Summer distribution and abundance of the giant devil ray (&lt;em&gt;Mobula mobular&lt;/em&gt;) in the Adriatic Sea: Baseline data for an iterative management framework

Caterina Maria Fortuna,Draško Holcer,Simonepietro Canese,Greg Donovan,Laurence Kell,Elio Filidei Jr,Peter Mackelworth

doi:10.3989/scimar.03920.30d

Abstract

The giant devil ray ( Mobula mobular ) is a poorly understood protected endemic species of the eastern Atlantic-Mediterranean region. However, to date there are no range-wide management actions in place. This paper provides the first overview of the summer distribution and abundance of this species and other Myliobatiformes within the Adriatic Sea based on an aerial survey. Although the survey´s primary targets were cetaceans and sea turtles, the study showed that it was possible to use the survey to monitor other species. Abundance estimates are derived using conventional distance sampling analysis. Giant devil rays were observed mainly in the central-southern Adriatic (88% of total sightings). A total of 1595 giant devil rays were estimated in the central-southern Adriatic Sea [coefficient of variation(CV)=25%, uncorrected estimate for perception and availability bias]. When corrected for availability bias the number of specimens was estimated at 3255 (CV=56%). Population growth rate was estimated using life history traits and a sensitivity analysis was conducted to evaluate the benefit of improving biological knowledge on this data-poor species. A power analysis showed that a long-term commitment to an aerial survey would be necessary to monitor population trends. Conservation implications and future work, including how the study could be used to conduct an ecological risk assessment are discussed.

Highlights

The conservation status of a species or population can be defined in several ways
This paper provides the first overview of the summer distribution and abundance of this species and other Myliobatiformes within the Adriatic Sea based on an aerial survey
A total of 1595 giant devil rays were estimated in the central-southern Adriatic Sea [coefficient of variation(CV)=25%, uncorrected estimate for perception and availability bias]

Summary

Introduction

The IUCN Red List of Threatened Species classifies species into categories (ranging from “Data Deficient” to “Critically Endangered”; see http://www.iucnredlist.org/) using criteria such as rate of decline, population size and distribution These categories require knowledge of the abundance, population structure, ecology and life history parameters, as well as anthropogenic or other factors that may threaten the population. For poorly understood species, classifications often rely on inferred and qualitative evaluations (see Camhi et al 2009), which can lead to inconsistencies among and within taxa Such inconsistencies make it difficult to compare population status within species, for instance using fisheries management reference points with the IUCN criteria (Rice and Legacè 2007)

Methods

Results

Discussion

Conclusion