In Australia, the gross value of fisheries production is US$1.7 billion annually, of which 68% is wild-catch and 32% is aquaculture. In New Zealand, the combined value of fisheries production is US$0.8 billion, of which 80% is from the commercial catch and 20% from the growing aquaculture sector (Seafood Industry Council, 2006), which continues to grow. Little research has been completed on impacts of climate change on freshwater fisheries and aquaculture.
Marine fisheries around the world are threatened by over-exploitation. In Australia, of 74 stocks considered in 2005, 17 were over-fished, 17 were not over-fished, and 40 were of uncertain status (ABARE, 2005). In New Zealand, of 84 stocks of demersal fish where landings were greater than 500 tonnes/yr, 5 were regarded as over-fished, 24 were assessed as not over-fished, and 55 were of uncertain status (Ministry of Fisheries Science Group, 2006). Climate change will be an additional stress (Hobday and Matear, 2005). The key variables expected to drive impacts on marine fisheries are changes in ocean temperature, currents, winds, nutrient supply, acidification and rainfall. Changes in four emergent biological properties are likely as a result of climate change, the first of which is best understood: (i) distribution and abundance of impacted species, (ii) phenology, (iii) community composition, and (iv) community structure and dynamics (including productivity). Few climate-change impact studies have been undertaken, so this assessment mostly relies on extrapolation of observed relationships between climate variability and fisheries. With sea-level rise, increasing marine intrusions are highly likely to affect coastal fisheries and inshore sub-tidal breeding and nursery areas (Schallenberg et al., 2003). Overall, future climate-change impacts are likely to be greater for temperate endemics than for tropical species (Francis, 1994, 1996) and on coastal and demersal fisheries relative to pelagic and deep-sea fisheries (Hobday and Matear, 2005).
Changes in sea surface temperature or currents are likely to affect the distribution of several commercial pelagic (e.g., tuna) fisheries in the region (Lehodey et al., 1997; Lyne, 2000; Sims et al., 2001; Hobday and Matear, 2005). In particular, circulation changes may increase the availability of some species and reduce others, as has been demonstrated in Western Australia for the Leeuwin Current. Different management regimes are likely to be required: fishers will be faced with relocation or face reduced catches in situ. Recruitment is likely to be reduced in cool-water species. For example, for New Zealand species such as red cod, recruitment is correlated with cold autumn and winter conditions associated with El Niño events (Beentjes and Renwick, 2001; Annala et al., 2004). In contrast, for snapper, relatively high recruitment and faster growth rate of juveniles and adults are correlated with warmer conditions during La Niña events (Francis, 1994; Maunder and Watters, 2003), with decreases in larval recruitment during El Niño events (Zeldis et al., 2005). A similar pattern of recruitment exists for gemfish (Renwick et al., 1998). Regarding physiological changes, temperature has a major influence on the population genetics of ectotherms, selecting for changes in abundance of temperature-sensitive alleles and genotypes and their adaptive capacity. For New Zealand snapper, differences in allele frequencies at one enzyme marker are found among year classes from warm and cold summers (Smith, 1979). If species cannot adapt to the pace of climate change, then major changes in distribution are likely, particularly for species at the edges of suitable habitats (Richardson and Schoeman, 2004; Hampe and Petit, 2005).
Projected changes in Southern Ocean circulation (see Section 11.3.1) are likely to affect fisheries. Seasonal to interannual variability of westerly winds and strong wind events are associated with recruitment and catch rates in several species (Thresher et al., 1989, 1992; Thresher, 1994). A decline in wind due to a poleward shift in climate systems underlies recent stock declines off south-eastern Australia and western Tasmania, and these are linked to changes in larval growth rates and recruitment of juveniles in two fish species around Tasmania (Koslow and Thresher, 1999; Thresher, 2002). Reductions in upwelling of nutrients and extension of warm water along the east Australian coast are likely to reduce krill and jack mackerel abundance, upon which many other species are reliant, including tuna, seals and seabirds (CSIRO, 2002).