Crawfish: Trending in South-west Britain

Posted byKeiron Derek BrownPosted inBlog, entoLIVE Blog

Crawfish (Palinurus elephas) are large, colourful crustacea that inhabit rocky seabeds along the west of Britain and Ireland, also known as spiny lobster. They were fished almost to extinction in south-west England towards the end of the last century. Excitingly, this economically valuable species has undergone a remarkable recovery in Cornwall and Devon since 2014. Angus will describe how we are now able to track and analyse trends in the crawfish population using citizen science records collected for Seasearch by volunteer divers. We need to understand such trends in abundance and distribution if we are to manage this recovering population into the future.

Dr Angus Jackson is the data officer for Seasearch. He is responsible for curating Seasearch data and for doing research to make the best use of this large and remarkable dataset.

Q&A with Angus Jackson

What do you mean by ‘landings’?
The weight of Crawfish that are brought to shore to be sold at the fish market. This is different to the ‘catch’ as this is the number that is caught in the net, but some of these will be put back as they are undersized individuals or females with eggs.

How are statutory restrictions monitored and enforced?
This has been open to exploitation in the past. Lots of the fisheries recognise the valuable opportunity that they have here and don’t want to shoot themselves in the foot by over-harvesting too early on in the recovery. I’m optimistic that there is enough collaboration between commercial fishermen, fisheries, academics and conservation agencies to hopefully avoid the disaster that happened last time,

Are Crawfish fished for export from the British Isles and could stronger restrictions help with their recovery?
Most of the market for Crawfish is within Europe (such as France, Spain and Portugal) rather than the UK. Anything that reduces the number of Crawfish being caught could potentially help their recovery. Reducing catch through by-laws or national legislation (i.e. the Fisheries Act 2020) would be the mechanism for reducing how many are caught, but I’m not clear what the mechanism would be for limiting export as this lies outside of my area of expertise.

Does the catch record also indicate a similar rise in populations in other UK regions?
That’s a really interesting question for a couple of reasons. We’re seeing almost identical patterns of recovery across the Channel in northwest France. Colleagues in Mer Iroise area of France have observed increases in crawfish populations and have noted the same 2-3 year lag and a big upturn in fisheries landings of Crawfish. However, we’re not seeing a similar pattern in landings or records in southwest Wales (which was historically a stronghold) or Western Scotland. There are some suggestions that there is also recovery on the west coast of Ireland but we have much fewer data for this area. We still don’t know if the populations in England and France are being seeded by reproduction happening locally or if they were originally (or are continually) being seeded from further afield. We’d need to see the results of some population genetics studies to understand this better.

Did Crawfish populations recover because commercial fishing stopped?
We don’t have a definitive answer why they started reappearing in 2014. There had been fishing throughout so it seems unlikely to be related to fishing pressure. Likewise, I don’t believe that it has anything to do with conservation measures, such as marine protected areas as there is no management specifically for Crawfish. It could be due to climate change or even chance – we really don’t know! However, what we can do is ensure that we have measures in place that look after the population and prevent it from suffering the same fate as last time.

Can Crawfish be raised in captivity and released in areas they are struggling to recolonise?
There is a possibility and a project in north Wales has been working to try and develop the ability to raise Crawfish from the tiny plankton stage up to the release stage in the same way that lobsters have been raised in hatcheries and released along the coastline. For various physiological reasons, it is a challenging process, requiring very specialist conditions and a high level of care. I believe there is one initiative that now has the ability to get through all of the necessary stages and grow them to a size where they could be released. That doesn’t mean that we’re at the stage where this is now financially viable or at a scale that would make a difference to a stock. It’s not going to give us a quick fix as a tool to supplement fisheries landings or for conservation purposes – but who knows in 10 years or so!

Literature references

Further info

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Published by Keiron Derek Brown

A blog about biological recording in the UK from the scheme organiser for the National Earthworm Recording Scheme.

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