Report on ongoing monitoring off Townsville and initial surveys
near Cardwell and Cairns, North Queensland
Research Report
Peter Speare and Marcus Stowar
Australian Institute of Marine Science
ISBN 9781921359057
Published May 2008
MTSRF Project 4.8.2 -
Effects of the Great Barrier Reef Zoning Plan on inshore habitats
and biodiversity: Shoals
Abstract
This report
encompasses baseline studies of fish and habitats on shoal ground
in the Cardwell and Cairns regions of the Great Barrier Reef, and
seasonal monitoring of an established set of contrasting sites
(closed and open to fishing) in the vicinity of Townsville.
Acoustic mapping techniques were utilised to provide topographical
imagery of all study sites for the purposes of directing towed
video for habitat classification, and the deployment of Baited
Remote Underwater Video Stations (BRUVS) for the acquisition of
fish species and their relative abundance in habitats on these
shoal areas.
Townsville: All sites in the Townsville
region were from unconsolidated sandy sediments supporting marine
plants with patches of structurally more complex and diverse
epibenthic communities of filter feeders and some hard corals. One
site, RAP 4 was centred on the wreck of a wooden trawler.
BRUVS sampled 150
species from 39 Families of fish over four discreet sampling events
between July 2006 and March 2007. There was roughly twice the
number of species recorded from each set on complex habitat
compared to the surrounding habitat (109 versus 71 species
overall). Species richness did not vary with the level of
protection or throughout the sampling period.
The distribution and
relative abundance of fish assemblages varied with protection and
location on each of the two principal habitat types. There was an
interaction between these two factors which was due to the fish
assemblages in the complex habitat on Magnetic Shoal having greater
similarity to those on the Mackerel Patch, and the fish assemblages
over sand at RAP 4 and RAP 16 being distinct from those in the
green zone and Magnetic Shoal.
The distributions and
relative abundances of 22 species potentially targeted by fishers
were similarly influenced by the level of protection, but possibly
because of a confounded site effect. There was believable evidence
of an increase in the abundance of Plectropomus maculatus
and Choerodon venustus in the new green zone.
Cardwell: The shoal study sites off Cardwell are
founded on rocky substrate with surrounding fine sand sediments.
Their inshore and relatively shallow water attributes ensure
relatively turbid conditions in response to wind driven wave and
tidal movements.
BRUVS sampled 65
species from 27 families with, on average, twelve species from the
rocky substrates and six species from the muddy sand bottom
surrounding these outcrops. While there was site-associated
differences in the fish communities (distribution and relative
abundance) the greatest dissimilarity between fish assemblages
could be attributed to the two principal habitat divisions (hard
rock and soft sediment). Parupeneus indicus,
Plectropomas maculatus, Choerodon schoenleinii
and Scarus ghobban were strongly correlated with hard
bottom habitat, whereas Scomberomorous queenslandicus,
Carangoides coeruleopinnatus and Nemipterus
furcosus were indicative of open bottom habitat. Fish
communities were similar across sites on rocky substrate, but there
was a site effect in relation to fish assemblages over the soft
sediments that was attributed to the more mobile species inhabiting
these areas.
Of fourteen targeted
species, there was evidence that Lutjanus erythropterus,
Epinephelus coioides, Scomberomorus
queenslandicus, Choerodon schoenleinii and
Lethrinus laticaudis are more abundant at Brook Shoal,
which was protected from fishing in 2004.
The limited extent of
rocky habitat at both Brook Shoal and Forty Foot Rock precluded
extensive sampling effort, which means that more temporal effort
must be employed to resolve any zoning effects.
Cairns: Three paired sites with contrasting
zoning were established in the Cairns region on deep-water shoals
in the vicinity of emergent coral reefs. In general, all sites
offered similar habitats except that the sites adjacent to Green
Island lacked marine plants, possibly in response to lower light
levels coincident with higher turbidity.
Cairns sites shared
140 fish species from diverse taxonomic and trophic functional
groups. Fish assemblages had a strong association with either the
sandy open bottom or the structurally and biologically diverse reef
habitats, with more than twice the number of species associating
with the complex habitat.
The distributions and
relative abundances of 24 species of interest to fishers were not
discriminated simply on the basis of protection because of
interactions between location and habitat effects. Plectropomus
leopardus and Lethrinus lentjan were more abundant at
the protected site adjacent to Michaelmas reef and Argyrops
spinifer at the protected site adjacent to Green Island, but
thus far the effects of the rezoning have not had a large impact
upon the fish communities of reefs near to Cairns.
