The present study evaluates the suitability of the Daily Egg Production Method (DEPM) for stock a... more The present study evaluates the suitability of the Daily Egg Production Method (DEPM) for stock assessment of blue mackerel, Scomber australasicus and assesses methodological options for future applications. In southern Australia, estimates of mean daily egg production were higher for Californian Vertical Egg Tow (CalVET) nets than bongo nets, and in eastern Australia, were higher in October 2003 than July 2004. Estimates of spawning area for southern Australia were three times higher for bongo nets than CalVET nets. Similar estimates of spawning area were obtained using standard (manual) gridding and natural neighbour methods. Large samples and reliable estimates of all adult parameters were obtained for southern Australia. Relatively few spawning adults were collected off eastern Australia. Preliminary best estimates of spawning biomass for southern and eastern Australia were 56 228 t and 29 578 t, respectively, with most estimates within the ranges of 45 000–68 000 t and 20 000–40 000 t respectively. The DEPM is suitable for stock assessment of S. australasicus. Several technical refinements are required to enhance future applications, including: genetic techniques for identifying early stage eggs; a temperature–egg development key; improved methods for sampling adults off eastern Australia; and measurements of the degeneration rates of post-ovulatory follicles at several temperatures.
Adult King George whiting were sampled at 12 localities representing a range of habitat types acr... more Adult King George whiting were sampled at 12 localities representing a range of habitat types across South Australia. Sampling was undertaken between March and May for a minimum of 2 years between 1995 and 1998. Fish were aged by otolith interpretation, and reproductive maturity was determined by gonad analysis using macroscopic and histological techniques. In total, 6961 fish comprising 3678 females and 3283 males were considered from four localities in each of three geographic regions. In both Gulf St Vincent and Spencer Gulf, age structures became more complex from north to south, associated with a shift in size towards larger fish. In the simplest age structures, >90% of fish were from the 3-year age class, whereas the age range of the most complex was 3–17 years, with the 3–5 age classes most numerous. Males were more abundant in smaller size classes and females in the larger. Although some fish from each locality showed some gonad development, only at three localities did s...
... to locate the layers of prey and to successfully capture food particles if the stability cond... more ... to locate the layers of prey and to successfully capture food particles if the stability conditions are favorable (Mac-Kenzie and Kiorboe 2000). ... ot( kgm3 ) Fig. 2. Example density profile (circles linked by thin line) from a station in the Spencer Gulf. The thick line represents the ...
McLeay, L. J., Page, B., Goldsworthy, S. D., Ward, T. M., Paton, D. C., Waterman, M., and Murray,... more McLeay, L. J., Page, B., Goldsworthy, S. D., Ward, T. M., Paton, D. C., Waterman, M., and Murray, M. D. 2009. Demographic and morphological responses to prey depletion in a crested tern (Sterna bergii) population: can fish mortality events highlight performance indicators for fisheries management? – ICES Journal of Marine Science, 66: 237–247. Disease-related mortality events in 1995 and 1998, which killed ∼70% of adult sardine (Sardinops sagax) biomass, provided an opportunity to assess whether crested tern (Sterna bergii) populations were affected by decreased prey abundance. We investigated the diet, age structure, and morphology of a population of crested terns to determine whether survival and growth were reduced for cohorts reared in years immediately following sardine mortality events. The diet of chicks and adults differed significantly. Australian anchovy (Engraulis australis) and sardine were the dominant prey in the diets of chicks, constituting an average of 36.3 and 14....
... representing regional biodiversity. Tim M. Ward Corresponding Author Contact Information , E-... more ... representing regional biodiversity. Tim M. Ward Corresponding Author Contact Information , E-mail The Corresponding Author , Shirley J. Sorokin, David R. Currie, Paul J. Rogers and Lachie J. McLeay. South Australian Research ...
The reproductive biology of the King George whiting, Sillaginodes punctata, was investigated for ... more The reproductive biology of the King George whiting, Sillaginodes punctata, was investigated for populations at two localities in South Australia. Analyses involved determination of gonadosomatic indices, macroscopic staging of gonads, size frequencies of oocytes, spawning fractions of females, and batch fecundities that were related to fish size and age. Size–frequency distributions of oocytes, measured from histological slides and whole preserved oocytes, were multi-modal but were continuous amongst development stages. All development stages of oocytes co-occurred in some gonads, and hydrated oocytes and post-ovulatory follicles also co-occurred. Such characteristics suggest that the King George whiting is a multiple batch spawner with asynchronous development and indeterminate fecundity. Spawning occurred at least through the months of March–May, with a peak in April. On one occasion spawning occurred in the early afternoon on a flooding tide. Fish ranged in age from 3 to 17 year...
The present study evaluates the suitability of the Daily Egg Production Method (DEPM) for stock a... more The present study evaluates the suitability of the Daily Egg Production Method (DEPM) for stock assessment of blue mackerel, Scomber australasicus and assesses methodological options for future applications. In southern Australia, estimates of mean daily egg production were higher for Californian Vertical Egg Tow (CalVET) nets than bongo nets, and in eastern Australia, were higher in October 2003 than July 2004. Estimates of spawning area for southern Australia were three times higher for bongo nets than CalVET nets. Similar estimates of spawning area were obtained using standard (manual) gridding and natural neighbour methods. Large samples and reliable estimates of all adult parameters were obtained for southern Australia. Relatively few spawning adults were collected off eastern Australia. Preliminary best estimates of spawning biomass for southern and eastern Australia were 56 228 t and 29 578 t, respectively, with most estimates within the ranges of 45 000–68 000 t and 20 000–40 000 t respectively. The DEPM is suitable for stock assessment of S. australasicus. Several technical refinements are required to enhance future applications, including: genetic techniques for identifying early stage eggs; a temperature–egg development key; improved methods for sampling adults off eastern Australia; and measurements of the degeneration rates of post-ovulatory follicles at several temperatures.
Adult King George whiting were sampled at 12 localities representing a range of habitat types acr... more Adult King George whiting were sampled at 12 localities representing a range of habitat types across South Australia. Sampling was undertaken between March and May for a minimum of 2 years between 1995 and 1998. Fish were aged by otolith interpretation, and reproductive maturity was determined by gonad analysis using macroscopic and histological techniques. In total, 6961 fish comprising 3678 females and 3283 males were considered from four localities in each of three geographic regions. In both Gulf St Vincent and Spencer Gulf, age structures became more complex from north to south, associated with a shift in size towards larger fish. In the simplest age structures, >90% of fish were from the 3-year age class, whereas the age range of the most complex was 3–17 years, with the 3–5 age classes most numerous. Males were more abundant in smaller size classes and females in the larger. Although some fish from each locality showed some gonad development, only at three localities did s...
... to locate the layers of prey and to successfully capture food particles if the stability cond... more ... to locate the layers of prey and to successfully capture food particles if the stability conditions are favorable (Mac-Kenzie and Kiorboe 2000). ... ot( kgm3 ) Fig. 2. Example density profile (circles linked by thin line) from a station in the Spencer Gulf. The thick line represents the ...
McLeay, L. J., Page, B., Goldsworthy, S. D., Ward, T. M., Paton, D. C., Waterman, M., and Murray,... more McLeay, L. J., Page, B., Goldsworthy, S. D., Ward, T. M., Paton, D. C., Waterman, M., and Murray, M. D. 2009. Demographic and morphological responses to prey depletion in a crested tern (Sterna bergii) population: can fish mortality events highlight performance indicators for fisheries management? – ICES Journal of Marine Science, 66: 237–247. Disease-related mortality events in 1995 and 1998, which killed ∼70% of adult sardine (Sardinops sagax) biomass, provided an opportunity to assess whether crested tern (Sterna bergii) populations were affected by decreased prey abundance. We investigated the diet, age structure, and morphology of a population of crested terns to determine whether survival and growth were reduced for cohorts reared in years immediately following sardine mortality events. The diet of chicks and adults differed significantly. Australian anchovy (Engraulis australis) and sardine were the dominant prey in the diets of chicks, constituting an average of 36.3 and 14....
... representing regional biodiversity. Tim M. Ward Corresponding Author Contact Information , E-... more ... representing regional biodiversity. Tim M. Ward Corresponding Author Contact Information , E-mail The Corresponding Author , Shirley J. Sorokin, David R. Currie, Paul J. Rogers and Lachie J. McLeay. South Australian Research ...
The reproductive biology of the King George whiting, Sillaginodes punctata, was investigated for ... more The reproductive biology of the King George whiting, Sillaginodes punctata, was investigated for populations at two localities in South Australia. Analyses involved determination of gonadosomatic indices, macroscopic staging of gonads, size frequencies of oocytes, spawning fractions of females, and batch fecundities that were related to fish size and age. Size–frequency distributions of oocytes, measured from histological slides and whole preserved oocytes, were multi-modal but were continuous amongst development stages. All development stages of oocytes co-occurred in some gonads, and hydrated oocytes and post-ovulatory follicles also co-occurred. Such characteristics suggest that the King George whiting is a multiple batch spawner with asynchronous development and indeterminate fecundity. Spawning occurred at least through the months of March–May, with a peak in April. On one occasion spawning occurred in the early afternoon on a flooding tide. Fish ranged in age from 3 to 17 year...
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