Population estimate and rate of increase of southern right whales Eubalaena australis in southeastern Australia

K Stamation,M Watson,C Charlton,J Bannister,P Moloney

doi:10.3354/esr01031

Abstract

In Australian waters, southern right whales Eubalaena australis form 2 genetically distinct populations that have shown contrasting patterns of recovery since whaling ceased: a western population in South Australia and Western Australia and an eastern population in southeastern Australia (Tasmania, Victoria and New South Wales). Here, we provide an abundance estimate derived from a breeding female superpopulation mark-recapture model for the southeastern southern right whale population. The population comprises 268 individuals (68 breeding females) and has increased at a rate of 4.7% per annum between 1996 and 2017. There has been no significant change in the annual abundance of mother-calf pairs sighted at the only calving ground (Logans Beach in Victoria) over the last 3 decades. The total number of southern right whales (i.e. all adults and calves) using the southeastern Australian coastline has increased by 7% since 1985. Unlike the population estimate (which was restricted to breeding females sighted prior to the post-breeding southward migration), this estimate is likely to include transiting whales from the southwestern population. The theoretical population model predicts 19 breeding females at Logans Beach in 2018 and 28 in 2028; the actual number of breeding females, as of 2018, is 14. This study provides the first complete estimate of population size and rate of increase of southern right whales along the southeastern Australian coastline. This knowledge is critical for assessing population status and recovery of southern right whales in Australia. It provides a basis for monitoring persistence and responses of the population to environmental stressors.

Highlights

Southern right whales Eubalaena australis were targeted for commercial hunting between 1790 and 1980, with at least 150 000 killed globally (Jackson et al 2008)
We report on the relative abundance of mother-calf pairs at Logans Beach, Victoria, over the last 3 decades
The total number of individual southern right whales identified in southeastern Australia in a season increased from 3 in 1993 to 27 in 2011, with a total of 199 individuals identified across those years

Summary

Introduction

Southern right whales Eubalaena australis were targeted for commercial hunting between 1790 and 1980, with at least 150 000 killed globally (Jackson et al 2008). In New Zealand and southeastern Australia, over 58 000 southern right whales were taken (Carroll et al 2014). Endang Species Res 41: 373–383, 2020 management units (Carroll et al 2011a). More recent work has shown the situation to be more complex, providing evidence of whales from different calving grounds mixing in the migratory corridors, which may lead to gene flow between these management units (Carroll et al 2015). Carroll et al (2011a, 2015) found no genetic distinction between southern right whales in New Zealand and those at Logans Beach, Victoria, the only recognised southeastern Australian calving ground. Carroll et al (2011a, 2015) hypothesised that some whales from the New Zealand population may be migrating to southeastern Australia or that whales from the 2 regions mix in the Tasman Sea

Objectives

Methods

Results

Conclusion