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Deepseawaters
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Sea Birds
Deep Sea Birds
Description
A
seabird is a bird that spends most of its time at
sea. Seabirds' is a general term used to
collectively describe any species of bird which spends a substantial
part of its life foraging and breeding in the marine environment.
Birds considered to be seabirds include gulls,
terns, albatrosses, petrels, shearwaters (muttonbirds), cormorants,
gannets and boobies.
Biology, diet and breeding
Seabirds
spend much of their lives roaming the oceans in search of
prey. Most species tend to forage on their own, though large
feeding flocks will gather at rich or passing food sources.
Squid, fish and krill are
common sources of food. Birds are known to follow fishing
vessels, aggressively competing for discarded fish and baits.
Many
seabirds, such as albatrosses
and petrels have long life spans with some
individuals known to live for more than 60 years. They have
low rates of natural mortality and low rates of mortality
among their offspring. Most species achieve sexual maturity
at 5-12 years of age and breed in colonies on remote islands,
with the pair-bond being reinforced by elaborate courtship
displays. While some species breed annually, others breed
only every second or third year.
Parental
duties are shared by both sexes. Petrels and shearwaters nest
in simple scrapes or in a burrow or natural hole. Albatrosses
nest in the open and, where nest material is available, build
large bowl-shaped nests. Each pair lay a single, large (relative
to body size), white egg which both parents incubate for 35-85
days in alternating shifts. After hatching, chicks are brooded
for a short period until they are able to regulate their own
temperature. After this period the chick is generally left
alone, with parents returning only to provide food. Both parents
feed the chick until it fledges at 110-304 days (depending
on the species).
Habitat
Seabirds
occur widely across the world's oceans. Twenty-two of the
world's 24 albatross species occur in the Southern Hemisphere.
Nineteen of these species occur in Australian waters, and
five of these also breed in Australia. Many species, such
as Grey-headed Albatrosses, are extremely dispersive, spending
most of their time over the surface waters of the High Seas.
In contrast, others, like adult Shy Albatrosses, tend to be
sedentary, regularly foraging over the coastal waters of southern
Australia throughout their adult lives.
Many
other seabirds species in Australia breed
at coastal mainland sites or on offshore islands, however
may forage widely over both Australian and international waters.
Threats
Past
threats to seabirds include being killed
for meat, eggs and feathers. Today, modification of breeding
habitats, oil spills and introduced feral animals are among
the threats that can impact considerably on seabird populations.
More recently, the global expansion of longline fisheries
has begun to pose the greatest overall threat to seabirds.
Longline
fishing is a method used to target finfish and shark
species. A longline consists of a main line with
numerous baited hooks attached to branchlines. The line can
be set parallel to the surface or on the sea-bed.
The number and type of hooks and the length of the branchlines
depend on the target species. Longlines can be up to 100km
long and have up to 10 000 hooks. Each year thousands of seabirds
are accidentally killed on longline hooks when birds ingest
baited hooks during the setting or hauling of the longline.
Birds hooked are subsequently pulled under the water by the
weight of the line and drown. The level of mortality that
occurs in longline fisheries is not sustainable for many populations
of seabirds.
However,
this threat can be greatly minimised by modifying fishing
practice and adopting seabird by-catch mitigation
measures. These include the use of bird-scaring lines and
streamers, weighted lines to reduce the amount of time baits
are available to birds, setting lines at night, setting lines
beneath the waters' surface, and seasonal closures of fisheries
to avoid fishing when birds are more susceptible to being
caught, such as around nesting colonies during the breeding
season. Adoption of these measures has now virtually eliminated
seabird by-catch in some fisheries.
Different
Kind of sea birds have been arranged here
in alphabetical order by scientific name.
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