that nowadays Harbour Porpoises are common in the National Park of the Oosterschelde in the South of the Netherlands. Only recently, since 2001, researchers dare to speak of a residency. The Oosterschelde really is an important nursery ground for porpoises: calves are born every year in the Park and spotted regularly along the coastline together with their mother. The Harbour Porpoises can be seen year round in the Oosterschelde, even from land observation points at certain ‘hotspots’, like Zierikzee. Stichting Rugvin is conducting in Harbour Porpoise Scans to provide information about distribution patterns in the Oosterschelde over time, and is therefore an important partner in Sea Mammal research in the Netherlands. And I am glad to help out!

Harbour and Grey Seals appear when the low tide sets in

The ‘counting day’ ended in the evening, and we have spotted four Harbour Porpoises with our group. In total 42 Harbour Porpoises were counted of which two were calves, less than the year before when 61 animals were counted. Considering so many strandings of dead porpoises this year, we already feared less animals would show up. If you want to know more about the Harbour Porpoise research, please visit the website of Rugvin.

Literature

Camphuysen CJ & Peet G (2006) Walvissen en dolfijnen in de Noordzee, Fontaine Uitgevers BV 's-Gravenland/Stichting de Noordzee Utrecht.

Camphuysen CJ & Siemensma ML (2011) Conservation plan for the Harbour Porpoise Phocoena phocoena in The Netherlands: towards a favourable conservation status, NIOZ-report 2011-07, Royal Netherlands Institute for Sea Research Texel.

Leopold M (2012) Steeds meer bruinvissen, Natura Magazine, No. 3, Volume 109, 14-16.

Meiniger PL, Witte RH & Graveland J (2003) Zeezoogdieren in de Westerschelde: knelpunten en kansen, Rapport RIKZ/2003.041. Rijksinstituut voor Kust en Zee, Middelburg.