8 March 2016

Since 2011, the International Seafood Sustainability Foundation (ISSF) has conducted ten at-sea research cruises – voyages built on scientific research and aimed at developing technologies and finding techniques and procedures that would result in more selective fishing in purse seine fisheries. The focus on these research cruises is twofold: reducing the incidental catch of non-tuna species and better understanding and prediction of the composition of tuna schools (which may contain skipjack, yellowfin and/or bigeye tuna).

A recent example is ISSF's October 2015 cruise in the eastern Atlantic Ocean, part of the Common Oceans/ABNJ Tuna project, which brings together a wide group of stakeholders to achieve sustainable and efficient tuna fisheries production and biodiversity conservation through the application of an ecosystem approach. A component of the project is reducing ecosystem impacts from tuna fishing, including bycatch and associated species. As such, the cruise set out to study the movement patterns and vertical behavior of tunas and silky sharks, building on previous ISSF investigations in the Indian Ocean and cruises in the Central Pacific ocean to examine the influence of fish aggregating devices (FADs) on tuna, pelagic sharks and non-target fish through the use of remotely monitored acoustic tags.

Because technical solutions to avoid bycatch may be region-specific, testing such solutions under different conditions across oceans is necessary. This effort was this first of its kind in the Atlantic Ocean tuna fishery. And because Atlantic Ocean bigeye tuna stocks are now considered heavily exploited, researching new ways to prevent bigeye overfishing is a priority.

Our research team set sail for nearly a month from October 4 -22 from the port of Dakar, Senegal aboard the 72-foot cutter rigged sailing vessel Sea Dragon, operated by Pangaea Exploration. Previous experiments were conducted primarily on commercial fishing vessels, where research needs can sometimes be at-odds with commercial fishing activities. The concept of this cruise, therefore, was to utilize a non-fishing vessel as a tagging platform to allow scientists as much time as needed at each research station.

Although working from a sailboat as a platform presented some difficult conditions for our team of three researchers, we realized our primary objective – investigating the spatial and temporal behavior of FAD-associated species captured in the Gulf of Guinea tuna purse seine fishery. Our efforts benefited greatly from cooperation by the French companies of CFTO and Saupiquet and the Spanish company Albacora, which provided full access to their GPS monitoring buoys attached to drifting FADs, which were within range of the Sea Dragon. These buoys provided the scientists the exact position and drift of the buoy and a display indicating the general amount of tuna and associated fish around the FAD. Using this information, the team was able to quickly locate and concentrate efforts on productive FADs suitable for the study.

Upon arrival at a drifting FAD, two scientists conducted a scuba survey to visually assess the presence of species needed for the study that included skipjack, yellowfin and bigeye tuna, silky sharks, and other non-tuna species. After determining that the required species mix was present and in sufficient abundance for the study, a free-drifting acoustic receiver was attached to the FAD. These devices record the presence of fish that are tagged with depth monitoring acoustic transmitter tags that are within range of the FAD. This information is reported via satellite transmission to the scientists on a daily schedule along with buoy position.

Once the satellite-linked receiver was attached to the FAD, fishing operations commenced. Anyone who has tried to land large fish from a high-sided sailing vessel will recognize the challenges, but experience and persistence paid off. Fish were landed in a padded cradle and an acoustic tag was quickly sewn into the body cavity employing a well-developed procedure used in fish tracking and monitoring studies. We were able to deploy all acoustic tags in the necessary fish species in record time and turn attention to the secondary objectives of the cruise. The receivers were left on the FADs to report buoy position and tagging data for as long as tagged individuals remain associated with the FADs, offering invaluable information on FAD residence times not otherwise available.

Not only were we studying the depth and movement of the different species, but we were also observing FAD design through underwater visual census. ISSF has worked to create and promote the use of non-entangling FADs in global tuna fisheries. Although no shark or other bycatch entanglements were observed during this cruise– due in part to the use of these non-entangling FAD designs by these vessel fleets – scientists can always benefit from studying FADs in action as we continually refine designs for maximum mitigation of bycatch.

In addition to the detailed FAD-associated data provided by acoustic tags, our team was also able to deploy 15 pop-up archival tags (PATs) in silky and oceanic white tip sharks – some of which were even double tagged with acoustic tags. Satellite tags are designed to collect vertical diving and position information over several months to more than a year; they detach and float to the surface at a pre-programmed date, report data by satellite transmissions. PAT data can provides a longer-term look at the movements of sharks when they are away from FADs or interacting with other FADs and fisheries. Importantly, double tagged fish provide critical comparisons of on and off-FAD behavior useful for designing strategies to reduce the impact of fisheries on oceanic sharks.

Similar to studies done in the central Pacific and western Indian Oceans, the research our team conducted last year in the Atlantic Ocean provides key findings that inform a greater goal – determining ways to identify which tuna species are present and reduce catching tuna of undesirable size or other non-target species. Through collaborative and successive efforts such as these bycatch research cruises, scientists can continue to identify and test solutions that catalyze progress on reducing bycatch and alleviating the strains of commercial fishing on fish stocks.

By David Itano

• Mr Alejandro Anganuzzi, Global Coordinator for the Common Oceans/ABNJ Tuna Project | [email protected]
• Ms Mary Sestric - VP, Communications International Seafood Sustainability Foundation | [email protected]