Sperm whale presence observed using passive acoustic monitoring from gliders of opportunity

P Testor,By Queste,P Cauchy,Kj Heywood,Nd Merchant,D Risch

doi:10.3354/esr01044

Abstract

Habitat use by the endangered Mediterranean sperm whale subpopulation remains poorly understood, especially in winter. The sustained presence of oceanographic autonomous underwater vehicles in the area presents an opportunity to improve observation effort, enabling collection of valuable sperm whale distribution data, which may be crucial to their conservation. Passive acoustic monitoring loggers were deployed on vertically profiling oceanographic gliders surveying the north-western Mediterranean Sea during winter 2012-2013 and June 2014. Sperm whale echolocation ‘usual click’ trains, characteristic of foraging activity, were detected and classified from the recordings, providing information about the presence of sperm whales along the glider tracks. Widespread presence of sperm whales in the north-western Mediterranean Sea was confirmed. Winter observations suggest different foraging strategies between the Ligurian Sea, where mobile and scattered individuals forage at all times of day, and the Gulf of Lion, where larger aggregations target intense oceanographic features in the open ocean such as fronts and mixing events, with reduced acoustic presence at dawn. This study demonstrates the ability to successfully observe sperm whale behaviour from passive acoustic monitoring gliders. We identified possible mission design changes to optimize data collected from passive acoustic monitoring glider surveys and significantly improve sperm whale population monitoring and habitat use.

Highlights

Sperm whales Physeter macrocephalus are widespread across the Mediterranean Sea (Drouot et al 2004c, Frantzis et al 2011, Carpinelli et al 2014, Lewis et al 2018) and constitute an isolated subpopulation, genetically distinct from the Atlantic population (Drouot et al 2004a, Engelhaupt et al 2009)
The Mediterranean sperm whale subpopulation contains fewer than 2500 mature individuals
This paper presents a case study on the ability to use passive acoustic monitoring (PAM) glider observations as a tool to study sperm whale habitat use

Summary

Introduction

Sperm whales Physeter macrocephalus are widespread across the Mediterranean Sea (Drouot et al 2004c, Frantzis et al 2011, Carpinelli et al 2014, Lewis et al 2018) and constitute an isolated subpopulation, genetically distinct from the Atlantic population (Drouot et al 2004a, Engelhaupt et al 2009). Di-Sciara 2014) and is considered Endangered by the IUCN (Notarbartolo di Sciara et al 2012) Anthropogenic pressures on this subpopulation include bycatch in fishing gear (Notarbartolo di Sciara 1990, Notarbartolo di Sciara et al 2004), ship strike (Carrillo & Ritter 2010, Frantzis et al 2019), ingestion of marine debris (de Stephanis et al 2013) and anthropogenic noise disturbance (Frantzis et al 2003, Weir 2008) and whale-watching activities (Gordon et al 1992, Notarbartolo-di-Sciara et al 2008). With increased observational effort in non-summer months (Mannocci et al 2018), to better understand the seasonality of sperm whale habitat use and identify key seasonal habitats, which will allow for appropriate management of shipping and fishing activities (Rendell & Frantzis 2016)

Methods

Results

Discussion

Conclusion