Impacts on dugongs - The Great Barrier Reef: An Environmental History - page 95

Impacts on dugongs
Introduction
The dugong ( Dugong dugon ) is a herbivorous marine mammal that occurs in, but
is not restricted to, the GBRWHA, including the nearshore waters of the Great
Barrier Reef which are considered to be one of the species' strongholds (Marsh
et al., 2002, 2005, 2011). The dugong is listed as vulnerable to extinction due to
various factors, including variations in seagrass availability, incidental drowning
in shark nets set for bather protection, accidental by-catch in commercial gill
nets, vessel strikes, habitat loss and over-fishing (IUCN, 2013). Since the
animal is long-lived and slow-reproducing, with considerable investment in
each dugong calf, the species is vulnerable to over-exploitation by humans.
Consequently, the maintenance of dugong numbers, and the recovery of depleted
dugong populations, is now difficult to achieve. Furthermore, dugongs are highly
mobile animals that sometimes migrate across large distances, and in remote
waters, with the result that impacts on dugongs are difficult to detect and assess
(Marsh and Lawler, 2001; Marsh et al., 2004). Some previous assessments of the
magnitude of European impacts on marine wildlife species, including dugongs,
have been based on relatively uncritical use of secondary sources; those studies
have been challenged recently on the basis of modern scientific methods and
improved understanding of the ecology of marine mammals. Given the current
conservation threats to dugongs, there is a need to use historical sources more
critically to reconstruct the operation and likely impacts of the human activities
that exploited those animals (Marsh et al., 2005).
The modern pressures on the species occur in the context of various forms of
historical exploitation: those historical activities are the subject of this chapter.
European commercial dugong fishing took place intermittently from 1847 until
1969 in the Moreton Bay area, and for shorter periods at other locations on the
Queensland coast. Dugongs were also caught to supply dugong oil to Aboriginal
settlements; in addition, dugongs have been hunted for their meat by Indigenous
Australians - a practice which long pre-dates European settlement. The
combined effect of those activities amounts to unsustainable exploitation - at
least at particular times and in localised areas - that has probably reduced dugong