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Biological
oceanography
of the NW Shelf
2002
|
Biological
oceanography
of the North West
Shelf
In
1997 AIMS instigated a multi-disciplinary study to describe pelagic
food chains in the vicinity of North
West Cape (21o49’ S, 114o14’ E),
Western Australia. The continental shelf off NW Australia receives
little freshwater run-off or nutrients from the land but it is one of
the country’s most productive fishing regions, and is well known for
seasonal aggregations of humpback whales and whale sharks. This work
represents an exciting opportunity to link physical processes to an
economically important fishery via biological oceanographic processes.
| The
Northwest Shelf Biological Oceanography Project was established to
develop a clearer understanding of the physical and ecological
processes that support the prawn fishery in Exmouth Gulf, and the
seasonal aggregation of large plankton feeders (whale sharks) at Ningaloo
Reef. Both of these phenomena may to be related to sporadically
high levels of pelagic primary production.
|
Whales on the
North West Shelf
 |
Ten
cruises were conducted during the summers of 1997/98 and 1998/99 in
the vicinity of NW Cape aboard the RV
Lady Basten.
Four programs operated
concurrently:
 Physical
Oceanography
Primary
and bacterial production
Secondary
production
Ichthyoplankton,
nekton, whale sharks and euphausiids
SPECIFICALLY, WE AIM
TO:
-
Increase
understanding of shelf seas and coastal trophodynamics and the
possible impact of ocean processes (eg. upwelling) on pelagic
production
-
Resolve
the quantities and fates of upwelled nutrients
-
Improve
understanding of krill resources
-
Determine
how inter-annual variations in primary production influence energy
transfers to higher trophic levels (prawns and krill)
-
Further
enhance our understanding of the distribution, abundance and dynamics
of the rich zooplankton community
WHERE WE’RE AT
| From the studies
conducted in 1997/98 and 1998/99 we know that the marine environment
at NW Cape is highly dynamic, variable, and potentially productive.
Pelagic production at times is very high, but our measurements of
microzooplankton grazing and our estimation of mesozooplankton grazing
combined do not account for all the primary production observed.
Moreover, the situation differs greatly from year to year. In the
first summer of our study (1997/98) conditions were characterised by
ENSO driven upwelling and high primary productivity, while in the
second (1998/99) upwelling did not occur, water temperatures were
warmer, and primary production was lower.
However, high primary
productivity in the first summer was not necessarily transferred to
zooplankton and may have been lost to detrital food chains.
|
Images
from WA
Rough weather in
the West
|
To our
surprise, however, growth and survivorship of fish larvae was higher
in the second (food poor) summer than the first (food rich) summer.
This may be related to the differences in temperature regimes in the
two years.
FUTURE GOALS
In 2002, the
Northwest Shelf Biological Oceanography Project continued research in
the vicinity of North West Cape. Information on these studies can be
found at:
 Biological
oceanography of the NW Shelf
2002
Northwest
Shelf Bibliography - Northwest Shelf Joint Environmental
Management Study web site. Contains a bibliography of research and
data relevant to marine environmental management of Australia’s
northwest shelf.
Staff
Contact Details
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|
