Risk and resilience: High stakes for sharks making transjurisdictional movements to use a conservation area

Abstract

Oceanic sharks are vulnerable to overexploitation due to their life-history strategies, and efforts to protect them in the wild have been stalled by transjurisdictional conflicts of interest. The pelagic thresher shark (Alopias pelagicus) is one such species that visits a seamount in the Philippines where its dependable presence has catalysed a burgeoning dive tourism industry and the designation of a conservation area. Nothing is known of the range and turnover of this population, but the regularity with which these sharks interact with cleaner wrasse on the seamount provides important stability for regional businesses that lack empirical knowledge of their vulnerability. We fitted 14 pelagic thresher sharks with acoustic tags and monitored their fine scale movements for 66 days (June to mid-August 2014). Individuals were present at the seamount for 32% of their days at liberty, and 42% of the tagged sharks were still being detected there at the end of the study. Thresher sharks showed preferences for visiting specific locations on the seamount where they interact with cleaner fish, and estimates of their fidelity to these sites provided scalars for visual census. Pelagic thresher sharks moved away from the seamount after early morning visits to cleaning stations using swim speeds of 3.79 km h-1 (± SD 1.43). These movements demonstrated that they have access to the jurisdictional waters of five provincial territories when dispersing from and returning to the seamount on a diurnal basis. While the seamount offers cleaner-associated services and refuge provision for pelagic thresher sharks, their scale of movement leaves them vulnerable to fisheries that operate in the region. Natural history observations provide context and reveal bias for their application in the management and conservation of this rare and vulnerable shark species.

Current strength, temperature, and bodyscape modulate cleaning services for giant manta rays

“…Similar temporal trends for giant manta rays visiting cleaning stations have been observed in Indonesia where they are known to move offshore to forage nocturnally in deep waters after they clean (Dewar et al 2008). Mantas' movements and use of our study area may be part of a strategy that considers both temporal variations in food availability and cleaner services without being mutually exclusive (Burgess et al 2016;Oliver et al 2019).…”

Vertical movements of a pelagic thresher shark (Alopias pelagicus): insights into the species’ physiological limitations and trophic ecology in the Red Sea

“…Effective fisheries management in the region could further be informed by long-term telemetry deployments (e.g. Oliver et al 2019) that elucidate the species' migration patterns and aggregation sites, as well as by genetic sampling (e.g. Cardeñosa et al 2014) that determines population structure within the Indian Ocean and across the Indo-Pacific divide.…”

Social Factors Affecting Sustainable Shark Conservation and Management in Belize

“…There is increasing scientific concern over the fishing of sharks and rays [6][7][8], which has made them "among the most valuable and vulnerable species in the sea" [9]. Sharks have biological traits, such as taking a long time to reach sexual maturity, long gestation period, carrying few young, and a long life span that make them especially vulnerable to overfishing [10,11]. There are now a wealth of studies showing worldwide declines in multiple shark species, both coastal and oceanic, including local extinctions [2,7,9,[12][13][14][15] and near extinctions [16,17].…”

“…Researchers, governments and conservationists agree that the management of sharks is challenging but a priority [5,11]. Despite a growing number of conservation initiatives, Illegal, Unreported and Unregulated (IUU) fishing remains a major issue [28,29] and marine protected areas and shark sanctuaries do not necessarily translate into compliance [28,30].…”