Responsible use of resources for sustainable aquaculture

Abstract

Comparisons of production, water and energy efficiencies of aquaculture versus an array of fisheries and terrestrial agriculture systems show that nonfed aquaculture (e.g. shellfish, seaweeds) is among the world’s most efficient mass producer of plant and animal proteins. Various fed aquaculture systems also match the most efficient forms of terrestrial animal husbandry, and trends suggest that carnivores in the wild have been transformed in aquaculture to omnivores, with impacts on resource use comparable to conventional, terrestrial agriculture systems, but are more efficient. Production efficiencies of edible mass for a variety of aquaculture systems are 2.5–4.5 kg dry feed/kg edible mass, compared with 3.0–17.4 for a range of conventional terrestrial animal production systems. Beef cattle require over 10 kg of feed to add 1 kg of edibleweight, whereas tilapia and catfish use less than 3 kg to add a kg of edible weight. Energy use in unfed and low-trophic-level aquaculture systems (e.g. seaweeds, mussels, carps, tilapias) is comparable to energy use in vegetable, sheep and rangeland beef agriculture. Highest energy use is in fish cage and shrimp aquaculture, comparable to intensive animal agriculture feedlots, and extreme energy use has been reported for some of these aquaculture systems in Thailand. Capture fisheries are energy intensive in comparison with pond aquaculture of low-trophic-level species. For example, to produce 1 kg of catfish protein about 34 kcal of fossil fuel energy is required; lobster and shrimp capture fisheries use more than five times this amount of energy. Energy use in intensive salmon cage aquaculture is less than in lobster and shrimp fishing, but is comparable to use in intensive beef production in feedlots. Life Cycle Assessment of alternative grow-out technologies for salmon aquaculture in Canada has shown that for salmon cage aquaculture, feeds comprised 87 percent of total energy use, and fuel/electricity, 13 percent. Energy use in landbased recirculating systems was completely opposite: 10 percent of the total energy use was in feed and 90 percent in fossil fuel/electricity. Freshwater use remains a critical issue in aquaculture. Freshwater reuse systems have low consumptive use comparable to vegetable crops. Freshwater pond aquaculture systems have consumptive water use comparable to pig/chicken farming and the terrestrial farming of oil seed crops. Extreme water use has been documented in shrimp, trout, and striped catfish operations. Water use in striped catfish is of concern to Mekong policy-makers, as it is projected that these catfish aquaculture systems will expand and even surpass their present growth rate to reach an industry of approximately 1.5 million tonnes by 2020. Water, energy and land usage in aquaculture are all interactive. Reuse and cage aquaculture systems use less land and freshwater but have higher energy and feed requirements, with the exception of “no feed” cage and seawater (e.g. shellfish, seaweeds) systems. Currently, reuse and cage aquaculture systems perform poorly in overall life cycle or other sustainability assessments in comparison to pond systems. Use of alternative renewable energy systems and the mobilization of alternative (non-marine) feed sources could improve the sustainability of reuse and cage systems considerably in the next decade. Resource use constraints on the expansion of global aquaculture are different for fed and non-fed aquaculture. Over the past decade for non-fed shellfish aquaculture, there has been a remarkable global convergence around the notion that solutions to user (space) conflicts can be solved not only through technological advances, but also by a growing global consensus that shellfish aquaculture can “fit in”, not only environmentally but also in a socially responsible manner, to many coastal environments worldwide, the vast majority of which are already overcrowded with existing uses. For fed aquaculture, new indicators of resource use have been developed and promulgated. Before this resource use in fed aquaculture was being measured in terms of feed conversion ratios (FCRs) followed by FIFO (“fish in fish out”) ratios. First publications a decade ago measured values of FIFO in marine fish and shrimp aquaculture. More comprehensive indicator assessments of fish feed equivalencies, protein efficiency ratios and fish feed equivalences will allow more informed decision-making on resource use and efficiencies. Over the past decade, aquafeed companies have accelerated research to reduce the use of marine proteins and oils in feed formulations, and have adopted indicators for the production efficiencies in terms of “marine protein and oil dependency ratios” for fed aquaculture species. Current projections are that over the next decade, fed aquaculture will use less marine fishmeals/oils while overall aquaculture production will continue its rapid growth. Over the past decade, new, environmentally sound technologies and resourceefficient farming systems have been developed, and new examples of the integration of aquaculture into coastal area and inland watershed management plans have been achieved; however, most are still at the pilot scale commercially or are part of regional governance systems, and are not widespread. These pilot-scale models of commercial aquaculture ecosystems are highly productive, water and land efficient, and are net energy and protein producers which follow design principles similar to those used in the fields of agroecology and agroecosystems. Good examples exist for both temperate zone and tropical nations with severe land, water and energy constraints. Increasing technological efficiencies in the use of land, water, food, seed and energy through sustainable intensification such as the widespread adoption of integrated multi-trophic aquaculture (IMTA) and integrated agricultureaquaculture farming ecosystems approaches will not be enough, since these will improve only the efficiency of resource use and increase yields per unit of inputs and do not address social constraints and user conflicts. In most developing countries, an exponentially growing population to 2050 will require aquaculture to expand rapidly into land and water areas that are currently held in common. Aquaculture expansion into open-water freshwater and marine waters raises the complex issues of access to and management of common pool resources, and conflicts with exiting users that could cause acute social, political and economic problems. The seminal works of 2009 Nobel Laureate Elinor Ostrom could provide important insights for the orderly expansion of aquaculture into a more crowded, resource-efficient world striving to be sustainable, and rife with user conflicts.