Globally, 60 percent of fish caught by recreational anglers
are released and many of those anglers use manual release techniques they
believe will help the fish survive.
However, according to a recent study, many of those fish
will live just a short period of time. The delayed mortality rate can be as
high as 35 percent and, as this study determines, catch and release is deadly
for female fish.
Overall, manual release techniques have little to no impact
on survival, the study concluded.
The study, published online June 2, 2015 in the Transactions
of the American Fisheries Society, concludes that the techniques of releasing
fish promoted by conservation and angling groups simply does not result in a
mortality benefit for fish, at least for the tens of thousands of sockeye
salmon caught and released by anglers every year in British Columbia’s Fraser
(In 2011, recreational anglers released 62,642 sockeye
salmon out of 145,291 caught in the Fraser River system, a 43 percent release
“This was the first study to examine the extent to which
different recovery techniques help fish to recover from catch-and-release
fishing events,” said co-author Dr. Steven Cooke, Associate Professor of
Environmental Science and Biology at Carlton University in Ottawa. “Given that
so many anglers spend time recovering fish after capture, we expected recovery
would be uniformly beneficial, but that was not the case.”
He added that the benefits of using recovery techniques
depends on the condition of the fish at release, with the “greatest benefits
for the fish that were in the roughest shape.”
Delayed mortality of fish released from anglers is due to
injury or the “inability of the fish to regain physiological homeostasis,” the
report says. It begins with the “burst swimming” the fish goes through while
being fought by the angler.
In technical terms, the report says, burst swimming events
are “fueled by anaerobic metabolism of glycogen resulting in the accumulation
of metabolites (e.g., lactate and protons) in white muscle and plasma, which
will ultimately alter the acid-base status and cause ion-osmoregulatory
And then there is the exposure to air when the fish is
landed, the hook is removed and, in some cases, the fish is photographed prior
The recovery technique most recommended by angling groups is
to cradle the fish in the water, holding its head upstream, allowing the fish’s
gills to work and to take in oxygen. That oxygen uptake must exceed the normal
metabolic rate of oxygen intake, according to the report.
The researchers did two field experiments. In the first
experiment on Harrison Rapids sockeye salmon, salmon were seined from the
river, put through stressful forced exercise to imitate burst swimming, then
released immediately, exposed to air and released or released after using the
manual recovery technique.
The second field experiment used actual anglers to catch and
release the fish from the Fraser River, releasing them immediately, after
exposure to air and after using the manual recovery technique.
In the first experiment, 25 of 140 (17.9 percent) salmon
survived to reach their natal spawning areas. Of these fish, there was no
significant effect of ventilation assistance, the report says.
Survival did not differ significantly between the group that
received assisted ventilation (4.3 percent) and the group that did not (9.8
percent). Some 42.9 percent of fish survived that were released immediately
following capture. Female fish did not survive to reach their natal spawning
areas unless they were released immediately after capture (in this case 36
percent survived, while 52.9 percent of males survived under this scenario).
Survival was better for the angling experiment, with short
term survival (72 hours) achieving 73.3 percent at an upstream receiver station
under all three scenarios (immediate release, after exposure to air, after
using the manual recovery technique).
The results of the field studies led the researchers to
conclude that there is no evidence of any benefit to migration success by using
the manual recovery technique. However, the most exhausted fish could still
benefit from the technique.
“More vigorous fish may not benefit from recovery, whereas
more impaired fish may reap the potential benefits of increasing the oxygen
available for uptake during excess post exercise oxygen consumption,” the
That is a clue for anglers as to when to use the recovery
technique. If the fish is unable to maintain equilibrium and drifts downstream
for an extended period, it would benefit from the technique.
On the other hand, if a fish is exhausted but able to
maintain equilibrium, “holding that animal in the river current may simply
represent an unnecessary and additional handling stressor.”
“The best strategy is to treat fish in a manner such that
they do not become totally exhausted and are able to swim away under their own
volition upon release,” Cooke said. “We suggest that efforts to help revive
fish should be limited to those individuals that are truly exhausted and unable
to maintain equilibrium or have the vigor to swim away.
“For those fish that are in good condition, retaining them
to ‘help them recover’ may in fact reduce their survival,” he said.
The report, “Influence of Postcapture Ventilation Assistance
on Migration Success of Adult Sockeye Salmon following Capture and Release,”
can be found at
In addition to Cooke, study authors are Kendra Robinson, at the
time of the study a Master of Science student at the University of British
Columbia and now with Fisheries and Oceans Canada; Scott Hinch and Michael
Donaldson, Pacific Salmon Ecology and Conservation Laboratory, UBC; Graham
Raby, Fish Ecology and Conservation Physiology Laboratory, Carleton University;
Dave Robichaud, LGL Limited Environmental Research Associates, Sidney B.C.; and
Donald Patterson, Fisheries and Oceans Canada.