How mariculture expansion is dewilding the ocean and its inhabitants

Abstract

The world's oceans are largely free from intensive farming, but momentum to intensify and expand mariculture-the cultivation of aquatic organisms in the ocean-is growing. Despite optimism that mariculture will create economic and nutritional benefits for humans, it can also generate a host of risks, including environmental degradation, harms to wildlife integrity and welfare, captivity effects, and shifts in how humans view the nonhuman world. Collectively, we refer to these four types of risks as "dewilding." In this systematic review, we searched Scopus and Web of Science for recent literature documenting mariculture's dewilding impacts to organize and collate this evidence under one unified framework. We find that mariculture's dewilding impacts are consistently documented, though often in isolation, and that captivity and conceptual dewilding impacts are recognized as potential harms far less than impacts on the environment and wildlife. Future work examining mariculture's dewilding impacts will be paramount to guiding human decision-making and activity going forward.

Fig. 1.. Mariculture’s dewilding impacts.

The leftmost portion of the figure depicts a scenario free from dewilding impacts, the middle of the figure depicts a scenario where moderate dewilding has occurred, and the right portion of the figure depicts a potential future scenario with severe dewilding. Longer arrows signify severe dewilding, and shorter arrows indicate moderate dewilding. For environmental dewilding, when it is absent, the water is free of pollutants but becomes polluted with fish waste and uneaten feed in the moderate dewilding scenario. In the potential future with severe dewilding scenario, artificial structures dominate the seascape and farm waste pollutes surrounding waters and sediments, driving loss of benthic macrofauna abundance and diversity (wildlife dewilding). For wildlife dewilding, when it is absent, dolphins are unaffected by mariculture. In the moderate dewilding scenario, farms attract some dolphins. In the potential future scenario with severe dewilding, sea pens dominate dolphins’ habitat and dolphins are threatened by lethal antipredator methods. For captive dewilding, when it is absent, farmed fishes are wild. In the moderate dewilding scenario, humans farm a small population of fishes at relatively low stocking densities. In the potential future severe dewilding scenario, multiple sea pens hold many fishes at high densities, fishes experience high rates of parasitic infection and disease, and humans construct onshore research facilities to study and enhance fish production. For conceptual dewilding, when it is absent, humans enjoy the ocean, viewing dolphins and fishes as wild. In the potential future with severe dewilding scenario, humans view dolphins as pests because they interfere with fish farming and may intentionally kill dolphins to protect mariculture interests. This figure generally depicts dynamics that could apply to a range of wild predators, e.g., cetacean and pinniped, and farmed fish species. Image credit: E. Bautista.

Fig. 2.. Number of mariculture dewilding dimensions documented (2020 to 2023).

Parenthetical numbers at the bottom of the bars indicate the number of publications per year.

Fig. 3.. Network of documented mariculture dewilding impacts.

Node sizes are proportional to the total number of publications documenting that dewilding dimension. Line widths are proportional to the number of publications containing both connected dimensions.

Fig. 4.. Mariculture dewilding publications by dewilding dimension.

Captive dewilding was documented most often and most inadvertently. Environmental and wildlife dewilding were often intentionally studied and regularly documented in the literature. Conceptual dewilding was the least documented dimension and often documented inadvertently.

Fig. 5.. Identification, screening, and inclusion of recent literature documenting mariculture’s dewilding impacts.

Diagram adapted from (105).