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!
Earlier this year the IUCN (International Union for Conservation of Nature) Shark Specialist Group took a close look at the status of chondrichthyes -that’s sharks, rays, skates, and chimaeras. Their findings did not make for happy reading. Just 23% of the species that make up this group were classified as ‘Least Concern’. But that doesn’t mean the remaining 77% of sharks are threatened, because the research also revealed that around 46% of the species that make up the chondrichthyes are classed as ‘data deficient’ – meaning we really don’t have enough information to figure out what their population status is. Given that many chondrichthyes are in bad shape, it is important that we rectify this data deficiency so we can better direct conservation management. The trouble is, data doesn’t come cheap – especially when it involves obtaining data on marine species.
One of the methods used for studying shark populations is to use acoustic telemetry. The exact details vary, but the general process is to 1) catch a shark 2) attach an acoustic tag to it 3) deploy acoustic receivers 4) collect ‘ping’ data (when a tagged shark comes in range of a receiver) from the acoustic receiver 5) analyse data to figure out which sharks have been where and when. Of course this method only tells us when a shark has come across a receiving station, so if a shark happens to spend a lot of time out of the range of a station, we wouldn’t get a ‘ping’ to analyse. There are other methods of monitoring shark movements that get around this problem but they are costly – more costly than acoustic monitoring which doesn’t come cheap. This isn’t to say that acoustic monitoring isn’t useful. If you have an area that is known to have resident sharks, or frequented by visiting sharks, deploying acoustic monitoring in those areas can act as a population monitoring point. With limited funds for research and conservation, there is always a balance between collecting the best data technology can provide, with collecting the best data that we can afford. Perhaps monitoring doesn’t always have to involve high-tech gadgets at all. After all, there are many parts of the world where scuba diving and snorkelling occurs regularly. Can these human eyes act as reliable data collectors? Continue reading Citizen Science shows promise for shark monitoring