Blue Whale Study aerial surveys, southern Australia, 2007-2012

Peter Gill

doi:10.15468/tar989

Blue Whale Study aerial surveys, southern Australia, 2007-2012

Citation

Gill, P. 2015. Blue Whale Study aerial surveys, southern Australia, 2007-2012. Data downloaded from OBIS-SEAMAP (http://seamap.env.duke.edu/dataset/1281) on yyyy-mm-dd. https://doi.org/10.15468/tar989 accessed via GBIF.org on 2024-11-09.

Description

Original provider: Blue Whale Study Inc. Dataset credits: Blue Whale Study Inc. Abstract: Wind-forced cold water upwelling occurs seasonally along the continental shelf of south-east Australia, where pygmy blue whales aggregate to forage. Seasonality and variability are apparent for both blue whale encounter rates and upwelling, within and between seasons. Here we quantify upwelling variability over 11 seasons (2001/02 to 2011/12) and relate it to blue whale encounter rates. Two indices, cumulative wind stress (Intensity) quantifying physical forcing, and surface chlorophyll-a (chl-a) quantifying the ocean’s biological response, revealed variability in upwelling at a variety of temporal scales. Within seasons, upwelling Intensity peaked during February, and chl-a during February–March. Blue whale encounter rate from 52 aerial surveys was modelled against upwelling indices and the climate signal SAM (Southern Annular Mode), at individual survey- and aggregated season-levels, using General Additive Models (GAMs). Survey-level GAMs showed that encounter rate increased with increasing chl-a, and with increasing upwelling Intensity to a point beyond which further increases in Intensity resulted in declining encounter rates. This indicated the importance of productivity, as well as relaxation of upwelling, in producing optimal blue whale foraging conditions. In exploratory season-level models, a strong influence of SAM was apparent, with higher encounter rates associated with positive SAM during the preceding 12 months. Including chl-a improved the model, indicating that both broad-scale climatic signals inherently incorporating environmental variability and uncertainty, as well as more proximal regional factors may influence blue whale occurrence in the study area. Measuring the complex relationships between whale occurrence and upwelling is complicated by the fact that the population of blue whales using the Bonney Upwelling is open, and moves between alternate foraging areas. The findings were interpreted in the context of blue whale foraging ecology in this system. Purpose: Relate variability in blue whale relative abundance to variability in upwelling off southern Australia

Purpose

Relate variability in blue whale relative abundance to variability in upwelling off southern Australia

Sampling Description

Study Extent

NA

Sampling

NA

Method steps

NA

Additional info

marine, harvested by iOBIS

Taxonomic Coverages

Scientific names are based on the Integrated Taxonomic Information System (ITIS).

Balaenoptera musculus brevicauda
common name: Pygmy blue whale rank: subspecies

Geographic Coverages

Australia

Bibliographic Citations

Contacts

Peter Gill
originator
position: Primary contact
Blue Whale Study Inc.
email: pete@bluewhalestudy.org
homepage: http://www.bluewhalestudy.org

OBIS-SEAMAP
metadata author
Marine Geospatial Ecology Lab, Duke University
A328 LSRC building
Durham
27708
NC
US
email: seamap-contact@duke.edu
homepage: http://seamap.env.duke.edu

OBIS-SEAMAP
distributor
Marine Geospatial Ecology Lab, Duke University
A328 LSRC building
Durham
27708
NC
US
email: seamap-contact@duke.edu
homepage: http://seamap.env.duke.edu

Peter Gill
owner
position: Primary contact
Blue Whale Study Inc.
email: pete@bluewhalestudy.org
homepage: http://www.bluewhalestudy.org

Peter Gill
administrative point of contact
position: Primary contact
Blue Whale Study Inc.
email: pete@bluewhalestudy.org
homepage: http://www.bluewhalestudy.org