Hydroacoustics as a tool to examine the effects of Marine Protected Areas and habitat type on marine fish communities

J. P. Egerton,I. Mascareñas-Osorio,J. Turner,L. LeVay,O. Aburto-Oropeza,A. F. Johnson

doi:10.1038/s41598-017-18353-3

Abstract

Hydroacoustic technologies are widely used in fisheries research but few studies have used them to examine the effects of Marine Protected Areas (MPAs). We evaluate the efficacy of hydroacoustics to examine the effects of closure to fishing and habitat type on fish populations in the Cabo Pulmo National Park (CPNP), Mexico, and compare these methods to Underwater Visual Censuses (UVC). Fish density, biomass and size were all significantly higher inside the CPNP (299%, 144% and 52% respectively) than outside in non-MPA control areas. These values were much higher when only accounting for the reefs within the CPNP (4715%, 6970% and 97% respectively) highlighting the importance of both habitat complexity and protection from fishing for fish populations. Acoustic estimates of fish biomass over reef-specific sites did not differ significantly from those estimated using UVC data, although acoustic densities were less due to higher numbers of small fish recorded by UVC. There is thus considerable merit in nesting UVC surveys, also providing species information, within hydroacoustic surveys. This study is a valuable starting point in demonstrating the utility of hydroacoustics to assess the effects of coastal MPAs on fish populations, something that has been underutilised in MPA design, formation and management.

Highlights

Marine Protected Areas (MPAs) have been suggested as one of a suite of spatial management tools attempting to reduce the pressures posed by anthropogenic threats on marine life and habitats[1,2]
These were an order of magnitude higher than numbers gained during the standard acoustic survey transects within the Cabo Pulmo National Park (CPNP) which combined both reef, rocky and sandy habitats (447 ± 141 fish/ha), and higher still in comparison to the control areas (PA = Punta Arena, the sandy control site: 130 ± 40, and boulder complex control site (BS) = Bajo del Salado, the rocky control site: 99 ± 17 fish/ha)
Pairwise comparisons between sites showed that CPNP acoustic transects had significantly higher fish density than BS whilst there was no significant difference between BS and PA, or the CPNP and PA (Table 1, Fig. 2)

Summary

Introduction

Marine Protected Areas (MPAs) have been suggested as one of a suite of spatial management tools attempting to reduce the pressures posed by anthropogenic threats on marine life and habitats[1,2]. Fish survey methods that provide more detail on the mid-water component within MPAs may reveal how pelagic species and the benthic-pelagic coupling respond to protection, an area of research that comparatively, is lacking[13,15,16] In this respect, active hydroacoustics have the advantage that they can sample almost the entire water column[17], whereas Underwater Visual Census (UVC) is focussed predominantly on demersal species (i.e. from the seabed to a given height above it). In this study we use a split beam echosounder to conduct hydroacoustic surveys to evaluate the effects of protection from fishing and habitat type by examining the total fish density, total fish biomass and mean fish size within the CPNP in comparison to sites outside the park. We comment on the efficacy of using hydroacoustic surveys to measure the effects of protection and habitat type on fish populations

Methods

Results

Conclusion