The Pacific Islands
Fisheries
Group has been administering a tagging project throughout the Hawaii
Archipelago that targets the seven deepwater bottomfish (the Deep
7)—onaga, ehu, opakapaka, kalekale, hapuupuu, gindai and lehi. As part
of the project, Hawaii bottomfish fishermen have been field-testing
developed techniques to release deepwater bottomfish in a manner to
promote their health and survivability.
When bottomfish are brought up rapidly from deepwater to the surface,
they can experience “barotrauma,” which is physical damage to body
tissue that is caused by rapid changes in the surrounding (or ambient)
pressure. Barotrauma occurs because gases are compressible but the
tissues are not. When bottomfish are brought rapidly from deep waters
where the pressure is high to the surface where the pressure is
significantly lower, the gas inside the air spaces in the body can
cause damage to the surrounding tissues if that gas becomes trapped.
Bottomfish that appear lively and are in good shape are not
experiencing barotrauma and can be returned to the ocean immediately
without any treatment.
Bottomfish that come up showing signs of barotrauma—bloating, bulging
eyes, stomach protruding through mouth and/or popped scales—should be
treated before released or should be released in a manner that quickly
returns them to higher pressure depths. These methods are explained
below.
METHODS FOR HANDLING
BOTTOMFISH SHOWING SIGNS OF BAROTRAUMA
1) Venting — Venting a fish’s swim
bladder is one way of treating barotrauma. Venting consists of
puncturing
or piercing the swim bladder to allow gases to escape. Once vented, the
fish can be released. The
faster the fish is treated the better its chance for a full recovery.
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Tools:
1/8-inch hollow
tube about 6
inches long with
one side sharpened
or a syringe
needle
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(left)
Ehu's
stomach
pushed
back
into
stomach
cavity
after
venting
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Steps for Venting the Swim Bladder:
Insert the hollow needle (or syringe) at
a
45-degree angle towards the bottom of the stomach in line with
the pectoral fin and below the 4th dorsal spine. Push the needle gently
through the skin to puncture the swim bladder.
If the procedure is done correctly, air should be heard escaping
through the hollow needle and the stomach will deflate. (The swim
bladder has been known to heal in a matter of days in some species and
weeks in others.)
If the fish is vented and the stomach protrudes out of the fish’s
mouth, use a smooth or rubberized dowel to push the stomach back into
the stomach cavity. This will prevent the stomach from obstructing
water flow through the fish’s gills as it descends to the bottom and is
recommended when using “drop shoot.”
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2) “Drop Shot Weight Release” - Fish
can be returned to the bottom by using a release weight. Test have
shown that fish do not require venting if using a release weight as
gases in the swim bladder recompress as the fish returns to the bottom.
However, if the stomach protrudes out of the fish’s mouth, use a smooth
or rubberized dowel to push the stomach back into the stomach cavity
after venting. This will prevent the stomach from obstructing water
flow through the fish’s gills as it descends to the bottom.
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A) Pass the hook on the release
weight from behind, along the gill
plate and gills out through the
fish’s mouth.
B) Next, drop the fish head first
into the water. If the fish is larger,
reduce the margin of error for
timingthe release of the fish with
the weight by using the optional “dropshoot.” (below) The drop shoot
provides safe handling of larger
fish during release and also eliminates
the need for two persons.
C) Once the released fish reaches a
minimum depth of 25 fathoms, pull
sharply on the line to release the
fish.
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Tools:
(above) Barbless hook mounted
on a 5-lb dead wieght and
attached to a release line.
(below) Optional "drop chute"
made of 8-inch by 3-foot
PVC pipe cut length wise
in half with a nylong
rope handle
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Optional
“Drop chute”
release for
larger fish
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The
Pacific Islands Fisheries Group is a 501c3 non-profit organization. For
more information about PIFG, the tagging
project or on the release techniques for bottomfish species, visit
www.fishtoday.org or call 808 265-4962.
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