title: Abundance of mysid shrimp (Tenagomysis chiltoni) in shallow lakes in the Waikato region and implications for fish diet

authors: Brijs, Jeroen

subjects: New Zealand

abstract: Tenagomysis chiltoni, a species of mysid shrimp, is widely distributed amongst the riverine lakes of the lower Waikato basin. They appear to thrive in turbid waters, with the greatest abundances found in lakes such as Waahi and Waikare, which have low Secchi transparencies and sparse aquatic macrophyte communities representing remnants of formerly dense beds (Kirk, 1983; Chapman el al., 1991). Maximum mysid abundances of 2,868 and 857 individuals m⁻² in Lake Waahi and Waikare respectively were recorded by Chapman et al. (1991) in March-April 1987. Anecdotal evidence suggests that mysid abundance in Lake Waikare is markedly reduced since the late 1980s (Gary Watson, Te Kauwhata, pers. comm.) with the arrival and proliferation of koi carp (Cyprinus carpio) presumed to be the cause. Koi carp arrived in Lake Waikare after 1987 and by 2007 it was estimated that over 80% of the fish biomass present in Lake Waikare was comprised of koi carp (Hicks, 2007). Sable isotope studies on carp (Matsuzaki et al., 2007) have shown that mysid shrimp can form a significant component of their diet. This suggests that mysid shrimp may be predated on by koi carp in the Waikato which has implications on mysid shrimp abundance as well as the abundance of native fish species which rely on mysid shrimp as a food source (Champman et al., 1991). The objective of this study was to measure mysid abundance in three shallow, turbid lakes in the lower Waikato basin (Lake Waikare, Whangape and Waahi) to compare with previous abundance estimates made in the late 1980s. A second objective was to determine whether mysid shrimp form a significant component of the diet of koi carp in the study sites by examining their stable isotope signatures.

text: Abundance of mysid shrimp (Tenagomysis chiltoni) in shallow lakes in the Waikato region and implications for fish diet Tenagomysis chiltoni, a species of mysid shrimp, is widely distributed amongst the riverine lakes of the lower Waikato basin. They appear to thrive in turbid waters, with the greatest abundances found in lakes such as Waahi and Waikare, which have low Secchi transparencies and sparse aquatic macrophyte communities representing remnants of formerly dense beds (Kirk, 1983; Chapman el al., 1991). Maximum mysid abundances of 2,868 and 857 individuals m⁻² in Lake Waahi and Waikare respectively were recorded by Chapman et al. (1991) in March-April 1987. Anecdotal evidence suggests that mysid abundance in Lake Waikare is markedly reduced since the late 1980s (Gary Watson, Te Kauwhata, pers. comm.) with the arrival and proliferation of koi carp (Cyprinus carpio) presumed to be the cause. Koi carp arrived in Lake Waikare after 1987 and by 2007 it was estimated that over 80% of the fish biomass present in Lake Waikare was comprised of koi carp (Hicks, 2007). Sable isotope studies on carp (Matsuzaki et al., 2007) have shown that mysid shrimp can form a significant component of their diet. This suggests that mysid shrimp may be predated on by koi carp in the Waikato which has implications on mysid shrimp abundance as well as the abundance of native fish species which rely on mysid shrimp as a food source (Champman et al., 1991). The objective of this study was to measure mysid abundance in three shallow, turbid lakes in the lower Waikato basin (Lake Waikare, Whangape and Waahi) to compare with previous abundance estimates made in the late 1980s. A second objective was to determine whether mysid shrimp form a significant component of the diet of koi carp in the study sites by examining their stable isotope signatures.

year: 2009

title: Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field

authors: Stribling, Troy

abstract: A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process.

text: Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process.

year: 1995

title: Factors of desistance in violent offenders: Interpretative phenomenological analysis of the Tai Aroha programme

authors: Beattie, Christopher James

subjects: Desistance

abstract: The phenomenon of desistance from crime is central to the process of rehabilitation. This study examines desistance narratives from the Tai Aroha programme to identify the aspects of participation in a community-based special treatment unit that are effective from the perspective of participants. A review of desistance literature is presented in a New Zealand context. Interpretative phenomenological analysis was used to present common themes in 64 exit interviews of individuals who completed this programme over a period of 6 years. These themes were compared to the factors of desistance identified in the literature review. The three key concepts that emerged from this study as factors of desistance evident in the Tai Aroha programme were the Morphic Self, Family and Whanau, and Mindfulness. The concept of the Morphic Self is a perspective on the process of identity change as experienced by participants, and is a key product of this research. Three other factors were identified as prerequisites for successful completion of the programme that also therefore contribute to desistance: Motivation, Sobriety, and Peers and Support. Also identified from this research were aspects of the experience termed Elements of Influence, which are the facets of the participants, the programme and the interactions between the two that can be considered in order to improve the delivery of the programme and therefore promote desistance. A distinctive quality of the Tai Aroha programme that was influential in the successful promotion of desistance was its strong commitment to tikanga Māori and the incorporation of these cultural values into the lifestyle and therapeutic approaches adopted by the facilitators.

text: Factors of desistance in violent offenders: Interpretative phenomenological analysis of the Tai Aroha programme The phenomenon of desistance from crime is central to the process of rehabilitation. This study examines desistance narratives from the Tai Aroha programme to identify the aspects of participation in a community-based special treatment unit that are effective from the perspective of participants. A review of desistance literature is presented in a New Zealand context. Interpretative phenomenological analysis was used to present common themes in 64 exit interviews of individuals who completed this programme over a period of 6 years. These themes were compared to the factors of desistance identified in the literature review. The three key concepts that emerged from this study as factors of desistance evident in the Tai Aroha programme were the Morphic Self, Family and Whanau, and Mindfulness. The concept of the Morphic Self is a perspective on the process of identity change as experienced by participants, and is a key product of this research. Three other factors were identified as prerequisites for successful completion of the programme that also therefore contribute to desistance: Motivation, Sobriety, and Peers and Support. Also identified from this research were aspects of the experience termed Elements of Influence, which are the facets of the participants, the programme and the interactions between the two that can be considered in order to improve the delivery of the programme and therefore promote desistance. A distinctive quality of the Tai Aroha programme that was influential in the successful promotion of desistance was its strong commitment to tikanga Māori and the incorporation of these cultural values into the lifestyle and therapeutic approaches adopted by the facilitators.

year: 2018