[MARMAM] Doctoral thesis on Humpback whales in Hervey Bay, Queensland, Australia

Wally Franklin wally at oceania.org.au
Thu Sep 10 19:39:24 PDT 2015

MARMAM Colleagues 

I am pleased to announce acceptance of my Doctoral thesis, which is now available online from Southern Cross University ePublications at: http://epubs.scu.edu.au/theses/422/ <http://epubs.scu.edu.au/theses/422/> 


Abundance, population dynamics, reproduction, rates of population increase and migration linkages of eastern Australian humpback whales (Megaptera novaeangliae) utilising Hervey Bay, Queensland

Hervey Bay is located to the south of the putative breeding and overwintering grounds of the eastern Australian humpback whale population in the Great Barrier Reef. Previous research has established that large numbers of humpback whales stopover in Hervey Bay during the early stages of the southern migration to Antarctic summer feeding areas.

In this study robust design modeling of long-term capture histories of individual humpback whales and analysis of photo-identification data – obtained during observations of humpback whales in Hervey Bay over 21 years (1992 to 2012) and from other locations across the Pacific, eastern Australia, western Australia, east Africa and Antarctic Area IV and V feeding areas - are used to address a core question: What is the role and function of Hervey Bay during the migration of eastern Australian (Group E1) humpback whales? The data are used to investigate the specific questions: how many humpback whales use Hervey Bay within season and over years; how long do humpback whales using Hervey Bay stay in the Bay; is there site-fidelity to Hervey Bay; what proportion of eastern Australian humpback whales are using Hervey Bay, what is the rate of reproduction and rates of population increase of humpback whales using Hervey Bay; and what patterns are evident for migratory movements and interchange with other regions, including potential feeding areas in Antarctica.

The estimated yearly abundance of humpback whales visiting Hervey Bay increased from 791 in 1997 (95% CI, 407-1176) to 4406 in 2009 (95% CI, 3343-5470). The trajectory of increase in estimated abundance over the 17 years was near linear and slightly greater than the trajectory of increase in the estimated abundance of the whole eastern Australian humpback whale population. A relatively constant proportion of eastern Australian humpback whales visited Hervey Bay each year (mean = 34%, standard deviation = 5.3%).

Between years apparent survival was estimated to be relatively constant over years at 95% (SE = 0.012, 95% CI, 0.918:0.966) and near to the upper limits of biologically plausible survival levels for humpback whales. The near constant proportion of whales occurring in Hervey Bay from the eastern Australian population and the very high site-fidelity of some of those whales in Hervey Bay, suggest that the same cohorts of humpback whales return regularly to Hervey Bay. This study provides the first evidence that a specific sub-group from the eastern Australian humpback whale population uses Hervey Bay and that the sub-group is growing at a greater rate than the eastern Australian population.

Between week entry probabilities display a regular form over years, with variation in the proportion of yearly visitors present prior to the beginning of sampling in each season (mean = 17%, SD = 6.5%), which may be related to the shifts in the timing of the migration.  Within season abundance is heavily skewed to the first half of the season, with approximately 83% of entries occurring in the first five weeks of the season and 17% of entries occurring during the last five weeks of the season. There are two distinct peaks in abundance within season; the highest in week 3 and the second highest abundance occurs in week 8 each year. The lowest probability of entry (1.2%, 95% CI, 0.0004-0.028) and the lowest between week apparent survival (1.3%, 95% CI, 0.062-0.262) occurs between weeks 5 and 6. These results coincide with the mid-season departure of the mature female, immature and older male, and female cohorts, and the arrival of lactating females with older calves and accompanying mature male escort cohorts that dominate the latter half of the season.

Temporary emigration was estimated to be constant over years at 14.1% (SE  = 0.038; 95% CI, 0.081:0.234) and is consistent with a hypothesis that two cohorts – each comprising of breeding females depending upon their breeding status - visit Hervey Bay in alternate years. The typical residency time of humpback whales visiting Hervey Bay is about 1.4 – 2.0 weeks (mean = 1.6 weeks, SD = 0.34).

The observed proportion of calves to whales in Hervey Bay (weekly average 1997 to 2009 = 17.9%) is consistent with the estimated growth rate of the eastern Australian population and calf survival of humpback whales that utilise Hervey Bay may be higher than for the eastern Australian population as a whole. Modelling of the population trajectory of humpback whales utilising Hervey Bay reveals that observed abundance estimates exhibit a logistic trend with a faster growth rate in the mid-1970s, near linear growth during the early and mid-2000s and a slightly decreasing growth rate by 2009. The average rate of increase in abundance of humpback whales utilising Hervey Bay between 1997 and 2009 was estimated at 14.2% (95%CI 11.1% to 15%).

The analysis of all natural marks - including ventral tail fluke marks, dorsal fin shapes and lateral body marks - observed on 79 individual humpback whales over long time-spans ranging from 2 to 21 years, showed very low levels of change in primary and secondary natural marks, no significant difference in the proportion of changes in the natural marks on ventral tail flukes compared the dorsal fin shapes and to the natural lateral body marks. The use of dorsal fin shapes and lateral body marks in conjunction with ventral tail fluke natural marks provides a reliable mechanism to minimise and manage misidentification in large humpback whale photo-identification datasets.

Analysis of photo-identification data of fluke matches between New Caledonia and Hervey Bay revealed low levels of intermingling between eastern Australia and New Caledonia, consistent with these populations being discrete breeding populations. Matches between eastern Australia and New Zealand provided the first evidence that eastern Australian humpback whales are travelling through southern New Zealand waters en-route to and from Antarctic feeding areas.

Analysis of photo-identification data of fluke matches between the Balleny Islands and Hervey Bay supports the hypothesis that Antarctic Area V waters, in the vicinity of the Balleny islands, is a summer feeding area for some eastern Australian humpback whales, including at least some whales resighted in Hervey Bay. While matching of fluke catalogues from Antarctic Area IV with fluke catalogues from Eastern Australia, Western Australia and East Africa provided evidence that the humpback whales photographed in the Antarctic Area IV feeding area are from a different population to the African and Australian populations. There was weak evidence supporting the hypothesis that the whales photographed in Antarctica are from the Western Australian population. Photo-identification photography data also showed that humpback whales from eastern Australia do not always travel directly to Antarctic Area V to feed and may exhibit a diverse range of feeding destinations after leaving Australian coastal waters

This study presents the first evidence that the humpback whales utilising Hervey Bay may be a sub-group of the eastern Australian (E1) humpback whale population. Hervey Bay provides a unique stopover for extended residency early in the southern migration for mature females, either early pregnant or resting, accompanying immature males and females, and lactating females with new calves during the latter season. Humpback whales from Hervey Bay use complex migratory pathways to and from Antarctic feeding areas and are involved in low levels of migratory interchange with nearby Pacific populations. This study provides the first evidence that eastern Australian humpbacks use the southern waters of New Zealand en-route to and from Antarctic feeding areas. Data presented in this study suggests that utilising Hervey Bay as a stopover may contribute to the social development and high survival rates of calves and younger humpback whales. This may provide a reproductive advantage to these eastern Australian humpback whales and be a factor in the relatively high rates of increase in abundance observed in humpback whales using Hervey Bay compared to the eastern Australian breeding populations and to other humpback populations.

Wally Franklin PhD, Southern Cross University, Lismore, NSW 

wally at oceania.org.au <mailto:wally at oceania.org.au> 

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