Njaratiana RABEARISOA
Informations
EMAIL : njaratiana.rabearisoa ird.fr
: 0499573204
Institut : /BOUCLE_groupemots>
IRD
LIEU GEOGRAPHIQUE : /BOUCLE_groupemots>
SETE
GRADE : /BOUCLE_groupemots>
IR
Thèmes de recherche : /BOUCLE_groupemots>
Approche écosystémique des pêches
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Publications
2020 |
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Marsac, F., et al. "Seamount effect on circulation and distribution of ocean taxa in the vicinity of La Perouse, a shallow seamount in the southwestern Indian Ocean." Deep-Sea Res. Part II-Top. Stud. Oceanogr.. 176 (2020): 104806.
Résumé: The La Perouse seamount (60 m depth) has so far been poorly studied despite it being a short distance (160 km) from Reunion Island. As part of the MADRidge project, a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology. Current measurements, temperature and chlorophyll-a profiles, and mesozooplankton and micronekton samples were collected between the summit and 35 km away. Micronekton data were supplemented with stomach content of pelagic top predators as well as fisheries statistics from the domestic longline fleet operating from Reunion. Vertical current profiles revealed distinct patterns between the offshore and seamount-flanked stations, giving evidence of topographical induced flow instabilities, notably on its leeward side (west) relative to the east flank. Distinct patterns in temperature and chlorophyll-a vertical profiles suggest the formation of convergent and divergent circulation cells as a result of the irregular and crescent-like summit topography. Spatial differences in zooplankton abundance were detected with higher biovolumes on the leeward flank. The overall acoustic backscatter for micronekton over the summit was weaker than offshore, but highly concentrated in the upper layer. Albacore tuna and swordfish dominate the longline catch west of Reunion, seemingly in association with a deep (900 m) topographic feature. Yet the largest catch is not directly associated with La Perouse which would be too shallow for top predators to aggregate around in the long term. Enhanced levels of phytoplankton or zooplankton enrichment at La Perouse were not demonstrated in this study, nor was there notable diversity of micronekton species. This might explain the relatively limited importance of this seamount to the tuna fisheries in this region.
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2018 |
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Rabearisoa, N., et al. "Toothed whale and shark depredation indicators: A case study from the Reunion Island and Seychelles pelagic longline fisheries." PLOS ONE. 13.8 (2018): e0202037.
Résumé: Depredation in marine ecosystems is defined as the damage or removal of fish or bait from fishing gear by predators. Depredation raises concerns about the conservation of species involved, fisheries yield and profitability, and reference points based on stock assessment of depredated species. Therefore, the development of accurate indicators to assess the impact of depredation is needed. Both the Reunion Island and the Seychelles archipelago pelagic longline fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by depredation from toothed whales and pelagic sharks. In this study, we used fishery data collected between 2004 and 2015 to propose depredation indicators and to assess depredation levels in both fisheries. For both fisheries, the interaction rate (depredation occurrence) was significantly higher for shark compared to toothed whale depredation. However, when depredation occurred, toothed whale depredation impact was significantly higher than shark depredation impact, with higher depredation per unit effort (number of fish depredated per 1000 hooks) and damage rate (proportion of fish depredated per depredated set). The gross depredation rate in the Seychelles was 18.3%. A slight increase of the gross depredation rate was observed for the Reunion Island longline fleet from 2011 (4.1% in 2007–2010 and 4.4% in 2011–2015). Economic losses due to depredation were estimated by using these indicators and published official statistics. A loss of 0.09 EUR/hook due to depredation was estimated for the Reunion Island longline fleet, and 0.86 EUR/hook for the Seychelles. These results suggest a southward decreasing toothed whale and shark depredation gradient in the southwest Indian Ocean. Seychelles depredation levels are among the highest observed in the world revealing this area as a “hotspot” of interaction between pelagic longline fisheries and toothed whales. This study also highlights the need for a set of depredation indicators to allow for a global comparison of depredation rates among various fishing grounds worldwide.
Mots-Clés: Indian Ocean; Seychelles; Sharks; Tuna; Fisheries; Economics; Killer whales; Whales
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2015 |
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Rabearisoa, N., P. Bach, and F. Marsac. "Assessing interactions between dolphins and small pelagic fish on branchline to design a depredation mitigation device in pelagic longline fisheries." ICES J. Mar. Sci.. 72.5 (2015): 1682–1690.
Résumé: Depredation by false killer whales (Pseudorca crassidens) and short-finned pilot whales (Globicephala macrorhynchus) in pelagic longlining is an issue leading to negative impacts on the economics of the fishery and on odontocetes themselves. We investigated the efficacy of a new depredation mitigation device called “DEPRED” in the interaction between bottlenose dolphins (Tursiops aduncus), spinner dolphins (Stenella longirostris), and small pelagic fish (SPF) attached to branchlines to simulate caught fish. We suggest implications for DEPRED efficacy with larger toothed whales interacting with pelagic longline capture in the open ocean. The design of the device uses streamers to both deter cetaceans and protect fish from predation. In controlled experiments, we tested its efficacy by observing changes in the dolphin's behaviour brought on by the presence or absence of the device on branchlines. First, dolphin–SPF interactions were observed at the small scale using video footage recorded with an underwater camcorder. Second, the efficacy of the device was quantified from interactions between dolphins and 80 branchlines deployed on a longline 500 m long baited with SPF. One half of the SPF on successive branchlines was protected by DEPRED and the other half was not. A total of 707 branchlines were set when dolphins interacted with SPF, and among them, 355 were equipped with DEPRED. Encouraging results were obtained: over the short term, the number of damaged unprotected SPF was on average more than twice the number of protected ones. Nevertheless, habituation behaviour was observed for a resident group of T. aduncus in the experimental area. The relation between the deterrent effect of the device and constraints related to the design of such a device to be used at a commercial operational level are discussed.
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2012 |
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Rabearisoa, N., et al. "Pelagic longline fishing trials to shape a mitigation device of the depredation by toothed whales." Journal of Experimental Marine Biology and Ecology. 432 (2012): 55–63.
Résumé: Depredation is defined as the damage or removal of fish from fishing gear by predators, and is a crucial issue leading to negative impacts on both animals involved in depredation and fisheries. Depredation in longline pelagic fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) involves short-finned pilot whales (Globicephala macrorhynchus), false killer whales (Pseudorca crassidens) and some pelagic sharks. Since no long-term solution could be found to date, we investigated fishing gear improvement by deploying a technology designed to physically protect the hooked fish by hiding it to predators: the DMD (depredation mitigation device). Two types of DMDs were designed: “spiders” and “socks”. The efficiency of “spiders” was tested in November 2007 during a fishing trial of 26 longline fishing operations when 12,480 hooks and 1970 devices were set. The efficiency of “socks” was tested in October 2008 during a fishing trial of 32 longline fishing operations when 13,220 hooks and 339 devices were set. 117 and 24 fish were hooked on branchlines equipped with spiders and socks, respectively and among those devices, 87.3% versus 69.2% were correctly triggered and 80% versus 15% of the fish were correctly protected. A low entanglement rate of the spiders with the fishing gear was found (3.6%), but a higher one was associated to the socks (17.8%). Operational constraints to routinely deploy “spiders” were examined. The number of sets impacted by shark depredation was significantly greater than the number of sets involving toothed whale depredation. However, when depredation occurred, the proportion of fish damaged by toothed whales was significantly greater. While more trials should be carried out to deeply verify the efficiency of DMDs, we remain convinced that considerations of fishing gear technologies might be more actively investigated to propose innovative measures to mitigate toothed whale depredation in pelagic longlining. For this type of gear, innovative technology is an important issue of the ecosystem approach to fisheries (EAF) framework.
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