Download PDF - COINAtlantic

Distribution patterns of migrating humpback whales (Megapteranovaeangliae) mother-calf groups in Jervis Bay, Australia: A geostatisticalanalysisEleanor Bruce 1 , Lindsey Albright 1 & Michelle Blewitt 1,21 Geocoastal Research Group, School of Geosciences, University of Sydney, NSW, 2006, AustraliaEleanor.Bruce@sydney.edu.au2 University of Sydney Institute of Marine Science, University of Sydney, NSW, 2006, AustraliaMichelle.Blewitt@sydney.edu.auAbstractIncreases in east Australian humpback whale populations, specifically in areas where sightings were previouslyinfrequent, highlight the importance of understanding the usage patterns and habitat preferences for resting groundsalong migration pathways. This study investigates the spatio-temporal distribution of humpback whales in JervisBay, New South Wales, Australia, based on group composition, to provide insight on the role of this shallow coastalembayment for mother-calf groups during the southern migration to polar feeding grounds. Sighting data collectedby commercial whale-watch operators during the 2007 to 2010 migration seasons were mapped to examine monthlyvariations in Bay usage and group composition. Differences in the distribution patterns of mother-calf and non-calfgroup sightings were examined using spatial cluster analysis. Mother-calf groups show a significant preference forthe shallow waters of Jervis Bay during October and November, indicating Jervis Bay may function as a preferredresting location during their southern migration.IntroductionFollowing near-extinction in the 1950s and early 1960s due to vessel and land-based hunting, there has been anincrease in the east Australian humpback whale population. Land-based surveys conducted at Point Lookout, southeasternQueensland since 1981 have shown a high but steady long-term rate of population growth of humpbackwhales on the east coast of Australia (Noad et al., 2011). Estimated growth rates predicted are one of the highest inthe world and may approach the theoretical reproductive limit of the species (Noad et al., 2011).Southern hemisphere humpback whales undertake extensive annual migrations between high latitude feedinggrounds where they spend the austral summers and the low latitude breeding grounds where they spend the australwinter, a distance of approximately 3,000 km (eg. Clapham, 2000). Humpback whales display high site fidelity,returning year after year to the same breeding and feeding grounds (eg. Clapham, 2000). These migrations predominantlyfollow near-shore migration corridors, providing protection from rough seas, predators and conspecifics (eg.Bryden, 1985). Some individuals have been observed moving into sheltered coastal embayments where they rest andsocialise before completing the migration (Corkeron et al., 1994). There is limited understanding of the migratorystages of humpback whales, particularly any social interactions and habitat constraints that may be exhibited(Valsecchi et al., 2002).Humpback whale calves are born in the warm, sheltered waters of the winter breeding grounds (Smultea, 1994).From there, the calf travels with its mother to the rich feeding grounds in the high latitudes and are rarely seen travellingin large groups or associated with other mother-calf pairs, generally preferring to travel with one additionalwhale, an ‘escort whale’ that may assist with caring, as well as protecting against predation or harassment by conspecifics(eg. Brown and Corkeron, 1995). Mother-calf pairs prefer shallow, calm waters, hugging the shorelinewhile migrating or resting in protected embayments or coastal waters (eg. Ersts and Rosenbaum, 2003). During acalf’s first southern migration, the mother is the primary provider of food, protection and training (Clapham, 2000).It is speculated that a calf’s experience with its mother may influence its later habitat choices, as well as behaviourssuch as foraging and migrating (Weinrich et al., 1992). Humpback whales exhibit high levels of maternally directedphilopatry, so the foraging success of an individual may depend on its familiarity with a number of different foraginghabitats (Weinrich, 1998).Several studies have been undertaken in habitat preferences of mother-calf humpback whale pairs. In Madagas-155