Researchers from ORCA and the University of Plymouth have explored common dolphin densities in keys areas covered by ORCA surveys.
The focus for this paper, published in PeerJ – The Journal of Life & Environmental Sciences, was to assess the density of common dolphins in the Bay of Biscay, English Channel and Celtic Sea, using data collected by our volunteers on board our ferry surveys.
The project was launched after concerns were raised over the growing number of stranded common dolphins around the North-East Atlantic and the shift that has been seen in their distribution.
Our research found that the highest densities (density refers to the number of common dolphins sighted per km) of common dolphins were found on the routes between Penzance and the Isles of Scilly and our route crossing the Bay of Biscay.
Interestingly, we saw different density patterns on different routes across the dates studied (2006 to 2017). These differences include:
- The number of common dolphins in the English Channel have increased since 2009
- On our Isles of Scilly route, the number of common dolphins have been stable since 2006
- In the Bay of Biscay, we found that the number of common dolphins peaked in 2013, but reduced up until 2017
The above map shows the densities of common dolphins in different regions. The greener the colour, the lower density (and hence, fewer common dolphins) and the redder the colour the higher the densities (hence, more common dolphins).
One of the key objectives of this paper was to explore the impact of citizen science data collection and establish how it compares to other research. We were delighted that the findings from our report mirror those of designated surveys conducted within these regions by other organisations. This highlights the vital role ORCA’s long term citizen science data collection can play in monitoring cetacean populations and helping to protect them.
We would like to say a huge thank you to all of our amazing volunteers who have dedicated their time to conduct surveys on board ferries to collect this valuable information for us.
Similarly, we would like to extend a huge thank you to our ferry partners who enabled us to conduct our surveys on these routes (Brittany Ferries and Isles of Scilly Travel), which has allowed us to produce this publication.
This is an open access publication and, if you are interested in reading about our findings, they can be found here