these showed the following remarkably similar post-
release mortality estimates: Striped marlin – 14%,
blue marlin – 10%, black marlin –14%, sailfish –10%
and white marlin – 11%.
A SURPRISE RESULT
One of the surprises of this key analysis was that gear
type had no effect on results. In other words, survival
rates were similar for fish caught on rod and reel and
on longline, or even when tags were placed in fish by
harpoon, as was done in Taiwan (one harpoon-tagged
marlin was predated upon). In fact, only one study
in which circle hooks and J-hooks were compared
showed a significant difference in gear type – circle
hooks being clearly superior with respect to survival
in that case.
Even fight time was not a significant factor in
predicting survival after release, although the authors
noted some caveats regarding this result, suggesting
that fight intensity may affect stress levels more than
fight duration.
The bottom line from this meta-analysis – an estimated
14% mortality (or 86% survival) of billfish caught and
released using normal game fishing methods – has
since been quoted widely. While this does not pose an
issue, the authors are also careful to point out that
more data added over time, especially from larger
studies, will help to further refine the overall figure, as
well as the figures for individual species.
LIFTING MARLIN FROM THE WATER
I’ll finish with a short discussion of one more study,
which was carried out on white marlin by Dr John
Graves and others. The results of the study were
widely reported that removing fish from the water for
relatively brief periods could prove to be fatal. This
message was quickly picked up in game fishing circles
and was used to amplify calls not to lift small marlin
from the water for photos, and that doing so may
prove to be a death sentence. However, this was not
entirely accurate.
The study involved the tagging of 18 white marlin
with pop-up tags. All fish were lifted onto wet mats
and their duration out of water timed. Six of the fish
were exposed to air for one minute before release,
five fish for three minutes and seven fish for a full five
minutes. During their time on the deck, their eyes
were covered with wet cloths and the PSATs carefully
applied. All fish were then resuscitated in the water for
three minutes before being released.
Tags were programmed to pop-up after 30 days,
with the subsequent results indicating that seven of
the 18 fish had died within this period. Of those, one
was eaten by a shark nine days after release, which
was assigned as a natural predation event. Of the
remaining six fatalities, one of the six fish on the deck
for one minute died, two of the five fish exposed to
air for three minutes died and four of the seven fish
exposed for five minutes died.
SURVIVED 5 MINUTES IN AIR
Overall, these mortality rates were much higher than
for white marlin not removed from the water, as shown
in earlier studies. However, looking at the results in
another way, the fact that 60% of fish exposed to air
for three minutes and 43% of the fish exposed to air
for a full five minutes survived was a very interesting
finding, and not at all indicative of many posts on
social media that were suggesting all marlin die if
lifted from the water even for a brief photo.
We have come a long way from the days of
speculating on the fate of billfish once they have been
released. The elation of watching that beautiful fish
swim away, slowly beating its tail, was often tinged
with a nagging doubt about its fate. However, with the
advent of electronic tags, we now know the survival
chances are high – even approaching 100% when
caught on circle hooks or lures – and providing it can
avoid predation, in the short term at least.Anglers are
sometimes criticised
for momentarily
holding small
billfish for a photo,
but these fish are
actually remarkably
hardy – as long
as they are not
dropped or otherwise
damaged, including
scraping off their
protective slime
coating. A study
showed that 60%
survived even after
exposed to air for
three minutes, and
an amazing 43%
of the fish survived
after being held out
of the water for a full
five minutes!bluewatermag.com.au 57Life after release