Vulnerabilities - Marine fisheries

Most of the commercially exploited species of sea fish are close to, or beyond, safe biological limits with many possible causes. Over-fishing is generally considered to be the major cause of the decline; however, pollution, eutrophication (enrichment of water with nutrients from, for example, agricultural runoff or sewage sludge), acidic runoff from forestry and changes in predator numbers may all contribute. It is very difficult to disentangle the potential impacts due to climate change and those due to fishing itself and other factors (1).

Resource over-exploitation has been described as the most important single factor directly affecting the sustainability of many fish species (2) and over-exploitation itself may also make fisheries more vulnerable to climate change. The fishing industry is adaptable and as fish stocks change, new geographic areas and species are being targeted for exploitation and this will most likely continue.

The belief that climate change could disrupt the aquaculture industry in Ireland appears to be well founded. For salmon production, climatic changes may have serious consequences. Salmon are near the southern range of their distribution and any increases in water temperature could result in farms becoming less commercially viable, subject to increased harmful algal bloom events and a number of pests and diseases (1).

The apparent spread of toxic phytoplankton species is of particular concern and the poor knowledge of the movement of pathogenic microorganisms and disease agents, with consequences for aquaculture and fisheries, must be a priority area for future investigation (1).

Changes in the distribution of fish species associated with European tidal estuaries along the northeast Atlantic seaboard were studied by comparing the mean latitude of distributions according to fish survey data from the 1970s with data from 2004–2007. 55 tidal estuaries from Portugal to Scotland were studied. Among the 15 most common species, 11 displayed a positive difference between current and past mean latitudes suggesting a northward shift of the populations. These results indicate that a number of fish species associated to estuaries seem to have migrated northwards over the last 30 years, possibly due to water warming (3).

Adaptation strategy

For some species, increased temperature may result in a longer growing season, lower natural winter mortality and faster growth rates, particularly of shellfish. The aquaculture industry is also adaptable and although climatic conditions may shift so too will the focus of the industry to more profitable and viable species.As fish stocks change, new geographic areas and species are being targeted for exploitation and this will most likely continue (1).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Ireland.

1. Environmental Protection Agency (2003)
2. Parry (2000), in: Environmental Protection Agency (2003)
3. Nicolas et al. (2011)