Fisheries, Aquaculture, & Sustainable Seafood

How deep is too deep for commercial fishing?

Our ever-improving technology has allowed us to fish longer, catch more, and move further from land.  It has also allowed us to fish deeper.  EU statistics indicate that between 1950 and 2006 fishing depths increased from an average depth of 407 metres, to 535 metres.

Life in the deep is slow-paced.  Food is scarcer than in the sunlit surface waters.  Species grow slower and live longer.  Some deep-sea corals, like the one in the image, are thought to be over 4,000 years old. Traits like these are why organisations like Marine Conservation Institute that ” The deep-sea is the world’s worst place to catch fish” .  It’s not just the sustainability of targeted species that is causing concern, but of those caught as bycatch, as well as damage to the seabed and the flora and fauna living in and on it – like the coral in the photo.  So can deep-sea fishing ever be managed sustainably?    A recently published study from Joanne Clarke, a PhD student at the University of Glasgow, and colleagues suggests that there might be a way to make the practice less damaging. Continue reading “How deep is too deep for commercial fishing?”

Fisheries, Aquaculture, & Sustainable Seafood

Reducing bycatch of skates and rays – stop tickling them!

Bottom-trawl fisheries may supply us with much of the tasty fish we like to enjoy, but it does come with its problems.  Also known as ‘dragging’, bottom trawling essentially involves dragging a large net, held open either with a beam (beam trawling) or large metal/wooden ‘doors’ (otter trawling) along the sea bed, or just above it.  It is used to catch a range of commercial species like cod, shrimp, flounder, and halibut.  One of the problems of trawling is that it is not a very selective form of fishing.  Other species are caught in the process, and this bycatch can include at risk species such as skates, rays and sharks.  As well as ecological implications, bycatch can be bad for fishers, who often end up throwing away bycatch either because it isn’t worth anything, or because they are not allowed to land it.  Bycatch reduction is a win-win for fishers and for the marine life caught.

Reducing bycatch of sharks, rays, and skates (collectively known as elasmobranchs) in bottom trawls is one of the many fishery-related issues on the mind of scientists at Marine Scotland Science.  As this piece of research from the Marine Scotland Science team shows, one possible solution (though not perfect) may not be all that tricky to implement. Continue reading “Reducing bycatch of skates and rays – stop tickling them!”

Conservation & Sustainable Management, Marine Life

A brighter future for the shy albatross

Predicting the future is a tricky business.  As then United States Secretary of Defence Donald Rumsfeld famously said “There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know” .  Then there is the interactions between all the variables that determine the outcome of a particular event.  However, few things work in isolation and species decline often results from the accumulation of different stressors.  If we want to put in place conservation management measures that are effective in the long term, then we need to be able to put our known (and measurable) stressors together and figure out what, cumulatively they mean for our potentially at risk species.

The shy albatross (Thalassarche cauta) is an endemic to Australia, breeding on just three Tasmanian islands, including the aptly named Albatross Island.  The albatross of Albatross Island have a long history of human interest.  In the early 19th century adult albatross were extensively hunted for their feathers and egg, taking their numbers down from an estimated 11,100 pairs to just 400.  The population is now recovering, but still faces a number of possible threats.  High on this list are two issues – changing climatic conditions, and the accidental capture of the albatross in longline and trawl fisheries.  To understand just what the combined impact of these stressors could mean for this vulnerable bird, Robin Thomson and colleagues from CSIRO Marine and Atmospheric Research​​​, together with the Tasmanian Government Department of Primary Industries, Parks, Water and the Environment (DPIPWE) put together a model that can hopefully direct management to ensure these birds survive in the long term.

Continue reading “A brighter future for the shy albatross”

Fisheries, Aquaculture, & Sustainable Seafood

UV LED lights reduce sea turtle bycatch

Bycatch – the accidental capture (and often mortality) of any species – or even a subset of a species (like juveniles) – in fishing does not make for a good fishing trip.  It takes up valuable space in your net, it can damage your gear, and it can cause population declines of species accidentally caught.  New ways to reduce bycatch are being tried out (some more successfully than others) more and more regularly.

When it comes to gillnets, bycatch of turtles is a big problem.  It doesn’t take much for a wayward turtle to find itself tangled up and unable to get out by itself.  For fishers, cutting the net to release them is often the only solution.  Enter Dr John Wang from the University of Hawaii.  He came up with an interesting proposal….what if turtles were better able to see the net, but the targeted fish couldn’t?

In this newly published piece of research, John demonstrates that by simply attaching UV LED lights to the gillnet floatlines (a line at the top of the net has floats on it which keeps it upright in the water), Green sea turtle (Chelonia mydas) bycatch declined by some 40%, but both the target catch size and the value of the catch didn’t decrease.

It all comes down to vision. The turtles are really quite good at detecting UV light…the fish not so much (in this study there was a variety of target species – mainly flounders – members of the family Pleuronectidae).  Clever stuff.  But John isn’t planning on stopping there.  He notes that different turtle and different fish species may react to different colours of UV light.  Watch this space for news on how that goes.

The paper is open access – talk a look at it here

Image: Green sea turtles entangled in a n abandoned small-scale net.  Credit Projeto Tamar Brazil/Marine Photobank

Fisheries, Aquaculture, & Sustainable Seafood

CCTV reduces fish discards at sea

Throwing fish away (discards) simply because they are too small or not included in a quota is a sore spot for fishers, conservationist and fisheries managers.  Many of the fish returned to the sea area already dead so there is no ecological value to returning them to the ocean, and there is no economical value to discarding them either.

Ideally, discards should be minimized by not catching non-targets in the first place.  After all, there are reasons why we should not catch fish that have not reached reproductive age, or why we should adhere to quotas (even if they are at times over-inflated beyond sustainable limits).

The Marine Management Organisation released the latest details on a trial to monitor how reducing the level of discards as proposed in the Common Fisheries Policy reform will play out in practice.  UK Fishers who entered into the trial were prohibited from dumping fish – even if undersized.  Electronic monitoring – essentially CCTV – was used to record what fish are being caught and processed on fishing vessels.

The results were interesting.  Fishers changed some of their gear types or fished in different areas to try minimize their bycatch.  Some fisheries found it harder than others to reduce bycatch for a variety of reasons – including species being just too similar in size, shape, and habitat preference for fishing gear to distinguish between them.  Never the less discards were reduced substantially. The ‘worst offender’ – the Western Hake beam trawl fishers who participated in the trial managed to reduce their discards from 18.2% in 2011 down to 1.7%.

If your on LinkedIN there is a good debate going on 


Image: Bycatch from prawn trawling makes up 1/4 of the annual discards.  Credit Stephen McGowan, Australian Maritime College, 2006/Marine Photobank.