Phase V-Enabling Sustainable Exploitation of the Coastal Tuna Species (Kawakawa and Skipjack) in the Western Indian Ocean

The Western Indian Ocean (WIO) serves as a crucial habitat for small migratory tuna species, specifically Kawakawa (Euthynnus affinis) and Skipjack tuna (Katsuwonus pelamis). These species hold significant importance for local economies and food security among coastal communities in South Africa, Mozambique, Tanzania, and Kenya. Historically, the Indian Ocean Tuna Commission (IOTC) operated under the assumption that these tuna populations were highly mobile and represented a single, panmictic spawning population, a notion that lacked empirical data. However, emerging evidence regarding distinct populations of other tuna species, such as yellowfin tuna, raised concerns about the adequacy of current management strategies for the sustainable and economically viable exploitation of Kawakawa and Skipjack.

To address these gaps, a comprehensive project was undertaken to investigate the genetic biodiversity of the Kawakawa and Skipjack populations within the WIO. The focus included assessing biological aspects, such as reproductive patterns and exploitation trends, alongside the influence of oceanographic factors on the distribution, genetic structure, and abundance of these species.

Despite setbacks due to the COVID-19 pandemic, the research team successfully gathered genetic samples from various locations, including reference samples from India, Sri Lanka, and Seychelles. Employing advanced methodologies like mitochondrial DNA sequencing and RADseq library construction, researchers processed these samples to create a dataset for evaluating population-level diversity and differentiation across the region. Complementary morphometric data were also collected to deepen the understanding of the relationship between genetic characteristics and physical traits.

In Kenya, detailed catch data from the artisanal fishery revealed significant insights into fishing practices. Between September 2019 and October 2020, a total of 129 metric tons of fish were recorded, primarily from two key locations: Vanga/Gazi and Watamu/Kilifi. The data highlighted a multispecies fishery, with Kawakawa comprising 57% of the total catch and Skipjack accounting for 12%. Notably, different fishing units displayed varying catch rates, significantly affected by geographical differences and the types of fishing gear employed. The research also identified seasonal fluctuations, with the northeast monsoon season contributing to the highest landings.

In Tanzania, the study reported substantial catches from both Tanga and Mtwara. Kawakawa was prevalent in both areas, while Skipjack catches were concentrated in Mtwara. A reproductive analysis indicated a high proportion of mature Kawakawa in Tanga, suggesting the presence of potential spawning grounds. Further data collection in Mozambique and South Africa added valuable dimensions to the fishery analysis, although findings from South Africa were more limited.

The socioeconomic component of the research involved extensive value chain analyses through structured questionnaires targeting fisheries in Kenya, Mozambique, and Tanzania, along with a survey on the recreational fishery in South Africa. Participants provided insights into fishing practices, catch distribution, and market dynamics. Initial findings noted the commonality of Kawakawa and Skipjack in catches, while various fishing methods, including handlines and gillnets, varied across regions.

Catch analysis revealed key fishing seasons, predominantly occurring between October and March, aligning with biological assessments of spawning patterns. In South Africa, the recreational fishery survey indicated that many anglers targeted these tuna species primarily for personal use and bait, highlighting their socio-economic significance.

The project also delved into oceanographic factors influencing tuna populations, particularly thermal fronts and upwelling zones. Initial satellite data analyses identified critical marine areas, which can inform effective fisheries management and conservation strategies.

In summary, this ambitious project has generated valuable insights regarding the genetic diversity, catch dynamics, and socio-economic ramifications of Kawakawa and Skipjack tuna fisheries in the WIO. The research team is currently finalizing a comprehensive report that will detail their findings and offer recommendations for sustainable management practices, with the aim of publication by the end of June 2022. This work aspires to empower stakeholders with essential data to optimize both the economic and social benefits derived from these vital fisheries.