Page 9 - Fishery_Regimes_2005

Forewords

The management objective of local fisheries has been to maintain the viability
of traditional fisheries and the existing fleets. In other words, to make
fisheries sustainable and prevent overfishing.

The traditional measures for the management of coastal fisheries rested on
the basis of singled-species models of population dynamics and the concept of
maximum sustainable yield. They consists in controlling the catch and
recommending a total allowable catch, and in to establish seasonal closures
and gear specifications to guarantee a minimum size of fished individuals of
target species and then, to ensure enough reproductive success and
recruitment.

Most fisheries biological research has been oriented to provide information on
the biological and ecological consequences of the reduction of the stock
abundance, to predict recruitment and to estimate the parameters which
define the population dynamics. Despite the huge amount of information and
knowledge accumulated during the last decades, the traditional management
tools have been insufficient to prevent overfishing of target and by-catch
populations and their ecological consequences. More recently, fishery
biologists have advocated a more ecological approach to fishery management
by developing the concept of “Ecosystem approach to fisheries”, based on a
series of principles whose general purpose is, as acknowledged by FAO, to
plan, develop and manage fisheries in a manner that addresses the multiple
needs and desires of societies, without jeopardizing the options for future
generations to benefit from the full range of goods and services provided by
marine ecosystems. This approach recognize explicitly that fisheries have the
potential to alter the structure, biodiversity and productivity of marine
ecosystems, and that natural resources should not be allowed to decrease
below their level of maximum productivity. Nevertheless, translation of these
aims, concepts and principles into actions is hard to achieve in practice.

In recent years, marine reserves have been strongly advocated as an ideal
tool for the management of coastal fisheries, and a large number of marine
protected areas (MPAs) have been established around the world, in an
attempt to halt further deterioration of sensitive habitats, or serving as
fisheries management tools. Marine fishery reserves are intended to protect
critical spawning stock biomass, intraspecific genetic diversity, population age
structure, recruitment supply and ecosystem balance, while maintaining
fisheries.

In theory, those effects are important, not only for the preservation of the
structure of populations where fishing is prohibited, but also for ensuring the
gene flow between more or less distant populations and to export biomass to
the surrounding areas so that fisheries take advantage of the protection.
Potential spillover could be important in larval phases and for pelagic species,
but also for non-pelagic fishes and some invertebrates such as lobsters or
shrimps that may spend enough time inside the reserve to experience a
significant reduction in fishing mortality while having the ability to move
outside the protected area.

The effect of fishing restrictions on the density, size structure and biomass of
fish populations inside the reserve has been thoroughly investigated and
demonstrated and some evidences that marine reserves also preserve the
gene pool and genetic diversity have been recently provided. However, the
quantification of the benefits on fisheries and the mechanisms involved are
still under speculation and numerous studies find difficulties in detecting the
exportation of biomass from MPAs to surrounding areas.