During the late 19th century, Atlantic cod, haddock and whiting stocks crashed in the Firth of Clyde. Despite fishing bans on these species and a cod spawning closure, fish stocks have yet to recover, and fish populations in these waters are now largely made up of juvenile whiting.
Ecologists have puzzled over why young whiting are doing better than cod and haddock. Now stereo underwater video cameras are providing them with important new clues. The research is presented this week at the British Ecological Society's annual meeting in Edinburgh and, together with other Clyde2020 projects, could help these fisheries recover.
Cod and haddock are fish and chip shop favourites in the UK but overfishing and other human impacts have depleted some stocks off our western shores. In the Firth of Clyde, populations of cod, haddock and whiting had been almost wiped out by 2005.
To get to the bottom of the relative abundance of juvenile whiting in the Firth of Clyde, researchers from the University of Glasgow used special Stereo Baited Remote Underwater Video systems (SBRUVs) -- waterproof video cameras that are baited with food to attract fish and lowered onto the seabed.
Working off the south coast of Arran last summer, the team led by PhD student Sophie Elliott filmed hundreds of fish in their natural habitats for the first time, giving a unique glimpse of juvenile cod, haddock and whiting in these coastal habitats.
The 186 hours of fishy footage allowed them to study the fishes' behaviour and distribution, as well as measure the size and relative abundance of each of the three species.
The results reveal that cod, haddock and whiting forage in very different ways: whiting were much more likely to approach the bait compared with haddock, while cod showed very little interest in the bait.
The footage also showed the fish were very different sizes, with the whiting being on average larger than haddock and cod, and that the juvenile whiting arrive in the coastal 'nursery' areas sooner than cod or haddock, giving them a head start.
According to Elliott: "The findings suggest that whiting are more opportunistic feeders than haddock or cod. Coupled with their larger size and the fact they get to the nursery areas earlier, this may give them a better competitive advantage and help explain why most of the fish in the Firth of Clyde are young whiting."
As well as providing important insight into managing the recovery of depleted UK fish stocks, SBRUVs could also be used in other conservation schemes, she says: "These video systems could feed into managing and monitoring marine protected areas around our coasts."
Co-author Brooke Allan of the University of Glasgow will present the results at the British Ecological Society Annual Meeting at the Edinburgh International Conference Centre on Tuesday 15 December 2015.
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