title: The status of fish in Hamilton Lake (Lake Rotoroa)

authors: Kane, Daryl Steven

abstract: The size, population structure, relative fish abundance, diet and heavy metal concentrations of fish in Hamilton Lake (Lake Rotoroa) were examined. A combination of gill nets, fyke nets and minnow traps were used at each of 11 sampling sites located primarily at stormwater inflows around the lake. Sampling was undertaken between 9 December 1993 and 2 March 1994, with one overnight sampling occurring at each site.
A total of 1073 fish were captured, comprising nine different species: catfish (Ictalurus nebulosus), common bully (Gobiomorphus cotidianus), goldfish (Carassius auratus), longfinned eel (Anguilla dieffenbachii), perch (Perca fluviatilis), mosquitofish (Gambusia affinis), rudd (Scardinius erythropthalmus), shortfinned eel (Anguilla australis), and tench (Tinca tinca).
Abundance of rudd has declined since 1990, with a decline in catch rates of 67%. Conversely, perch abundance has increased since 1990, with catch rates increasing by 300%. During this period perch have surpassed rudd as the most abundant fish species. The declines in rudd abundance are probably associated with the disappearance of submerged aquatic macrophytes, largely Egeria densa, from Hamilton Lake during 1990.
Ages of rudd were determined using scales, while perch were aged using opercular bones. Back-calculation of fish length involved the use of both scale proportional (SPH), and body proportional hypotheses (BPH). Results from the SPH appeared more accurate, due to better compatibility with actual observed fish lengths. Sizes of one and two year old rudd appear to have declined over the past six years in Hamilton Lake. In 1987, the mean lengths of one and two year old rudd were 87 mm and 207 mm respectively, while in 1991 the same aged fish were 69 mm and 127 mm in length. Perch growth rates, however, do not appear to have changed. Poorly formed growth rings on both scales and operculum prevented tench from being aged.
Despite the total collapse of submerged aquatic macrophytes, which formed the bulk of the rudd diet (84% by volume), aquatic vegetation still remained the most important food item of adult rudd in the present study, although this now comprised entirely of emergent marginal vegetation. This suggests that rudd >200 mm in length are obligate herbivores. Perch fed largely on invertebrates, before a transition to a largely piscivorous diet at approximately 200 mm in length. Tench appeared to be specialist feeders on molluscs.
Concentrations of four heavy metals (arsenic, lead, copper, and zinc) in the white muscle of fish were examined. Concentrations of the majority of heavy metals analysed were well below maximum permitted levels. Arsenic concentrations were highest in bottom feeding fish, particularly catfish (mean=0.778 mg kg⁻¹ wet weight, compared to the maximum permitted level of 2 mg kg⁻¹ wet weight) due to high arsenic concentrations in the lake sediment resulting from sodium arsenate application for weed control in 1959. Arsenic in the present study was analysed using a dry ashing technique. Arsenic concentrations were higher than those of previous studies in the lake undertaken using a wet ashing technique, which fails to liberate all arsenic from the fish flesh.

text: The status of fish in Hamilton Lake (Lake Rotoroa) The size, population structure, relative fish abundance, diet and heavy metal concentrations of fish in Hamilton Lake (Lake Rotoroa) were examined. A combination of gill nets, fyke nets and minnow traps were used at each of 11 sampling sites located primarily at stormwater inflows around the lake. Sampling was undertaken between 9 December 1993 and 2 March 1994, with one overnight sampling occurring at each site.
A total of 1073 fish were captured, comprising nine different species: catfish (Ictalurus nebulosus), common bully (Gobiomorphus cotidianus), goldfish (Carassius auratus), longfinned eel (Anguilla dieffenbachii), perch (Perca fluviatilis), mosquitofish (Gambusia affinis), rudd (Scardinius erythropthalmus), shortfinned eel (Anguilla australis), and tench (Tinca tinca).
Abundance of rudd has declined since 1990, with a decline in catch rates of 67%. Conversely, perch abundance has increased since 1990, with catch rates increasing by 300%. During this period perch have surpassed rudd as the most abundant fish species. The declines in rudd abundance are probably associated with the disappearance of submerged aquatic macrophytes, largely Egeria densa, from Hamilton Lake during 1990.
Ages of rudd were determined using scales, while perch were aged using opercular bones. Back-calculation of fish length involved the use of both scale proportional (SPH), and body proportional hypotheses (BPH). Results from the SPH appeared more accurate, due to better compatibility with actual observed fish lengths. Sizes of one and two year old rudd appear to have declined over the past six years in Hamilton Lake. In 1987, the mean lengths of one and two year old rudd were 87 mm and 207 mm respectively, while in 1991 the same aged fish were 69 mm and 127 mm in length. Perch growth rates, however, do not appear to have changed. Poorly formed growth rings on both scales and operculum prevented tench from being aged.
Despite the total collapse of submerged aquatic macrophytes, which formed the bulk of the rudd diet (84% by volume), aquatic vegetation still remained the most important food item of adult rudd in the present study, although this now comprised entirely of emergent marginal vegetation. This suggests that rudd >200 mm in length are obligate herbivores. Perch fed largely on invertebrates, before a transition to a largely piscivorous diet at approximately 200 mm in length. Tench appeared to be specialist feeders on molluscs.
Concentrations of four heavy metals (arsenic, lead, copper, and zinc) in the white muscle of fish were examined. Concentrations of the majority of heavy metals analysed were well below maximum permitted levels. Arsenic concentrations were highest in bottom feeding fish, particularly catfish (mean=0.778 mg kg⁻¹ wet weight, compared to the maximum permitted level of 2 mg kg⁻¹ wet weight) due to high arsenic concentrations in the lake sediment resulting from sodium arsenate application for weed control in 1959. Arsenic in the present study was analysed using a dry ashing technique. Arsenic concentrations were higher than those of previous studies in the lake undertaken using a wet ashing technique, which fails to liberate all arsenic from the fish flesh.

year: 1995

title: Biodiversity enhances the multitrophic control of arthropod herbivory

authors: Barnes, Andrew D.

subjects: Science & Technology

abstract: Arthropod herbivores cause substantial economic costs that drive an increasing need to develop environmentally sustainable approaches to herbivore control. Increasing plant diversity is expected to limit herbivory by altering plant-herbivore and predator-herbivore interactions, but the simultaneous influence of these interactions on herbivore impacts remains unexplored. We compiled 487 arthropod food webs in two long-running grassland biodiversity experiments in Europe and North America to investigate whether and how increasing plant diversity can reduce the impacts of herbivores on plants. We show that plants lose just under half as much energy to arthropod herbivores when in high-diversity mixtures versus monocultures and reveal that plant diversity decreases effects of herbivores on plants by simultaneously benefiting predators and reducing average herbivore food quality. These findings demonstrate that conserving plant diversity is crucial for maintaining interactions in food webs that provide natural control of herbivore pests.

text: Biodiversity enhances the multitrophic control of arthropod herbivory Arthropod herbivores cause substantial economic costs that drive an increasing need to develop environmentally sustainable approaches to herbivore control. Increasing plant diversity is expected to limit herbivory by altering plant-herbivore and predator-herbivore interactions, but the simultaneous influence of these interactions on herbivore impacts remains unexplored. We compiled 487 arthropod food webs in two long-running grassland biodiversity experiments in Europe and North America to investigate whether and how increasing plant diversity can reduce the impacts of herbivores on plants. We show that plants lose just under half as much energy to arthropod herbivores when in high-diversity mixtures versus monocultures and reveal that plant diversity decreases effects of herbivores on plants by simultaneously benefiting predators and reducing average herbivore food quality. These findings demonstrate that conserving plant diversity is crucial for maintaining interactions in food webs that provide natural control of herbivore pests.

year: 2020-11-01

title: Enacting Kaitiakitanga Challenges and Complexities in the Governance and Ownership of Rongoā Research Information.

authors: Boulton, Amohia

subjects: Indigenous

abstract: This article explores the tensions one research team has faced in securing appropriate governance or stewardship (which we refer to as kaitiakitanga) of research data. Whilst ethical and regulatory frameworks exist which provide a minimum standard for researchers to meet when working with Māori, what our experience has highlighted is there is currently a “governance” gap in terms of who should hold stewardship of research data collected from Māori individuals or collectives. In the case of a project undertaken in the traditional healing space, the organisation best placed to fulfil this governance role receives no funding or support to take on such a responsibility; consequently by default, this role is being borne by the research team until such time as capacity can be built and adequate resourcing secured. In addition, we have realised that the tensions played out in this research project have implications for the broader issue of how we protect traditional knowledge in a modern intellectual property law context, and once again how we adequately support those, often community-based organisations, who work at the interface between Indigenous knowledge and the Western world.

text: Enacting Kaitiakitanga Challenges and Complexities in the Governance and Ownership of Rongoā Research Information. This article explores the tensions one research team has faced in securing appropriate governance or stewardship (which we refer to as kaitiakitanga) of research data. Whilst ethical and regulatory frameworks exist which provide a minimum standard for researchers to meet when working with Māori, what our experience has highlighted is there is currently a “governance” gap in terms of who should hold stewardship of research data collected from Māori individuals or collectives. In the case of a project undertaken in the traditional healing space, the organisation best placed to fulfil this governance role receives no funding or support to take on such a responsibility; consequently by default, this role is being borne by the research team until such time as capacity can be built and adequate resourcing secured. In addition, we have realised that the tensions played out in this research project have implications for the broader issue of how we protect traditional knowledge in a modern intellectual property law context, and once again how we adequately support those, often community-based organisations, who work at the interface between Indigenous knowledge and the Western world.

year: 2014