Center for Marine Biodiversity and Conservation

Today, world capture fisheries have reached their maximum capacity and the future of seafood supply is threatened by global environmental factors such as climate change, ocean pollution, acidification, and overfishing. Waste reduction, or a fuller utilization of every part of the wild caught fish, represents anopportunity to meet the increased demand in seafood consumption without further stressing the resource, while helping to sustain high standards fisheries by adding value to the landed catch. In order to better manage waste, it is necessary to identify and quantify by-raw material (waste to be repurposed) along theseafood value chain. This project describes the bigeye (Thunnus obesus) fresh tuna market in San Diego using a metabolism approach. Specifically, the goals were to: (1) describe the bigeye tuna supply chain in San Diego, (2) quantify where losses are occurring, and (3) briefly describe opportunities to utilize by-raw materials. The project serves as a proof of concept that applying this method can successfully identify and follow the biomass throughout a particular seafood system. Every step of the value chain was included, from harvest at sea, to the processing facility, to the seafood counter. For the year 2018, this research estimated that the fishery provided 596 metric tons (MT) of fresh seafood to the local market while an additional 187 MT of wild resource was lost along the way with some at sea and some concentrated at the processor. Of the 187 MT of loss, 136 MT of losses happen at sea and consist of catch released alive or dead, lost bait, guts and gills, and 51 MT of bigeye by-raw material are left in the processing facility and comprise head, collar, tail, carcass, skin and bloodline. While the model shows that most of the losses occur at sea and consist of by-catch, it is important to note that by-catch data from the Western and Central Pacific longlining fishery was used as a proxy and may not be representative ofWest Coast fisheries that have different fishing grounds. Therefore, the robustness of this number should be tested in the near future when West Coast by-catch data become available. Bigeye yield is known by the industry to be ca. 50% but because losses are diffused along the value chain only 18% of by-rawmaterial is shown by this study to be found at the processing facility, this includes head and tail currently used as lobster bait or turned into compost. There are a number of additional uses for bigeye by-raw material. To move towards a full utilization of the fish, the industry could target unused and actionableby-raw material such as tuna skin for leather, in addition to exploring new processing and marketing strategies for the lower grade filets that currently are under-sold or eventually discarded. Despite the relatively small size of the San Diego bigeye fishery, the integration of all data streams of the supply chain demonstrated that this approach could be replicated to evaluate by-raw materials in other fisheries or locations. If exploring culinary and non-culinary uses of our wild-caught fish is an important step to move toward greater sustainability, further research at a larger scale as well as a regulatory framework analysis are needed to understand and estimate the impact of a full utilization movement for marine conservation in California.