The opportunistic foraging strategies of the minke whale

A short guide by Dr Michael Tetley, member for the IUCN Joint SSC/WCPA Marine Mammal Protected Areas Task Force 

Minke whales aren't usually associated with the dramatic feeding spectacles more regularly seen by fin and humpback whales. However, during my own field studies across Canada, Iceland, and here in Scotland, this can certainly be the case for these tenacious little hunters...well little by whale standards at least.

A section of minke whale baleen - these keratin (same substance as hair or fingernails) plates are line the inside of the whale's upper lip - like an inside-out moustache!

As with many other baleen whales, minke whales use the rough plates of hairy baleen to separate the seawater from their prey - usually small shoaling fish like sandeel and sprat. However, don’t be fooled to think this is a slow, passive procedure. In fact, it takes a lot of speed, power, and good timing to perfect the best gulp; ensuring a good-sized ball of prey into their gaping mouths. Minke whales need to invest a lot of energy to feed in this way. The average minke whale gulp can result in as much as a 20 cubic metre mouthful of prey-laded water. No wonder they need the expandable pleats of their lower jaws to be able to fit, and then expel, that water out through their baleen, with the remaining catch of sandeel left behind to swallow. Unlike their larger fin, humpback, and blue whale cousins, the smaller minke whales are under even more nutritional pressure to make their foraging as efficient as possible.

It’s a tough ocean when the likes of the mighty blue whale can gulp as much as 80,000 litres of prey in a single mouthful. So the clever little minke needs to be flexible and exploit many opportunities as it can to find a meal where others aren’t competing with them.

Minke whales utilise two methods of capturing prey which are divided into different techniques: near surface foraging (NSF) and foraging at depth (FAD). When you think about all the times you may have seen a whale feeding - in person or on screen - most behaviours observed take place at the water’s surface. This is because the water’s surface acts like a wall to many fish species. When you are trying catch as many fish in one gulp, using the surface of the water as a barrier helps to push the fish together tightly into a single big shoal or ‘bait-ball’. When these patches of prey regularly occur in the same place over a stable period, minke whales can invest their energy in maximising the amount of prey they can eat in this ‘hotspot’. Using tactics like bubble blowing, head slapping, and flashing their startling white fin-patches, minkes can scare lots of fish together, creating a more tightly packed bait-ball to gulp. Such active ‘corralling’ is very effective and seen in Scotland occasionally when there are times of highly abundant productivity associated to the spring and summer blooms of plankton.

This photo captures the moment a minke whale breaks the surface during a lunge feed, propelling it's body through the water to take a massive mouthful of water and prey

Scottish seas are unpredictable due the influences of the North Atlantic current and the volume of fresh water running off the land from regular heavy rains. This leads to fluctuations in where exactly the hotspots of concentrated prey are likely to be each year. This means that for whales it’s an effective strategy to try to return to the same place each year and do all the work themselves: using corralling behaviours to forage if the density of prey is too low, then make big bait balls to swallow in fewer gulps and lunges.

Minke whales are master opportunists, and benefit from the feeding behaviours of many other species who forage on the same fish species. When different species of seabirds, such as northern gannets, kittiwakes, and terns - or submerged swimmers like auks, puffins, and predatory fish like mackerel - all attack a shoal of sandeel or sprat, they further herd the smaller prey fish into tightly packed bait-balls. As such, it is common in Scottish Seas to see minke whales making the most of this ‘pre-packaged’ feast by lunging straight into the feeding activities of these other species. In behavioural ecology terms, these roles are described as ‘Beaters’ - the species who are doing the work of herding together, or flushing prey out into the open - and ‘Pirates’ which describe those species which steal the prey from the beater species. For minke whales in Scotland, it makes a lot of ecological sense therefore to forage in areas where there are many species of seabirds feeding. They can then expend their valuable energy reserves on searching for these pre-made bait-balls, rather than investing in working a patch with highly energetically cost corralling behaviours in an area where the productivity (and prey density) could change rapidly between the seasons and between different years in the same location.

This incredible footage of a bait ball feeding frenzy, was captured by Sharyn Murray, while out with Staffa Tours at the start of June 2022. This video from Sharyn is an incredible recording of a minke whales taking advantage of high-density prey - the bait ball is visible as the darker area of water.

There is still much to learn about the minke whales we find in Scottish seas. In 2023, we published a digital Minke Whale Catalogue which documents over 300 individual whales identified off the west coast. The data which underpins this work to better understand the species has been gathered by the public, or citizen scientists.

HOW CAN I GET INVOLVED?

Join a research expedition on board our vessel, Silurian. This unique experience is more than a wildlife watching holiday…the data gathered is having a significant impact on the protection of cetaceans in Hebridean waters.

Join our Whale Track community of citizen scientists and report what you’ve spotted. Whale Track is a free and user-friendly app which can be downloaded to your phone, providing an easy platform for reporting. Whale Track now has over 7,000 users from all over Scotland, who have collectively contributed over 8,000,000 rows of data - a staggering public effort!