By Rhiannon Jehu
A friend and I went to the Discover Shetland’s Sharks and Skates event at the Ness Boating Club a few weeks ago. We both enjoy nature, but I don’t know that much about individual marine species lifestyles, so this felt like a great opportunity to learn more.
Before I went I decided to swat up on flatfish since they are superficially so similar to skate but are really very different. They are a great example of convergent evolution – being flat and living close to the seabed is a good niche and has been selected as a strategy by many species through deep time. So, here is some of what I learned before and during the event.
Bony fish (Osteichthyes) & Bony flatties:
The bony fish ‘standard’ model has bilateral symmetry and use their whole bodies as one big muscle to drive through the water in a streamlined way – fast, efficient and sort of rocket shaped. They move up and down in the water column through the use of a swim bladder which is essentially a built in buoyancy aid.
Plaice (Pleuronectes platessa) are a good example of a bony flatfish. They start life with the standard symmetrical body shape, but then gradually their left eye migrates round their head, and the fish lies on its side and flattens out so it has 2 eye’s on the top (right side) of its body. This means that when a flattie beats their tail they are beating up and down, rather than the more usual side to side. Plaice have white undersides that are hidden from the world, but the topside becomes the colour of the seabed. This camouflage varies a lot in colour, usually a grey/brown base with a range of stars and spots – white, yellow, orange.
So what are skate?
Skate are cartilaginous fish (chondrichthyans) and are related to rays and sharks. Cartilage is resilient, rigid, flexible, and light weight. Chondrichthyans don’t have swim bladders but their pectoral fins are rigid enough and large enough to allow the fish to move around the water column as easily as bony fish do. Bony fish have an active pump system for pushing water through their gills however most (pelagic) chondrichthyans need to keep swimming to keep breathing. Bottom living (demersal) species (generally) have a small hole found behind each eye (a spiracle) where they take in water before pushing it out through their gills. This better suits their lifestyles, and, their mouths are on their undersides, unlike flatties whose mouth is at the front.
Skate are flat like plaice but instead of their body providing the power to swim, they flap their large, pectoral fins (wings). They then use their long thin tails for direction and balance (bony fish use their fins to steer). Essentially skate have strong arm muscles and use their tail as a rudder while plaice have strong tail muscles and use their arms to steer.
|Mouth||at front, sideways opening||underside|
|Propulsion||tail muscles||pectoral fins (rigid)|
|Guidance system||pectoral fins (flexible and fan like)||tail (flexible with fins on top)|
|Breathing style||in from the front, out from the top and underside||in from the top out from the underside|
Types of skates
We have a range of batoides (skate and ray) in Scottish waters. Including the common skate which is one of the largest species in the world – it has a wingspan that can reach almost 3m. In recent years this species has been divided into 2 separate ones – flapper and blue, with the flappers being more common in our northern waters.
These giants of the marine world produce egg cases ‘mermaid’s purses’ up 28cm in length that are tethered to the seafloor. The young take around 18 months to hatch and then take a long time to reach sexual maturity – on average, females mature at 21 years of age, while males mature at around age 14. Marine Scotland Critically endangered flapper skate study – Marine Scotland (blogs.gov.scot) These factors and the skate body shape make them very vulnerable to disturbance and over fishing. Ultimately, this has resulted in the once common skate being one of our rarest sea creatures.
Though flapper skate were overfished throughout the 19th and 20th centuries they are now protected and there are ways that fishermen can avoid accidentally capturing them, for example, some fishing vessels use nets fitted with skate panels which allow juvenile flappers to escape without the fisherfolk having to release their entire catch Home – Orkney Skate Trust
In 2021 our neighbours in the Western Isles got a site within the Inner Sound of Skye temporarily listed as a ‘Marine Protected Area’ (Red Rocks and Longay MPA). The aim was to protect the largest flapper nursery found in Scottish waters by prohibiting some marine activities (fishing, diving and construction). This temporary designation was under review earlier this year – do people want the site to become a permanently protected? RIFG
The skate event was great fun. There was a 5-6 foot paper skate for people to leave their mark on – ‘skate art’. It’s only when I think about it now, that I realise that the model skate was a realistic size. To imagine something so big gliding through the water – it’s spectacular.
There were interesting and fun videos showing some of the chondrichthyans that visit or live in our waters and also showing how skate embryos develop in the safety of mermaids purses. We then saw a range of egg cases that we tried to identify from shape, size and features – including a flapper ‘purse’ that was bigger than my hand.
The event had 2 microscopes that we could play with; a small digital one and a traditional laboratory type. We spent quite some time chasing and identifying different micro beasties in a few drops of sea water.
I had one question – What is the difference between a skate and a ray? They are all lumped together as chondrichthyans. Sharks look very different to skate and ray, but these last 2 have very similar body shapes. It turns out that skate lay eggs while ray’s lay live young. But that is for another time.
We know very little about our local marine species and their lifestyles. It’s only in recent years that we have come to identify 2 separate (un)’common skate’. And learning about their slow development suggests to me that we need to take special care to protect them as a species. By protecting the flappers, other species are given respite too. Experimenting with new fishing technology to allow fisherfolks to harvest the seas, whilst at the same time reducing bycatch seems so important for us to find ways of living with nature, supporting it as it supports us.
Surveying for flapper skate eggs | Scotland’s Nature (scotlandsnature.blog)