They say a picture paints a thousand words and I’d probably not have looked into this subject had it not been for an image attached to a sighting report by IWDG Cork member and ecologist Conor Rowlands, taken from Cloghna Head, overlooking Rosscarbery Bay on June 3rd. During this watch Conor observed about four minkes and some were close enough inshore that he captured this image. It’s a nice record shot of the animal which shows the diagnostic white pectoral fin patches and narrowly tapering rostrum, but this is not why the image stands out. In fact in this instance, I’ve far less interest in the actual whale than I do the environment in which it finds itself.
Minke whale surfaces in heavily nutrified water, Cloghna Hd, 03/06/2024 © Conor Rowlands
Author’s Wildlife pond, Rossmore, Co. Cork © Pádraig Whooley
The water in this image looks alarmingly like the still water in our garden pond (see image), i.e. a soupy algal mess.
“This is created when there is too much nutrient in the water. It’s the direct result of wet weather, washing nutrients from the land in huge amounts, into our seas. The nutrients that cause most of this problem are a toxic mix of slurry from livestock and agricultural chemical fertilisers. Slurry is put out as a liquid, and in our increasingly wet climate, it is inevitably picked up by rainwater and washed into every drain, brook, stream and river; by the miracle of gravity it is promptly delivered it into the sea. Water soluble chemical fertilisers, much the same.” excerpt from Colin Barnes’ Skippers Log.
In small amounts and at the right time of year such inputs are beneficial, helping kick start the food chain as phytoplankton feed on these nutrients in huge blooms which in turn feed a vast array of zooplankton, creating the food biomass for all our forage fish and so on, as the energy pushes up the food chain to the very top grazers and predators, including our minke whales. But there is what ecologists refer to as simply “too much of a good thing”, when these blooms persist well into the summer and it is this over nutrification that can result in de-oxygenated water and red algal blooms, none of which are good for healthy marine ecosystems.
These vast blooms have been photographed from space, extending up to >25 kms offshore but may be difficult to detect from land due to local light conditions, i.e., with the sun in front of you the sea will look dark or on sunny days the sea can be full of glare. Flying a drone overhead can be very revealing. If you are out on a boat, it may not be that obvious either, but if you have dolphins bow riding ask yourself how they disappear from view pretty much as soon as they dive? The answer is probably due to the lack of clarity in this same green water. So the next time you are on, in or looking out at sea, trying to establish the water’s colour, may influence the results of your whale watch. But does the data support there being a correlation between water colour and sightings? 
My focus in recent months has been on processing basking shark sightings and with this shark season all but over now, we can say 2024 has been a record shark year. However, the same cannot be said for our three main coastal whale species, the minke, humpback and fin whale. Clearly what’s good for basking sharks, may not be so good for whales.
For the six month period January-June 2024 we have recorded just 165 minke sighting events, which compares with 228 for the same period in 2023. The number of individuals recorded however is of greater concern as this number has seen fallen from 797 (2023) to just 371 (2024). So we’re receiving fewer minke sightings of smaller group size (3.5 v 2.2). Talking to local whale watch operators in my own area of West Cork, what they are seeing, (or not seeing), is quite consistent with the bigger All-Ireland picture. Up to a few years ago colleagues like Colin Barnes quite routinely recorded staggering numbers of minkes between April and June, which on occasion ranged from counts of 40-75 animals over a single four hour trip. I’ve been out on many of these trips and can confirm such numbers were not the result of any over-estimation on his part. Nick Massett would have on occasion recorded similar numbers in Dingle Bay. This year however, Colin’s trips have struggled to find minkes in anything like these numbers.
Another aspect of this issue that is likely to keep whale numbers down is the fact that many of the forage fish species that our whales feed on are visual animals, that need good visibility in order to aggregate. Being able to locate and maintain contact with one another is central to species like sprat forming larger bait balls; a little like starlings forming a murmuration. Without bait balls there is very little incentive for whales to invest energy foraging. It’s a simple enough calculation for whales; if there is insufficient forage available to them, they’ll move on. They are likely to make the same call when our waters are too nutrient rich.
The caveat to all this is that our whale season has a long way yet to run. With most of the summer still ahead of us, all of autumn and if the weather gods oblige us with high pressure, we could find whales along the southeast up to Christmas and even into January. However, the early indicators are not good. At time of writing (June 21st) we have only documented 18 humpback sightings, which is in sharp contrast to the 73 sightings for the same period in 2023. Fin whales too are showing a small percentage drop, but as they tend to have a preference for autumn/winter, it’s premature to read too much into these early exit polls!
On a brighter note the minke remains our most widespread baleen whale, with sightings so far occurring in all areas and in recent weeks, there has even been a flurry of reports off the Dublin coast, one of which were photographed by Dave O’ Connor from his Howth Head perch on June 14th.
Minke, bottom left of image, from Howth Head during effort watch, © Dave O’ Connor
Please do continue to report any whale sightings to IWDG on www.iwdg.ie or on our Reporting App. Your sightings are a critical tool in helping us monitor both the movements of these highly mobile animals in Irish waters and the impacts of human activities on their habitats.
If you live in the Irish northwest and would like to learn more about cetacean and basking shark sightings in the area and how to identify and report them to IWDG, you may be interested in a free, one day whale watching course being delivered by IWDG in Kilcummin harbour, Co. Mayo on Saturday 6th July @ 10:00am. Bring your own optics, dress appropriately for the weather on the day. No bookings required. Enquiries to Siún Ni Cheallaigh, email: siunn.c@gmail.com or Ph. 083 4709819.
By Pádraig Whooley,
IWDG Sightings Officer