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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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