When you study wild populations there is generally two main simple questions that need to be answered:
- How many animals in the population?
- Where are they living?
Those surprisingly simple questions are essential to the conservation of the wild ecosystem, but they are difficult to answer.
For the first question, it would be very difficult to manually count one by one the individuals in a population, even more when those animals stay most of their time under the surface. So, scientist imagined ingenious ways to estimate the population, using photo-identification, statistics and mathematical models.
The second question is frequently asked by passengers on the whale-watching boats that are eager to see the whales. Our answer is often that we don’t know exactly. Those beautiful marine mammals are free and living in their natural environment. They move in and out of the bay, changing from an area to another following the fish or travelling. Yet we do have a few areas where we have been lucky many times in the past that we like to explore in search of cetaceans.
Since 2013, we bring an iPad onboard of one of our whale-watching boats and with spotter pro take information on the localisation and behaviour of the animals. We use it to register every sighting of megafauna that we have including all the cetacean species and basking sharks. Thanks to this information we could produce interesting maps about where the animals are. Of course, those maps have limitations. The whale-watching boats are not doing random transects in the bay. The boats go where the animals were seen previously, trying to optimise the chance to see whales as much as possible, which creates bias. It would be interesting in the future to put those maps in relation with effort maps, showing where the boats spent most of their search time.
First, we can have a look to this interactive map showing the localisation of all the sightings made from the 2013/07/09 until 2022/03/03.
This first map shows us where all the sightings are done, but they are so many that its not easy to read it! We then created another interactive map with the total number of individuals seen in each area.
This map shows that one area in particular is very busy and full of animals. The fact that this area is right in front of Reykjavik might be a result of the bias mentioned a bit earlier. We leave from Reykjavik and have logically more chances to cross animals in this area than for example in the south of the bay near Keflavik where we rarely go. It is still interesting to see how dense this area is, and it would be good to look in depth the environmental and geographical variables that might explain it.
Also, all species are mixed in those maps, hiding the information of the specific localisation of each species.
Let’s see a few heat maps, showing the density of sighting of the four main species of Faxafloí. In those maps, the colour intensity increases with the density of sightings, going from a pale light colour for the low density to a bright red colour for the high density.
Density of sightings for (a) white-beaked dolphins, (b) humpback whales, (c) minke whales and (d) harbour porpoises between 2013 and 2022 in Faxafloí
From those four maps, we can observe that the species share a similar hot spot in red, maybe an area that is richer in food. Harbour porpoises wear their name well with more presence than other species in closer areas from the harbour. They also seem to be often seen slightly more in the south of that hot spot than the other species. Minke whales seem to have the most restrained area. They can be quite shy animals so it is not that surprising to see that they are not very bold explorers. On the contrary, humpback whales who are often considered to be quite a dominant species seem to spread more, with many sightings made further north and south than the main area but also many times very close of Reykjavik. White-beaked dolphins seem to spread more than minke whales and harbour porpoises but less than humpback whales.
It is exciting to see where those species are distributed in the bay, it would be even more informative and interesting to understand which factors explain this distribution.
To be continued…
By Miquel Pons