Sea trout - Swimming out of the shadows

As reflected in the work of a recent WKTRUTTA workshop, the story of the unsung sea trout is both
interesting and one that has been attracting more scientific study to meet a practical need.
Published: 18 December 2013

​The sea trout is often perceived as the poor relation of Atlantic salmon and has historically kept a low profile both in terms of marine science and public imagination. There is, however, nothing like a crisis to focus minds. In the late 1980s, sudden stock collapses in Western Ireland and Scotland, coupled with persistent decline in parts of the Baltic Sea, highlighted the lack of scientific understanding and fisheries assessment information on the species.

A resurgence in scientific interest in the fish has since taken place, and new information on its exposure to potential risks and migratory behaviour is now helping to continue raising its status.

Sea trout are the anadromous (journeying from salt to fresh water to spawn and then back to feed), migratory form of the brown trout. Although the Atlantic salmon and sea trout have similar sea and fresh water life-cycles, the former head to distant feeding grounds across the North Atlantic whilst the latter's migrations are believed to be more restricted. Despite this, sea trout is also exploited in coastal and estuarine net fisheries, which often target both species indiscriminately.

Nevertheless, it is salmon with its historically major marine fisheries, valuable river sport fisheries, and extensive presence in aquaculture that has been in the spotlight. Moreover, trout research, management and conservation have tended to focus on the resident form of brown trout, an iconic fish in fresh waters, rather than its saltwater sibling. This however is changing as sea trout gain ground.

Much recent scientific enquiry has centred around the life history processes that determine the balance of the trout's dual sea and fresh water lifestyle – why do they return to sea? – and delving into the "black box" of their life at sea, their marine ecology, distribution, genetic structuring and stock mixing. Furthermore, the trout's phenotypic (physical and biochemical makeup as a result of environmental interaction), variety and ubiquity make it an ideal species for studying evolutionary biology, life history traits, and genetics, and for integrating ecosystem understanding across freshwater, transitional and marine habitats.

Driving such research are new pressures that potentially compromise sea trout migrations and survival. These vary in importance geographically, but include the development of renewable energy sources in marine areas, especially at migratory pinch points, hydroelectric power generation in rivers, and the environmental quality of rivers, estuaries and coastal waters. The widespread influence of climate change is already changing the nature of marine trophic webs. These could alter marine growth opportunities and predation risks for sea trout, thus the balance of optimal life-history strategies and, ultimately, sea trout abundance. Overfishing in marine recreational fishing, commercial by-catch and illegal fisheries continues to represent a serious risk in places.

The WKTRUTTA Workshop on Sea Trout, that took place in November and led by chairs Nigel Milner and Stig Pedersen, was a meeting of 35 ICES experts from Baltic and Atlantic coastal states charged with reviewing the latest progress in sea trout research, weighing up dangers to stocks and fisheries that should be looked at in terms of Marine Spatial Planning. Also important to the group is the adoption of ecosystem assessment approaches. Although foodweb shifts might be of great significance for the species, the monitoring of its key food species – including juvenile sand eel and sprat – is insufficient, meaning the data picture needed for ecosystem assessments is incomplete.

A significant issue of inconsistent availability and quality of assessment data around ICES Member Countries is also evident, probably stemming from the trout's lower priority compared to salmon and the lack of perceived drivers for international assessment.

Strong collaborative efforts are being made, however, on cross-border mixed stock fisheries issues across Baltic waters by the Working Group on Baltic Salmon and Trout (WGBAST). No such formal coordination exists for the Atlantic stocks, but cross-border study has been funded through the Interreg project. In the Irish Sea, the Celtic Sea Trout Project (Interreg IVA, Ireland-Wales, Cross Border programme) is concluding four years of analysis into the fish. In the English Channel, meanwhile, the ARC project has advanced progress whilst the Living North Sea Project brought together agencies and scientific resources from all bordering nations.

WKTRUTTA will report on its findings by February next year.

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Sea trout - Swimming out of the shadows

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