On the record 2024 shark season

By: Pádraig Whooley, Irish Whale and Dolphin Group (IWDG) Sightings Officer

Note: The IBSG is grateful for our collaboration with the Irish Whale and Dolphin Group (IWDG), who compile reports of shark sightings on their platform for our collective use.

On the week of the All Ireland Whale Watch Day, it seems a little odd to be writing about a species that is neither whale nor even a mammal, but a fish. However, the basking shark is no ordinary fish, and IWDG have always looked on them more like honorary whales, reflecting their size, demeanour, and ecological niche.

Drying off after a morning dip on Red Strand, west Cork last Sunday I watched one of about a dozen sharks breach completely out of the water towards Galley Head and this had pretty much the same impact on me as any breaching humpback might. A simply awesome sight, and a reminder of why IWDG and colleagues at the IBSG (Irish Basking Shark Group) are so passionate about recording sightings of the “Great Fish of the Sun”.

This time last month I wrote about the early shark season and how it was shaping up nicely with 62 unique sightings up to April 12th.  Now on May 21st , this number has rocketed to 304 sightings and counting, long surpassing the record shark year of 2009, when we validated 241 unique records.  The actual number of reports received will always be higher, as sharks are often so close to the shore, that the same animal(s) can be reported by multiple observers. With one good month of this 2024 shark season left, it’s hard to see this number not passing the 400 mark.  So, let’s delve a little deeper into what the data from your sighting reports is telling us.

A good comparator is that record year 2009 as some 15 years and 2,150 shark sightings later, provides us with a useful baseline. But before we start crunching shark numbers, I’ll start by saying that so far 2024 is a record year for reports of all species received by the IWDG sighting scheme with 1,104 records, comprising 9 cetacean species, which compares with just 804 for the same period in 2023; an increase of 37%. You could make the case that the increase in shark records simply reflects this overall increase…. “the rising tide lifts all boats”  so to speak, but the increase in shark sightings between this year and the same period last year is almost three-fold and remember we’re still only two- thirds into our 2024 shark season.

Thus far we’ve only referred to the number of records, however this is a pretty crude measure of shark activity as sharks are rarely alone and when you are filling in reports we always ask for a group size (min/max/best estimate) and the animal count is equally telling.

Year 2009, number sightings: 241, shark count: 642, average no. animals per sighting = 2.6

Year 2024 (to date), number sightings: 303, shark count: 2,574, average no. animals per sighting = 8.5.

So not only have we a lot more records, but it looks like the sharks are here in significantly bigger feeding aggregations, as the mean group size this year so far is > 3 times larger than in 2009.

Figure 1. at a glance illustrates how these 2024 sharks break down by county and despite their being recorded in 10 coastal counties, just two, Cork & Kerry, make up 70% of the total and while this is an interesting soundbite, you have to bear in mind that Co. Cork from the tip of the Beara in the West to Youghal in the east is a big chunk of coastline at just over 200 km.

Interpreting shark sightings never seems as straightforward as whales, who seem in many cases to be creatures of habit, making it easier to spot the trends over the years. Basking sharks are a little trickier, as there often appears to be neither rhyme nor reason to their movements. The 3 years 2021-2023 are very interesting, as they were all reasonably good years for shark sightings: 2021 (161), 2022 (168) & 2023 (156). In each of these years, the first sharks arrived in March, typically along the south coast, they peaked in April and tailed off in May.  By June/July they were all but gone.  This is in contrast with 2009, a little over 10 years earlier, which showed a strong June peak.  In 2010 and 2014 this became a May peak. So perhaps in common with the likes of humpback whales our basking sharks appear to be arriving earlier each year and the data suggests they are now peaking a whole two months earlier.

2024 began like the previous three years, with the first arrivers in March, which were very faithful to the Islands along the west coast, in particular those of North Galway and Mayo.  The leeward sides of which likely provided the only shelter from the prevailing Atlantic weather systems that bashed us this spring, enabling zooplankton to settle and build in sufficient biomass to drawn in these grazers.

Figure 2: Map of 303 validated basking shark sighting records to May 20th 2024.

As with the previous 3 years there was the expected peak in April with 107 sightings along the entire west coast, but the drop off in May never occurred. It was like as Dr. Simon Berrow (IBSG/IWDG) put it, we had a “second wave” which was almost exclusively in the southwest counties of Cork and Kerry. At time of writing, the only thing that’s stopping a new shark sighting landing on my PC every 10 minutes is that the wonderful spell of settled weather has been replaces by a return of Atlantic low pressure systems.  So it will be interesting to see when our high pressure returns this weekend, just how many sharks we get to count from the 11 watch sites on Whale Watch day this Saturday 18th May. Why not join us to find out?

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Please watch basking shark watch responsibly this year. These wild animals now  have protection under the Irish Wildlife Act from wilful interference. If you are out on a boat, please stay on your boat and don’t be tempted to swim with either cetaceans or basking sharks.*

*Updated Codes of Conduct are now available on our Downloads page