Project number: 1995-035
Budget expenditure: $258,699.00
Principal Investigator: Tony Koslow
Organisation: CSIRO Oceans and Atmosphere Hobart
Project start/end date: 28 Jun 1995 - 30 Jan 1998
1. Overall objective: To develop the use of the egg proiduction method to assess the biomass of blue grenadier on the west Tasmania spawning ground. To achieve this overall objective requires completion of the following sub-objectives
2. Surveys of the blue grenadier egg distribution be completed during the 1995 and 1996 spawining seasons, covering the full period and area of blue grenadier spawning. The initial (1994) survey will provide a biomass estimate
3. The mean fecundity of the blue grenadier will be determined
4. The development rate of the blue grenadier eggs will be assessed as a function of temperature
ISBN: 0 643 06153 3
Author: Tony Koslow
Final Report • 2017-09-29 • 956.64 KB
The blue grenadier stock is potentially the largest fish stock in the SEF, and following the decline in quota of orange roughy, the need to assess its potential became urgent. The stock has been surveyed using traditional trawl methods and acoustics, but both methods provide only 'snapshot' estimates and are unable to provide absolute estimates. There are two reasons for this: first, the stock is not currently being fished down so relative biomass estimates cannot be calibrated, and second, the proportion of fish spawning on the ground at any time -a factor by which the "snapshot" estimates must be multiplied to obtain an absolute estimate-is unknown.
Annual egg production estimates of stock size based upon egg surveys have been widely and successfully used since 1895 and this method has recently been used in the SEF with orange roughy. The method can provide an absolute measure of spawning stock biomass. Egg surveys tend to be less precise statistically than acoustic surveys, but there is less nonstatistical error associated with the supplementary data required for egg production biomass assessment compared with those for an acoustic assessment.
Blue grenadier met the criteria for use of the annual egg production method of stock assessment. The blue grenadier spawning stock off western Tasmania was first surveyed from June through September 1994. The survey design was refined and the area resurveyed the following year.