Bruinvissen voor de kust bij Den Helder

This paper reports the increase of Harbour Porpoises off Den Helder in recent years, their tidal rhythm, and spring migration. Harbour Porpoises tend to appear each spring near Den Helder (Noord-Holland) when the frequency of sightings off the mainland coast of Zuid-Holland is declining. Animals tend to swim fast and in northerly direction at relatively large distance when the tide is flooding, while the drift (float) south during ebbing. Foraging behavior was most commonly seen when the tide was turning. Sightings in 2010 confirmed that the animals travelled north overall (spring migration), and that numbers rapidly declined shortly after peak-numbers mid March had been recorded.