The breeding success of the Little Penguin was significantly higher in northern
populations compared with documented southern colonies. Several southern colonies
including Phillip Island in Victoria and colonies in Tasmania, have been characterised by
poor breeding success, increasingly later commencement of breeding, and declining
populations. This study aimed to compare and contrast the ecological attributes of a
thriving northern population with other documented colonies. I collected long term data
on breeding success (1987 to 1997) of the Little Penguin on Bowen Island, and related
variability in breeding success to ocean currents and climate patterns, foraging behaviour
and diet, nesting habitat, and inter-specific and fisheries competition. The benefits of
successional changes to nesting habitat on Bowen Island since active habitat management
commenced in 1989 were examined, including the importance of burrow depth, aspect,
distance to water from the burrow, and vegetation type on breeding success of the Little
Penguin.
Morphological measurements of east coast penguins indicated a north-south
cline, similar to that described in New Zealand. The Little Penguin was larger at higher
latitudes. Whilst adults were sedentary and displayed a high degree of nest site fidelity,
juveniles dispersed widely in their first three years, but then returned to the colony,
sometimes to their natal burrow, to breed. This appears to be an adaptive mechanism,
which selects for high quality nesting habitat. The study confirmed earlier findings that
mature vegetation assemblages, namely woodland and forest, support higher breeding
success than structurally simpler grassland and herbland habitat. This may contribute to
observed differences in breeding success between northern and southern colonies,
because many of the southern colonies have degraded nesting habitat.
Most important to the diet of the Little Penguin were clupeoids, which dominated
the fish species of Jervis Bay. The substantial clupeoid resources were targeted by the
tuna fishery for bait, in the same areas and coinciding with maximum demands (chick
raising and fledging), as penguins. The potential quantity of baitfish taken from Jervis
Bay was over 10, 000 tonnes per year, which was well beyond the quantities raising
concerns in other regions, although the fishery remains unregulated. Nevertheless, the
foraging range of Bowen Island penguins was smaller than has previously been
described Little Penguins on Bowen Island had a heavy reliance on relatively shallow
waters of the Bay, within 5 km of the island. Daily foraging distances exceeding 20 km
coincided with low breeding success, sometimes below that required for population
replacement. Greater daily foraging range during the breeding season in southern
Victoria may explain in part why these populations are declining.
The principal mechanism for nutrient enrichment of Jervis Bay waters was the
East Australia Current (EAC). This is a large and powerful, warm water boundary
current of 250 km diameter and 1000 feet depth, which promoted slope water intrusion
through upwelling along the New South Wales coast during the study, particularly
during the penguin breeding season. The EAC effects northern colonies, but less so
southern colonies.
The Bowen Island colony was prone to periodic breeding failure, which was
related to the El Nino Southern Oscillation (ENSO) phenomenon, indicated in Australia
by the Southern Oscillation Index (SOI). ENSO warm events, corresponding with
negative values of the SOI, depressed the EAC and caused downwelling, leading in some
seasons to increased breeding failure. There was a correlation between both fledging
success and adult mortality, and the SOI. The mean breeding success of the Bowen
Island colony, at 1.46 chicks per pair over the ten-year study, was the highest recorded
for the Little Penguin, and the population was increasing.
| Identifer | oai:union.ndltd.org:ADTP/218939 |
| Date | January 1998 |
| Creators | Fortescue, Martin, n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Martin Fortescue |
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