Aquaculture refers to the breeding, rearing, and harvesting of plants and animals in all types of water environments.
Aquaculture is the production of marine and freshwater organisms under controlled conditions. This includes fish and shellfish for human consumption, sport fishing, backyard ponds, and release to enhance wild populations. Some types of aquaculture are practiced in the open ocean and in bays where products such as mussels, clams, oysters, salmon, flounder, and cobia are grown. Other aquaculture occurs throughout the U.S. in artificial earthen ponds that are the primary source of farm-raised catfish, tilapia, bass, shrimp, crawfish, baitfish, and ornamental fish and plants.
Aquaculture provides numerous economic and ecological benefits. According to the 2012 United Nations Food and Agriculture Organization (UN FAO) report on The State of World Fisheries and Aquaculture, the United States ranks 15th in total aquaculture production. Marine aquaculture in the United States contributes to seafood supply, supports commercial fisheries, restores habitat and at-risk species, and maintains economic activity in coastal communities and at working waterfronts in every coastal state.
NOAA reports that the majority of marine aquaculture production – approximately two-thirds by value – consists of bivalve mollusks such as oysters, clams, and mussels. Salmon and shrimp constitute most of the rest, but advances in technology and management techniques are increasing the availability of other species for the American public. Aquaculture also supports commercial and recreational fisheries. About 40% of the salmon caught in Alaska and 80-90% in the Pacific Northwest start their lives in a hatchery – contributing over 270 million dollars to the commercial fishery. Aquaculture is an important tool for habitat and species restoration as well. Hatchery stock is used to rebuild oyster reefs, enhance wild fish populations, and rebuild threatened and endangered abalone and corals.
Climate change may affect fisheries and aquaculture directly by influencing fish stocks and the global supply of fish for consumption, or indirectly by influencing fish prices or the cost of goods and services required by fishers and fish farmers. Fisheries and aquaculture are threatened by changes in temperature and, in freshwater ecosystems, precipitation. Storms may become more frequent and extreme, imperiling habitats, stocks, infrastructure and livelihoods. Large waves and storm surges as well as terrestrial flooding may create salinity changes and cause flooding episodes that can introduce disease or predators into aquaculture facilities. These impacts may cause loss of aquaculture stock as well as damage to facilities and equipment, resulting in higher capital costs to design cage moorings, pond walls, and jetties that can withstand storms as well as higher insurance costs.
Changing sea temperatures and ocean acidification are posing increasing threats to coral reefs, which provide habitat for many important fish species as well as provide a wide range of valuable ecosystem services. Declining reef health may also result in changes in species composition or species loss. As temperatures warm, more frequent harmful algal blooms are likely, which can increase operating costs and alter ecosystems upon which aquaculture relies. High inland water temperatures can further impact fish stocks by increasing stratification and reducing mixing in lakes, which may negatively impact dissolved oxygen levels and increase fish mortality. Warmer temperatures may also increase primary productivity and raise metabolic rates if water quality, dissolved oxygen levels, and food supplies are sufficient, which may yield benefits for some aquaculture activities – especially those using intensive or semi-intensive pond systems. Changes in water temperatures may also alter the timing and success of migrations, spawning, and overall species composition and abundance.
Sea level rise also threatens aquaculture activities. Loss of land and critical coastal systems such as mangrove forests reduces the land available for aquaculture and may result in reduced recruitment and stocks for capture fisheries and seed for aquaculture. The loss of mangroves and coral reefs increases exposure to waves and storm surges, heightening inundation risks to coastal aquaculture and fisheries. Saltwater intrusion into groundwater can further impact fisheries, reducing freshwater availability and necessitating stocking shifts to more brackish species. Changes in precipitation and water availability can also impact fish migration and recruitment patterns, altering the abundance and composition of native stock. Droughts can further lower water quality and availability for aquaculture, resulting in increased production costs and potentially limiting production, especially in freshwater aquaculture operations. Downstream delta ecosystems are likely to be some of the most sensitive because of upstream changes in water availability and discharge, leading to shifts in water quality and ecosystems in these areas.
Overall, climatic changes impacts on aquaculture are predicted to be very variable, depending on regions and production methods. The more negative impacts are likely to be on aquaculture operations in temperate regions due to high temperatures that exceed optimal ranges for body functions and increase virulence of disease. Greater climate variability and uncertainty complicate the task of identifying impact pathways and areas of vulnerability, requiring research to devise and pursue coping strategies and improve the adaptability of fishers and aquaculturists.
By identifying challenges and opportunities to aquaculture presented by climate change, fisheries and aquaculture managers can work to reduce the vulnerabilities of these systems. For example, freshwater fish production facilities and work to integrate their aquaculture practices with local agriculture to help farmers cope with drought while reducing their own management costs. In some areas such as the Pacific Northwest, shellfish producers have been engaged in climate change education and lobbying efforts to encourage mitigation policies that reduce the risks of increasing ocean acidification and water temperatures that can compromise their stocks. Groups such as the Western Rivers Initiative have also engaged fisheries managers in policy dialogs to improve terrestrial land use activities to protect fish populations, and have worked to protect and restore vital cold-water fish habitat.
Based on current practices, marine cage aquaculture requires adaptive measures to withstand extreme weather events. Increased aquaculture may also be seen as an adaptive measure to provide alternative livelihood means for terrestrial farming activities that may no longer be possible or cost effective due to salt water intrusion and frequent coastal flooding.
In addition to advocating aquaculture diversification and improved aquaculture zoning and monitoring as adaptation measures that may reduce long-term risks, the UN FAO has identified the following policy priorities to support healthy fisheries:
In the wake of climate change, aquaculture has an increasingly important role to play by increasing carbon sequestration, furthering the increased production of fish and mollusks feeding low in the food chain and of algae and seaweeds. Aquaculture can offer a high degree of elasticity and resilience to adapt to changes that could further reduce the sector’s contribution to climatic change.