R
ecreational anglers release a lot of fish, and
they do so for two main reasons – because they
are either required by law to do so, or because
they choose to. Many anglers choose to release
legally caught, highly desirable fish, often targeting
them with release being the intention right from the
outset – with or without a tag.
Whether mandatory or voluntary, there is an inherent
expectation that the majority of the fish returned to
the water will survive and reproduce. For example, a
national survey of Australian anglers in 2002 found
that 84% believed that released fish benefit the fish
stock, and that 76% believed that most fish survived
post-release. But what proportions of fish really do
survive being caught and then let go again?
One way to find out is to keep fish contained after
catching them and see how many survive, which is
exactly what has been done in studies right around
Australia. Over the past decade or so, pen-holding
experiments have been conducted on many of the
popular angling species of fish, including bream,
whiting, flathead, snapper, tailor, Australian bass and
even tropical reef species such as coral trout and red
emperor. The results show variable survival rates, with
most ranging from 75% to 90% survival, and some
even approaching 100%.
However, for highly mobile, oceanic fishes such as
billfish, tuna and pelagic sharks – which obviously
can’t be held in captivity for observation – some other
way of determining post-release survival rates was
needed. The solution to this problem came in the form
of electronic tags.ACOUSTIC TRACKING
Acoustic or ultrasonic tags emit audible pings by which
fish can be tracked in real time using underwater
microphones – also known as hydrophones. The first
acoustic tags attached to billfish were ‘home-made’
models used with some success in the late 1970s
on small numbers of sailfish off Florida. Commercial
‘pingers’ came on the market in the late 1980s and
proved effective in the tracking of striped marlin off
California and blue marlin off Hawaii. Not only did
each of these early studies reveal new information
on the behaviour of these species, they also were the
first to record actual mortalities of some released fish.
I was fortunate to be involved in some of this early
work, in large part thanks to David Tomlinson and
the use of his 46ft Bertram Flamingo Bay. Over three
trips to the Great Barrier Reef, we managed to tag
eight black marlin using acoustic tags. One of thoseBefore pop-up satellite tags
gave us a definitive answer,
we were never quite sure
whether the billfish we released
survived. Now we know the
great majority do.bluewatermag.com.au 51