Clyde Sea's fish stocks bouncing back - but not as expected

WRITTEN BY Oceanographic Staff

According to a new study, fish populations in Scotland’s Clyde Sea have recovered, with biomass now 4 times higher than in the late 1980s. But while historically, the herring dominated the area, sprat are now primarily found in the region.

The paper, published in the journal Current Biology, found that the marine ecosystem of Scotland’s Clyde Sea shows signs of recovery. However, sprat is now the dominant fish species instead of herring. This is a prime example of “an unexpected trajectory of recovery of an impacted marine system”.

While the region once had productive herring fisheries, the species disappeared at the turn of the century. Subjected to intense fishing activity for over 200 years, the North Sea had a herring fishing ban introduced at the end of 1977, which included the Clyde Sea area.

Using acoustic surveys of the pelagic ecosystem, researchers behind the study estimated that the Clyde Sea supports 100 times as many forage fish as in the late 1980s, with one exceptional finding: the once abundant herring was replaced by sprats, despite virtually no fishing on herring for 20 years.

The paper’s lead author, Dr Joshua Lawrence, said: “We’ve seen no recovery in the herring stock, as one would normally hope for following a reduction in fishing pressure. Instead, we have seen a huge increase in the biomass of sprat in the area.”

“Sometimes management interventions can have unexpected consequences, most likely due to unforeseen ecosystem interactions and processes. These can be hard to predict, and may vary greatly from one system, or even species, to another,” he added.

The authors of the study suspected that “the combination of a warming sea, bycatch of herring in the prawn fishery, and susceptibility of herring to poor recruitment” could have contributed to the recovery of sprat stocks. Similar unexpected developments were recently seen in the North Sea where hake made a return, as well as in Peru where pelagic squat lobster numbers increased significantly.

The lesson learned: reducing fishing pressure might not always be sucessful and ensuring that stocks do not get overfished in the first place might be essential. The study argues that the lack of sprat fishing in the Clyde could hold the unique opportunity of developing a healthy ecotourism industry. After all, megafauna such as whales and dolphins could be attracted into the area by the abundance of forage fish, “further restoring the biodiversity of the region after centuries after overexploitation”.

For more from our Ocean Newsroom, click here.

Photography courtesy of Unsplash, graphical abstract found here.

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