Diving behaviour of albatrosses: implications for foraging ecology and bycatch susceptibility

L K Bentley,R A Phillips,A Manica,A Kato,Y Ropert-Coudert

doi:10.1007/s00227-021-03841-y

Abstract

Diving is an ecologically important behaviour that provides air-breathing predators with opportunities to capture prey, but that also increases their exposure to incidental mortality (bycatch) in commercial fisheries. In this study, we characterised the diving behaviour of 26 individuals of three species, the black-browed albatross Thalassarche melanophris, grey-headed albatross T. chrysostoma and light-mantled albatross Phoebetria palpebrata, breeding at Bird Island, South Georgia. Individuals were tracked using Global Location Sensor (GLS)-immersion loggers and time-depth recorders (TDRs) and, for two species, Global Positioning System (GPS) loggers. Although the TDRs recorded 589 dives (defined in this paper as submersion > 1 m), average dive depths and durations were just 1.30–1.49 m and 2.5–3.3 s, respectively, for the three species. In addition, many individuals (22% of black-browed, 20% of grey-headed, and 57% of light-mantled albatrosses; total n = 9, 10 and 7 individuals, respectively) did not dive at all. Most dives occurred at the distal end of foraging trips and were rare during the commuting phase. No dives took place in darkness, despite long periods spent on water at night. The limited and shallow dive activity contrasts with impressions from a previous study using capillary-tube depth gauges (which are less accurate than TDRs) and has implications for the susceptibility of albatrosses to bycatch on longlines. This study provides further support for regulations requiring night setting and increased sink rates of baited hooks to help mitigate albatross bycatch.

Highlights

Many seabirds, including penguins, cormorants, alcids, diving petrels and some shearwaters are considered specialist divers, often foraging at depths > 10 m, whereas most other seabird species undertake only brief, shallow dives or feed largely at the surface (Croxall and Prince 1980; Harper 1987; Navarro et al 2014)
A combined Global Location Sensor (GLS)-immersion logger (Mk19, British Antarctic Survey, Cambridge, UK; 2.5 g) attached by a cable-tie to a plastic ring was deployed on one tarsus, and a time-depth recorders (TDRs) (Cefas G5, Cefas Technology Ltd, Lowestoft, UK; 2.7 g or 6.5 g), on a plastic ring, on the other tarsus. (Details of devices used for each individual available in the electronic supplementary material.) Attachment of devices took < 10 min
We provide detailed data on diving depths, durations, frequencies and timing for albatrosses using TDRs, and show that dives are infrequent, diurnal and shallow in all species

Summary

Introduction

Many seabirds, including penguins, cormorants, alcids, diving petrels and some shearwaters are considered specialist divers, often foraging at depths > 10 m, whereas most other seabird species undertake only brief, shallow dives or feed largely at the surface (Croxall and Prince 1980; Harper 1987; Navarro et al 2014). As various types of fishing gear (e.g. gillnets, trawls, pelagic and demersal longlines) are set and operate at different depths, diving capability is a key determinant of the likelihood of incidental mortality (bycatch) Many seabird species are of high conservation concern because of negative interactions with fisheries (Phillips et al 2016). As such, quantifying their diving behaviour is fundamental to understanding not just their ability to access prey, and their susceptibility to this anthropogenic threat

Objectives

Methods

Results

Conclusion