fish were being noted in studies of movement and
behaviour, generally speaking, only fish considered
to be healthy were selected to carry the expensive
equipment (what we might call ‘high-grading’).
Funding has since been found for some serious
studies devoted to answering the question of survival
rates of billfish and other species caught and released
under normal recreational fishing practices.
In what was probably the earliest study of this kind,
colleagues of mine, Drs John Graves and Eric Prince,
tagged nine blue marlin with PSATs off Bermuda to
specifically measure post-release survival. All fish were
caught on rod-and-reel using lures or skirted baits.
Importantly, fish were not selected for condition. The
tags were set to pop-up five days after release. The
results showed that eight of the nine marlin survived,
with one tag failing to report. Assuming for the sake of
the argument that the non-reporting tag was the result
of a short-term mortality, blue marlin survival rate in
this pioneering study translated to 89% – a figure that,
as we will see, is very close to a generalised survival
rate calculated from the accumulated data from many
other later billfish studies.
In another important series of experiments, Dr Graves
and his team used PSATs to tag a total of 41 white
marlin. Twenty of these were caught on baits rigged
on circle hooks, with the remaining 21 caught on baits
rigged on ‘J’ hooks. Tags were programmed to pop-up
after 5 or 10 days. Remarkably, survival rates were up
to 100% for fish caught on circle hooks and 65% for
fish caught on ‘J’ hooks. And then to test the effects of
hook design, Graves conducted a larger experiment in
which 20 white marlin were caught on each of three
slightly different shapes of circle hooks. Of the 59
PSATs that reported, only one indicated a mortality,
indicating a survival rate of 98% for this study.
In another study that has not been very well
publicised, researcher Dr Michael Musyl and others
used PSATs to tag and release 37 lure-caught blue
marlin off Hawaii. Thirty tags reported, of which only
one indicated a mortality. That occurred 82 days after
release and was regarded as a natural predation
event. As is often the case in these studies, it is
possible that some of the non-reporting tags were
also due to mortalities, although this is impossible to
confirm or disprove.POSSIBLE FALSE ASSUMPTIONS
In a large study of striped marlin post-release survival
off California, Drs Michael Domeier and Nicole Nasby-
Lucas tagged 80 fish with PSATs. Fish were all caught
by standard recreational fishing methods in that fishery
using livebait, with no high-grading of fish based on
condition undertaken. Results were interpreted as
showing 16 of 61 fish died within five days of release,
for a mortality rate of 26%. Furthermore, 100% of fish“Survival
rates were up
to 100% for
fish caught on
circle hooks
and 65% for
fish caught on
‘J’ hooks.”
Billfish caught
with circle hooks- especially non-
offset circle hooks –
showed an extremely
high percentage
of survival after
release.
bluewatermag.com.au 55Life after release