Man-made floating objects in the surface of tropical oceans, also called drifting fish aggregating devices (DFADs), attract tens of marine species, including tunas and non-tuna species. In the Indian Ocean, around 80% of the sets currently made by the EU purse-seine fleet are on DFADs. Due to the importance and value of this fishery, understanding the habitat characteristics and dynamics of pelagic species aggregated under DFADs is key to improve fishery management and fishing practices. This study implements Bayesian hierarchical spatial models to investigate tuna and non-tuna species seasonal distribution based on fisheries-independent data derived from fishers' echo-sounder buoys, environmental information (Sea Surface Temperature, Chlorophyll, Salinity, Eddie Kinetic Energy, Oxygen concentration, Sea Surface Height, Velocity and Heading) and DFAD variables (DFAD identification, days at sea). Results highlighted group-specific spatial distributions and habitat preferences, finding higher probability of tuna presence in warmer waters, with higher sea surface height and low eddy kinetic energy values. In contrast, highest probabilities of non-tuna species were found in colder and productive waters. Days at sea were relevant for both groups, with higher probabilities at objects with higher soak time. Our results also showed species-specific temporal distributions, suggesting that both tuna and non-tuna species may have different habitat preferences depending on the monsoon period. The new findings provided by this study will contribute to the understanding of the ecology and behavior of target and non-target species and their sustainable management.
Tuna regional fisheries management organizations (RFMOs) have long suffered from the domination of distant water fishing nations (DWFNs) in decision-making processes. The Indian Ocean Tuna Commission (IOTC) is no exception. In recent years, coastal states of the Indian Ocean (IO) have tried to change this dynamic - led by countries like the Maldives, Kenya, South Africa, and Australia - to deliver greater benefits to the region, including East Africa. These countries are gathered under the informal group of G16 and have increasingly improved their involvement in the IOTC. Here, we ask how the rise of the G16 benefited coastal States through participation and collective understanding in the Indian Ocean. To do this, we analyzed proposals submitted by the G16 for conservation and management measures and the participant lists of the Commission meetings in the past ten years. Our results show that, individually and collectively, the G16 has played a significant role in shaping the IOTC's rules. The coastal States have established a good representation, with only a handful of Members absent in some years. Unveiling the efforts of coastal countries is essential to guide further capacity building in the region in terms of negotiations. We also call for international oversight of the actions of DWFNs, such as the EU, whose efforts often differ markedly from their claims of being sustainability champions. The G16's work is essential to keep the coastal States of the Indian Ocean in the driver's seat for managing Indian Ocean fisheries to benefit future generations.