A six-year UBC study finds injuries from hooks, nets and handling as leading to high mortality rates of coho and Chinook salmon.
Using smaller hooks, having wet hands when handling, and de-hooking and measuring fish in the water are among the 15 solutions in the study, presented Friday at the Sports Fishing Institute of B.C. conference in Vancouver.
“Historically, research into this area has been pretty scant,” said Scott Hinch, lead author and head of UBC’s Pacific Salmon Ecology and Conservation Lab, in an interview before the conference.
Capture and release has become increasingly common in B.C. as salmon stocks have declined and regulations have restricted the size and number of fish that anglers can keep, the study notes. However, catch and release allows fishing opportunities to continue. But the downside, said Hinch, is that many die later from injuries sustained during the process.
For more than half a decade, the UBC team has worked with several agencies, including the sports fishing institute and Canada’s Fisheries Department, to conduct a large-scale acoustic telemetry tracking program that included more than 100 underwater listening stations.
“We used that infrastructure to be able to track the movements and survival of our coho and Chinook,” said Hinch, adding the team also involved graduate students who caught and tracked more than 1,500 Chinook and coho salmon in B.C. waters.
And what they found was that many Chinook and coho salmon that had been caught and released didn’t survive because of injuries to fins, scales and eyes. Coho were the most vulnerable to injury.
“We looked at the amount of bleeding, how much scales they had lost, how wounded, and the damage to their fins. And so we brought this all together to relate that to the survival, because we can track these fish,” he said.
The study shows these injuries reduced survival by 20 per cent up to 10 days after release compared with fish in good condition when released, and another 20 per cent after 40 days, he added.
“This is a simple fix. If you were to release a fish that didn’t have an eye injury, did not bleed very much, did not lose too many of its scales, it would have 100 per cent survival for the first 10 days. So that’s a pretty dramatic difference,” said Hinch.
Ocean temperatures above 18 C also contributed to higher mortality among fish that were caught and released, which is why experts are recommending anglers don’t use this practice in warmer waters.
Hinch is confident that their recommendations will be adopted because they have been working with industry partners throughout the project.
“We’re expecting we’ll get pretty rapid uptake, both from a DFO perspective, but also from the anglers themselves, who are kept informed by our partners at the Sport Fishing Institute,” he said.
Another recommendation in the report is to avoid exposure to air, which increases fish recovery time and the probability of mortality. If it’s not possible to avoid air exposure, limit to 10 seconds, said Hinch.
Here are the 15 recommendations to improve catch and release methods:
1. 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.
2. 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.
3. Avoid tandem hook point setups
Multi-hook setups are prone to multiple hooking locations, which increases the likelihood of a lethal hooking location.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 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.
12. 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.
13. 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.
14. 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.
15. 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.