Releasing pollack at depth could benefit their long-term survival, study suggests

(Press-News.org) During 2026, new legislation – the result of an agreement between the UK Government and the European Union – is planned to come into force for recreational pollack fishing that limits catches to three fish per angler per day.

It will result in more fish being released after they are caught, but new research has suggested changing how that release happens could have a marked difference on the fisheries’ long-term sustainability.

Specifically, it suggests that releasing pollack closer to the depths they are normally caught could improve their chances of survival by almost 25%.

This, the researchers say, is down to the fact that deeper release quickly counters many of the effects they experience when captured at depth and brought to the surface, something often described as barotrauma.

The research was conducted as part of the Pollack Fisheries Industry Science Partnership project (Pollack FISP), an initiative supported through the government’s £100m UK Seafood Fund.

Led by researchers at the University of Plymouth, the Pollack FISP project also involved scientists from the University of York, Marine Biological Association, Centre for Environment, Fisheries and Aquaculture Science (Cefas) and University of East Anglia, as well as representatives from the Professional Boatman’s Association and the Angling Trust.

Dr Thomas Stamp, who led the project and is now a Visiting Research Fellow in the University of Plymouth’s School of Biological and Marine Sciences, said: “When pollack are caught deeper than around 20m and brought onto fishing boats, they go through something similar to what humans experience during the bends, with gases expanding in their bodies and potentially resulting in various injuries. However, our study suggests that releasing them close to their catch depths can results in their survival rates increasing from 56% for surface-released fish to more than 80%. There are various techniques already in development to support these practices, and we hope this could be a positive initial finding from a conservation and a commercial perspective.”

Pollack is of major socio-economic importance to the recreational charter fishing fleet, and is the fourth most valuable finfish for commercial vessels under 10 metres. It also plays a key role in the UK’s marine ecosystem.

However, with evidence that pollack catches across the English Channel, Celtic and Irish Seas had declined by more than 70% over around 20 years, the Pollack FISP project aimed to provide an initial assessment of post-release survival of pollack under different capture conditions, and assess the use of recompression to mitigate the barotrauma the fish experience.

The researchers assessed this using an experimental weighted cage which the fish were placed in after being caught, and which could be lowered to various depths within the water column. The cage was fitted with cameras to monitor the fish’s initial response and showed that they recovered vital reflexes within one to four minutes of being back in the water.

When caught, the fish were also fitted with small electronic tags and monitoring through acoustic telemetry – deployed through the FISH-INTEL project and other programmes – demonstrated that individuals dispersed up to 25km from their release site and were recorded actively moving in the water column for up to six months post-release.

While the results using the cage are positive, the researchers believe commercially available descending devices – for example, Seaqualizers – would likely provide a more viable and low-cost solution which could be adopted as part of normal fishing procedures

Hannah Rudd, Head of Marine at the Angling Trust, was a co-author on the research. She added: “The Angling Trust has worked extensively with the charter boat sector, anglers and the scientific community in recent years to find measures to ensure the recreational pollack industry can survive and thrive. The use of descending devices to improve post-release mortality outcomes for pollack has shown the potential to be one such measure. We appreciate there is some hesitancy within the angling and charter community regarding their use and effectiveness. However, while further work is needed to test particular devices, this study hopefully goes some way to providing independent evidence for the principles behind them as a way of avoiding a complete closure of the fishery while supporting pollack recovery.”

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