Fish as feed inputs for aquaculture – Practices, sustainability and implications: a global synthesis 27
consume fish eggs and larvae (http//: http://www.fishbase.org),,) and sprat and herring prey
on cod eggs (Stokes, 1992; Köster and Möllmann, 2000). As the abundance of the
larger predatory gadoids has been reduced to low levels, the industrial feedfish that
prey on their juveniles and eggs may now be exerting a higher level of mortality than
previously, and may potentially affect gadoid stock recruitment and slow recovery.
However, it should be noted that such profound trophic impacts are difficult to verify,
given the lack of information and the confounding effects of other impacts.
Genetic impacts
Overfished populations may exhibit the “Allee effect”, which is an inverse density
dependence at low densities (e.g. the per capita birth rate declines at low densities).
The primary factors involved in generating inverse density dependence include genetic
inbreeding and loss of heterozygosity and demographic stochasticity, including sex
ratio fluctuations (Courchamp, Clutton-Brock and Grenfell., 1999). Common factors
behind the Allee effect are not of a genetic nature and can include gregariousness,
sperm competition and cultivation effects.
If a stock collapses and recovers, its genetic viability is harmed due to the reduced
number of genes in the population. However, Stephenson and Kornfeld (reported in
Beverton, 1990) concluded that the Georges Bank herring, which reappeared after a
collapse in 1977 to 1/1000th of the 1967 peak of over 1 million tonnes, has an unchanged
genetic constitution. This result may be an artifact of the limited DNA technology at
the time.
Feed-fish species are characterized by a tendency to shoal. Fishing pressure causes
shoaling fish to reduce their range number and maintain the same average school size
(Ulltang, 1980; Winters and Wheeler, 1985). Consequently, there can be a high number
of individuals in a shoal, which may lead to a high level of genetic diversity within the
shoal (Ryman, Utter and Laikre, 1995). The next question is: what size can a genetically
distinct shoal/or population be reduced to and still recover? Beverton (1990) calculated
that the smallest size that a collapsed population could drop to and subsequently
recover is in the order of a million fish, but local density has to play a role.
4 .2 Criteria and indicators used to measure the sustainability of reduction
fisheries
The FAO Code of Conduct for Responsible Fisheries (CCRF), adopted in 1995, aims to
ensure that the right to fish “carries with it the obligation to do so in a responsible manner
so as to ensure effective conservation and management of the living aquatic resources”.
Together with its Technical Guidelines for implementation and the other international
fisheries instruments developed and adopted within its framework (e.g. International
Plan of Action for Reducing Incidental Catch of Seabirds in Longline Fisheries, IPOA-
Seabirds; International Plan of Action for the Conservation and Management of Sharks,
IPOA-Sharks; International Plan of Action for the Management of Fishing Capacity,
IPOA-Capacity; International Plan of Action to Prevent, Deter and Eliminate Illegal
and Unreported and Unregulated Fishing; IPOA-IUU fishing), the CCRF is now
widely recognized by governments and non-governmental organizations (NGOs) as
the global standard for setting out the aims of sustainable fisheries and aquaculture and
as a basis for reviewing and revising national fisheries legislation.
FAO has also produced technical guidelines on indicators for sustainable development
of marine capture fisheries (FAO, 1999) that outline the process to be followed at the
national or regional levels to establish a Sustainable Development Reference System
(SDRS). The guidelines were produced in support of the CCRF and cover all
dimensions of sustainability (ecological, economic, social and institutional), as well as
the key aspects of the socio-economic environment in which fisheries operate.