Distribution, abundance and biology of Group V humpback whales ...

During the northern migration there is a distinct peak in
abundance during late June and early July observed off
North Stradbroke Island (Paterson 1984) but no such peak
is observed during the southern migration that occurs
in late August off the Whitsunday Islands (Malcom and
Duggan 1997). In Hervey Bay, the Pacifi c Whale Foundation
(1997) reported humpbacks appearing at earlier dates
in successive years. The peak abundance of humpbacks
in Hervey Bay varies from days to weeks (Corkeron et
al.1994). Dawbin (1956) observed a variation in the peak
abundance of migrating humpbacks past New Zealand to be
as much as fi ve-and-a-half weeks.
The structure of pods was identifi ed by a genetic study by
Brown et al.(1995). They noted the northward migrating
pods were signifi cantly smaller than southward migrating
pods and that more male humpback whales were found in
the larger pods than females. The most common pod type
observed during the study was the male-female pair, which
is suggestive of either mating on migration and/or mate
guarding.
There is growing support for the hypothesis that not all
females migrate annually to winter grounds but remain on
the feeding grounds during rest years, or produce offspring
in the higher latitudes of Antarctica (Chittleborough 1958a;
Brown et al.1995; Craig and Herman 1997; Mikhalev 2000).
Chittleborough (1965) and Brown et al.(1995) documented
the ratio of migrating Group V males to females, sampled in
south-east Queensland, and is approximately 2:1. This is a
similar ratio for other humpback stocks in the North Pacifi c
(Medrano et al.1994; Calambokidis 2000; Craig and Herman
2000). However, researchers from the North Atlantic argue
that there is no evidence for a male-biased sex ratio in
wintering humpbacks in the North Atlantic.
The migration southward may be delayed by some
individuals due to their mating drive being stronger than
hunger as individuals and groups of humpback whales have
been observed to continue to seek mates, at least in the
early stage of the southern migration (Paterson 1984).
5.3 Site fi delity and habitat preference
Humpback whales exhibit a high degree of site fi delity
both towards feeding and wintering grounds (Clapham et
al.1993). Urban et al.(2000) determined that the migratory
movements of eastern Pacifi c humpbacks were clearly
non-random. Photographic comparisons between areas
showed clear evidence for preferred migratory destinations.
Kaufmann (1990) describes the movements of an adult
humpback whale sighted in Antarctic Area V that was
resighted 19 months later in Platypus Bay, Queensland,
Australia. The re-sightings were verifi ed using both tail-fl uke
and lateral body markings. The resighting of this animal
is the fi rst photographic documentation of movement
between the described areas, and provides support for the
assumption, based upon discovery tags, that whales
found along the east cost of Australia migrate from
Antarctic Area V.
Genetic studies demonstrate that, despite the nearly
unlimited migratory potential of the species, there is a
striking degree of genetic structure both within and
between oceanic populations of humpback whales
(Baker et al.1994). Several authors have concluded that
site fi delity in humpbacks is a maternally driven trait
(Baker et al.1994; Palsbøll et al.1995; Urban et al.2000).
Photo-identifi cation studies are not consistent in their
fi ndings in relation to sex biases in site fi delity. Garrigue
et al.(2000) and Sladen et al.(1999) concur in their
conclusions of male exhibiting less fi delity than females. In
New Caledonia Garrigue et al.(2000) found that there is an
interchange of males between winter grounds. In Hawaii
males are more likely to wander between wintering grounds
than females (Sladen et al.1999). However, a photoidentifi
cation study by Craig and Herman (1997) suggests
males show greater site fi delity than females in Hawaiian
wintering grounds.
Baker et al.(1994) concluded from their genetic data that
there was no obvious evidence of sex biases in site fi delity
and that humpbacks used a strategy that is a combination of
imprinting and genetic traits to return to the winter grounds.
Craig and Herman (2000) used photographic techniques
to investigate sex differences in site fi delity and migration.
They concluded that the wintering areas utilised by breeding
females is dependent upon their reproductive status.
Gregr and Trites (2000) used positional information and
oceanographic data (bathymetry, temperature, and salinity)
to predict critical habitat off the coast of British Columbia
for fi ve whale species including humpback whales. Using
six predictor variables (month, depth, slope, depth class,
and sea surface temperature and salinity) the model
developed identifi ed critical habitat for sei, fi n, and male
sperm whales. However, due to the small sample size, the
model was relatively insensitive to the predictor variables
for humpback whales. However, the habitat predictions
did identify humpback whale habitat in sheltered bays
and straits throughout the coast. The application of this
model could be considered for identifying humpback whale
habitat in Queensland. The high degree of site fi delity
exhibited by humpbacks, especially females, is an important
consideration for the management and planning of marine
protected areas.
The high degree of site fi delity exhibited by humpbacks
is likely to have implications for breeding success. It has
been suggested site fi delity is maternally driven and that
females with calves favour habitats that provide protection
from predators and rough sea conditions. If this is the case,
there are only limited areas breeding females can utilise.
If females have already expended huge energy budgets
during migration, the energy required to search for other
suitable breeding habitat may be enough to cause a decline
in breeding success over a long period.
10 • Distribution, abundance and biology of Group V humpback whales Megaptera novaeangliae: A review • August 2002