title: Age composition, growth, and reproduction of koi carp (Cyprinus carpio L.) in the lower Waikato, New Zealand

authors: Tempero, Grant Wayne

subjects: Polyacrylamide degradation

abstract: A total of 566 koi carp (Cyprinus carpio) from the lower Waikato region were aged from scales and opercular bones, and growth was modelled with the von Bertalanffy growth function. There was no difference in growth rate between male and female carp. Growth of koi carp between zero and 3 years of age was lower than that of common carp in Europe and Australia. However, after 5 years of age the growth of koi carp was higher than that of common carp in Europe, but still below that of carp in Australia. Males rarely lived in excess of 8 years, whereas females lived to 12 years. Mean total fecundity calculated from 44 running-ripe females was 299 000 oocytes (±195 600 SD) (range 29 800–771 000). Relative fecundity ranged from 19 300 to 216 000 oocytes kg–1 total body weight, with a mean of 97 200 (±35 000 SD) oocytes kg–1. Feral koi carp in the Waikato are capable of multiple spawnings within their lifetimes. Within a spawning season, Waikato populations of feral koi carp contained females that spawned once, and females that had the potential to have spawned repeatedly. Female gonadosomatic index (GSI) varied with season and was negatively related to water temperature.

text: Age composition, growth, and reproduction of koi carp (Cyprinus carpio L.) in the lower Waikato, New Zealand A total of 566 koi carp (Cyprinus carpio) from the lower Waikato region were aged from scales and opercular bones, and growth was modelled with the von Bertalanffy growth function. There was no difference in growth rate between male and female carp. Growth of koi carp between zero and 3 years of age was lower than that of common carp in Europe and Australia. However, after 5 years of age the growth of koi carp was higher than that of common carp in Europe, but still below that of carp in Australia. Males rarely lived in excess of 8 years, whereas females lived to 12 years. Mean total fecundity calculated from 44 running-ripe females was 299 000 oocytes (±195 600 SD) (range 29 800–771 000). Relative fecundity ranged from 19 300 to 216 000 oocytes kg–1 total body weight, with a mean of 97 200 (±35 000 SD) oocytes kg–1. Feral koi carp in the Waikato are capable of multiple spawnings within their lifetimes. Within a spawning season, Waikato populations of feral koi carp contained females that spawned once, and females that had the potential to have spawned repeatedly. Female gonadosomatic index (GSI) varied with season and was negatively related to water temperature.

year: 2006

title: Investigation into factors affecting perceptual stability of the world during smooth pursuit eye movements

authors: Boer, Alexandra (Sasha)

subjects: perceptual stability

abstract: During pursuit eye movement, a stationary background projected on the retina shifts in the direction opposite to that of the eye movement. This complicates the perception of objects because during an eye movement the retinal and head-centric motions differ. Nevertheless, our visual system is somehow able to compensate for the added eye motion so that the world is perceived as stable. The eye movement compensation is traditionally assumed to consist of a combination of a retinal motion signal and an extra-retinal estimate of eye velocity (Von Holst & Mittelstaedt, 1950; Sperry, 1950).  This view has been expanded upon by a number of researchers in the last few decades with the introduction of vector addition-like models. However, it is not well known how closely the eye movement compensation mechanism follows the rules of vector algebra. Evidence for the presence of a signal coming from the moving eye has come from a variety of neurophysiological and perceptual research on the cortical Medial Superior Temporal (MST) area in primates. 

Previous studies have shown that the spatio-temporal structure of the background plays an important role in the perceptual accuracy of the velocity of a moving object in the visual field. Background characteristics have been shown to influence not only the retinal signal, but also the extra-retinal signal to some degree. The current thesis provides new information on factors that affect the degree of compensation for retinal motion during smooth pursuit eye movement. The findings are based on several experiments that were designed to use a range of pursuit target and stimulus dot velocities across different backgrounds and stimulus exposure times, in order to reveal details about how the retinal and extra-retinal signals are combined. Participants were asked to determine the direction of a moving stimulus by rotating an arrow on the screen. In a separate experiment, participants were also asked to assess the speed of a stimulus using a magnitude estimation task. A linear vector model was developed to separate the retinal and extra-retinal signal contribution to the overall compensation. This model was used to assess the degree of perceptual stability across different visual conditions. Generally, the data indicate that the perceived stimulus motion is well predicted by a vector subtraction mechanism postulated to be occurring in the human brain. However, in situations where there is weak visual stimulation, participants’ estimates of motion are less accurate and tend to follow the retinal image motion. In the current thesis I identify how the type of background, directions of eye movements, and stimulus velocities relative to the eye movements affected participants’ perceptual performance. Based on the data and the model fitting, it was concluded that the visual system appears to utilize the eye-movement related signal differentially depending on the retinal motion content.

text: Investigation into factors affecting perceptual stability of the world during smooth pursuit eye movements During pursuit eye movement, a stationary background projected on the retina shifts in the direction opposite to that of the eye movement. This complicates the perception of objects because during an eye movement the retinal and head-centric motions differ. Nevertheless, our visual system is somehow able to compensate for the added eye motion so that the world is perceived as stable. The eye movement compensation is traditionally assumed to consist of a combination of a retinal motion signal and an extra-retinal estimate of eye velocity (Von Holst & Mittelstaedt, 1950; Sperry, 1950).  This view has been expanded upon by a number of researchers in the last few decades with the introduction of vector addition-like models. However, it is not well known how closely the eye movement compensation mechanism follows the rules of vector algebra. Evidence for the presence of a signal coming from the moving eye has come from a variety of neurophysiological and perceptual research on the cortical Medial Superior Temporal (MST) area in primates. 

Previous studies have shown that the spatio-temporal structure of the background plays an important role in the perceptual accuracy of the velocity of a moving object in the visual field. Background characteristics have been shown to influence not only the retinal signal, but also the extra-retinal signal to some degree. The current thesis provides new information on factors that affect the degree of compensation for retinal motion during smooth pursuit eye movement. The findings are based on several experiments that were designed to use a range of pursuit target and stimulus dot velocities across different backgrounds and stimulus exposure times, in order to reveal details about how the retinal and extra-retinal signals are combined. Participants were asked to determine the direction of a moving stimulus by rotating an arrow on the screen. In a separate experiment, participants were also asked to assess the speed of a stimulus using a magnitude estimation task. A linear vector model was developed to separate the retinal and extra-retinal signal contribution to the overall compensation. This model was used to assess the degree of perceptual stability across different visual conditions. Generally, the data indicate that the perceived stimulus motion is well predicted by a vector subtraction mechanism postulated to be occurring in the human brain. However, in situations where there is weak visual stimulation, participants’ estimates of motion are less accurate and tend to follow the retinal image motion. In the current thesis I identify how the type of background, directions of eye movements, and stimulus velocities relative to the eye movements affected participants’ perceptual performance. Based on the data and the model fitting, it was concluded that the visual system appears to utilize the eye-movement related signal differentially depending on the retinal motion content.

year: 2011

title: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change

authors: Newnham, Rewi M.

subjects: New Zealand

abstract: Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

text: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

year: 2018