Sharks and other marine mammals found in the seas of Arran

Small spotted cat shark. Photograph: Howard Wood.

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Standfirst

The Community of Arran Seabed Trust (COAST) is running a year-long media campaign to raise awareness of the many exciting habitats and species to be found in Arran’s seas, many protected by the South Arran Marine Protected Area. Each month, they will focus on a particular habitat or collective group of inter-linked species. Their July instalment features marine mammals and sharks and is sure to interest a wide audience. There is more information on COAST social media or visit www.arrancoast.com.

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The annual bloom of plant and animal plankton, as reported in articles in the Banner last month, provides food for many species including small fish which in turn provide food for larger fish and many seabirds around our coast.

Mass plankton blooms, like the one reported around Arran in June this year, give hope that the increase in food abundance will herald the arrival of some of Scotland’s most iconic marine species: marine mammals and sharks.

There are more than 30 species of sharks, skates and rays – fish species known as elasmobranchs that have a skeleton made out of cartilage instead of bone – recorded in Scottish waters. Around Arran, snorkellers and divers often happen across small-spotted catshark, also known as dogfish, and in 2017 the first cuckoo ray was spotted in the South Arran Marine Protected Area (MPA) in 30 years.

Arguably the most noteworthy shark in our seas is the basking shark – the biggest fish in UK waters and second largest in the world – which can grow more than 10m (33 feet) long and weigh up to several tonnes. Unlike most other sharks, these gentle giants feed entirely on plankton, one of only three shark species worldwide to do so.


Basking sharks used to be common visitors to the Firth of Clyde, but their oil-rich livers led to them being hunted here and elsewhere in Scottish waters, with an active fishery in the Clyde until as recently as the 1990s when laws were introduced to protect them.

Today, basking sharks are seasonal visitors to Arran and are most commonly seen in August and September, with numbers varying from year to year. A distinctive ‘classic’ triangular shark fin is the most visible sign to look out for, along with the tip of the tail fin that can often also be seen.

Elsewhere in Arran’s seas, you may get lucky and see an array of marine mammals, with seals the easiest to observe. Around the island we have a number of sites where these delightful animals haul out on to rocks to rest, moult and breed. Scotland supports internationally important populations of grey and harbour – also known as common –  seals, with Arran’s coastlines and seas supporting healthy ‘bobs’, or herds, of both. Although the grey seal is more abundant in Scotland, locally you’re most likely to see the harbour seal.

At first glance, both species look similar, however, the harbour seal has more of a puppy dog face, while the grey has a longer head and Roman nose. Both species are long lived – approximately 30 years – and feed on a variety of marine species including fish, squid, molluscs and crustaceans.

Whilst venturing around the coast, always remember to look out to sea as you may see a cetacean – whale, dolphin or porpoise. The smallest species – the harbour porpoise – are year-round residents in Arran’s waters and commonly seen from the ferry. Growing to between 1.3m and 1.8m long, they are easy to miss, as only their rounded backs and small dorsal fin briefly break the water’s surface as they travel around in small pods.

If you witness to a more flamboyant spectacle, you are likely watching bottlenose dolphins, which enjoy leaping and breaching clear of the water, or playing the waves created by boats. These charismatic creatures grow up to 3.5m long and have a much larger, more pointed dorsal fin than their smaller cousins.

Other cetaceans you could be lucky enough to spot are minke whale, orca, risso’s dolphin and common dolphin, all very rare but they have been recorded around the Clyde.

Otters, too, can be readily seen around Arran on any walk around the coast, although they are not always easy to spot. While not a fully marine species – they need ready access to freshwater – otter feed in the shallow waters around the coast, eating crabs and small fish.

Historically the abundance of marine mammals and sharks recorded in the Clyde region were much greater, so much so it is hard for us to appreciate just how numerous they might once have been. Our seas were once bubbling with marine mammal activity, as described by fisherman P Wilson in 1887 ‘at least 40 whales in pairs and hundreds of porpoise feeding’ just alongside his boat. It is therefore important to remember the numbers we see now are a fraction of much larger populations that once existed and that action to properly protect and recover these species is still urgently needed.

As top predators, these charismatic animals are vulnerable to any impacts on the marine food web, such as changes in plankton distribution as a result of warming seas and over-fishing of various prey species. All cetacean species, basking sharks, seals and otters are to some degree protected in law, but they are still vulnerable to many other impacts. They continue to be affected by persistent chemicals that can accumulate in their body tissues; they become entangled in marine debris including litter, aquaculture and fishing gear; irresponsible tourism disrupts important breeding, feeding and rest periods and they can be disturbed by boat traffic and underwater noise.

The protection of seabed habitats and marine life within the Lamlash Bay No Take Zone (NTZ) and South Arran MPA clearly has direct benefits for otters, seals and some of the smaller elasmobranch species, but for wide-ranging transient species such as basking shark and cetaceans, the NTZ and MPA can only provide a limited amount of direct protection. To ensure the conservation of these charismatic animals we are so fortunate to see around Arran, effective spatial management must be implemented more widely in Scottish seas.

Basking shark. Photograph: Jenny Stark No_B30CoastJuly01

Bottlenose dolphin. Photograph: Clyde Porpoise.No_B30CoastJuly02

Cuckoo ray. Photograph: Howard WoodNo_B30CoastJuly03

Minke whale. Photograph: Jenny Stark No_B30CoastJuly04

Otter. Photograph: Jenny Stark. No_B30CoastJuly05

Porpoise. Photograph: Clyde Porpoise No_B30CoastJuly06

Small spotted cat shark. Photograph: Howard Wood. No_B30CoastJuly07