from the Columbia Basin Bulletin
www.cbbulletin.com
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 to air.
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 stops;
-- 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 Physiology
Laboratory.
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
study says.
“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 action.” |
