Using fisheries data to model the oceanic habitats of juvenile silky shark (Carcharhinus falciformis) in the tropical eastern Atlantic Ocean

López, Jon; Alvarez-Berastegui, Diego; Soto, Manu; Murua, Hilário

doi:10.1007/s10531-020-01979-7

Cited by 27 publications

(17 citation statements)

References 95 publications

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“…The distribution and movement of pelagic predators has been shown to correlate with environmental conditions, such as thermal fronts, chlorophyll-a concentrations and upwelling events (Block et al, 2011;Lezama-Ochoa et al, 2016;Braun et al, 2019;Lopez et al, 2020). The two silky sharks with the largest displacement distances within this study displayed divergent movement trajectories, with one heading east and the other west.…”

Section: Discussionmentioning

confidence: 72%

“…Such data are crucial to inform future stock assessments for the species that are currently uncertain and data-poor, resulting in management advice being unclear (IOTC, 2017). Further, such data could support the development of adaptive spatial management or dynamic ocean management (Lopez et al, 2020), which are seen as promising tools to improve the conservation and management of these species, and are being considered by several fisheries management organizations (Hobday et al, 2013;Maxwell et al, 2015;Hazen et al, 2018;Welch et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

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Behavior and Ecology of Silky Sharks Around the Chagos Archipelago and Evidence of Indian Ocean Wide Movement

et al. 2020

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Silky sharks (Carcharhinus falciformis) represent a major component of global shark catch, both directly and as bycatch, and populations are declining as a result. An improved understanding of their movement ecology is needed to support conservation efforts. We deployed satellite and acoustic tags (2013–2018) and analyzed historical fisheries records (1997–2009), to investigate the spatial ecology of silky sharks in the central Indian Ocean and a large Marine Protected Area (MPA; 640,000 km2) around the Chagos Archipelago. We observed high fidelity to the MPA, and a sustained diurnal association with a seamount complex, with individuals moving off at night and returning at sunrise. Yet, we also observed large-scale divergent movements in two satellite tagged individuals and documented the furthest recorded displacement distance for a satellite tagged silky shark to date, with one individual moving from the MPA to the Kenyan coast—a displacement distance of 3,549 km (track distance ∼4,782 km). Silky sharks undertook diel vertical migrations and oscillatory diving behavior, spending > 99% of their time in the top 100 m, and diving to depths of greater than 300 m, overlapping directly with typical deployments of purse seine and longline sets in the Indian Ocean. One individual was recorded to a depth of 1,112 m, the deepest recorded silky shark dive to date. Individuals spent 96% of their time at liberty within water temperatures between 24 and 30°C. Historic fisheries data revealed that silky sharks were a major component of the shark community around the archipelago, representing 13.69% of all sharks caught by longlines before the fishery closed in 2010. Over half (55.88%) of all individuals caught by longlines and purse seiners were juveniles. The large proportion of juveniles, coupled with the high site fidelity and residence observed in some individuals, suggests that the MPA could provide considerable conservation benefits for silky sharks, particularly during early life-history stages. However, their high mobility potential necessitates that large MPAs need to be considered in conjunction with fisheries regulations and conservation measures in adjacent EEZs and in areas beyond national jurisdiction.

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Section: Discussionmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

Behavior and Ecology of Silky Sharks Around the Chagos Archipelago and Evidence of Indian Ocean Wide Movement

et al. 2020

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“…Relationships between oceanographic processes and the distribution of pelagic/semi-pelagic elasmobranchs and bycaught species have been previously studied in the eastern tropical Atlantic Ocean (Escalle et al 2016, Lezama-Ochoa et al 2016, Lopez et al 2017, Gaube et al 2018, Braun et al 2019. Lopez et al (2020) found relationships between silky sharks, mesoscale features and seasonal upwelling events in the eastern tropical Atlantic Ocean. In that sense, remote sensing data offers the opportunity to study in detail the oceanographic processes that explain the distribution of large marine species (Hazen et al 2013).…”

Section: Discussionmentioning

confidence: 87%

“…AUC: Area Under the Curve; TSS: True Skill Statistic induced divergence of the surface waters and is considered to be different than the Guinea and Angola Domes (Wyrtki 1981). Specifically, the productivity system that originates around the Cape Lopez area during the beginning of the cold season is the result of both warm and less saline waters in the north that are separated from cold, more saline waters coming from the south (Lopez et al 2020). In addition, during the spring and summer, discharge from the Congo River can increase nutrients in the water and, therefore, the productivity of these waters during this time of year.…”

Section: Discussionmentioning

confidence: 99%

“…Day 290), with lower productivity and warmer sea surface waters (for more details see Lopez et al 2020). Given that our study focused on a species bycaught in the same fishery and in the same areas as the ones investigated by Lopez et al (2020), the same environmental regimes proposed by Lopez et al (2020) were considered in this study. These 3 environmental regimes (i.e.…”

Section: Regime Shifts Identificationmentioning

confidence: 99%

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

Lezama-Ochoa

López

Hall

et al. 2020

Endang. Species. Res.

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The distribution of the spinetail devil ray Mobula mobular in the eastern tropical Atlantic remains poorly known compared to the Pacific and Indian Oceans. We used fisherydependent data and generalized additive models to examine the environmental characteristics associated with the presence of M. mobular in the eastern Atlantic Ocean. Results revealed that the distribution of M. mobular is significantly associated with seasonal upwelling systems in coastal and pelagic areas. Our model predicted the presence of the species in areas where there is evidence of its occurrence, such as the Angolan upwelling system and the coast of Ghana. In addition, our model predicted new hotspot areas, including locations around the Mauritanian upwelling system, the Guinea coast, offshore Ghana and the south coast of Angola and Brazil, where sample sizes are limited. Those areas, as well as the environmental preferences depicted by the model, provide valuable information about the habitat and ecology of the spinetail devil ray. Future research lines derived from this study, as well as its limitations, are discussed. Furthermore, in light of our results we discuss the improvements that are needed to contribute to the conservation and management of this vulnerable species.

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Identifying the drivers of silky shark distribution and an evaluation of protection measures

et al. 2023

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The silky shark (Carcharhinus falciformis) has experienced a significant population decline associated with intense targeted and incidental fishing pressure. Large marine protected areas (MPAs) are increasingly advocated for the conservation of oceanic species like silky sharks, recognising that the benefits of MPAs to such species depend on a comprehensive understanding of their distribution, abundance and life history. We combined mid-water stereo-baited remote underwater video system (BRUVS) records with environmental, geographic and anthropogenic variables to document the distribution and abundance of silky shark populations, identify the most important predictors of their presence, abundance and body size, and determine if their abundance is greater within MPAs than in locations not designated as MPAs. From 1418 deployments of mid-water BRUVS across three ocean basins, 945 silky sharks were identified at 18 locations, with young-of-year (< 87 cm TL) observed at four of these. Our study revealed generally low abundances of silky sharks as recorded on mid-water BRUVS across their cosmopolitan distribution, although our models identified seamounts as hotspots of abundance. Human pressure was a significant variable within our models, with proximity to human populations and ports being key drivers of silky shark abundance and body size. We did not observe a higher abundance of silky sharks inside MPAs compared to locations not designated as MPAs, suggesting that these MPAs have not been placed in areas where silky sharks remain relatively abundant. We therefore recommend expanding the current MPA network in line with the 30 × 30 initiative to more effectively protect key habitats such as seamounts.

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Using fisheries data to model the oceanic habitats of juvenile silky shark (Carcharhinus falciformis) in the tropical eastern Atlantic Ocean

Cited by 27 publications

References 95 publications

Behavior and Ecology of Silky Sharks Around the Chagos Archipelago and Evidence of Indian Ocean Wide Movement

Behavior and Ecology of Silky Sharks Around the Chagos Archipelago and Evidence of Indian Ocean Wide Movement

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

Identifying the drivers of silky shark distribution and an evaluation of protection measures

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