Biodiversity and environmental characteristics of the bycatch assemblages from the tropical tuna purse seine fisheries in the eastern Atlantic Ocean

Abstract

The impact of human activities such as fishing has been identified as a main factor in diversity loss in the open ocean. This paper studies the diversity patterns and environmental characteristics of the bycatch assemblages in Fish Aggregating Devices (FADs) and Free School sets (sets made on schools of tuna) from the tropical tuna purse seine fishery in the eastern Atlantic Ocean (35°W–15°E and 20°N–15°S). Data were collected from scientific observer programmes carried out between 2003 and 2011 on board Spanish and French fleets. The results showed different structure and diversity patterns of the bycatch assemblages depending on the fishing mode, with higher number of species and diversity found in FAD sets than in Free School sets. Bycatch assemblages showed preferences for specific oceanographic characteristics of the Atlantic Ocean, such as the equatorial and seasonal coastal upwelling systems, the Cape Lopez front system and the Guinea dome. The type of set and sea surface temperature play an important role to describe the diversity patterns of these species. These results confirm the importance of integrating different methods to study the marine ecosystem towards the correct implementation of the Ecosystem Approach to Fishery Management (EAFM).

Association dynamics of tuna and purse seine bycatch species with drifting fish aggregating devices (FADs) in the tropical eastern Atlantic Ocean

“…Several pelagic fish species are known to regularly associate with floating objects in the open ocean (Lezama-Ochoa et al, 2018;Taquet et al, 2007). Commercially valuable species, such as tropical tunas, are among the most abundant species found around floating objects.…”

Environmental characteristics associated with the presence of the Spinetail devil ray (Mobula mobular) in the eastern tropical Pacific

“…These models have been used for target and non-target species in commercial fisheries using different gears: longliners, trawlers or purse-seiners [26, 28–32], but never applied to mobulid rays. In the case of the purse-seine fishery, Generalized Additive Models (GAMs) have been applied to model the habitat preferences of diverse bycatch species [13, 25, 26, 33–40]; but again have not yet been applied to mobulid rays datasets.…”

Spatio-temporal distribution of spinetail devil ray Mobula mobular in the eastern tropical Atlantic Ocean

“…Data recorded by the observer programs include information about all fishing activities conducted during the trip: set day and hour, set type, set position and catch of target (tunas) and bycatch species (in number or biomass). Bycatch groups include billfish, sharks, bony fish, rays, turtles and mammals (Lezama-Ochoa et al 2018). Mobulid rays used to be identified by the observer program simply as 'Mantas' or to family level (Mobulidae).…”

“…Sets associated with whales (mysticetes) were considered free school sets. Natural (logs) and artificial (man-made) objects, as well as sets associated with whale sharks, were considered FADs (Amandè et al 2011, Escalle et al 2016, Lezama-Ochoa et al 2018.…”

“…These models can be used to inform management options, design protected areas or forecast climate change effects for the development of future mitigation measures, among other uses (Graham et al 2012). Regarding the tropical tuna purse-seine fishery, different SDMs have been developed to understand the distribution of target and non-target species (Martínez-Rincón et al 2012, 2015, Sequeira et al 2014, Lezama-Ochoa et al 2016, Montero et al 2016, Druon et al 2017, with generalized additive models (GAMs) being the most used tool for modeling the distribution and environmental preferences of large marine species in the eastern Atlantic Ocean (Escalle et al 2015, Lopez et al 2017, Lezama-Ochoa et al 2018. However, these methods have not been widely used to study mobulid rays, and specifically M. mobular, in the Atlantic Ocean.…”