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Quantifying the sub-lethal effects of recreational angling on Atlantic salmon

August 10, 2015

 

Robert Lennox is a PhD candidate in Dr Steven Cooke’s Fish Ecology and Conservation Physiology Lab in

Ottawa. Robert works with Dr Eva Thorstad and Dr Ingebrigt Uglem at the Norwegian Institute for Nature Research to study Atlantic salmon migration and recreational fisheries.

 

Atlantic salmon are an iconic fish in Europe and Eastern North America where aboriginal, commercial, and recreational fisheries have existed for centuries. Humans have harvested salmon from rivers for millennia. In modern times, the importance of Atlantic salmon fisheries has necessitated management, with Atlantic salmon management appearing in the Magna Carta (1215). Nonetheless, the complex life history of salmon coupled with their value as a food fish resulted in considerable effort to capture salmon both in rivers and in the high seas where salmon from mixed stocks aggregate for feeding. Exploitation, pollution, and habitat loss (especially due to damming and channelization) combined to extirpate them from iconic European rivers such as the Seine in France and runs endemic to Lake Ontario disappeared more than 100 years ago. Today, they have nearly disappeared from Spain, Portugal, France, Germany, and the United States. Salmon conservation has emerged as a priority but a difficult proposition. Although commercial fisheries in the high seas have mostly closed, they were replaced by a new threat to wild salmon in the form of coastal aquaculture, which resulted in proliferation of sea lice and introgression of non-native genes in rivers when farmed salmon escaped net pens.

 

Although modern Atlantic salmon stocks remain threatened throughout their range, sport fishermen still consider Atlantic salmon among the ultimate prizes; the “kings of the river,” salmon are difficult to capture and more difficult to land. In the 19th century fly fishing for Atlantic salmon spread from the British Isles and around the world and in spite of conservation concerns recreational salmon fishing remains important throughout their persistent range. Salmon fishing has the potential to be positive for conservation because it generates awareness of salmon and creates jobs and revenue that replace commercial fishing. Anglers are often willing to pay large sums of money for good angling opportunities, making the salmon and their habitat valuable to protect. In many rivers, however, salmon anglers can capture a large proportion of the total annual run (0.20-0.70). When recreational anglers harvest a large proportion of their catch, recreational fisheries can have similar damaging effects to commercial fisheries by reducing spawning biomass or generating selection against large body size. In response, catch-and-release is emerging as a strategy to offset the potential damages associated with recreational fisheries. In salmon fisheries, catch-and-release can exist in many forms including mandatory release of important or rare stock components (e.g. large salmon, female salmon). Ideally, fish that are released will continue migrating, make it to spawning grounds on time, and spawn with similar success to salmon that were not captured.

 

Determining whether and how Atlantic salmon are affected by fishing is the topic of Robert Lennox’s PhD thesis, which focuses on these sublethal effects of catch-and-release angling. In Norway, where Robert’s research is conducted, wild Atlantic salmon are highly valuable and historically Norway has the most native Atlantic salmon rivers. To quantify the sublethal effects of angling on salmon migration, Robert uses radio telemetry to track the migration and spawning distribution of salmon after catch-and-release in Norwegian rivers. In 2013 and 2014, Robert collaborated with anglers in the River Gaula, South Trondelag County and River Lakselva, Finnmark where he radio tagged Atlantic salmon captured

by anglers to assess the movement and spawning distribution of salmon in the river after catch-and-release. Although salmon had high survival from catch-and-release (0.89 in Gaula, 0.97 in Lakselva), it was noted that salmon released by anglers tended to spawn in lower areas of the river than salmon that were uncaptured, representing a potential sublethal effect of recreational angling. Next year, Robert will work toward generating a better understanding of how spawning position and migration success are influenced by angling activities to determine whether there are quantifiable effects of angling on the spawning behaviour, physiology, or output of salmon that are released by anglers.

 

 

Although anglers that release fish usually do so with the intention and belief that fish survive, telemetry provides an excellent opportunity for exploring this assumption and determining which factors influence survival. Atlantic salmon are a very well-studied species in recreational fisheries and are therefore a great model species for studying sublethal as well as lethal effects of angling. When working alongside the river, Robert enjoys discussing catch-and-release practice and sharing recommendations for science-based best practices with anglers. He recommends that anglers avoid fishing in warm water (> 20 °C), bring proper gear (rod size, line breaking strength, knotless mesh landing net) to avoid excessively long fights, and limit the handling and air exposure of salmon. Usually, salmon can be netted, unhooked with forceps, and lifted out of the water for < 10 s to take a good photo, then the salmon will be released in good condition to continue migrating to spawning grounds.

 

 

 

 

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