LEWISTON — According to a study by a University of Idaho graduate student, anglers are more likely to catch hatcheries than wild rainbow trout in the Snake River Basin.
The student, guided by a professor from the Idaho Cooperative Fish and Wildlife Research Unit, documented catch-and-release mortality rates were below the 5% level assumed by state fisheries officials and of the federal government. Both of these findings could help fisheries managers justify sometimes controversial recreational fishing seasons that target hatchery fish but also involve handling protected wild rainbow trout.
“Overall encounter rates with hatchery fish are actually higher than encounter rates with wild fish, and we’ve seen that pretty consistently over the two years of spawning,” said Will Lubenau, student. graduate, who recently defended his master’s thesis based on this work. “It’s about 20% higher on average.”
Lubenau spent two years tracking rainbow trout on the Snake River and its tributaries. In a cooperative study involving the Idaho Department of Fish and Game, UI, and the US Geological Survey, Lubenau placed visible tags on wild and hatchery adult rainbow trout intercepted at the Lower Granite Dam or captured by him and IU Professor Michael Quist on the Clearwater River. . Anglers who subsequently caught tagged fish were asked to remove and report the tags, some of which carried rewards of up to $200.
The fish were also implanted with tiny passive embedded transponder tags that can be detected by PIT tag readers placed at the mouths of spawning tributaries, at hatchery facilities and at downstream dams.
The combination of tags allowed Lubenau and Quist to track the fish in the study and determine how many of them were caught or not caught, and how many of each group were later detected entering the streams. spawning, hatcheries or attempting to pass the Snake or Columbia River dams. with the aim of returning to the ocean after spawning.
The researchers were also able to calculate a mortality rate for fish caught and released by comparing the subsequent detection rate of fish known to have been caught with fish whose capture was not documented.
Lubenau said that in the 2019-20 season, about 30% of wild rainbow trout in the study were caught at least once and 57% of hatchery fish were caught. In the 2020-21 season, 37% of wild fish and 52% of farmed fish were caught. In both years, approximately 35% of wild fish and 53% of hatchery fish were caught by anglers.
He documented a catch-and-release mortality rate of approximately 3.8%. When he looked at the mortality rate only for fish with reward tags, he found a mortality rate of 3.9%.
Quist said the work gives Idaho Fish and Game biologists a better idea of the more accurate encounter rates of wild fish. The agency now assumes that wild and hatchery rainbow trout are caught at the same rate.
Wild rainbow trout in the Snake River Basin are listed as threatened under the Endangered Species Act and anglers who catch them while fishing for hatchery rainbow trout are required to release them. State fisheries agencies must obtain federal permits to ensure that their fisheries do not further harm endangered species. Throughout the Northwest, state fisheries agencies assume that 5% of wild rainbow trout that are caught and released die from encounters.
The study showed that the 5% assumption is close and probably sufficiently conservative. He also illustrated the supposed encounter rate of wild fish is considerably higher than what happens. Work by a former UI graduate student, Stacey Feeken, suggests that wild fish are likely caught at a lower rate. Feeken tracked hatchery and wild rainbow trout in a previous study, as well as where anglers concentrate their fishing efforts, and showed that wild and hatchery fish often occupy different stretches of river. , and that fishermen focus their efforts in areas with more hatchery fish.
Lubenau’s study builds on Feeken’s work, and Quist said the results are good news for anglers, wild fish and fisheries managers.
“It’s relevant to the conservation of wild fish and it’s also relevant to recreational fishing, so it’s good news all round, really, because it shows the rate of impact – how many wild fish are handled by fishermen and eventually die as a result of fishing – is going to be pretty trivial,” he said.
The study found that some fish are caught more than once, about 31 over the two years. But these twice-caught fish had almost identical post-capture detection rates as fish documented as having been caught once.
“These fates are essentially the same, 70% versus 71%, which is going to suggest that the multiple captures – first of all, they don’t happen that often in the basin, and when they do happen, they seem to survive the encounter several times quite well,” Lubenau said. “It just doesn’t seem like a big concern.”
Brett Bowersox, a fish and game fisheries biologist in Lewiston, said the results should not prompt the agency to make any changes to how it manages rainbow trout fishing seasons in short term.
“It illustrates the management scheme or how we calculate the impact of fishing has been conservative,” he said. “That’s the good side of that equation that we want to be on, to manage prudently when it comes to a valuable wild fish resource and a valuable recreational fishery.”
Lance Hebdon, fisheries chief for the Idaho Department of Fish and Game in Boise, said the study results could prompt the agency to examine how it calculates wild fish encounter rates. , but he would like it to be repeated. He noted that the work was done during a period of low rainbow trout abundance.
“For the last five years we’ve operated on wild runs and pretty weak hatchery runs,” he said. “It would be nice to repeat that when the races rebound.”