Humpback High-Jinks in the Clyde

The small crowd on the pier and esplanade watch in wonder at the majestic activity in front of them. The water surface out in the channel periodically boils and then a large form launches out of the water crashing back down.

This activity is interspersed with views of the massive mouth of the creature as it lunges out of the surface of the water. Last month and for the past few weeks numerous people around the Clyde have been treated to the sight of a humpback whale (Megaptera novaeangliae) actively feeding and displaying in the area.

This sight is normally associated with warmer climes and waters much further North. Additionally, the sightings of porpoise, dolphin and Minke whale have also increased on the Clyde in the last few years. So why are we seeing an increase in this incredible activity – it is all related to food supply.

Humpback whale can be found in all of the worlds oceans and undergo amazing migrations. They spend the winter months in the tropics and subtropics breeding, and summer months in temperate and colder waters feeding. They are large baleen whales measuring between 12 – 16 m, and can weigh up to 38 tonnes!

So why have we been seeing them in the Clyde for the last few years? From the video footage and photographs people have sent in, and my own luck in watching one of the whales for a few hours, it is apparent that the whale/whales are feeding in a variety of different ways during these sightings.

Humpback are baleen whales; they have large, sieve like plates of baleen hanging down from the inside of their mouths which can filter organisms from the water. They lunge into a school of fish or shrimp-like organisms, open their massive mouths widely and engulf huge quantities of water along with their prey. Some of the photos taken show the head of the whale as it emerges out of the surface water during this ‘lunge-feeding.’

Humpbacks are able to take in large quantities because they have ‘throat grooves’ which expand as they take in water. As the water is forced back out of the whales’ mouth, prey is then sieved from the water using the baleen plates and eaten. Humpback display another spectacular activity called ‘bubble netting’ where the whale dives down and emits a continuous stream of air which traps fish in the centre of the ring, the whales then surface up through their bubble 'net' feeding on the trapped and confused fish. This is the form of feeding I viewed from Cumbrae a couple of weeks ago. At times the whale was only a couple of metres from the rocks – much to the surprise of some seals which were basking in the area.

Amazingly, humpbacks must feed intensely during the summer months as they do not feed again during either their long migration or the time spent in tropical breeding grounds. As they are not breeding here, the spectacular acrobatic aerial display (breaching), falling back into the water with a crash, is probably not related to breeding displays but may just be happy exuberance. The whales we are seeing may be migrating from the Caribbean and are either choosing to spend their entire summer feeding period on the Clyde or are using it as a feeding stop-over on the way to better feeding grounds in Norwegian waters.

In addition to increased sightings of the larger whales in the Clyde over recent years. Sightings have also increased of our slightly over-looked small, resident cetacean the harbour porpoise.

Frequently these sightings have also been associated with large numbers of gannets diving – over the weekend I counted several diving gannet flocks with over a hundred birds in them. These are all good indications that there are good-sized shoals of small and medium sized fish on the Clyde at the moment. Perfect prey for porpoise to humpback whales and all other sizes of cetacean in-between. Humpback can be very faithful to good feeding grounds and visit year after year, so hopefully we will be seeing more of Hamish in the years to come.

Whales, dolphins and porpoise are facing a wide range of serious Conservation issues including increasing levels of acoustic noise, entrapment in fishing ropes, marine pollution, ship-strikes and change in prey abundance through climate change. The more information we obtain about them the easier it is to conserve these iconic creatures which deserve our protection. Please report any sightings of these to the excellent new charity the Clyde Marine Mammal Project (http://www.clydemarinemammalproject.org/). If you take any good photos – especially of dorsal fins and flukes please also send these to the website. These can be used to identify individuals.

While it is a delight to see cetaceans in the Clyde, water users should be very careful around them. They are extremely sensitive to disturbance and boat users need to be responsible and not directly approach them. Please remember all cetaceans are protected and it is an offence to intentionally disturb or harass them. So enjoy these magnificent creatures but keep your distance!