Fish and Shellfish

In 2021, Scotland celebrates the Year of Coasts and Waters, and COAST celebrates 25 years of the community of Arran’s efforts to protect our seas.

Here we bring you a little bit closer to the variety of fish and shellfish we find in our seas.

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If we are asked what the sea provides for us, most of us probably think of the food that it produces. This will include fish and shellfish (such as lobsters, crabs, prawns, scallops and mussels) which are some of the more familiar species that we find around Arran and elsewhere around Scotland and the UK.

Fisheries were once seen as a limitless resource, a viewpoint illustrated by the words of the Victorian scientist T. H. Huxley in his inaugural address to the Fisheries Exhibition in London in 1883: “I believe that .… probably all the great sea fisheries are inexhaustible: that is to say that nothing we do seriously affects the number of fish.

Today we now know that it is all too easy to over fish wild stocks of marine life with serious consequences for both ourselves and the marine environment.

The community on Arran experienced this directly with the catastrophic decline of commercial fish stocks in the Clyde through the 1980’s and its associated loss of livelihoods, income and even island events such as the annual Lamlash Fishing Festival. Action by COAST and the Arran community to establish the Lamlash Bay No Take Zone and protect the South Arran Marine Protected Area from dredging and trawling was a direct response to this loss of fish stocks and marine life.

The importance of fish and shellfish

Altogether around 500 fish species may occur in UK seas although only around 250-300 of these are likely to be permanent residents; both the largest European fish species, the basking shark, and the second-smallest European fish, the diminutive goby, have been recorded around Arran, the latter seen for the first time this year during citizen science surveys as part of the UK-wide Seasearch project. Fish can be masters of camouflage, and many are able to modify their body colouration to blend with that of the seabed they are living on. Consequently, identifying a fish from its colour may be difficult or even impossible and many fish change colour when stressed (taken out of water) or when they die.

As with fish, we have a wealth of different shellfish in our seas, with some, such as winkles, dogwhelk, shore crabs and hermit crabs, relatively easy to find. Others, however, can be more cryptic – but more on that later in the month!

Fish and shellfish have important ecological roles in the marine environment as many are larger marine species further up the food web. Through their own feeding activities, both fish and shellfish play an important role in the cycling of nutrients in the sea and influence the structure of marine life communities. Some shellfish, such as lobsters and crabs scavenge on dead and decaying material as well as feeding on smaller animals and organic particles within the seabed sediment. Others, such as limpets and winkles, graze on marine plants or, in the case of scallops and other bivalves, feed on small food particles that they extract from the sea water they filter through their bodies. 

Special Species

There are a number of cryptic species of fish and shellfish we find in our seas. One such species is the Nut crab, a tiny crab with a body the size of a fingernail! They are generally found amongst gravel and broken shells and so can be very hard to spot.

One creature which does the complete opposite of trying to hide is the Cuckoo wrasse. This male of this fish species is highly colourful, and definitely reminiscent of warm tropical seas rather than the temperate waters off our shores. The Cuckoo wrasse is a fascinating fish species, as all individuals start life as a female. When there is a need, they change to males – usually there is one dominant male to an area and, when he dies, the most senior female will change gender.

Another particularly fascinating fish in our seas is the Gurnard, pictured is a streaked gurnard. These fish have large heads with a steep forehead. The streaked species are armed with small spines along their bodies and their dorsal fins are also armed with spines and rays. Most interestingly, the three lowermost pectoral rays on each fin are detached, allowing this fish to lazily crawl across the seabed.

Our local creel fishermen target the European lobster to earn a living. These decapods (10-limbed) creatures are a lovely blue-purple in colour and are usually found within 50m of water. The two foremost limbs form large claws – one “crushing” claw (with molar-like structures on the inside) and one “cutting” claw (with jaggy, serrated components that act like our canine teeth). Usually, the “handedness” of the lobster is dictated by which side of their body the stronger crushing claw is attached to.

Lobsters are one of many species of shellfish who have a hard exoskeleton which protects the internal soft tissues of the animal. To grow, the lobster has to undergo a process known as moulting, whereby it sheds this hard exoskeleton and forms a new one. This moulting process can take a few hours to several weeks, largely dependent on the size of the individual and the availability of calcium in the water (it can gain this Calcium by consuming its previous exoskeleton). The moulting process involves the tissues in the animal absorbing water, causing the lobster to swell and break the outer skeleton. Further swelling occurs after the creature has broken free from the broken exoskeleton and over time the new exoskeleton begins to harden to create a new suit of armour to protect the animal. Amazingly, the body (carapace) length of an individual can increase by up to 15% in just one moult, and increase the total weight by almost 50%!

Like all flat fish, Lemon sole go through a very unusual and unique anatomical change when they are very small, where the eye on one side of the body moves round so that both eyes are on the upper side of the fish, while the other side becomes the underside in contact with the seabed; the lemon sole lies left-handed with its eyes on the left side of its body. These fish are also very good at camouflaging, and have a habit of flicking their body and fins to partially cover themselves with sand to the point where sometimes only their eyes are visible.

Lemon sole reach up to 30cm in length and they have deep oval bodies with small heads and tiny mouths.

Human Benefits

If we asked: “what is the key benefit humans get from fish and/or shellfish?” many would answer “food”. This of course is one way we have a relationship with these animals, but there are other ways these creatures benefit us that don’t result in them ending up on our plates – largely all to do with economic benefit.

We’ve already mentioned this month that fish and shellfish – through their feeding habits – can help stabilise marine nutrients and balance food chains, which then helps us as stocks of other species in the sea will remain abundant and healthy. One such example is the fish eating cetaceans such as bottlenose dolphin and harbour porpoise which are the key focus of many marine-based tourism operators.

The South Arran MPA and Lamlash Bay NTZ are showing the potential for protected and recovering seabed habitats to contribute to the recovery of commercially important fish, shellfish and other species; increasing numbers of snorkellers and scuba divers want to see this recovery for themselves bringing additional economic benefit to the island. Healthy stocks also attract increased numbers of recreational sea anglers to the area, in turn feeding into the local economy further.

Threats to fish and shellfish

Fish and shellfish are affected by a range of different human impacts in addition to those associated specifically with fishing, including loss and damage to marine habitats as a result of developments and pollution. Warming seas as a result of climate change are leading to shifts in the distribution of marine fish in UK waters and, as a result, some species such as cod are shifting their range further northwards. Research has found that while juvenile fish of some species are getting bigger as sea temperatures rise, adult fish are getting smaller. Warming seas can also lead to more frequent and severe harmful marine algal blooms which can be directly harmful to fish and shellfish and increase the risk of marine biotoxins being present in shellfish.

Get involved to help our fish and shellfish

It is in our own interests to look after our seas – evidence shows how fish and shellfish populations can respond when areas are protected and not-overfished or degraded. A well-managed South Arran MPA has significant potential to support sustainable fisheries and other sustainable marine-based businesses into the future.

The hard-won protection of the South Arran MPA and Lamlash Bay No Take Zone is working, as shown by the results of collaborative projects with Universities and researchers – increased marine life in parts of the NTZ and MPA, and larger shellfish in the NTZ which produce more eggs. Studies also show that young cod prefer areas with more seabed marine life. While we do not yet know whether fish stocks in the Clyde will ever recover, the NTZ and MPA are showing the potential for protected and recovering seabed habitats to contribute to the recovery of commercially important fish, shellfish and other species.

Of course, protecting the species is one thing, protecting the habitats they rely on is another. Inshore bottom-fishing to capture creatures like prawns and scallops is damaging sensitive inshore habitats that are vital in the fight against climate change and biodiversity loss. Please help protect these by supporting the Our Seas coalition in their call for a just transition for a modern inshore limit.

There are many ways to make a difference and get involved at protecting fish and shellfish in our oceans.

* By making safe and sustainable seafood choices, you can help reduce demand on overexploited species. Due to high demand, loss of habitat and unsustainable fishing practices our fish and shellfish populations are rapidly being depleted. If you consume fish or shellfish, ask questions about where your seafood is coming from. Ask for hand-dived scallops and consume creel-caught langoustine and lobsters.

* Reduce, Reuse, Recycle. Plastic in our seas doesn’t just threaten the larger charismatic creatures that we see on the surface or on the shore. Fish and shellfish easily consume micro-plastics as they mistake them for tiny particles of food. Many plastics contain toxins, and these become more prevalent the higher up the food chain, meaning us as consumers are most affected if we eat a fish that is contaminated.

* Get involved in citizen science projects like Seasearch, to report which fish and shellfish you see on your snorkels or dives and contribute to our knowledge of what is found around our coastlines.

Cover image: Lobster © Howard Wood