title: Detailed description of grazing systems using nonlinear optimisation methods: A model of a pasture-based New Zealand dairy farm

authors: Doole, Graeme J.

subjects: optimisation

abstract: Grazing systems constitute the most extensive land use worldwide. However, economic analysis of these systems has mainly involved the use of linear optimisation methods that provide a general description of the complex processes contained therein. This paper describes a nonlinear optimisation model of a New Zealand dairy farm that incorporates a detailed depiction of key biophysical processes present within grazing systems. The capacity of this optimisation model to provide rich insight into the effects of higher stocking rates within grazing systems is demonstrated in an empirical application. In accordance with system trials, this application shows that higher stocking rates on pasture-based New Zealand dairy farms generally increase pre-grazing pasture biomass, decrease post-grazing pasture biomass, increase pasture utilisation, decrease herbage allowance, decrease intake and energy consumption per cow, decrease milk production per cow, increase milk production per ha, and reduce conception rate. Nevertheless, an intermediate stocking rate is optimal, as greater milk production with a higher stocking rate is not sufficient to offset the associated costs.

text: Detailed description of grazing systems using nonlinear optimisation methods: A model of a pasture-based New Zealand dairy farm Grazing systems constitute the most extensive land use worldwide. However, economic analysis of these systems has mainly involved the use of linear optimisation methods that provide a general description of the complex processes contained therein. This paper describes a nonlinear optimisation model of a New Zealand dairy farm that incorporates a detailed depiction of key biophysical processes present within grazing systems. The capacity of this optimisation model to provide rich insight into the effects of higher stocking rates within grazing systems is demonstrated in an empirical application. In accordance with system trials, this application shows that higher stocking rates on pasture-based New Zealand dairy farms generally increase pre-grazing pasture biomass, decrease post-grazing pasture biomass, increase pasture utilisation, decrease herbage allowance, decrease intake and energy consumption per cow, decrease milk production per cow, increase milk production per ha, and reduce conception rate. Nevertheless, an intermediate stocking rate is optimal, as greater milk production with a higher stocking rate is not sufficient to offset the associated costs.

year: 2013

title: Life history analysis of chinook salmon (Oncorhynchus tshawytscha) from lakes Mapourika and Paringa, West Coast, South Island, New Zealand, by otolith microchemistry

authors: Hicks, Brendan J.

abstract: Otolith microchemistry is an established technique for determining fish migrations between the sea and freshwater. The aim of our study was to determine life history patterns of chinook salmon collected from rivers and lake tributaries along the West Coast of the South Island, New Zealand using otolith microchemistry. Specifically, we compared relative concentrations of barium and strontium in salmon otoliths as a proxy of fresh and seawater migration and related this to individual fish ages. Using this approach, fish migrations between the sea and freshwater are often determined by changing patterns in strontium (Sr) and barium (Ba) concentrations across the otolith growth axis. Time spent in the sea is characterised by high relative strontium and low barium concentrations, whereas freshwater phases have relatively higher barium and low strontium concentrations. When fish move from the sea to freshwater or vice versa a pronounced change in relative concentrations is usually seen.
Ten chinook salmon were collected as carcasses or by fishing from the Hokitika and Taramakau rivers, Lake Mapourika and its tributary, MacDonalds Creek, and Lake Paringa and its tributary, Windbag Stream. A previous preliminary report investigated otoliths from 11 salmon captured in tributaries of lakes Mapourika and Paringa during 2008. This study showed lower ⁸⁷Sr/⁸⁶Sr ratios (0.707-0.709) that were interpreted as freshwater residence and higher ratios (0.710-0.712) that suggested sea residence. This approach uses strontium isotopic ratios instead of Sr and Ba elemental concentrations to determine freshwater and marine occupancy. Ratios of ⁸⁸Sr/V (vanadium) were also examined, and showed a reciprocal relationship to ratios of ⁸⁷Sr/⁸⁶Sr. All 11 otoliths examined from 2008 showed freshwater rearing followed by a period of marine residence of varying length.
Chinook salmon in our study showed a wide variety of life histories, and microchemical analysis of the otoliths partly confirmed the presumed life history of each salmon. The freshwater phase was evident from strontium concentrations, expressed as ⁸⁶Sr/⁴³Ca x 1000, of between 100 and 400 and variable barium concentrations of between 2 to 8 expressed as ¹³⁷Ba/⁴³Ca x 1000. The marine phase was characterised by high strontium concentrations of 500 to 900, with low barium concentrations, generally less than 2. Five individuals from the Hokitika and Taramakau rivers, MacDonalds Creek (L. Mapourika), and Windbag Stream (L. Paringa) exhibited normal chinook salmon life histories with early rearing in freshwater followed by an extensive period of growth to adulthood in the sea. Most salmon from MacDonalds Creek showed extensive freshwater residence, and two of these were lakelocked, with exclusively freshwater residence. A further two fish collected in May 2012 from MacDonalds Creek had lived most of their life in freshwater but showed evidence of a brief period in the sea late in life at ages 2 and 3 year respectively. Curiously, one fish from MacDonalds Creek had apparently entered a marine environment, possibly an estuary, just before its recovery as a carcass.

text: Life history analysis of chinook salmon (Oncorhynchus tshawytscha) from lakes Mapourika and Paringa, West Coast, South Island, New Zealand, by otolith microchemistry Otolith microchemistry is an established technique for determining fish migrations between the sea and freshwater. The aim of our study was to determine life history patterns of chinook salmon collected from rivers and lake tributaries along the West Coast of the South Island, New Zealand using otolith microchemistry. Specifically, we compared relative concentrations of barium and strontium in salmon otoliths as a proxy of fresh and seawater migration and related this to individual fish ages. Using this approach, fish migrations between the sea and freshwater are often determined by changing patterns in strontium (Sr) and barium (Ba) concentrations across the otolith growth axis. Time spent in the sea is characterised by high relative strontium and low barium concentrations, whereas freshwater phases have relatively higher barium and low strontium concentrations. When fish move from the sea to freshwater or vice versa a pronounced change in relative concentrations is usually seen.
Ten chinook salmon were collected as carcasses or by fishing from the Hokitika and Taramakau rivers, Lake Mapourika and its tributary, MacDonalds Creek, and Lake Paringa and its tributary, Windbag Stream. A previous preliminary report investigated otoliths from 11 salmon captured in tributaries of lakes Mapourika and Paringa during 2008. This study showed lower ⁸⁷Sr/⁸⁶Sr ratios (0.707-0.709) that were interpreted as freshwater residence and higher ratios (0.710-0.712) that suggested sea residence. This approach uses strontium isotopic ratios instead of Sr and Ba elemental concentrations to determine freshwater and marine occupancy. Ratios of ⁸⁸Sr/V (vanadium) were also examined, and showed a reciprocal relationship to ratios of ⁸⁷Sr/⁸⁶Sr. All 11 otoliths examined from 2008 showed freshwater rearing followed by a period of marine residence of varying length.
Chinook salmon in our study showed a wide variety of life histories, and microchemical analysis of the otoliths partly confirmed the presumed life history of each salmon. The freshwater phase was evident from strontium concentrations, expressed as ⁸⁶Sr/⁴³Ca x 1000, of between 100 and 400 and variable barium concentrations of between 2 to 8 expressed as ¹³⁷Ba/⁴³Ca x 1000. The marine phase was characterised by high strontium concentrations of 500 to 900, with low barium concentrations, generally less than 2. Five individuals from the Hokitika and Taramakau rivers, MacDonalds Creek (L. Mapourika), and Windbag Stream (L. Paringa) exhibited normal chinook salmon life histories with early rearing in freshwater followed by an extensive period of growth to adulthood in the sea. Most salmon from MacDonalds Creek showed extensive freshwater residence, and two of these were lakelocked, with exclusively freshwater residence. A further two fish collected in May 2012 from MacDonalds Creek had lived most of their life in freshwater but showed evidence of a brief period in the sea late in life at ages 2 and 3 year respectively. Curiously, one fish from MacDonalds Creek had apparently entered a marine environment, possibly an estuary, just before its recovery as a carcass.

year: 2013

title: Māori and English textbooks designed for language learners at intermediate level: A comparison in terms of the occurrence and use of insights from research on discourse analysis

authors: Fester, Anthea

subjects: New Zealand

abstract: Over the past two decades, research in the area of discourse analysis has expanded rapidly and has yielded insights that could usefully inform the teaching and learning of languages. In this paper, we report on the results of a comparative study of a number of commercially available textbooks designed for learners of English and learners of te reo Māori at intermediate level in terms of the extent to which they can be shown to have been influenced by specific aspects of discourse analysis research. In the textbooks designed for learners of English, there is some evidence that the writers are aware of, and have been influenced by some aspects of discourse analysis research, particularly in the teaching of writing skills. In the textbooks designed for learners of te reo Māori, however, there is almost no sign of influence of research of this type. In view of the importance of the teaching and learning of te reo Māori in relation to the maintenance of the language, and in view of the fact that many young people in New Zealand now learn a range of academic subjects through the medium of te reo Māori, this raises issues that we believe need to be addressed.

text: Māori and English textbooks designed for language learners at intermediate level: A comparison in terms of the occurrence and use of insights from research on discourse analysis Over the past two decades, research in the area of discourse analysis has expanded rapidly and has yielded insights that could usefully inform the teaching and learning of languages. In this paper, we report on the results of a comparative study of a number of commercially available textbooks designed for learners of English and learners of te reo Māori at intermediate level in terms of the extent to which they can be shown to have been influenced by specific aspects of discourse analysis research. In the textbooks designed for learners of English, there is some evidence that the writers are aware of, and have been influenced by some aspects of discourse analysis research, particularly in the teaching of writing skills. In the textbooks designed for learners of te reo Māori, however, there is almost no sign of influence of research of this type. In view of the importance of the teaching and learning of te reo Māori in relation to the maintenance of the language, and in view of the fact that many young people in New Zealand now learn a range of academic subjects through the medium of te reo Māori, this raises issues that we believe need to be addressed.

year: 2007-11-21