While mulloway are still juveniles, they are captured
using a small otter trawl, with a six-metre mouth. The
trawl is towed behind our zodiac at a speed of about
1-2 meters per sec., and each tow lasts for anywhere
between 5 minutes and 30 minutes.
Trawl being towed behind the Zodiac in Smiths
Lake, New South Wales. The person in the aluminium
dingy is inspecting the operation of the trawl.
Trawl being retrieved after a tow. The trawl
is deployed and retrieved manually by two people, while
a third person operates the Zodiac and records information.
As well
as catching mulloway in the trawl, we also get yellowfin
bream, small fish including gobies, glassfish, hardyheads
and dragonets, and small mysid shrimp and school prawns.
All fish are quickly counted on board the Zodiac and returned
to the water, while the mysid shrimp and school prawns
are taken back to the lab and quantified in terms of weight
of length frequency. Mysids and prawns are among the favorite
food of juvenile mulloway, so by monitoring their abundance
over time we tell if the mulloway are overgrazing these
species in an area.
After the fish have been released for
around 6-8 months, they grow too large and smart and are
able to escape the trawl. At this point they must be sampled
using hook and line, in much the same fashion as recreational
fishers catch them.
