Ten seconds is all the time an angler should take to remove
the hook, take pictures and return a fish to water, according to a
recommendation in a recent survey of studies about the impacts of exposing fish
While the length of time of recommended exposure has a lot
to do with the condition of the fish, as well as the temperature of the air and
water, air exposure has a significant impact on post release survival and
behavior, the study says
Air exposure causes inadequate oxygenation of the blood,
known as hypoxia, and damages the gill lamellae, causing physiological stress
and physical damage in the fish that increases with the time the fish is
exposed to air, the study says.
“Our review outlines how extreme care needs to be taken to
reduce air exposure when the landed fish is exhausted, water temperatures are
beyond the normal range, or with known sensitive species,” Katrina Cook said.
She is a PhD student in the Pacific Salmon Ecology and Conservation Laboratory
at the University of British Columbia in Vancouver, BC.
As simple as this may sound, catch and release fishing
regulations seldom require a precise release procedure that would require a
limited exposure to the air, even though air exposure duration is an easy
metric to measure and enforce.
“However, with the appropriate tools, there is little need
for air exposure at all for unhooking and releasing or even measuring and
photographing the fish,” Cook said. “To meet the 10 second target, or even
eliminate air exposure all together, fish should be hooked superficially in the
jaw, not played to or beyond exhaustion, and unhooked while submerged in a
knotless mesh net.”
Longer exposure to air often occurs when a hook is deeply
lodged in the fish, but this can be avoided with the use of tackle appropriate
for the target species.
“The bait and hook types that are best for the welfare of
the fish will depend on the target species,” Cook said. “Generally, however, single barbless circle
hooks (if using organic bait) and artificial lures, especially artificial
flies, typically result in superficial hooking, short handling times, and
limited tissue damage, which will all reduce air exposure.”
In addition, Cook recommended using lines of appropriate
breaking strength so to not excessively exhaust the fish.
When a fish is removed from water, the study says, “a
cascade of physical and physiological disturbances supervene.”
-- damaged gill lamellae, which are responsible for gas
exchange, collapse, gas exchange with capillaries and aerobic respiration
-- the fish develops an oxygen debt, carbon dioxide (acidic)
accumulates and combined with the lactic acid developed during anaerobic exercise,
blood pH drops;
-- the heart rate slows until the fish is returned to the
water. At that point, the heart becomes tachycardic and the longer the fish is
exposed to air, the longer the heart disturbances occur.
These stress responses can be cumulative. In fact, air
exposure is just one issue for a fish that has been hooked or netted: injuries,
exercise and environmental conditions also cause stress that are only
exacerbated by air exposure, according to the study.
“In fisheries where fish ‘fight’ to exhaustion burst
swimming and the resulting power output from locomotory muscles, fueled by
anaerobic metabolism, depletes tissue energy stores and initiates a stress
response,” the study says.
Rainbow trout mortality has been shown to be highest from
air exposure when the trout has struggled to escape. Survival is higher for
fish that remain calm.
Temperature is important, the study says. Bringing a fish up
from cooler water depths to a warmer surface can cause thermal shock. Summer
water temperatures regularly approach critical temperature thresholds “beyond
which only passive anaerobic metabolism is possible, a phenomenon that will
increase as the climate warms,” the study says.
Air exposure can have other affects, as well. A study of
Atlantic salmon found that fish not exposed to air – presumably also not
exposed to a fight for their life – produced twice as many offspring as fish
exposed up to 10 seconds and three times as many offspring as those exposed for
more than 10 seconds.
The survey of literature about fish and exposure to air,
“Fish out of water: how much air is too much?” was published online in the
journal Fisheries http://www.tandfonline.com/doi/abs/10.1080/03632415.2015.1074570?journalCode=ufsh20
Cook’s co-authors are Robert Lennox, a PhD student in the
Fish Ecology and Conservation Physiology Laboratory at Carleton University in
Ottawa, Ontario; Scott Hinch, professor of Fisheries Conservation at the
University of British Columbia and leader of the Pacific Salmon Ecology and
Conservation Laboratory; Steve Cooke, professor of Environmental Science and
Biology at Carleton University and leader of the Fish Ecology and Conservation
Fish exposed to air during commercial fishing operations is
more complicated, more difficult to avoid and more often gear dependent, Cook
said, but overall the 10 second rule sticks.
There are a number of “interacting factors” at play during capture
and handling. While air exposure is a
good way to measure fish behavior, other stressors should also be assessed to
determine “the severity of the capture event,” she said.
“Gillnet capture often results in severe injuries which can
have lasting effects and will act as a cumulative stressor in addition to air
exposure,” she said. “Therefore, as with
any fish-capture scenario, probability of survival following gillnet release
will be improved if air exposure can be reduced or eliminated.”
She went on to say that with severely impaired fish,
“on-board facilitated recovery has shown promise in improving survival.”
Still, reducing air exposure to less than 10 seconds during
commercial fishing is difficult and would require changing methods or gear, the
“Where air exposure cannot be minimized, regulatory agencies
should consider the argument of whether it is ethical to release captured
fish,” the study says. “If a fish suffers physiological or physical trauma from
which recovery is unlikely, harvesting the fish may be the more appropriate