Harbour porpoises off Texel island, new study


This video is called Harbour porpoise (Phocoena phocoena).

From the Journal of Sea Research, 17 July 2015:

Going with the flow: Tidal influence on the occurrence of the harbour porpoise (Phocoena phocoena) in the Marsdiep area, The Netherlands

Highlights

Porpoise presence in the Marsdiep is studied as a function of tide related covariates.

• Sighting rate is best described by salinity with highest rate at high salinity level.

• This indicates that porpoises enter the area in bodies of saline North Sea water.

• Other studies have shown a higher fish abundance during high tide.

• Therefore, tidal influx of porpoises is most likely related to prey availability.

Abstract

One of the most important factors explaining the distribution and behaviour of coastal marine mammals are tides. Tidal forces drive a large number of primary and secondary processes, such as changes in water depth, salinity, temperature, current velocity and direction. Unravelling which tidal process is the most influential for a certain species is often challenging, due to a lack of observations of all tide related covariates, strong correlation between them, and the elusive nature of most marine organisms which often hampers their detection.

In the Marsdiep area, a tidal inlet between the North Sea and the Dutch Wadden Sea, the presence of harbour porpoises (Phocoena phocoena) was studied as a function of tide related covariates. Observations were carried out in early spring from a ferry crossing the inlet on a half hourly basis. Environmental and sightings data were collected by one observer, while an on-board Acoustic Doppler Current Profiler (ADCP) and temperature sensor continuously recorded current velocity profiles and temperature, respectively. Sea surface temperature and salinity were measured at a nearby jetty. Sightings (n = 134) were linked to tidal elevation, geographical position, local depth-averaged current velocity, water temperature (with and without trend correction) and salinity.

Variation in sighting rate was best described by salinity, with highest sighting rate at high levels of salinity (> 30 g kg− 1), indicating that porpoises enter the area in bodies of (more saline) North Sea water. Second best variable was time of day, with the highest sighting rate early morning, and decreasing during the day. However, surveys in the morning happened to coincide more often with high water and hence, the apparent time of day effect could be due to collinearity. Most porpoises were present in the northern part of the Marsdiep, particularly during high tide.

Tide dependent sighting rates confirmed that porpoises reside in the North Sea, and enter the western Wadden Sea during the flood and leave during ebb. This tidal influx is most likely related to prey availability, which corresponds to other recent studies in this area showing higher fish abundance during high tide. Documenting information on tide related patterns could be used in practice, when e.g. planning anthropogenic activities or assessing critical habitats for this species.

22 thoughts on “Harbour porpoises off Texel island, new study

  1. Pingback: Rottumerplaat desert island birds, wardens’ report | Dear Kitty. Some blog

  2. Pingback: Seal eats cod, video | Dear Kitty. Some blog

  3. Pingback: Common smoothhound shark on Texel island beach | Dear Kitty. Some blog

  4. Pingback: Vlieland fungi and birds | Dear Kitty. Some blog

  5. Pingback: Mudskipper fish of Kuwait | Dear Kitty. Some blog

  6. Pingback: Flowers and eider ducks of Vlieland island | Dear Kitty. Some blog

  7. Pingback: Pilot whales asphyxiated by eating flatfish | Dear Kitty. Some blog

  8. Pingback: Harbour porpoises, what do they eat? | Dear Kitty. Some blog

  9. Pingback: Harbour porpoises in Scotland, video | Dear Kitty. Some blog

  10. Pingback: Dead minke whale beaches on desert island | Dear Kitty. Some blog

  11. Pingback: Belgium’s favourite marine animals | Dear Kitty. Some blog

  12. Pingback: Sperm whales beach in Germany yet again | Dear Kitty. Some blog

  13. Pingback: Will beached porpoise Nena survive? | Dear Kitty. Some blog

  14. Pingback: Beached young porpoise Nena can swim again | Dear Kitty. Some blog

  15. Pingback: Texel sanderlings, turnstones and oystercatchers | Dear Kitty. Some blog

  16. Pingback: Harbour porpoise beached on Texel, video | Dear Kitty. Some blog

  17. Pingback: Beached porpoise brought to rehab, video | Dear Kitty. Some blog

  18. Pingback: Beached porpoise Sven can swim again | Dear Kitty. Some blog

  19. Pingback: Wounded harbour porpoise freed after recovery | Dear Kitty. Some blog

  20. Pingback: Beached porpoise Nena can catch fish again | Dear Kitty. Some blog

  21. Pingback: Young shark saved by seal rehabilitation workers | Dear Kitty. Some blog

  22. Pingback: Beached young harbour porpoises in rehab, video | Dear Kitty. Some blog

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.