Fish and Fisheries is
one of the five modules in
the large marine ecosystem approach to ecosystem-based management.
It merits special consideration because of
the importance of fisheries to countries for food security,
for their economic value,
and also for their links to cultural heritage.
But it also is important because fishing operations impact marine ecosystems.
Information in the Fish and Fisheries module is used to assess the abundance,
and the health of important marine species targeted by
capture fisheries and mariculture and also the health of the ecosystem.
These assessments can draw on traditional fisheries data and stock assessments,
but when interpreting changes in fish populations and fisheries,
the direct impacts of fishing can be difficult to
disentangle from other influences caused by climate change,
pollution, ocean acidification, and a range of other factors.
For adaptive ecosystem-based management,
these effects of multiple factors need to be considered.
Information is also required to consider the impacts of
fishing on the whole ecosystem through its effects on habitats,
biodiversity, and the marine food web
all of which feedback to the state of the fish stocks.
Mean annual global fish catches can be analysed and presented in various ways,
but these generally show that the catches peaked in the 1990s.
The available reported data indicate a leveling off of catches from the 1990s onwards,
but when these data are supplemented by
unreported catches the reconstructed data set indicates a decreasing trend.
Today, many large marine ecosystems have fish stocks that are
classified as being collapsed or over-exploited and
over-fishing is a common ecosystem issue identified in
TDA reports from almost all large marine ecosystems.
In addition to impacts on the fish that are caught,
fishing also impacts marine ecosystems in a number of ways.
Ecological impacts result when a fished population is
reduced causing cascading effects up and down marine food webs.
There can be impacts on the prey, the predators,
and the competitors of the fished population as well as
on other species caught as bycatch in the fishing operations.
Ultimately, unregulated and poorly regulated
fishing activities impact human welfare in terms of food security,
employment, and economic benefits.
The indicators for fishing generally are constructed by combining
information in order to summarize complex processes often as a single number,
which then needs to be easy to understand and to communicate.
Fisheries indicators are used in traditional fisheries management where information
is collected and analysed for single fish species or sometimes for species groups.
Traditional fisheries indicators can be used
to guide single species fisheries management,
but under an ecosystem approach,
these need to be supplemented by ecosystem indicators to allow
assessments of the state of the whole fish community or of the whole ecosystem.
A number of research groups have been working on developing and applying
indicators to support an ecosystem approach to fisheries management.
Another useful resource for indicators is provided
by the Sea Around Us Project in which scientists from
the University of British Columbia have developed and made
available indicators for assessing fisheries in large marine ecosystems.
One of the ecological indicators that they use to show the impact of fishing is
the Marine Trophic Index which tracks
how the mean trophic level of the catches changes over time,
assuming, that a decrease in this indicator typically
indicates that large predatory fish have been overfished in the ecosystem.
So, in summary, the Fish and Fisheries module is important for
ecosystem-based assessment and management of the world's large marine ecosystems.
The module is closely linked to the productivity module and the pollution and
ecosystem health module because these two
affect the carrying capacity of the large marine ecosystem.
It also has strong links to the two modules on the human dimensions,
because good governance is so important for
effective fisheries management and fisheries are so
important for coastal countries around the globe.