Question

1. How does climate change affect world fisheries? give 5 examples

Answer 1

2.1. Overview of the Impact of Climate Change on Fisheries Natural climatic fluctuations, particularly those at medium (decadal) scale, have always affected fisheries as well as their management performance (Garcia and Rosenberg, 2010). The atmosphere and the ocean will continue to warm over the next 50-100 years, sea level wil rise due to thermal expansion of water and melting of glaciers, ocean pH will decline (become acidic) as more carbon dioxide is absorbed, and circulation patterns could change at local, regional and global scales (Bindoff et al., 2007 in Munday et a., 2008) The major aquatic habitats in SSA include the Great Rift Lakes such as Lakes Malawi and Victoria; man-made reservoirs such as Lake Kariba; large river and floodplain systems

Salinity is also considered one of the most important variables determining the survival of organisms in estuarine ecosystems; either by having a direct impact on the organisms or indirectly by destroying their habitat, ncluding their breeding and nursery grounds (Marshall and Elliot, 1998 in Abowei, 2010). Blaber (1997) states that all estuarine fish are euryhaline (able to cope with salinity fluctuations), but their ability to do so varies from species to species and hence changes in salinity may influence their distribution. Even though salinity changes may not have a direct negative impact on estuarine fish species per se, it can have a negative impact on their habitat. For example, increase in water salinity has contributed to destruction of 60 per cent of mangrove areas in Senegal (IPCC, 2007). According to Parkins (2000), each acre of mangrove forest destroyed leads to an estimated 300 kg loss in marine harvest. Therefore, change in water salinity are going to have a tremendous negative impact on fishery in the region, threatening the livelihoods of many impoverished coastal 2.1.1.4. Ocean Acidification Oceans are believed to have the capacity to absorb most of the anthropogenic COz emissions Caldeira and Wickett, 2003). Co2 is soluble in water and reversibly converts to carbonic acid. As a result of this chemical reaction, the world's oceans are acidifying at an alarming rate (Dupont and Thorndyke, 2009). While this has a positive impact in slowing down global warming, increased acidity as a result of dissolved CO2 in seawater has negative a impact on ocean ecosystems. The impact to the ecosystem is difficult to estimate as different species at different stages of life history respond differently to different pH changes. According to Dupont and Thorndyke (2009), ocean acidification rescarch is in its infancy and although the field is moving forward rapidly, good data is stll scarce. Although the science base is still limited, there is a clear need to provide timely advice and a balanced perspective on the possible impacts on marine fisheries (Le Quesne and Pinnegar, 2011). Quantifying the effects of ocean acidification on human communities requires assessing the direct and indirect chemical impacts on valuable marine ecosystem services such as fisheries (Cooley et al., 201). According to Le Quesne and Pinnegar (2011), direct effects include changes in physiological processes such as reduced growth of calcified structures otolith development, and fertilization success. These may ultimately lead to direct impacts at the whole-organism level, including reduced growth and reproductive output, increased immunocompetence and reduced thermal tolerance. Indirect effects include alteration in predator or pray abundance, effects on biogenic habitats such as coral reefs, and changes in nutrient recycling. While adult fish seem well-equipped to deal with low pH waters, or higher levels of CO2 in seawater, their egg and larval life stages may not be so fortunate (Painting 2011). For example, increased CO2 level in oceans can potentially narcotize male gametes indicating that acidification may impair fertilization, exacerbating problems of sperm limitation, with dire implications for marine life (Byrne et al., 2010). Ocean acidification could potentially slow the growth of plankton and invertebrates that are at the bottom of the food chain. Thus acidification can alter the productivity at certain trophic levels, thereby disrupting the complex food chain of aquatic ecosystems with effects on the productivity of fisheries. One of the very likely socio-cconomic impacts of ocean acidification in SSA is a decrease in populations of calcifying organisms such as mollusks. This may have tremendous socio-cconomic effects either by () lowering export earnings of net mollusk exporting

2.1.2.2. Changes in Fish Distribution Change in fish distribution is among the most commonly reported ecological responses of marine species (Sumaila et al., 2011). Fish species are believed to respond to environmental changes such as warming water temperatures by shifting their latitudinal and depth ranges. Changes in ocean dynamics could lead to changes in migration patterns of fish and possibly reduce fish landings, especially in coastal fisheries of many African countries (African Action, 2007 in Urama and Ozor, 2010). Marine fisheries are an important food source, and therefore, changes in the total amount or geographic distribution of fish available for catch could potentially affect food security (Cheung et al., 2009). The effects of changes in fish-stock distribution vary across latitudes. Some fish species will migrate due north in search of habitats with optima water temperature and thus potentially increasing fish harvest in higher latitudes. On the other hand, counties in lower latitudes such as SSA are very likely going to lose some fish species and stocks. Cheung et al. (2009) depict that changes in fish-stock distribution could range from a 30-70 per cent increase in high latitude regions to a drop of up to 40 per cent in the tropics. This poses a tremendous challenge to the predominantly artisanal fishers in SSA mainly because is economically prohibitive to follow the fish-stock, i.e. restricted to economic exclusive zones. Therefore, according to OECD (2010), such changes in fish stock distribution will change the distribution of benefits and costs of fisheries with some winning and some including fishers from Sub-Saharan African countries) losing