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

• Published in: Environmental biology of fishes Vol. 106; no. 8; pp. 1693 - 1713
• Main Authors: Murray, Shona, Meeuwig, Jessica J., Thompson, Christopher D. H., Mouillot, David
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-08-2023; Springer Nature B.V
• Subjects: Abundance; Animal Systematics/Taxonomy/Biogeography; Anthropogenic factors; Biodiversity and Ecology; Biomedical and Life Sciences; Body size; Carcharhinus falciformis; Carnivorous animals; Cosmopolitan species; Distribution; Environment; Environmental Sciences; Fish conservation; Fish populations; Fishing; Fishing effort; Fishing pressure; Freshwater & Marine Ecology; Global Changes; Human populations; Life history; Life Sciences; Locations (working); Marine fishes; Marine parks; Marine protected areas; Nature Conservation; Ocean basins; Population decline; Populations; Protected areas; Seamounts; Sharks; Zoology; Baited remote underwater video systems; Marine predator; Spatial protection; Seamount; Marine protected areas; Silky shark
• ISSN: 0378-1909; 1573-5133; 1573-5133
• DOI: 10.1007/s10641-023-01437-7

The silky shark (
Carcharhinus falciformi
s) 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.