Finding the science-policy nexus for shark conservation at the Indian Ocean Tuna Commission
Written by Emma Gee (Fisheries Opportunity Fund Fellow 2024)
The Indian Ocean is unique among oceans in many ways. It does not meet the Atlantic and Pacific Oceans in the Arctic because its northern portion is landlocked. This also makes it the warmest ocean basin on average. Importantly, the Indian Ocean is also one of the most ecologically data-poor regions in the world, despite its bordering countries being home to a third of the world’s population.
I have been working with Drs. Francesco Ferretti and Evgeny Romanov since 2018 to try to address this knowledge gap. Dr. Romanov was a research scientist aboard a series of exploratory longline research cruises that the former USSR conducted throughout the Indian Ocean starting in the 1960s and ending in 1989. During these cruises, scientists identified sharks they caught to the species level, which is extremely rare data for the spatial scale at which they were working because of the challenges in identifying different shark species. For example, the Indian Ocean Tuna Commission (IOTC), the managing body for sharks in the Indian Ocean basin, currently collects catch data on five shark species, and these data only go back to the early to mid-2000s. Industrial-scale fishing started in the Indian Ocean in the 1950s, and considering only recent data creates the risk of a shifting baseline.
My previous Master’s thesis work focused on modeling the shark catches from the USSR data to generate a standardized index of abundance known as the catch per unit effort (CPUE). CPUEs can be used in a stock assessment to understand whether a population is being overfished. Until this year, the IOTC had only conducted a stock assessment of one shark species, the blue shark, which is the most commonly caught shark in industrial fisheries. Early this year, it started the stock assessment process for another, the shortfin mako shark.
While my Master’s was focused on computation and modeling, I have shifted toward policy and trying to understand how to integrate science into decision-making since graduating and starting my PhD. I was excited at the prospect of contributing to the shortfin mako stock assessment, because the International Union for Conservation of Nature (IUCN) has determined it to be globally endangered, and I hoped that a regional assessment would spur more conservation action in the Indian Ocean. I participated virtually in the data preparation process to advocate for our CPUEs to be included in the model. The Fisheries Opportunity Fund enabled me to travel to the Seychelles for the IOTC Working Party on Ecosystems and Bycatch (WPEB) meeting in summer 2024 where the stock assessment was finalized.
The WPEB meets for 5 days to discuss items on its work plan relating to bycatch and the species affected by it. In total, we spent over a day on the shortfin mako stock assessment. I was impressed by the number of sensitivity analyses that the organizers ran to validate the model. I also found it interesting to note which components of the model people took issue with. I had expected people to be concerned about the inclusion of our CPUEs in the stock assessment because they didn’t come from fishery data. Instead, we spent a fair amount of time discussing the Japanese CPUE series, which indicated a sharp decline in abundance in the 1990s.
These discussions reiterated for me the importance of historical data and historical ecology. Our only evidence for what happened to the shortfin mako shark population in the 1990s was the Japanese data. In this case, removing the Japanese data did not change the model’s performance, but if it had, we may not have been able to adopt the model. And, previous attempts at stock assessment models using only recent data had not found the population to be declining. This model with historical data did find a decline, in agreement with assessments in other oceans.
We formally adopted the model on the final day of the meeting, making it the second shark stock assessment the IOTC has completed. Once it was adopted, we workshopped the text in the executive summary, and I was able to contribute text about the trends we saw in the historical period in our research. During the meeting, we did not discuss the issue of catch reduction, as the stock assessment concluded that the stock needed a 60% reduction in catch to halt its decline. It will hopefully be hashed out at the Scientific Committee meeting in December by the national delegations of the IOTC’s member countries. I was interested to learn that there are factors outside the IOTC that have already helped to reduce catch and could contribute to further catch reduction. The levers we discussed were the new Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) protections for the shortfin mako, and national-level policies relating to catch. Some countries such as Spain target shortfin makos for their meat, so regulations from these countries could have a larger impact on the conservation of these species.
Many thanks to the Fisheries Collaborative Program, the Fisheries Opportunity Fund, and the Environmental Studies Department for the opportunity to attend this meeting, as well as to Dr. Rui Coelho for leading the shortfin mako stock assessment.
Emma Gee (Environmental Studies Graduate Student)