The main aim of this research program was to determine the potential for reducing the density of urchins to encourage the return of seaweeds and an improvement in urchin roe quality and quantity from remaining urchins. Tasmanian Sea Urchin Developments used two widely-separated sub-tidal experimental lease areas. One of these areas was at Meredith Point, on the east coast, and the other at Hope Island, on the south coast. Both sites had been subject to some overgrazing by urchins. At Meredith Point, the study area was divided into plots containing urchins at three densities: artificially enhanced, continually harvested and control (undisturbed). At Hope Island, controlled clearings of urchins and limpets from barrens areas were conducted. Recovery of vegetation was monitored as well as urchin roe quality and quantity. The data represented by this record was collected at Meredith Point.
Maintenance and Update Frequency: notPlanned
Statement: Further details can be found in Section 3 of main report.
At Meredith Pt, the effect of varying urchin densities obtained through differing harvesting strategies on roe yield of urchins was investigated. This was determined by partioning parts of the coast into plots (squares) and subjecting each to differing treatments.
These treatments were:
1. Control squares. These were left relatively untouched for the period of the project.
2. Transplants. Urchins were transplanted into these areas from outside the lease site. This would show the effect of elevated densities on roe condition. It may also show if it was possible to improve the roe quality of the transplanted urchins. Transplanted urchins were from an area of low roe recovery.
3. Harvested squares. These squares were continuously harvested for the period of the project and so maintained a low density. The squares consisted of 50m sections of the coast with the boundaries perpendicular to the shore to the limit of hard substrate, marked by ropes weighted with concrete filled tyres. There were three blocks, each with three treatments. The three blocks are the eastern (E), middle (M) and western (W).
Urchin density was monitored through 20 - 5 x 1 m quadrats and vegetations with 20 - 0.5 x 0.5 m quadrats for each square. The 0.5 x 0.5 m quadrat used for vegetation and substrate cover was subdivided with seven horizontal and vertical lines giving 49 intersection points. These and one of the corners gave 50 points. Algal cover and substrate were given a reading based on the number of points intersected. Total cover for algae can come to a number greater than 50 (100%) due to successive layers of algae. Algae were divided into species as best as possible underwater.
For urchin density and algal cover, two transects were laid parallel to the coast for each square at distances of approximately, 15 and 25 m from shore. For urchin density, the diver recorded the number of urchins in contiguous 5 meter quadrats. For algae and substrate, the diver used a 0.25m2 quadrat positioned at each 10m mark.
Density of the urchins was determined approximately every six months.
Fisheries Research and Development Corporation (FRDC): 93/221
To develop cost-effective, commercial enhancement techniques which will restore biological balance and maximise the fishery's value and employment potential by increasing both roe weight and roe quality.