title: The recruitment dynamics of post-settlement juvenile toheroa and the potential applications for aquaculture

authors: van der Lee, Marieka

subjects: Toheroa

abstract: Managing the recovery of threatened species due to anthropogenic disturbance is one of the most challenging problems in ecological monitoring. Researching species ecology is vital to help us improve ecosystem health and subsequently develop better management strategies in the environment. Humanity is entirely reliant on ecosystem services for food security. With the world population expected to reach ten billion by 2050, there is a growing need for more sustainable food sources. With the exploitation of many environmental resources worldwide, aquaculture has been championed as a sustainable option for future seafood production. In New Zealand, the toheroa (Paphies ventricosa) has been identified as a potentially valuable asset to the aquaculture industry and for possible conservation strategies via the implementation of reseeding populations with hatchery-reared spat.

Toheroa faced inadequate resource management and exploitation in the 1900s which ultimately led to the closure of an important recreational, cultural and commercial fishery. However, toheroa populations have failed to recover despite over 40 years of protection. It has been proposed that the continued decline of toheroa populations is not due to a lack of juvenile recruitment. Very little is known about juvenile toheroa recruitment, and there is no available information that could facilitate restoration management or determine the appropriate action to take for monitoring juvenile populations. From both a conservation and an aquaculture perspective, understanding the underlying ecology will be pivotal for future endeavours.

My thesis aimed to investigate the distribution dynamics of post-settlement juvenile toheroa on Ripiro Beach and the potential applications for aquaculture. Population surveys were conducted on Ripiro Beach in February and May to establish a sampling methodology that accurately captures the juvenile population both spatially and temporally. Surveys on vertical substrate stratification significantly affected both density and shell size with increasing sediment depth. Additionally, in contrast to the hypothesis formed on the basis of traditional knowledge that juvenile distribution is limited to the dunes and upper intertidal, spat appeared to have far more varied littoral distributions than previously theorised. The data from these surveys were used to make estimates of the total juvenile population on Ripiro Beach with attention to changes spatially (habitat type), temporally (seasonally), and by size cohorts (mm). My results indicated that toheroa populations are not recruit-limited. Estimates for the total February population ranged between 580 (±190) million and 650 (±200) million. By May, large abundance losses (> 90%) dropped the estimated population to between 30 (±15) million and 37 (±17) million, indicating significant bottleneck mortality during the early growth stages. However, the high abundances of small spat (< 5 mm) indicate that toheroa aquaculture is potentially viable. In aid of future aquaculture applications, I investigated how handling, harvesting, and different transportation methods could impact toheroa health, survival, or performance. This experiment aimed to mimic real-world applications wherein juvenile spat would be harvested and ongrown in hatcheries. To do this, I utilised the burrowing behaviour of juvenile toheroa as a quantitative indicator of stress. I found that if appropriate storage methods were implemented, initial handling and harvesting had a greater impact than actual transportation.

The research in this thesis demonstrated that populations do not appear to be recruit-limited. Furthermore, the findings indicate that aquaculture built on the foundation of wild-harvested juveniles is potentially viable. However, further research is required in order to quantify potential annual recruitment variation both spatially and temporally. Additionally, in order to establish a conservation approach, we must first define the niche requirements of toheroa to determine the obstacle (or obstacles) inhibiting recovery.

text: The recruitment dynamics of post-settlement juvenile toheroa and the potential applications for aquaculture Managing the recovery of threatened species due to anthropogenic disturbance is one of the most challenging problems in ecological monitoring. Researching species ecology is vital to help us improve ecosystem health and subsequently develop better management strategies in the environment. Humanity is entirely reliant on ecosystem services for food security. With the world population expected to reach ten billion by 2050, there is a growing need for more sustainable food sources. With the exploitation of many environmental resources worldwide, aquaculture has been championed as a sustainable option for future seafood production. In New Zealand, the toheroa (Paphies ventricosa) has been identified as a potentially valuable asset to the aquaculture industry and for possible conservation strategies via the implementation of reseeding populations with hatchery-reared spat.

Toheroa faced inadequate resource management and exploitation in the 1900s which ultimately led to the closure of an important recreational, cultural and commercial fishery. However, toheroa populations have failed to recover despite over 40 years of protection. It has been proposed that the continued decline of toheroa populations is not due to a lack of juvenile recruitment. Very little is known about juvenile toheroa recruitment, and there is no available information that could facilitate restoration management or determine the appropriate action to take for monitoring juvenile populations. From both a conservation and an aquaculture perspective, understanding the underlying ecology will be pivotal for future endeavours.

My thesis aimed to investigate the distribution dynamics of post-settlement juvenile toheroa on Ripiro Beach and the potential applications for aquaculture. Population surveys were conducted on Ripiro Beach in February and May to establish a sampling methodology that accurately captures the juvenile population both spatially and temporally. Surveys on vertical substrate stratification significantly affected both density and shell size with increasing sediment depth. Additionally, in contrast to the hypothesis formed on the basis of traditional knowledge that juvenile distribution is limited to the dunes and upper intertidal, spat appeared to have far more varied littoral distributions than previously theorised. The data from these surveys were used to make estimates of the total juvenile population on Ripiro Beach with attention to changes spatially (habitat type), temporally (seasonally), and by size cohorts (mm). My results indicated that toheroa populations are not recruit-limited. Estimates for the total February population ranged between 580 (±190) million and 650 (±200) million. By May, large abundance losses (> 90%) dropped the estimated population to between 30 (±15) million and 37 (±17) million, indicating significant bottleneck mortality during the early growth stages. However, the high abundances of small spat (< 5 mm) indicate that toheroa aquaculture is potentially viable. In aid of future aquaculture applications, I investigated how handling, harvesting, and different transportation methods could impact toheroa health, survival, or performance. This experiment aimed to mimic real-world applications wherein juvenile spat would be harvested and ongrown in hatcheries. To do this, I utilised the burrowing behaviour of juvenile toheroa as a quantitative indicator of stress. I found that if appropriate storage methods were implemented, initial handling and harvesting had a greater impact than actual transportation.

The research in this thesis demonstrated that populations do not appear to be recruit-limited. Furthermore, the findings indicate that aquaculture built on the foundation of wild-harvested juveniles is potentially viable. However, further research is required in order to quantify potential annual recruitment variation both spatially and temporally. Additionally, in order to establish a conservation approach, we must first define the niche requirements of toheroa to determine the obstacle (or obstacles) inhibiting recovery.

year: 2022

title: Perceptions of coarse anglers and freshwater managers, and the impact of these perceptions on management of non-indigenous invasive fish

authors: Duggan, Kathryn S.

abstract: This report examines coarse angler attitudes and behaviours to determine the reasons for, and develop incentives to successfully discourage, deliberate spreads of coarse fish species. The perceptions of freshwater managers, and the ways in which these human perceptions influence management of non-indigenous invasive fish, are also explored. To achieve this two main methodological strategies were employed: (1) semi-structured interviews with representatives from management agencies, research providers, iwi, the New Zealand Federation of Coarse Anglers, and individual coarse anglers: and (2) an internet survey with individual coarse anglers. In contrast to many New Zealanders, coarse fish species are highly valued by coarse anglers and the practice of coarse fishing is an important part of their lives. While a large portion of coarse anglers state they would like more fishing opportunities (especially outside of the Auckland/Waikato region), they argue that they do not practice or support illegal spread of coarse fish.

text: Perceptions of coarse anglers and freshwater managers, and the impact of these perceptions on management of non-indigenous invasive fish This report examines coarse angler attitudes and behaviours to determine the reasons for, and develop incentives to successfully discourage, deliberate spreads of coarse fish species. The perceptions of freshwater managers, and the ways in which these human perceptions influence management of non-indigenous invasive fish, are also explored. To achieve this two main methodological strategies were employed: (1) semi-structured interviews with representatives from management agencies, research providers, iwi, the New Zealand Federation of Coarse Anglers, and individual coarse anglers: and (2) an internet survey with individual coarse anglers. In contrast to many New Zealanders, coarse fish species are highly valued by coarse anglers and the practice of coarse fishing is an important part of their lives. While a large portion of coarse anglers state they would like more fishing opportunities (especially outside of the Auckland/Waikato region), they argue that they do not practice or support illegal spread of coarse fish.

year: 2015

title: Reshaping the learning experience through apps: Affordances

authors: Calder, Nigel Stuart

subjects: Digital technologies

abstract: This paper reports on how the affordances of the app Math Shake reshaped the learning experience—an aspect of a research project examining the ways mobile technologies are used in primary-school mathematics. Students used different digital tools within the app to solve word problems, while the affordances, including simultaneous linking, focussed constraint, creative variation, dynamic and haptic, made the learning experience different from when using pencil-and-paper technology. However, while the affordances of the mobile technologies are important, the teacher’s pedagogical approach was also influential in the learning.

text: Reshaping the learning experience through apps: Affordances This paper reports on how the affordances of the app Math Shake reshaped the learning experience—an aspect of a research project examining the ways mobile technologies are used in primary-school mathematics. Students used different digital tools within the app to solve word problems, while the affordances, including simultaneous linking, focussed constraint, creative variation, dynamic and haptic, made the learning experience different from when using pencil-and-paper technology. However, while the affordances of the mobile technologies are important, the teacher’s pedagogical approach was also influential in the learning.

year: 2018