Global fish production and climate change

Abstract

Current global fisheries production of approximately 160 million tons is rising as a result of increases in aquaculture production. A number of climate-related threats to both capture fisheries and aquaculture are identified, but we have low confidence in predictions of future fisheries production because of uncertainty over future global aquatic net primary production and the transfer of this production through the food chain to human consumption. Recent changes in the distribution and productivity of a number of fish species can be ascribed with high confidence to regional climate variability, such as the El Niño-Southern Oscillation. Future production may increase in some high-latitude regions because of warming and decreased ice cover, but the dynamics in low-latitude regions are governed by different processes, and production may decline as a result of reduced vertical mixing of the water column and, hence, reduced recycling of nutrients. There are strong interactions between the effects of fishing and the effects of climate because fishing reduces the age, size, and geographic diversity of populations and the biodiversity of marine ecosystems, making both more sensitive to additional stresses such as climate change. Inland fisheries are additionally threatened by changes in precipitation and water management. The frequency and intensity of extreme climate events is likely to have a major impact on future fisheries production in both inland and marine systems. Reducing fishing mortality in the majority of fisheries, which are currently fully exploited or overexploited, is the principal feasible means of reducing the impacts of climate change.

Fig. 1.

World fisheries production from capture fisheries (open squares) and aquaculture (crosses). (Left) Global totals, including China. (Right) Global totals, excluding China (because of doubts over the reliability of the statistics) and showing the marine (black) and inland (red) production separately. Note that the right-hand scale applies for aquaculture (crosses).

Fig. 2.

Schematic representation of impacts of climate change and fishing activity on the marine ecosystem and its fish component.

Fig. 3.

Schematic effect of a 2°C increase in temperature. The shading represents temperature regions with progressively more adverse effects. The red lines show seasonal temperatures that are 2°C above the black lines. (Left) The black seasonal temperature pattern enters the adverse region in winter but not in summer. The red pattern escapes from adverse winter temperature but enters the adverse region in summer. The mean temperatures are the same in both panels, but seasonal amplitude is reduced in Right, and neither pattern enters the adverse region. Climate change may, of course, affect the amplitude of such seasonal cycles, as well as the mean.

Fig. 4.

Temperature profile at Hell's Gate (Fraser River, BC, Canada) in 2004 (blue line), also showing the 60-year mean (black solid line), ±1 standard deviation (yellow lines), and 60-year minimum and maximums (black dashed lines). For several days in mid-August, Fraser River water temperatures, as measured at Hell's Gate, were the highest ever recorded (from Canadian Standing Committee on Fisheries and Oceans, 2005, www-comm.pac.dfo-mpo.gc.ca/publications/2004psr/Williams5_e.htm).