Type of business:
- Fisheries
CITEB, Store No. 10 - Port Ouest, 97420 Le Port, Réunion Island
Project Manager:
Evgeny ROMANOV
The swordfish Xiphias gladius is the primary target species of the coastal longline fishery in Réunion. In 2023, 165 tons were caught, with a value of over 1 million euros (SIH, 2024). The profitability of driftline fishing depends heavily on environmental conditions, bait supply, and fuel prices.
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Drift longlines are fishing gear several miles long that have highly variable impacts on pelagic fauna. Shark and sea turtle species are regularly caught as bycatch. Fishing time using this technique is quite long: a set, or line deployment, can last between 6 and 8 hours depending on the number of hooks. This exposes the target catch to predation by marine mammals or sharks, and to increased mortality among bycatch. It can also lead to a deterioration in the quality of the fish meat if the fish are caught early in the fishing operation.
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To improve the quality of swordfish catches, enhance longline selectivity, reduce operational costs for small vessels, and deepen our understanding of this species, Citeb has developed the PESCARUN project in partnership with the University of Réunion to study the effectiveness of an innovative fishing gear: the vertical drift longline.
Objectives applied:
- 🎣Improvefishing selectivity, reduce bycatch
- 🎣Improvingthe survival of non-target species and post-release survival
- 🎣Reducingfishing effort and the impact on marine ecosystems
- 🎣Saveon bait and reduce the industry’s carbon footprint (fuel savings)
- 🎣Improvingthe quality of the fish caught
- 🎣Diversifyingfishing practices (targeting deep-water species)
Scientific objectives:
- 🐟Describe the habitats of the swordfish (particularly its daytime habitats)
- 🐟Studying the behavior of the swordfish during the day
- 🐟Gain a deeper understanding of the swordfish’s food web relationships
- 🐟Mesoscale and macroscale movements
- 🐟Studying population connectivity
- 🐟Modeling the environments traversed (in situ data: real-time buoy drifts, water temperature, thermocline depth).
What is a drifting vertical longline?
Drift-net fishing is currently used in Florida to target swordfish. It can be deployed during the day at great depths (where swordfish spend the day) or at night near the surface.
A single hook set at the greatest depth is baited with squid.
An electrolume-type light can be used to make a lure for swordfish.
A GPS tracking buoy helps track the drift of the longline so it can be retrieved in the event of a catch or at the end of the fishing operation
For the purposes of the study, the line was equipped with a depth and temperature sensor, as well as a hook timer to measure the time elapsed since the hook was struck.
The following line lengths were used:
at night: 60, 100, 140, 150 meters
Daytime: 400, 500, 600, 650, 700 meters
Tagging of swordfish:
Little is known about the migratory behavior of the local swordfish. Only one swordfish has been tagged off the coast of Réunion. The data showed that the swordfish headed north in a nearly straight line toward the equatorial countercurrent. The estimated distance traveled over 69 days was more than 4,300 km, or 48 km per day.
Analysis of stomach contents:
What are the swordfish’s favorite prey species in the waters around Réunion?
What size bait is best?
Results
Experimental fishing operations:
Nighttime surface buoy fishing (20 coastal fishing operations) + 2 offshore tagging campaigns (20 days),
Daytime deep-sea fishing with buoys (20 coastal fishing trips) – deep-sea fishing up to 800 m.
Eleven night fishing trips were conducted, with between 4 and 9 longlines set per trip. Swordfish were targeted at depths between 60 and 150 meters. The total fishing effort was 70 hooks. Two swordfish were caught at night using this technique.
Six fishing trips were conducted during the day, with 4 to 8 longlines set per trip. Swordfish were targeted at depths between 400 and 740 meters. The total fishing effort amounted to 52 hooks, but no swordfish were caught.
