DOI: 10.5061/dryad.g98b456
title: Data from: Shark movement strategies influence poaching risk and can guide enforcement decisions in a large, remote Marine Protected Area

description: Large, remote marine protected areas (MPAs) containing both reef and
 pelagic habitats, have been shown to offer considerable refuge to
 populations of reef-associated sharks. Many large MPAs are, however,
 impacted by illegal fishing activity conducted by unlicensed vessels.
 While enforcement of these reserves is often expensive, it would likely
 benefit from the integration of ecological data on the mobile animals they
 are designed to protect. Consequently, shark populations in some protected
 areas continue to decline, as they remain a prime target for illegal
 fishers. To understand shark movements and their vulnerability to illegal
 fishing, three years of acoustic tracking data, from 101 reef-associated
 sharks, were analysed as movement networks to explore the predictability
 of movement patterns and identify key movement corridors within the
 British Indian Ocean Territory (BIOT) MPA. We examined how space use and
 connectivity overlap with spatially-explicit risk of illegal fishing,
 through data obtained from the management consultancy enforcing the MPA.
 Using individual-based models, the movement networks of two sympatric
 shark species were efficiently predicted with distance-decay functions
 (&gt;95% movements accurately predicted). Model outliers were used to
 highlight the locations with unexpectedly high movement rates where MPA
 enforcement patrols might most efficiently mitigate predator removal.
 Activity space estimates and network metrics illustrate that silvertip
 sharks were more dynamic, less resident and link larger components of the
 MPA than grey reef sharks. However, we show that this behaviour
 potentially enhances their exposure to illegal fishing activity. Synthesis
 and applications. Marine protected area (MPA) enforcement strategies are
 often limited by resources. The British Indian Ocean Territory MPA, one of
 the world’s largest ‘no take’ MPAs, has a single patrol vessel to enforce
 640,000 km2 of open ocean, atoll and reef ecosystems. We argue that to
 optimise the patrol vessel search strategy and thus enhance their
 protective capacity, ecological data on the space use and movements of
 desirable species, such as large-bodied reef predators, must be
 incorporated into management plans. Here, we use electronic tracking data
 to evaluate how shark movement dynamics influence species mortality
 trajectories in exploited reef ecosystems. In doing so we discuss how
 network analyses of such data might be applied for protected area
 enforcement.
description: Acoustic detection data
 2013-2016All acoustic detection
 data used for analysis of silvertip and grey reef sharks in the British
 Indian Ocean Territory between 2013 and 2016. Receiver locations have been
 removed from the data and are referred to by station
 name.Acoustic Data
 DJacoby.csv
description: Acoustic tags were surgically implanted in 101 sharks reef sharks
 during February-April between 2013 and 2016. Sharks were tracked for three
 years across five isolated atoll systems in the north of the British
 Indian Ocean Territory Marine Protected Area. The study array consisted of
 a total of 52 Vemco acoustic receivers (Vemco, Nova Scotia, Canada, 46
 VR2Ws, plus four VR2W-UWM and two VR4Gs) with additional receivers placed
 further afield in the archipelago excluded from the analyses due to later
 deployment dates or lack of data from this cohort of animals. Sharks were
 caught at various locations around the northern atolls using hand-lines
 with barbless circle hooks and brought alongside or into the boat. Vemco
 V16 acoustic tags were surgically implanted into the shark and had a
 expected duration of up to 10 years. Data were downloaded on an annual
 basis and filtered for false detections prior to finalising the data for
 analysis.