Animal welfare risks of global aquaculture

Abstract

The unprecedented growth of aquaculture involves well-documented environmental and public-health costs, but less is understood about global animal welfare risks. Integrating data from multiple sources, we estimated the taxonomic diversity of farmed aquatic animals, the number of individuals killed annually, and the species-specific welfare knowledge (absence of which indicates extreme risk). In 2018, FAO reported 82.12 million metric tons of farmed aquatic animals from six phyla and at least 408 species-20 times the number of species of farmed terrestrial animals. The farmed aquatic animal tonnage represents 250 to 408 billion individuals, of which 59 to 129 billion are vertebrates (e.g., carps, salmonids). Specialized welfare information was available for 84 species, only 30% of individuals; the remaining 70% either had no welfare publications or were of an unknown species. With aquaculture growth outpacing welfare knowledge, immediate efforts are needed to safeguard the welfare of high-production, understudied species and to create policies that minimize welfare risks.

Fig. 1. Diversity and scope of global animal aquaculture production (data FAO, 2018).

(A) At the global level, each FAO listing typically corresponds to the production of a particular species, but a listing may also refer to a higher taxonomic grouping such as a genus, class, or phylum not listed elsewhere in the data. The number of FAO listings is therefore a conservative estimate of the total diversity of species involved in aquaculture production. Bars represent the total number of FAO aquaculture animal listings by phylum and the dotted gray line refers to the total number of FAO listings for all of terrestrial animal agriculture combined. (B) Estimates of the number of individual animals in aquaculture production for 2018. The error bars represent the present analyses’ upper and lower estimates for the number of individuals involved in global animal aquaculture by phylum. The dotted gray line refers to the total number individuals involved across all of terrestrial animal agriculture combined.

Fig. 2. Welfare knowledge and number of individuals per FAO listing (2018).

Each FAO listing typically refers to the production tonnage of a particular species, in which case we searched the WOS for species-specific welfare publications and recorded whether there were no publications (no welfare), one to four publications (little welfare), or five or more publications (5+ welfare). We recorded FAO listings that referred to higher taxonomic grouping (such as genus or class) as species unknown. The dots represent the lower-bound estimate of number of individual animals involved for that listing and are jittered vertically to minimize overlap. Dots size corresponds to aquaculture production tonnage.

Fig. 3. Maximum weight (from FishBase) determines the percentage at which aquatic animals are harvested (from FishCount).

In aquaculture, smaller-bodied species are typically harvested at weights nearer their biological maximum, i.e., at a higher percentage of their maximum weight. Larger-bodied species, on the other hand, are harvested at a smaller percentage of their biological maximum. Note the large range of percentages from less than 1 to more than 70%. Dots represent individual species with several representative species identified by their common name. Dark-gray line is the best fit line and shading represents the 95% confidence interval of the fit (R² = 0.64, P < 0.0001).