Environmental Engineering Reference
In-Depth Information
for each individual to harvest as much as possible of the resource as quickly as
possible before others can do the same. For example, in the early 1990s, it took
24 h for the Alaskan halibut fleet to catch their annual TAC (Barlow and
Bakke n.d.). However, it is generally necessary to have a TAC underpinning
other management measures. More workable catch restrictions include giving
individual harvesters the right to take a proportion of the TAC, or to kill a cer-
tain number of individuals each year. If these permits are then made tradeable
(called an
Individual Transferable Quota
), a market can develop for them,
which can give substantial advantages in terms of economic efficiency (Kerr
et al
. 2003; Job Monkey 2005).
●
There are lots of restrictions possible on the type of individual caught. These
can include the species caught (e.g. resilient species only), sex (perhaps males
only), age (e.g. adults only) or size class (over a certain length or weight). One
key problem with these kinds of restrictions is
by-catch
—people uninten-
tionally catching the wrong type, and then having either to discard it or sell it
illegally—discards being wasteful and still contributing to mortality of the
protected component of the population, and illegal sales undermining the
whole management plan. Even if by-catch is avoided, there is a need for quite
a sophisticated understanding of population dynamics in order to ensure that
these management rules have the desired effect on sustainability of resource
use. For example, catching only males may work at low levels of harvest,
depending on the mating system, but may cause reproductive collapse at
higher harvest levels (Ginsberg and Milner-Gulland 1994). Restricting
catches to larger individuals can be useful if it ensures enough individuals
reach reproductive age, but in some species (such as fish), the largest individ-
uals are also the most fecund, and removing them can have a disproportion-
ately large effect on population growth. Using restrictions on the type of
individual caught in conjunction with other measures can produce a more
nuanced management strategy, however. For example, giving out permits to
kill only a certain number of full-grown adult males per year is the usual
management method for trophy hunting (Whitman
et al
. 2004).
●
The majority of management plans involve
effort restrictions
, which limit
the amount or type of effort that people can put into harvesting. This then
indirectly limits the amount of catch they can obtain. Typical effort restric-
tions include granting licences to access the resource and limiting the type of
gear that people can use. Effort restrictions are widely used in fisheries because
they are relatively easy to enforce; it can be easier to monitor whether people
have a permit to use a resource, and what type of weapon or boat they are
using, than to monitor their offtake. However, there is a strong incentive to
circumvent them. People will plough their profits from harvesting back into
improving their technology. For example, if the number of harvesters in an
area is restricted to give a sustainable offtake when the calculation is first
made, this same number of harvesters could be taking substantially more a
few years later, when they have all upgraded their hunting equipment.
