Thirteen years of Whale Diaries - Report summary

In a previous post, we were trying to answer to the question "Where is the whale?".

It is now time to discuss about the other main question in ecology and conservation "How many?".

Humpback whale super group in the west coast of South Africa, Picture by Chris Fallows.

The bay of Reykjavik is one of the main whale watching areas in Iceland. Our vessels leave the harbour daily with passengers to observe the marine wildlife of Iceland largest bay, with a frequency and consistency that most research centers would envy.

Since many years, Elding research team uses Elding ships as a platform to collect opportunistic data. In this study, we use a long term whale diaries dataset. Whale diaries are short but informative texts that our naturalist guides, experienced marine biologists, write after every tour, giving information about the weather, sea conditions, number of cetaceans of each species observed and their behaviour.

Throught those field notes, we can extract informations about the abundancy of cetacean species through time, describe seasonal patterns, look for correlations between species and try to identify ecological or observational drivers of change.

The dataset consists of whale-watching sightings records collected between 2013 and 2025 in Faxaflói Bay. The extracted data includes date, time of the tour, species sighted and number of individuals sighted. We analysed temporal trend (annual changes in sightings) and seasonal patterns. The data base consisted of 9285 sightings!

In this post, you will find a summary of an analysis done on our whale diary data. The full report will be uploaded on our "Publication" section. The same models have been used for each species to simplify the analysis, but more personnalised models should be done in the future.

To start

Let's first have a overall look at all the tours Elding has done through the years, and what proportion of those tours were successful with at least one good sighting.

The proportion of successful tour has generally been increasing through the year, peaking with a staggering 94.5% success rate in 2025!

Lets see now how the species sightings have been evolving through the year.

Humpback whales

We will start with the star of our tours, the humpback whale.

Over the 13 years, humpback whales have dramatically increased in the bay, with a growth rate of almost 22% per year. Going from less than 0.25 humpback whale per tour to almost 3 per tour. From less than 10% chance of sighting success, to see a humpback whale during a tour, to over 70%.

Let's also look at the evolution of humpback whale sightings per month.

Humpback whales are not only seen more frequently but their seasonal distribution has shifted. In early years, sightings were mainly between March and August. From 2021 onward, sightings are almost all year long, with humpback whales visiting our bay even in the coldest months. The abundance is still much higher in the summer, but a few individuals stay around the islands near Reykjavík in the winter.

For humpback whales, years have a stronger impact on the likelihood of a successful sighting than the season. The year is a better factor than season to see a change in humbpback whale abundance. The peak months have changed through time. Most humpbacks were seen around March and April in early years. That period of sightings extended to all year long and has a peak around June-July.

Minke whale

Minke whales sightings are stable through years with no statistically significative change.

Minke whales have a very clear seasonal pattern, coming in Iceland generally from March to October, with recently some sightings around the end of the year.

White beaked dolphin

This graph shows us a slight but consistent decrease of white beaked dolphin sightings throught the years. Every year between 2013 and 2025, we have a 3.31% decrease.

White beaked dolphins are in Iceland all year long, so it is not surprising to not observe any strong seasonal pattern here.

It is interesting to see that a lot of white beaked dolphins are seen in the bay around the same period of the year, in March. Most of the super pods we have observed, with over a hundred individuals joining together, were seen in March, in February in 2013 and more recently in April.

Harbour porpoise

Same for harbour porpoises, the sightings have been steadily been decreasing (-9.06% per year).

Same than for the white beaked dolphins, we don't see any clear, particular seasonal effect on harbour porpoises. Lots of them were seen in early years between April and June.

Orca and fin whales

Less frequent species like orcas and fin whales also have seen their sighting probability change through years. Orcas are less common with a -12.84% decrease per year. Fin whales, the second biggest animal on the planet, are much more likely to enter the bay with an increase of 37.46% per year since 2013.

How does the occurences vary through time

Minke whales follow a strict seasonality and are mainly seen in the summer (April to September), with season having a higher impact on likelihood of observing them than the year. The season is a better factor than year to see a change in minke whale abundance.

Conclusion

The increase in humpback whale sightings is consistent with broader North Atlantic recovery trends and may reflect population growth. The concurrent decline in toothed whales could indicate ecological shifts, although observational bias cannot be excluded. We might spend more time with humpback whales, the most popular whales, easier to watch and enjoy by our passengers, so we have less time left to encounter other smaller species.

Monitoring implications

Our data has a bias. We do not do random transects, we go where we think the whales are and stay longer with the ones that are the most entertaining for our passengers, which are often the humpback whales. However, the dataset reveals changes in the cetacean dynamics in Faxaflói Bay. Combined with environmental data would help understand those changes. Integrating opportunistic data with standardised surveys would improve knowledge and robustness on touristic areas, allowing to adapt the conservation measures.

Find the full report here!

Miquel Pons