Estimating Space Use of Mobile Fishes in a Large Marine Protected Area With Methodological Considerations in Acoustic Array Design

Aaron B Carlisle,David Tickler,Taylor K Chapple,Robert J Schallert,Michael Castleton,Francesco Ferretti,Jonathan J Dale,David J Curnick,Barbara A Block

doi:10.3389/fmars.2019.00256

Abstract

Marine protected areas (MPAs) have become an increasingly important tool to protect and conserve marine resources. However, there remains much debate about how effective MPAs are, especially in terms of their ability to protect mobile marine species such as teleost and chondrichthyan fishes. We used satellite and acoustic tags to assess the ability of a large oceanic MPA, the British Indian Ocean Territory MPA (BIOT MPA), to protect seven species of pelagic and reef-associated teleost and chondrichthyan fishes. We satellite-tagged 26 animals from six species (Blue Marlin, Reef Mantas, Sailfish, Silky Sharks, Silvertip Sharks, and Yellowfin Tuna), producing 2,735 days of movement data. We also acoustically tagged 121 sharks from two species (Grey Reef and Silvertip Sharks), which were monitored for up to 40 months across a large acoustic receiver array spanning the MPA. We found that the activity spaces of all satellite-tagged animals, including pelagic species, were much smaller than the area of the BIOT MPA, even taking into account errors associated with position estimates. Estimates of space use of acoustically tagged sharks, based on dynamic Brownian Bridge Movement Models (dBBMM), were also much smaller than the size of the MPA. However, we found important limitations when using dBBMM and demonstrate its sensitivity to both study duration and array design. We found that Grey Reef Sharks should be monitored for at least 1 year and Silvertip Sharks for 2 years before their activity space can be effectively estimated. We also demonstrate the potentially important role that intraspecific variability in spatial ecology may play in influencing the ability of MPAs to effectively protect populations of mobile species. Overall, our results suggest that, with effective enforcement, MPAs on the scale of the BIOT MPA potentially offer protection to a variety of pelagic and reef species with a range of spatial ecologies. We suggest that animals need to be tagged across seasons, years, and ontogenetic stages, in order to fully characterize their spatial ecology, which is fundamental to developing and implementing effective MPAs to conserve the full life history of target species.

Highlights

The need to effectively manage marine resources and ecosystems in the face of increasing human exploitation and climate change is one of the pressing conservation issues of our time
Electronic tagging of pelagic and reef species in the BIOT Marine protected areas (MPAs) suggests that the MPA is large enough to provide significant spatial protection to marine species with diverse spatial ecologies, and that even some highly mobile pelagic species may spend extended periods within its borders
Our ability to fully characterize the full space use of animals in the BIOT MPA is hindered by limitations that are typical of electronic tagging studies, including low sample size, limited deployment duration, acoustic receiver coverage, and a limited ability to tag both sexes across ontogenetic stages and seasons

Summary

Introduction

The need to effectively manage marine resources and ecosystems in the face of increasing human exploitation and climate change is one of the pressing conservation issues of our time. The total area protected is accelerating even more rapidly, in particular due to an emphasis in recent years on the creation of very large MPAs, which typically encompass hundreds of thousands of square kilometers of remote, oceanic habitat, often enclosing entire reef or island systems (e.g., Phoenix Islands Protected Area, Pacific Remote Islands Marine National Monument, Rapa Nui Marine Park, and Pitcairn Islands Marine Reserve) (Letessier et al, 2017) Despite their increasing implementation, much remains unclear about how to best design MPAs to achieve specified goals, that of protecting mobile marine taxa of management and conservation interest, which includes many teleost and chondrichthyan fishes (Sibert et al, 2012; Kaplan et al, 2014; Boerder et al, 2017). Even for highly mobile species, appropriately designed MPAs have the capacity to protect key habitats that fulfill important ecological or life history needs for a species, such as reproduction or foraging (Runge et al, 2014; Hays et al, 2019)

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