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Use of artificial habitats to detect spawning sites for the conservation of Galaxias maculatus, a riparian-spawning fish
Abstract
Galaxias maculatus is a diadromous riparian-spawning fish that supports an important fishery. Eggs develop
terrestrially as with several other teleost fishes. Spawning habitat occurs in specific locations near rivermouths
and its protection is a conservation priority. However, quantifying the areas involved is hampered by high egg
mortality rates on degraded waterway margins. We hypothesised that temporary artificial habitat would detect
spawning in these situations producing a useful indicator for riparian management. We installed arrays of straw
bales as artificial habitat in two independent experiments over consecutive years and assessed their impact using
pairwise Before-After-Control-Impact (BACI) experimental designs. We tested degraded gaps within the distribution
of known spawning sites and also areas further upstream and downstream.
Nine spawning occurrences
were recorded on artificial habitats in 2015, 22 in 2016, and two on paired controls. Both experiments produced
a significant effect for artificial habitats deployed in degraded gaps within the known spawning site distribution
(p=0.0001) providing evidence that these locations should be regarded as actual or potential spawning sites. In
2016 the technique also produced a significant effect downstream of known sites in one of the study catchments
(p=0.0375).
We believe the use of artificial habitats as a detection tool could be useful in a variety of management
contexts. These include identifying areas for protection, as confirmation of site suitability prior to
making restoration investments, and in investigations to support the migration of habitats to new locations
under climate change, since these may currently be degraded.
... Although the biogeography of G. maculatus spawning grounds has been relatively well characterised in tidal rivers where they are strongly influenced by spring high tides (Benzie 1968;Taylor 2002;Orchard et al. 2018aOrchard et al. , 2018b, many nontidal rivers also support fish populations. In New Zealand, these rivers are particularly common on the east coast of the South Island and south-eastern North Island where they are often associated with mixed sand-gravel beaches at the coast (Kirk 1980(Kirk , 1991. ...
... In the first month of the study (February 2019) intensive eggs searches and environmental measurements were completed in all catchments by a team of three researchers in all catchments beginning at the rivermouth and working upstream, with the distribution of spawning sites (if any) being unknown. Although March and April were expected to be the months of peak spawning activity based on previous work in tidal waterways in the Canterbury region (Orchard et al. 2018a(Orchard et al. , 2018b, significant spawning activity was detected in February that was apparently triggered by a rain event. This finding helped to establish the general location of spawning in the study catchments and define areas for repeat surveys in the following months. ...
Galaxias maculatus is a declining amphidromous fish that supports New Zealand’s culturally-important whitebait fisheries targeting the migratory juvenile stage. Spawning ground protection and rehabilitation is required to reverse historical degradation and improve fisheries prospects alongside conservation goals. Although spawning habitat has been characterised in tidal rivers, there has been no previous study of spawning in non-tidal rivermouths that are open to the sea. We assessed seven non-tidal rivers over four months using census surveys to quantify spawning activity, identify environmental cues, and characterise fundamental aspects of the biogeography of spawning grounds. Results include the identification of compact spawning reaches near the rivermouths. Spawning events were triggered by periods of elevated water levels that were often of very short duration suggesting that potential lunar cues were less important, and that rapid fish movements had likely occurred within the catchment prior to spawning events. Spawning grounds exhibited consistent vertical structuring above typical low-flow levels, with associated horizontal translation away from the river channel leading to increased exposure to anthropogenic stressors and associated management implications for protecting the areas concerned. These consistent patterns provide a sound basis for advancing protective management at non-tidal rivermouths. Attention to flood management, vegetation control, and bankside recreational activities is needed and may be assisted by elucidating the biogeography of spawning grounds. The identification of rapid responses to environmental cues deserves further research to assess floodplain connectivity aspects that enable fish movements in emphemeral flowpaths, and as a confounding factor in commonly-used fish survey techniques.
... In some rivers this increases the size of the area that requires protection for spawning (Orchard & Hickford 2020), and is also reflected in the spatio-temporal dynamics of spawning locations which may 'move around' within a rivermouth system. This can create difficulties for reliable detection (Orchard & Hickford 2018;Orchard et al. 2018a), and drive new interactions with disturbance threats such as vegetation clearance, mowing, and grazing (Orchard et al. 2018b). On the other hand, it could also be used to advantage when planning for the restoration of spawning sites alongside other land uses by offering more potential 'room to move' (Orchard 2017;Orchard & Hickford 2016). ...
A range of literature was reviewed and summary information compiled to support the development of a conservation prioritisation strategy for two migratory fish species (īnanga and shortjaw kōkopu) on the South Island’s West Coast. This strategy will support the development of migratory species recovery plans under the government-funded Bio18 programme being implemented by the Department of Conservation. Existing datasets were evaluated and a desktop assessment completed to provide an initial characterisation of conservation value and threat intensity at regional scale. Recommendations are provided for a progressive conservation prioritisation strategy using the best available data. Results of the desktop assessment are presented in this summary report and include a set of spatial data and maps prepared for the use of operational staff who will lead implementation of this project in the coming years.
Findings of the desktop analyses included the characterisation of existing information on conservation value and the distribution of threats to the security of these species. Spatial disparities between species distribution models (SDMs) produced on different versions of the River Environment Classification were identified and are described. Model discrepancies may indicate the influences of differences in environmental predictor variables, areas of heightened uncertainty due to environmental conditions, or both.
Since both models were able to simulate training data with high levels of accuracy, the uncertainties relate mostly to their ability to extrapolate into new spatial domains. This suggests a useful role for targeted ground-truthing surveys, both within areas of model congruence and also model discrepancy, and is recommended for inclusion in the Bio18 operational work. For the purposes of prioritising actions, these results also indicate challenges for the adoption of model predictions as indicators of conservation value. To address this, a linked-model approach is proposed that takes into account both data sources. A four-tier ‘priority class’ classification is assigned based on the strength of evidence for species presence.
... Limitations of this study include egg detection issues that may arise from sedimentation events, as noted in relation to the April survey. Mortality between the date of spawning and the date of survey also introduces variation (Hickford & Schiel 2011b;Orchard et al. 2018b). These affects can have a bearing on the number of sites detected, the observed AOO, and estimates of egg production. ...
This report summarises results from field surveys of the Arahura River lagoon system to support the Arahura River Restoration Project on the South Island’s West Coast. The focus of these surveys was to improve the understanding of locations used by īnanga (Galaxias maculatus) for spawning. Īnanga is a migratory fish that is the most abundant of the five galaxiid species that support New Zealand’s whitebait fishery. At the Arahura River the fishery has important cultural values for Te Rūnanga o Ngāti Waewae and the Arahura Marae is located close to the river a short distance from the coast. Investigations were undertaken to characterise the tidal range and locate spawning sites to provide a baseline for future monitoring and support restoration work. Prior to this project, there were no previously reported spawning sites in the river system despite there being an abundance of suitable habitat for adult fish.
... Observations of shoaling fish that were not physically spawning creates a particular issue since adult īnanga typically spend several days searching riparian vegetation before the actual spawning event (Benzie 1968). The area in which these pre-spawning shoals could have been observed may be relatively large compared to the dimensions of typical spawning grounds (Orchard et al. 2018b).To address this, the Department has reviewed the NISD to remove records that were considered unreliable as confirmed spawning locations (D. West, pers. ...
Īnanga (Galaxias maculatus) is a highly valued diadromous fish that supports a popular recreational fishery. However, the species is currently listed in the ‘at risk - declining’ category of the New Zealand Threat Classification System in recognition of historic declines. The scope of this project included development of a draft methodology for guiding decisions on re-survey (and new survey) priority for inanga spawning sites, and a methodology for assigning conservation priorities to spawning sites. These were applied to develop a GIS shapefile layer showing conservation prioritisation results within defined spatial areas, in this case being the Department of Conservation's diadromous fish management units.
Galaxias maculatus is a declining amphidromous fish that supports culturally-important whitebait fisheries in New Zealand and elsewhere in the Pacific. As a largely annual species, the seasonal productivity of spawning grounds has a strong influence on the availability of recruits. Spawning ground protection is urgently required to reverse historical degradation and improve prospects for the maintenance of sustainable fisheries. Although spawning habitat has been well characterised in tidal rivers where it is structured by water level changes on spring high tides, there has been no previous study of spawning in non-tidal rivermouths. We assessed seven non-tidal rivers over four months using a census survey approach to quantify spawning activity, identify environmental cues, and characterise fundamental aspects of the biogeography of spawning grounds. We report conclusive results that include a) identification of compact spawning reaches near the rivermouths, b) triggering of spawning events by periods of elevated water levels that were often of very short duration, suggesting that potential lunar cues were less important and that rapid fish movements had likely occurred within the catchment prior to spawning events, and c) consistent vertical structuring of spawning grounds above typical low-flow levels with associated horizontal translation away from the river channel, leading to increased exposure to anthropogenic stressors and associated management implications for protecting the areas concerned. These consistent patterns provide a sound basis for advancing the management of non-tidal rivermouths. Attention to flood management, vegetation control, and bankside recreational activities is required and may be assisted by quantifying spawning ground biogeography. The identification of rapid responses to environmental cues deserves further research to assess implications for floodplain connectivity management to support fish movements in emphemeral flowpaths, and as a potential source of bias in commonly-used fish survey methodologies.
This study provides a review of the main published studies on artificial reefs to evaluate scientific trends, impacts and challenges for the development of artificial reef research. The review includes more than 620 studies published worldwide from 1962 to 2018. In general, publications on artificial reefs have focused on investigating the ability for artificial reefs to attract fishing resources and on constructing artificial reef structures with new materials. Artificial reef science has made significant advances in recent decades with the increased use of more elaborate construction methods and data analyses. Nevertheless, the field has encountered difficulties in minimizing the negative effects of some materials, filling gaps in socio-economic data, developing integrated management assessments and overcoming regional inequalities. There are promising opportunities to overcome these obstacles that depend on the development of inert materials, an increase in the number of long-term and large-scale studies, the regulation of an evaluation protocol, the development of conservation policies and investments in scientific dissemination. We hope that this systematic review can not only advance artificial reef science but also provide important information for overcoming obstacles to the future development of this topic.
There may be problems concerning the appropriate design of sampling programs to assess the impact upon the abundance of biological populations of, for example, the discharge of effluents into an aquatic ecosystem at a single point. Key to the resolution of these issues is correct identification of the statistical parameter of interest, which is the mean of the underlying probabilistic 'process' that produces the abundance, rather than the actual abundance itself. An appropriate sampling scheme was designed to detect the effect of the discharge upon this underlying mean. Detection of the effect of the discharge is achieved by testing whether the difference between abundances at a control site and an impact site changes once the discharge begins. -from Authors
Some anamniotic aquatic vertebrates lay eggs in a terrestrial habitat that is hostile to the survival of hatchings or larvae. These terrestrial eggs are ready and able to hatch at a particular developmental time, but do not hatch until presented with suitable conditions for aquatic larval survival. Beyond this time, hatching is possible whenever aquatic conditions occur. The duration of extended terrestrial incubation is dependent on the availability of energy for metabolism from the yolk. Extended incubation is useful for anamniotic eggs laid in terrestrial habitats where conditions suitable for larval survival arrive with unpredictable or variable timing. Examples of anamniotes with delayed hatching and extended terrestrial incubation can be found among teleost fishes, anurans, and caudate amphibians. This paper characterizes the embryonic period, compares this mode with other forms of developmental plasticity in anamniotes, evaluates the constraints and advantages of this life history mode, and examines how some fishes and amphibians are able to obtain the benefits of terrestriality for their eggs when the timing of the return to aquatic conditions is not entirely predictable.
Resilience of ecological communities to perturbation is important in the face of increased global change from anthropogenic stressors. Monitoring is required to detect the impact of, and recovery from, perturbations, and before-after-control-impact (BACI) analysis provides a powerful framework in this regard. However, species in a community are not observed with perfect detection, and occupancy analysis is required to correct for imperfect detectability of species. We present a Bayesian community occupancy before-after-control-impact (CO-BACI) framework to monitor ecological community response to perturbation when constituent species are imperfectly detected. We test the power of the model to detect changes in community composition following an acute perturbation with simulation. We then apply the model to a study of the impact of a large hurricane on the forest bird community of Sweden, using data from the national bird survey scheme. Although simulation shows the model can detect changes in community occupancy following an acute perturbation, application to a Swedish forest bird community following a major hurricane detected no change in community occupancy despite widespread forest loss. Birds with landscape occupancy less than 50% required correcting for detectability. We conclude that CO-BACI analysis is a useful tool that can incorporate rare species in analyses and detect occupancy changes in ecological communities following perturbation, but, because it does not include abundance, some impacts may be overlooked.
Much sampling to detect and quantify human environmental disturbances is flawed by a lack of appropriate replication. BACI (Before-After-Control-Impact) designs have only a single control location, and any conclusions from them are illogical. Asymmetrical designs using one putatively impacted and several control locations can reliably detect a variety of environmental impacts, including those that do not affect long-run mean abundances, but do alter temporal variance. When abundances of populations in different locations show temporal interaction, the asymmetrical designs allow tests for impact that are not possible in BACI designs. Asymmetrical designs are also extendable to sample at hierarchical spatial and temporal scales. The power of tests using asymmetrical designs is great for non-interactive sets of abundances, but greatest for pulse (short-term) responses to disturbances, large alterations of temporal variance, or combinations of sustained, press responses in mean abundance coupled with altered temporal heterogeneity. Power in temporally interactive sets of data is generally poor. Alternatives to pre-disturbance sampling, including generalized assessment of spatial and temporal variances and experimental impacts, may provide better guidance for detection of human disturbances.
Pseudoreplication is defined as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experimental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudoreplication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict randomization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specific alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' understanding of experimental design and statistics might be improved.