title: Optimal sample type and number vary in small shallow lakes when targeting non-native fish environmental DNA.

authors: Picard, Maïlys H. V.

subjects: Environmental DNA

abstract: Non-native fish have been shown to have deleterious impacts on freshwater ecosystems in New Zealand. Early detection is critical for their effective management. Traditional capture-based techniques may not detect newly introduced fish, especially if they are present in low abundance. Molecular techniques that target environmental DNA (eDNA) have been shown, in many instances, to be more sensitive, cost-effective and require lower sampling effort. However, appropriate sampling strategies are needed to ensure robust and interpretable data are obtained. In this study we used droplet digital PCR assays to investigate the presence of two non-native fish in New Zealand, the European perch (Perca fluviatilis) and rudd (Scardinius erythrophthalmus) in three small lakes. Samples were collected from water and surface sediment at near-shore and mid-lake sites. Probabilistic modelling was used to assess the occupancy of fish eDNA and develop guidance on sampling strategies. Based on the detection probability measures from the present study, at least six sites and five replicates per site are needed to reliably detect fish eDNA in sediment samples, and twelve sites with eight replicates per site for water samples. The results highlight the potential of developing monitoring and surveillance programs adapted to lakes, that include the use of assays targeting eDNA. This study focused on small shallow lakes, and it is likely that these recommendations may vary in larger, deeper, and more geomorphologically complex lakes, and this requires further research.

text: Optimal sample type and number vary in small shallow lakes when targeting non-native fish environmental DNA. Non-native fish have been shown to have deleterious impacts on freshwater ecosystems in New Zealand. Early detection is critical for their effective management. Traditional capture-based techniques may not detect newly introduced fish, especially if they are present in low abundance. Molecular techniques that target environmental DNA (eDNA) have been shown, in many instances, to be more sensitive, cost-effective and require lower sampling effort. However, appropriate sampling strategies are needed to ensure robust and interpretable data are obtained. In this study we used droplet digital PCR assays to investigate the presence of two non-native fish in New Zealand, the European perch (Perca fluviatilis) and rudd (Scardinius erythrophthalmus) in three small lakes. Samples were collected from water and surface sediment at near-shore and mid-lake sites. Probabilistic modelling was used to assess the occupancy of fish eDNA and develop guidance on sampling strategies. Based on the detection probability measures from the present study, at least six sites and five replicates per site are needed to reliably detect fish eDNA in sediment samples, and twelve sites with eight replicates per site for water samples. The results highlight the potential of developing monitoring and surveillance programs adapted to lakes, that include the use of assays targeting eDNA. This study focused on small shallow lakes, and it is likely that these recommendations may vary in larger, deeper, and more geomorphologically complex lakes, and this requires further research.

year: 2023-05-02

title: Canine (Canis familiaris) scent detection of invasive brown bullhead catfish (Ameriurus nebulosus) in lake water samples

authors: Hopkins, Lauren Renee

abstract: Brown bullhead catfish (Ameiurus nebulosus) were deliberately introduced to New Zealand from North America in the 1880s and populations have since increased significantly in the Auckland, Waikato, and Bay of Plenty regions. Catfish pose a major threat to New Zealand’s freshwater ecosystems, preying on and competing with native species for food, and decreasing water clarity through bioturbation and nutrient release. 

Early detection of the spread of catfish is crucial as it allows for containment and eradication measures to be set up, preventing the establishment of new catfish populations. However, traditional methods such as visual surveying, netting, and electrofishing are time-consuming and resource intensive, resulting in high costs and restricting the number of locations that can be surveyed. In addition, they can be relatively insensitive when the target biomasses are low, such as in newly establishing populations. False negatives can result in a lack of action from governmental agencies, allowing populations to establish and spread undetected. 

Domestic dogs (Canis familiaris) have previously been used for conservation management programmes, detecting reptiles, birds, insects, and larger wildlife animals. Although the use of dogs to detect targets in aquatic environments is relatively new, research has indicated domestic dogs have the ability to discriminate between similar aquatic species and previous projects related to catfish scent detection have shown domestic dogs can detect the presence of catfish in dechlorinated water samples at biologically relevant concentrations. 

The aim of this research was to determine whether domestic dogs could detect the presence of catfish in lake water samples at a biomass concentration equivalent to 43.5 kg/ha (based on the assumption of a 2 m deep waterbody), a concentration consistent with the estimated populations of catfish in New Zealand lakes. The first stage of the experiment determined whether dogs could detect the presence of catfish in dechlorinated water samples at a biomass concentration of 43.5 kg/ha. Water samples were collected from tanks containing a standard catfish biomass concentration of 15.5 g/L (equivalent to 38,700 kg/ha) and diluted to 311 kg/ha. As the dogs achieved the discrimination criteria, the sample concentration was progressively decreased. All three dogs were able to detect the presence of catfish at a biomass concentration of 43.5 kg/ha. The next stage of the experiment determined whether domestic dogs could detect the presence of catfish in lake water samples. Lake water samples were collected from catfish-absent Lake Rotomā and spiked with catfish aquaria. As the dogs achieved the discrimination criteria, the catfish concentration was progressively diluted. The majority of the dogs in this study successfully detected the presence of catfish at a biomass concentration of 43.5 kg/ha in lake water samples, with one dog successfully detecting catfish at a biomass concentration of 1.55 kg/ha. In New Zealand, it is highly unlikely significant environmental impacts would occur from a catfish biomass of 1.55 kg/ha. However, targeted eradication of a population density this size would be highly advisable and may be feasibly managed depending on available resources, size of the target water body and its connections to other waterways. The findings in this study indicate the potential utility of dogs in the early detection and management of invasive freshwater species. According to the theory of generalisation, the performance of these dogs may be generalised to different lakes and to different biomass equivalent concentrations without specific training on those lakes or concentrations. However, it would be important to test for this generalisation in future research as differences in stimuli can affect generalisation, with less generalisation occurring as stimuli become increasingly dissimilar from the original training stimulus. Therefore, the differences between the conditions in this study and those in an operational scenario will be important in determining whether the obtained performance will generalise to the operational scenario.

text: Canine (Canis familiaris) scent detection of invasive brown bullhead catfish (Ameriurus nebulosus) in lake water samples Brown bullhead catfish (Ameiurus nebulosus) were deliberately introduced to New Zealand from North America in the 1880s and populations have since increased significantly in the Auckland, Waikato, and Bay of Plenty regions. Catfish pose a major threat to New Zealand’s freshwater ecosystems, preying on and competing with native species for food, and decreasing water clarity through bioturbation and nutrient release. 

Early detection of the spread of catfish is crucial as it allows for containment and eradication measures to be set up, preventing the establishment of new catfish populations. However, traditional methods such as visual surveying, netting, and electrofishing are time-consuming and resource intensive, resulting in high costs and restricting the number of locations that can be surveyed. In addition, they can be relatively insensitive when the target biomasses are low, such as in newly establishing populations. False negatives can result in a lack of action from governmental agencies, allowing populations to establish and spread undetected. 

Domestic dogs (Canis familiaris) have previously been used for conservation management programmes, detecting reptiles, birds, insects, and larger wildlife animals. Although the use of dogs to detect targets in aquatic environments is relatively new, research has indicated domestic dogs have the ability to discriminate between similar aquatic species and previous projects related to catfish scent detection have shown domestic dogs can detect the presence of catfish in dechlorinated water samples at biologically relevant concentrations. 

The aim of this research was to determine whether domestic dogs could detect the presence of catfish in lake water samples at a biomass concentration equivalent to 43.5 kg/ha (based on the assumption of a 2 m deep waterbody), a concentration consistent with the estimated populations of catfish in New Zealand lakes. The first stage of the experiment determined whether dogs could detect the presence of catfish in dechlorinated water samples at a biomass concentration of 43.5 kg/ha. Water samples were collected from tanks containing a standard catfish biomass concentration of 15.5 g/L (equivalent to 38,700 kg/ha) and diluted to 311 kg/ha. As the dogs achieved the discrimination criteria, the sample concentration was progressively decreased. All three dogs were able to detect the presence of catfish at a biomass concentration of 43.5 kg/ha. The next stage of the experiment determined whether domestic dogs could detect the presence of catfish in lake water samples. Lake water samples were collected from catfish-absent Lake Rotomā and spiked with catfish aquaria. As the dogs achieved the discrimination criteria, the catfish concentration was progressively diluted. The majority of the dogs in this study successfully detected the presence of catfish at a biomass concentration of 43.5 kg/ha in lake water samples, with one dog successfully detecting catfish at a biomass concentration of 1.55 kg/ha. In New Zealand, it is highly unlikely significant environmental impacts would occur from a catfish biomass of 1.55 kg/ha. However, targeted eradication of a population density this size would be highly advisable and may be feasibly managed depending on available resources, size of the target water body and its connections to other waterways. The findings in this study indicate the potential utility of dogs in the early detection and management of invasive freshwater species. According to the theory of generalisation, the performance of these dogs may be generalised to different lakes and to different biomass equivalent concentrations without specific training on those lakes or concentrations. However, it would be important to test for this generalisation in future research as differences in stimuli can affect generalisation, with less generalisation occurring as stimuli become increasingly dissimilar from the original training stimulus. Therefore, the differences between the conditions in this study and those in an operational scenario will be important in determining whether the obtained performance will generalise to the operational scenario.

year: 2023

title: Environmental aspects of storm runoff discharge from a timber port, Tauranga, New Zealand

authors: Tian, Fengming

subjects: storm runoff water

abstract: An investigation was undertaken into storm runoff water quantity and quality, contaminant input to the receiving tidal waters from the Mt. Maunganui wharf, accumulation of potentially toxic resin acids in adjacent sediments, and the dilution of the wharf runoff in the receiving tidal waters, in order to assess the possible adverse environmental impact associated with the log operation at the Port of Tauranga Ltd.
Based upon field data and rainfall records, about a half of the annual precipitation over the log handling areas is converted to surface runoff (117,000 m³a⁻¹). Annual runoff volume per hectare of wharf surface is estimated as 7,500 m³ha⁻¹a⁻¹ for the sealed area and 3,700 m³ha⁻¹a⁻¹ for the gravelled area.
The optical quality of the wharf runoff is degraded due to addition of bark and soil particles. The black disk visual clarity (0.01-0.02 m) was only 0.5-1.0% of that in the receiving tidal waters. The wharf runoff appears very dark gray to yellowish brown in apparent colour (10YR1/3 to 10YR5/6 Munsell colour chart) and has a soluble yellow substance concentration of about 25 m⁻¹. Power relationships between the traditionally used parameters, for example, suspended solids and turbidity, were identified. The wharf surface pavement types had a significant influence on visual clarity, but little influence on yellow substance concentration.
The potentially toxic resin acids in the wharf runoff have been determined with SIM GC-MS. The average total resin acid level (1,030 ppb) is comparable to that of 1,000 ppb reported at which acute toxicity is likely to be exhibited. A relationship of resin acids against volatile suspended solids was established. Tests undertaken suggest that conventional treatment methods of natural sedimentation and flocculation-sedimentation are able to remove the resin acids effectively.
The levels of biological oxygen demand (BOD), total phosphorus and nitrogen in the wharf runoff are considerably higher than those of common urban runoff. However, the wharf runoff contributes little nitrate nitrogen and oil and grease to the receiving environment.
About 87,500 kg of suspended solids, 43,000 kg of volatile suspended solids, 14,200 kg of BOD, 500 kg of phosphorus, and 103 kg of resin acids are discharged to the Tauranga Harbour annually from runoff from the Mt. Maunganui wharf.
Analyses show that the impact on adjacent sediments from the storm runoff is limited to a distance of about 100 m from the discharge points and the resin acid levels in the sediments within this distance are not significantly higher compared to that of the storm runoff. The net resin acid accumulation rate in the shipping channel (Stella Passage) beside the log handling areas was estimated to be in the range of 300 to 370 ppb per year.
Based on field investigation and numerical simulations, the findings on dispersion and dilution of the wharf runoff in the receiving tidal waters are as follows: (i) the sea water around Stella Passage experiences an obvious natural salinity stratification, the extent of which depends greatly on the weather conditions; (ii) the wind drag stress and the pressure gradient caused by the addition of runoff had the greatest influence on the plume dynamics during the flood tide. The plumes basically remain within the top 2-3 m of the water column under different winds; (iii) the plume is unlikely to advect to the Whareroa Marae under strong (30-40 knots) easterly or northeasterly winds for a storm with a 5-year return period. However, there is an obvious influence on the Whareroa Marae under 30- 40 knot northerly winds; and (iv) the short duration and restricted region of the low dilution pulse of effluent around slack water may explain why there has been no reports of acute toxic events.
Sealing the gravel covered wharf area, improving the sweeping efficiency, and extending the present outfalls to the sea floor might be potential options for mitigating the environmental impact associated with discharge of the wharf runoff.

text: Environmental aspects of storm runoff discharge from a timber port, Tauranga, New Zealand An investigation was undertaken into storm runoff water quantity and quality, contaminant input to the receiving tidal waters from the Mt. Maunganui wharf, accumulation of potentially toxic resin acids in adjacent sediments, and the dilution of the wharf runoff in the receiving tidal waters, in order to assess the possible adverse environmental impact associated with the log operation at the Port of Tauranga Ltd.
Based upon field data and rainfall records, about a half of the annual precipitation over the log handling areas is converted to surface runoff (117,000 m³a⁻¹). Annual runoff volume per hectare of wharf surface is estimated as 7,500 m³ha⁻¹a⁻¹ for the sealed area and 3,700 m³ha⁻¹a⁻¹ for the gravelled area.
The optical quality of the wharf runoff is degraded due to addition of bark and soil particles. The black disk visual clarity (0.01-0.02 m) was only 0.5-1.0% of that in the receiving tidal waters. The wharf runoff appears very dark gray to yellowish brown in apparent colour (10YR1/3 to 10YR5/6 Munsell colour chart) and has a soluble yellow substance concentration of about 25 m⁻¹. Power relationships between the traditionally used parameters, for example, suspended solids and turbidity, were identified. The wharf surface pavement types had a significant influence on visual clarity, but little influence on yellow substance concentration.
The potentially toxic resin acids in the wharf runoff have been determined with SIM GC-MS. The average total resin acid level (1,030 ppb) is comparable to that of 1,000 ppb reported at which acute toxicity is likely to be exhibited. A relationship of resin acids against volatile suspended solids was established. Tests undertaken suggest that conventional treatment methods of natural sedimentation and flocculation-sedimentation are able to remove the resin acids effectively.
The levels of biological oxygen demand (BOD), total phosphorus and nitrogen in the wharf runoff are considerably higher than those of common urban runoff. However, the wharf runoff contributes little nitrate nitrogen and oil and grease to the receiving environment.
About 87,500 kg of suspended solids, 43,000 kg of volatile suspended solids, 14,200 kg of BOD, 500 kg of phosphorus, and 103 kg of resin acids are discharged to the Tauranga Harbour annually from runoff from the Mt. Maunganui wharf.
Analyses show that the impact on adjacent sediments from the storm runoff is limited to a distance of about 100 m from the discharge points and the resin acid levels in the sediments within this distance are not significantly higher compared to that of the storm runoff. The net resin acid accumulation rate in the shipping channel (Stella Passage) beside the log handling areas was estimated to be in the range of 300 to 370 ppb per year.
Based on field investigation and numerical simulations, the findings on dispersion and dilution of the wharf runoff in the receiving tidal waters are as follows: (i) the sea water around Stella Passage experiences an obvious natural salinity stratification, the extent of which depends greatly on the weather conditions; (ii) the wind drag stress and the pressure gradient caused by the addition of runoff had the greatest influence on the plume dynamics during the flood tide. The plumes basically remain within the top 2-3 m of the water column under different winds; (iii) the plume is unlikely to advect to the Whareroa Marae under strong (30-40 knots) easterly or northeasterly winds for a storm with a 5-year return period. However, there is an obvious influence on the Whareroa Marae under 30- 40 knot northerly winds; and (iv) the short duration and restricted region of the low dilution pulse of effluent around slack water may explain why there has been no reports of acute toxic events.
Sealing the gravel covered wharf area, improving the sweeping efficiency, and extending the present outfalls to the sea floor might be potential options for mitigating the environmental impact associated with discharge of the wharf runoff.

year: 1997