Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Four different techniques for determining the stock structure of a marine fish species were compared, using as a subject the jackass morwong. The four techniques examined were allozyme analysis, mitochondrial DNA analysis and two techniques based on measuring the composition of otoliths ('ear stones') - electron probe microanalysis and proton probe microanalysis, each of which measures the concentrations of different sets of elements. The comparison was based on all four techniques being applied to the same samples, obtained from 14 sites distributed geographically from Perth to NZ.

The principal result was that both genetic techniques distinguished between NZ and Australian samples, indicating strongly at least two genetically distinct stocks. The otolith analysis, however, suggested much greater structuring of the Australian samples, and suggests perhaps four stocks in Australian waters: off NSW and Victoria, off southern Tasmania, in the Great Australian Bight, and off Western Australia. There appears to be considerable mixing of individuals among sites, however, at least some of which appears to be the result of large scale seasonal movements of stocks. Otolith analysis could not separate the southern Tasmanian and NZ samples, which could be either because the environments in which the fish develop are similar in the two areas or because they are the same stock. Although the genetic analysis does not separate the southern Tasmanian sample (Maatsuyker) from other Australian sites, in practice sample size for genetic analysis of this site is too small for an effective comparison and, therefore, the genetic affinities of the SW Tasmanian and NZ stocks are not yet clear.

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).

Orange roughy is one of Australia's most valuable finfish However, its aggregating behaviour during spawning, slow growth, and longevity render it vulnerable to over-exploitation. Some stocks in New Zealand are at extremely low levels after only ten years of exploitation.

Good management is vital to maintaining orange roughy as a sustainable fishery. The model currently used for management estimates maximum sustainable yield (MSY) from estimates of natural mortality, M, and virgin biomass, Bo. Virgin biomass is estimated from the total catch to date and current stock size. Current stock size was the parameter about which there was greatest uncertainty.

Several methods of stock assessment appeared inadequate for orange roughy. Catch per unit effort indices are not very useful for highly aggregating species. Trawl surveys were also deemed to be of limited value because the fish occur largely over rough, untrawlable ground. Acoustic and egg production methods appeared feasible and were proposed to assess the orange roughy stock that spawns off eastern Tasmania. Egg surveys have been used world-wide to assess stocks of species such as anchovy, sardine, and mackerel (Lasker 1985; Lockwood et al .. 1981; Lo et al. 1992). However, until now, this method had only been used on one deepwater species, Dover sole (Lo et al . 1992).