Editor's commentThe work summarised here is an outstanding background source for anyone wanting a solid and reasonably comprehensive overview of the probable impacts of climate change on global fisheries and aquaculture.

The work was done as input to ongoing intergovernmental fisheries and aquaculture policy and planning work sponsored by the FAO.

Three teams of recognised global experts in the various fields conducted the studies, and the results are summarised in the three papers referenced here.
One major element of the work was a review of some five hundred published scientific papers in an attempt to assess and present what is known. Some of the work is scenario driven and as such speculative, although based on what the teams believed at the time was the most reliable evidence and science.

This work is widely regarded as a valuable input to the debate and at time of publication was considered the most comprehensive global assessment of the subject.

The effects of climate change on the world’s capture fisheries and aquaculture resources and the people who depend on them for their food and livelihoods are examined in a set of three technical papers published by FAO.

The three papers together form a staff publication published by FAO as input to The State of the World Fisheries and Aquaculture 2010.

The three papers cover the following areas.
  1. The physical effects of climate change and their impacts on marine and inland capture fisheries and aquaculture
  2. The consequences of these changes for fishers and their communities
  3. The consequences for aquaculture

The entire work represents a synthesis of about 500 technical reports and articles on the subject and presents a comprehensive picture of what is known about the effects of climate change on fisheries and aquaculture. Climate change implications for fisheries and aquaculture Overview of current scientific knowledge

This body of work is a significant and substantial contribution to understanding and presenting what is currently known about the role of climate change in fisheries and aquaculture past, present and with interesting and useful forecasts and scenarios regarding the future.
Some of the key findings of the three papers are summarized below.

1. Ecological and physical impacts of climate change

Marine fisheries
Under climate change, the oceans are warming but this warming is not geographically homogeneous. The combined effect of temperature and salinity changes caused by climate warming is expected to reduce the density of surface waters and thus increase vertical stratification. These changes are likely to reduce nutrient availability in the surface layer and, therefore, primary and secondary production in a warmed world. Moreover, there is evidence that upwelling seasonality may be affected by climate change, with impacts across the food web.

The consequences of climate change will probably affect community composition, production and seasonality processes in plankton and fish populations.

Increasing acidity (decreasing pH) of the world’s oceans is a significant and pervasive longer-term threat to coral reefs. In the short term, increased temperatures linked to coral bleaching may lead to steady degradation of reefs and other ecosystems. In the long term, increasing water acidification and a weakening of the structural integrity of reefs is forecast. The potential for coral reef systems to adapt to these environmental stresses is uncertain.

As temperatures warm, marine fish populations at the poleward extents of their ranges will increase in abundance whereas populations in more equatorward parts of their range will decline in abundance.

In general, climate change is expected to drive the ranges of most terrestrial and marine species towards the poles, expanding the range of warmer-water species and contracting that of colder-water species.

The most rapid changes in fish communities will occur with pelagic species that are expected to shift to deeper waters to counteract rising surface temperatures. Moreover, the timing of many animal migrations will be affected.

Ocean warming will also alter the predator–prey matches because of the differential responses between plankton components (some responding to temperature change and others to light intensity).

Potential long term ecological impacts in Arctic  FAO

Fresh water fisheries
There is evidence that inland waters are also warming but that there are differential impacts of climate change on the river runoff that feeds these waters.

In general terms, high-latitude and high-altitude lakes will experience reduced ice cover, warmer water temperatures, a longer growing season and, as a consequence, increased algal abundance and productivity.

In contrast, some deep tropical lakes will experience reduced algal abundance and declines in productivity, probably owing to reduced supply of nutrients. Regarding freshwater systems in general, there are also specific concerns over changes in timing, intensity and duration of floods, to which many
fish species are adapted in terms of migration, spawning and transport of spawning products, as a result of climate change.

The paper also summarizes the consequences of climate change along “rapid”, intermediate and long time scales. These encompass impacts on physiology of fish (including consequences for aquaculture), ecology of short-lived species and changes in species distributions and abundance. The paper notes that information is lacking for the long time scale and there are considerable uncertainties and research gaps that the paper outlines.

2. Impact on fishers and their communities

Fisheries-dependent economies, coastal communities and fisherfolk are expected to experience the effects of climate change in a variety of ways. These include:
  • displacement and migration of human populations;
  • effects on coastal communities and infrastructure due to sea-level rise, and
  • changes in the frequency, distribution or intensity of tropical storms; and
  • less stable livelihoods and changes in the availability and quantity of fish for food.

In 2008 capture fisheries and aquaculture supplied the world with about 142 million tonnes of fish. Of this, 115 million tonnes was used as human food, providing an estimated apparent per capita supply of about 17 kg (live weight equivalent), which is an all-time high. Aquaculture accounted for 46 percent of total food fish supply.

Global fish and aquaculture production 2006

3. Aquaculture impacts

Aquaculture now accounts for almost 50 percent of fish consumed by humans, and this share is expected to increase further to meet future demand. Of considerable concern is the long-term ability of capture fisheries production to produce the fishmeal and fish-oil supplies used as feed components in aquaculture. Alternatives, such as soybean, corn meal, rice bran and others, have not been perfected according to fish requirements, and the increased demand for these agricultural products created by expanding aquaculture could also have consequences.

Climate change impact on aquaculture FAO

Direct and indirect impact of climate change
The vulnerability of fisheries and fishing communities depends on their exposure and sensitivity to change, but also on the ability of individuals or systems to anticipate and adapt. This adaptive capacity relies on various community assets and can be constrained by culture, current institutional and governance frameworks or marginalized access to adaptive resources.

Vulnerability varies between countries and communities and between demographic groups within society. Generally, poorer and less empowered countries and individuals are more vulnerable to the effects of climate change, and the vulnerability of fisheries is likely to be higher where the resources already suffer from overexploitation, the ecosystems are degraded and the communities face poverty and lack sufficient social services and essential infrastructure.

Direct and indirect impacts of climate change FAO

(These FAO reports are used as direct inputs to FAO and other UN system intergovernmental policy and planning studies, negotiations and programme and project discussions. The reports include many case studies and policy notes. In this vein the reports note: "Fisheries are dynamic social-ecological systems and are already experiencing rapid change in markets, exploitation and governance. The combined effects of these changes and the biophysical and human impacts of climate change make it difficult to predict the future effects of climate change on fisheries social-ecological systems."

"Human adaptation to climate change includes reactive or anticipatory actions by individuals or public institutions. These range from abandoning fisheries altogether for alternative occupations to developing insurance and warning systems and changing fishing operations."

"Greenhouse gas contributions of fisheries and related supply chain features are small when compared with other sectors but, nevertheless, can be reduced with identifiable measures already available.
There may also be important interactions for the sector with respect to environmental services (e.g. maintaining the quality and function of coral reefs, coastal margins, inland watersheds), and potential carbon sequestration and other nutrient management options, but these will need further research and development.")

[http://www.fao.org/docrep/013/i1820e/i1820e.pdf|FAO. The State of World Fisheries and Aquaculture 2010. Rome, FAO. 2010. 19