|
||||||||||||||
|
|
||||||||||||||
|
|
 |
| An underwater visual fish survey. Photo by CRC Reef. |
These surveys are done once or twice a year by divers on SCUBA counting fish in a 50m by 5m strip at 30 locations around each ELF reef cluster. By doing this, we hope to get an estimate of the number of fish on the different reefs, independent of the ELF catch surveys.
As well as counting the species of fish that are targeted by line fishers, such as coral trout, red throat emperor and stipey bass, fish that coral trout feed on are also counted. Included in this group are the fusiliers, bait fish (hardy heads) and parrot fish, as well as all the small damsel fishes that are so common on the reef.
Records of the amount of hard and soft corals are also obtained to gain information on habitat changes, as well as changes in the fish stocks over the duration of the experiment.
 |
| A catch survey. Photo by CRC Reef. |
Catch Surveys are carried out by the research team with the help of a commercial master fisherman and his dorymen contracted by CRC Reef. These surveys are generally timed to coincide (but not directly overlap) with the underwater visual surveys.
Throughout the day, each dorymen is accompanied by an ELF researcher who ensures that the designated sampling regime is followed. Each fish caught is tagged and measured immediately by the researcher, allowing the ELF researches to keep track of the sex and age of that fish for later determination.
Upon the day's end, all recorded fish caught (up to the quota limits imposed by GBRMPA and QFMA permit conditions), are brought back to the dorymen's mothership to where further ELF researchers are awaiting for weighing and the extraction of gonads and otoliths.
The gonad and otolith samples are then returned to the ELF laboratory, where they are analysed for age determination and sex determination.
Prior to the commencement of the ELF Experimental manipulations, ELF scientists needed information on what the status of fish stocks were. This was necessary so that any changes in the fish stocks due to changes in fishing pressure could be measured.
The researchers carried out both catch surveys and underwater visual surveys of all the reefs in the ELF Experiment in 1995 and 1996. These surveys also provided essential information on the variation in fish stocks over a wide area in the Great Barrier Reef.
In general, these surveys found that there were marked differences in stocks of coral trout and red throat emperor in different areas of the Great Barrier Reef .
There were relatively more individuals, and fish of greater sizes, in the southern areas of the Great Barrier Reef off Mackay and Gladstone, where-as areas off Townsville and Cooktown seemed to have fewer individuals per area.
Throughout the Great Barrier Reef Marine Park, various reefs have been given varying levels of protection from fishing and other uses.
The ELF Experiment showed there were variations in the apparent effects of protection from fishing in the various areas of the Great Barrier Reef. In the southern areas of the reef, it appears that there were a greater number of common coral trout, and larger individuals on reefs that were protected from fishing compared to those reefs where fishing is allowed. However, in the northern areas of the reef, there appears to be little difference at all in reefs that are opened or closed to fishing. This may be due to lower levels of fishing pressure in the northern reefs surveyed, or may be due to differences in habitats, population dynamics are in frequent of closed reefs.
 |
| Coral trout of at least minimum size were still present 12 months after closed areas were re-opened to fishing. Photo by CRC Reef. |
As expected, at least in some areas of the Great Barrier Reef, opening protected reefs to fishing for one year as part if the ELF Experiment resulted in a substantial increase in fishing effort as fishers came to take advantage of the good fishing.
More importantly though, the catch taken from these opened reefs compared to surrounding reefs in each area, were also increased. The result was sharp decreases in the relative abundance, and size, of common coral trout and to a lesser extent red throat emperor on those reefs opened to fishing. There did not appear to be any significant change in other species of fish, even though line fishers catch many species of fish, not just common coral trout and red throat emperor.
Importantly, even after the 12 months of fishing on those reefs that were opened to fishing, ELF surveys showed there were still coral trout that had reached the minimum legal size as set out by the Queensland Fisheries Service and could be taken by fishers.
These results provide us with the raw materials from which to build an accurate picture of the effects of line fishing on the Great Barrier Reef fish stocks. This information is central to fisheries managers when considering current and future management strategies.
The thematic link in all the work we are doing in the Fishing and Fisheries Project is an understanding of the responses of the fish stocks, the fisheries and, as far as feasible, the ecosystem to line fishing.
The initial step is to identify key factors that affect fish stocks, including both environmental and man-made elements. These factors (termed parameters), collated from ELF Scientists specifically for the Queensland Reef Line Fishery, is then incorporated into ELFSim.
ELFSim is a computer model designed by the ELF scientists in collaboration with CSIRO scientists who are experts in the field of fisheries computer modelling.
ELFSim contains simply, very sophisticated sets of mathematical equations that allow us to calculate changes to a number of parameters over a wide range of possible scenarios. These scenarios include; size limits, efficiency of alternative types of management, increased amounts of fishing pressure and spawning closures.
The outcomes of ELFSim will provide essential tools for managers of the Queensland Reef Line Fishery and those groups who advise them.
These tools are referred to as Management Strategy Evaluation, or MSE. Specifically, MSE involves using computer models to evaluate the relative performance of different management strategies in meeting management objectives for the Reef Line fishery.
The ability to predict the reactions of the fishing fleet and fish stocks to future conditions will be invaluable to managers. It will allow them to manage the Great Barrier Reef , and the line fishery in a pro-active manner, making timely decisions if required, hopefully before any large detrimental effects occur.
The result is more effective, efficient management of our precious resource.
Four reefs in the Elf experiment are re-opened to fishing from 6 March 2005 in the final phase of the ELF experiment. Find out more about the reefs to re-open.
ELF researchers will continue monitoring all reefs in the ELF Experiment until 2006 when all reefs in the experiment revert back to their normal management arrangements. This monitoring will provide essential information on how fish stocks recover from the impacts of fishing pressure.
Effects
of Line Fishing (ELF) Project
The
ELF Experiment involves 24 reefs located between Lizard Island north of
Cooktown, and the Swains reefs off Gladstone , in the South. These reefs
are grouped into four clusters of 6 reefs each.