A study has found catch-and-release sportfishing practices that leave salmon with injuries, particularly to their eyes, cause higher mortality than earlier research suggested.

Scott Hinch, who led the study by researchers at the University of British Columbia, said mortality among chinook salmon could be as high as 40 per cent, depending on environmental conditions and injuries sustained during capture and release.

At the same time, the years-long research that was supported by the Sport Fishing Institute of B.C. found that a series of changes in anglers鈥� practices could boost salmon survival.

Hinch said it may be as simple as using smaller hooks, avoiding landing nets and handling fish as little as possible.

鈥淵ou can make those decisions as an angler, you know, make sure that when you are releasing, you鈥檙e doing it the best way possible,鈥� said Hinch, associate dean and professor in the university鈥檚 department of forest and conservation science.

鈥淚鈥檓 not sure how this will flesh out in the near term, but I certainly would like to see all our recommendations, in some fashion, become regulations,鈥� he added.

The study found chinook salmon caught off the east coast of Vancouver Island that were released in good condition had short-term mortality rates between zero and eight per cent over the course of the study, while good-condition coho were less resilient with 17 per cent short-term mortality.

But different injuries, environmental conditions and fishing practices could affect survival significantly.

The research, which involved tagging and tracking more than 1,500 salmon off B.C.鈥檚 coast, found injuries to eyes, fins and scales reduced survival rates for chinook by 15 to 20 per cent within 10 days of release.

Eye injuries were linked to a further 20 per cent mortality boost after 40 days.

鈥淪o (it) could be as high as 40 per cent mortality, depending on the context, depending on how the fish was injured,鈥� Hinch said in an interview.

He said previous studies were shorter term, generally observing fish in holding pens for a few days and finding mortality of five to 10 per cent.

The new study shows certain types and sizes of fish don鈥檛 respond well to the practice, and catch-and-release is 鈥渘ot the panacea鈥� for salmon鈥檚 woes, Hinch said.

Still, he said the findings allowed researchers to identify practical solutions to help boost survival rates while supporting the long-term sustainability of salmon populations struggling with the effects of climate change and habitat degradation.

The study found a 鈥渟trong size effect鈥� on survival, with smaller coho and chinook both suffering higher mortality rates than larger fish. Every one-centimetre decrease in length was associated with a six per cent increase in coho mortality about three days after release.

鈥淚f you have to make a decision of whether you鈥檙e going to keep the fish or not, and it鈥檚 legal to keep, and it鈥檚 got a serious eye injury, maybe you keep that one even though maybe it鈥檚 not quite as big as the one you were hoping to get,鈥� Hinch said.

The researchers recommend that anglers use smaller hooks and avoid flashers 鈥� a shiny type of fish attractor 鈥� as well as treble and tandem-hook setups, all of which are linked to higher mortality.

The list of best practices also includes landing fish as quickly as possible and avoiding landing nets, even those marketed as 鈥渇ish friendly,鈥� Hinch said.

鈥淏oth chinook and coho, when those nets are used to bring them out of the water, into the boat, they still get their fins damaged. Their fins split, regardless of what the webbing material is made of,鈥� he said. 鈥淎nd we showed pretty clearly that when you start damaging the fins 鈥� the poorer the survival outcomes were.鈥�

If a net must be used, the report says anglers should ensure it鈥檚 loose, and salmon should remain in the water throughout the process to minimize exposure to air.

The study was largely funded through the B.C. Salmon Restoration and Innovation Fund, a joint initiative with Ottawa, while a steering committee involved the federal Fisheries Department and members of the Sport Fishing Institute of B.C.

Members of the sport fishing institute helped with some of the field work, and Hinch was set to present the paper at the group鈥檚 annual conference on Friday.

鈥淭hey are a strong supporter of our recommendations,鈥� said Hinch, adding the Fisheries Department has also expressed interest in adopting them.

Hinch said the study also revealed a link with climate change and warming waters, as salmon will start struggling in water temperatures of 18 C and higher.

鈥淲hen you start to capture fish in those temperatures and you鈥檙e making them struggle 鈥� and then you鈥檙e exposing them to air, possibly, depending on your practices, that can have really strong negative outcomes,鈥� he said. 鈥淭he temperature is the facilitator that makes air exposure and handling even more lethal.鈥�

The findings have led the researchers to suggest that anglers avoid catch-and-release altogether when water temperatures hit 18 C or warmer.

鈥淚t鈥檚 simple things 鈥� but we have to then enact them, and hopefully there鈥檚 enough goodwill and understanding among anglers,鈥� Hinch said. 鈥淚鈥檓 pretty sure there is, because I鈥檝e worked with a lot of them now, and they all want to do the right thing.鈥�

Brenna Owen, The Canadian Press