Rethinking Release Strategies

Nov 25, 2024|inBlog, Salmon Steward

With funding through the British Columbia Salmon Restoration and Innovation Fund, this reasearch was conducted by the Pacific Salmon Ecology and Conservation Laboratory at the University of British Columbia. PSF co-funded this project to support ways of improving fishing practices for salmon in the recreational sector.

Photos: Steve Johnston and Rod Hsu.

Catch and release – a conservation measure that requires a captured fish to be returned to the water – is a fisheries management practice intended to protect vulnerable salmon stocks.

In the past few decades, the practice has become increasingly common in B.C. as certain salmon stocks have declined and regulations have restricted the size and number of fish that anglers can keep.

Catch and release allows fishing opportunities to continue.

But the downside – which is under increased scrutiny – is that some released fish die, and scientists don’t have all the answers to what is causing mortality, or how many experience post-release mortality.

To evaluate effects of catch and release on Pacific salmon, UBC’s Dr. Scott Hinch led a five-year research project aiming to improve future practices and policies.

“We have to make sure we understand what the consequences are of catch and release so we can improve the practice,” says Dr. Hinch.

UBC Report Executive Summary

A team of graduate students caught and tracked more than 1,500 Chinook and coho salmon in areas frequented by recreational fishers, such as the east coast of Vancouver Island, Barkley Sound, and Juan de Fuca Strait.

Results revealed several factors impact post-release mortality rates, some of which were unexpected. These included hook size and type, air exposure, landing net use, injury level, species, age, and body size.

UBC Researchers catch salmon near Bamfield for catch and release study

UBC researchers take a non-invasive gill biopsy from a captured Chinook salmon to study infectious agents.

Injuries sustained during fishing particularly impacted released salmon. Fish with injuries to fins, scales, and eyes had on average up to 20 per cent poorer survival in the 10 days after release compared to fish that were in good physical condition.

Eye injuries, which are related to larger hook sizes, showed a further 20 per cent reduction in survival after 40 days.

“What really surprised me was just how delicate marine salmon are,” says Hinch. “We all know that scales come off these fish when you handle them, but we found the level of scale loss and fin damage caused by landing nets and handling were directly related to their subsequent survival.”

Other findings suggest that coho are less resilient than Chinook to catch and release practices – although more research is needed to determine why.

Hinch and his team have submitted 15 recommendations to Fisheries and Oceans Canada and hope their work can make releasing salmon more fish-friendly.

Among them, they suggest using smaller hook sizes and avoiding gear like treble hooks, tandem hook point set ups, and flashers.

Hinch noted that “anglers should avoid landing nets and keep fish submerged as much as possible during release.”

“There are ways to release fish that will create good survival outcomes,” says Hinch.

A tagged salmon is released back into the water.

Download UBC Full Report

Release strategies best practices

UBC’s report proposes 15 recommendations to improve catch and release methods.

Use smaller hook sizes
Larger hooks are related to more severe injuries and larger gap widths increase probability of eye injury and decrease survival probability. Not all hook sizes are relative across brands or styles, and a gap width of 15 mm (e.g., 3/0 ‘Octopus’ hook) or smaller is recommended.
Avoid treble hooks
Although treble hooks were less likely to cause eye injuries, their use increased hook wound severity and decreased survival probability. This was especially pronounced in smaller fish that are non-retainable in the fishery (e.g., Chinook salmon less than 62 cm) and when hooks are located inside of the mouth.
Avoid tandem hook point setups
Multi-hook setups are prone to multiple hooking locations, which increases the likelihood of a lethal hooking location.
Avoid flashers
In-line flashers cause higher metabolic rates during landing and prolong the metabolic recovery of the ‘fight’ after release. This means fish are less likely able to swim rapidly post-release and would be at higher predation risk.
Land fish as quickly as possible
Prolonged anaerobic exercise (aka burst swimming) increases the metabolic oxygen debt, which can lead to cardiac collapse and increase the cost and time of recovery. This is particularly a problem when water temperatures are warm, flashers are used, and fish are exposed to air prior to release.
Avoid air exposure
Air exposure limits gas exchange across gill tissue, increases anaerobic metabolic costs, and thus, increases recovery time and the probability of mortality. If it’s not possible to avoid air exposure, limit this to less than 10 seconds if fish are to be released.
Avoid using landing nets
The use of landing nets, including ‘fish-friendly’ ones made of rubber-coated mesh or nylon, are all associated with fin splitting, scale loss, and mucous removal. If a net must be used so that fish can be measured, ensure fish remain in the water, and the net remains loose to help avoid contact with fins, dermal tissue, and the mucous layer.
Limit touching of fish
Reduce physical handling as much as possible. Do not use fabric ‘fish-handling’ gloves to handle fish. Physical contact with a fish may remove protective mucous and loosen scales, and while these injuries may appear minor, they provide a pathway for pathogen infection.
Handle with wet hands
When required to handle fish, only do so with bare wet hands. Only touch areas like the caudal peduncle and under the pectoral fins where the fish can be evenly supported, and never hold fish vertically by the tail or touch the gills.
Release fish at the water line
Bringing the fish aboard with a net and handling the fish will cause injuries that can lead to delayed mortality. Use a gaff, or other purpose-built tools, to release fish at the water line to avoid the risk of any physical contact.
Release immediately
Release the fish immediately rather than trying to ‘revive’ them. Revival techniques prolong the stress response and can cause more harm than good. Attempts at reviving when surface waters are warm will further stress fish and can increase post-release mortality. Only delay the release of fish if they appear moribund or have lost full equilibrium.
Avoid small fish
Move fishing locations or increase the size of lures to limit interactions with smaller (e.g., sub-legal) fish as these individuals are more susceptible to injuries and mortality associated with catch and release interactions.
Avoid fishing locations if predators are present
Marine mammals may remove fish from your lines, injure fish during the fight, or capture fish post-release before they have had time to recover from the fight.
Avoid catch-and-release when surfaces waters are at or above 18°C
These temperatures are known to increase mortality post-release. Fish may appear healthy when released, however, the added thermal stress interacts with all other capture and handling factors leading to a much higher probability of mortality.
Lessen your interactions
If you catch a fish that is legal to keep, do so. Do not continue fishing for salmon once you have your legal limit thereby reducing the number of fish that must be released and the number that will experience post-release mortality.

Rethinking Release Strategies

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Release strategies best practices

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