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Biological
oceanography
of the North West
Shelf
Ichthyoplankton and nekton
Personnel:
Mark Meekan, Peter Doherty, Andrew
Halford, Alison Sampey and Kendra Flynn
Objective:
To study the growth, feeding,
distribution and survivorship of fish larvae in the Northwest Cape
region.
| Research To Date:
Throughout the summers of 1997/98 and
1998/99, light
traps and bongo
nets were used on the RV Lady Basten to capture larval and
juvenile fish. Bongo nets capture early larvae and small juveniles,
but light traps capture later stage fish that are about to settle.
The
distribution and abundance of fish in the area has been studied, and
for selected species we have measured growth rates by examining the
otoliths (ear bones). Another study, which will describe the diet of
early larvae and correlate it to plankton dynamics in the area, is in
progress.
Light
traps capture pre-settlement fish and
macro-invertebrates such
as krill.
|
 Mark
Meekan washing the catch from bongo nets used to capture
larval fish.
 |
 Fish
data from light traps
Whale Sharks and euphausiids
|
Diver with whale
shark
(Photo: Geoff
Taylor)
For more information
about whale
sharks of WA visit Geoff Taylor's
 Whale
Sharks of Ningaloo |
 |
Personnel:
Steve Wilson (UWA), Tim Pauly
(Antarctic Division), Mark Meekan and John Carleton
Objective:
To develop a better understanding of
the link between krill swarms and the seasonal aggregation of
plankton-feeding megafauna (eg. whale sharks) at Northwest Cape and
Ningaloo Reef.
The aims are to:
-
Map the temporal and spatial
distribution and abundance of euphausiid schools along the
shelfbreak using bioacoustic techniques.
-
Investigate the composition and
dynamics of euphausiid schools with deep fishing light traps to
improve descriptions of the population size, distribution age
structure and growth rate
Research to Date:
The role of euphausiids in tropical,
coastal systems is poorly understood, and the oceanographic and
ecological processes that underlie the production and aggregation of
tropical krill at Ningaloo Reef are not well known.
-
There is a circumstantial link
between the seasonal occurrence of whale sharks off Ningaloo Reef,
the occurrence of surface swarms of krill, and inter-annual
variability in upwelling and subsequent pelagic production.
-
Grazing by large schools of
euphausiids may account for the consumption of the excess primary
production near the reef and the possible export of nutrients off
the shelf.
-
Preliminary analyses have found the
guts of euphausiids to contain mostly amorphous material
suggesting these animals feed on detrital material close to the
bottom or on marine snow in the water column.
Data
for euphausiid catches
Future Studies
-
Bioacoustic techniques will be used
to map the distribution, size, shape and density of schools.
-
Stereo video cameras and deep
fishing light traps will be lowered into individual schools to
determine school composition (species and age class composition,
length frequency distributions, sex ratios), school dynamics
(spacing, orientation of individuals, feeding/non-feeding
activity) and to "ground truth" the acoustic signals.
Pelagic fish associated with krill
schools will be identified and measured by in-situ video
photography, and gut analysis conducted. The population size,
distribution, age structure and growth rate of krill populations will
be measured to estimate their potential as a sink for pelagic
production.
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