A University of Canterbury mathematician is urging a
revolution in the way the Western world catches fish.
Dr Michael Plank believes fish populations would be
healthier, and catches bigger, if there was less emphasis on
catching big fish.
Dr Plank is a senior lecturer in the department of
mathematics and statistics at the University of Canterbury
and was guest speaker at a meeting of the Wanaka branch of
the Royal Society of New Zealand last week.
He told the Otago Daily Times his group's mathematical
modelling showed it would be beneficial to introduce
''balanced harvesting'' - so more smaller fish and fewer
larger fish were caught.
''It's very ingrained in people's thinking that you shouldn't
catch small fish and you should target big fish.
''We think it might be better to catch a range of sizes so
you are catching a balanced cross-section.''
Dr Plank said his mathematical modelling consisted of
creating computer-based fish populations.
''And essentially I play God with them.
''By using the models we have gained an understanding and
intuition about the way that how we fish affects what happens
to the fish populations in the long term.
''That process has suggested this idea and it has suggested
it is promising and that it's something to test.
''It's not a silver bullet that's going to solve all our
fishing problems. You have still got to make sure you don't
Dr Plank said deep-sea trawlers had the technology to target
Their trawl gear was equipped with a grill known as a
''turtle exclusion device'' and that could be used to stop
big fish entering the net.
Dr Plank said fishing practices of the industrialised West
were less well balanced than those of poorer African
countries, which were ''less regulated''.
''It's essentially men going out in boats to catch whatever
they can find.''
Dr Plank said he was not advocating changing fishing
practices ''completely tomorrow''.
However, the fishing industry and regulators could begin to
make a gradual change to balanced harvesting by catching a
few less big fish and a few more smaller fish.
Dr Plank said there were two big advantages in balanced
It kept the ecosystem in a ''natural state of balance'' and
it increased the amount of fish that could be taken.
''By targeting this cross-section of sizes, our results show
you can actually catch a greater overall weight of fish.''
Dr Plank agreed it would be difficult to catch a range of
sizes of fish species that intermingled but it was not
impossible: ''you have quotas for different species but you
also have quotas for different sizes as well.''
The results his group had achieved so far were ''feeding
into'' European Community policy-making.
''It's starting to get a bit of traction with the
The change to smaller fish would require consumers to adapt
but Dr Plank said there were already big markets for small
fish in Asia and the Mediterranean.
''They eat them whole - fish, bones and all. They are healthy
and good for you.''