title: Boat electrofishing survey of five Waitakere City ponds

authors: Hicks, Brendan J.

subjects: New Zealand

abstract: We conducted a fish survey of five ponds (Lake Panorama, Paremuka Pond 1 & 2, Danica Esplanade and Longbush Pond) in the Waitakere District by single-pass boat electrofishing on 18 and 19 of July 2007. We caught 337 fish comprising four introduced and two native fish species in 2.89 km of fished distance from all 5 ponds. Assuming that each of the two bow-mounted anodes caught fish within a 1 m radius, the width fished was 4 m, and the total area fished was 11,537 m² or 1.154 ha. The water temperature for the 5 different ponds ranged between 10.8°C and 14.9°C.
In Lake Panorama, shortfinned eel (Anguilla australis) were the most numerous species caught (130 fish ha⁻¹ ), followed by perch (Perca fluviatilis) (100 fish ha⁻¹) and tench (Tinca tinca) (40 fish ha⁻¹).
In Paremuka Pond 1, koi carp (Cyprinus carpio) were the most numerous species caught (120 fish ha⁻¹), followed by shortfinned eels (50 fish ha⁻¹).

In Paremuka Pond 2, koi carp were again the most numerous species caught (340 fish ha⁻¹), followed by tench (250 fish ha⁻¹) and shortfinned eels (70 fish ha⁻¹).

In Danica Esplanade and Longbush Pond, shortfinned eels were the most numerous species caught (140 and 550 fish ha⁻¹respectively), followed by mosquitofish (Gambusia affinis). There was more macrophyte cover around the edges of Danica Esplanade compared to Longbush Pond and this decreased the catch rate as a large number of eels in Danica Esplanade were sighted but were unable to be captured. 

Koi carp were only caught in the Paremuka ponds. The majority of koi carp were caught on the edges of the lake in macrophytes and rushes. Koi carp biomasses were highest in Paremuka Pond 2 at 261 kg ha⁻¹ compared to 106 kg ha⁻¹ in Paremuka Pond 1. Biomass is a more accurate reflection of the potential ecological impact of koi carp than their density. Previous results suggest that 21-73% of the total population is caught on the first removal, depending on water visibility. As we fished the area at each site only once, the estimates in this survey represent a minimum abundance, and true population sizes are likely to be 1.4-4.8 times greater. The density of eels in both the Paremuka ponds is also likely to be higher as a large proportion of eels were able to escape into the macrophytes before they could be captured in the nets. Mosquitofish were also observed to be living in both the Paremuka ponds. Of ecological concern for the Paremuka ponds is the dominance of the fish biomass by introduced koi carp, which have a deleterious impact on aquatic habitats. Another concern for these ponds is the presence of small koi carp (<200 mm), which suggests that natural spawning is most likely occurring, although recent releases of carp into the ponds in another possibility.

The fate of the introduced fish varied depending on what species they were. Perch and tench were released back into the ponds after captures as they are classified as sports fish. Koi carp and mosquitofish are classified as unwanted organisms and were humanely destroyed with an anaesthetic overdose (benzocaine), and retained for further analysis.

text: Boat electrofishing survey of five Waitakere City ponds We conducted a fish survey of five ponds (Lake Panorama, Paremuka Pond 1 & 2, Danica Esplanade and Longbush Pond) in the Waitakere District by single-pass boat electrofishing on 18 and 19 of July 2007. We caught 337 fish comprising four introduced and two native fish species in 2.89 km of fished distance from all 5 ponds. Assuming that each of the two bow-mounted anodes caught fish within a 1 m radius, the width fished was 4 m, and the total area fished was 11,537 m² or 1.154 ha. The water temperature for the 5 different ponds ranged between 10.8°C and 14.9°C.
In Lake Panorama, shortfinned eel (Anguilla australis) were the most numerous species caught (130 fish ha⁻¹ ), followed by perch (Perca fluviatilis) (100 fish ha⁻¹) and tench (Tinca tinca) (40 fish ha⁻¹).
In Paremuka Pond 1, koi carp (Cyprinus carpio) were the most numerous species caught (120 fish ha⁻¹), followed by shortfinned eels (50 fish ha⁻¹).

In Paremuka Pond 2, koi carp were again the most numerous species caught (340 fish ha⁻¹), followed by tench (250 fish ha⁻¹) and shortfinned eels (70 fish ha⁻¹).

In Danica Esplanade and Longbush Pond, shortfinned eels were the most numerous species caught (140 and 550 fish ha⁻¹respectively), followed by mosquitofish (Gambusia affinis). There was more macrophyte cover around the edges of Danica Esplanade compared to Longbush Pond and this decreased the catch rate as a large number of eels in Danica Esplanade were sighted but were unable to be captured. 

Koi carp were only caught in the Paremuka ponds. The majority of koi carp were caught on the edges of the lake in macrophytes and rushes. Koi carp biomasses were highest in Paremuka Pond 2 at 261 kg ha⁻¹ compared to 106 kg ha⁻¹ in Paremuka Pond 1. Biomass is a more accurate reflection of the potential ecological impact of koi carp than their density. Previous results suggest that 21-73% of the total population is caught on the first removal, depending on water visibility. As we fished the area at each site only once, the estimates in this survey represent a minimum abundance, and true population sizes are likely to be 1.4-4.8 times greater. The density of eels in both the Paremuka ponds is also likely to be higher as a large proportion of eels were able to escape into the macrophytes before they could be captured in the nets. Mosquitofish were also observed to be living in both the Paremuka ponds. Of ecological concern for the Paremuka ponds is the dominance of the fish biomass by introduced koi carp, which have a deleterious impact on aquatic habitats. Another concern for these ponds is the presence of small koi carp (<200 mm), which suggests that natural spawning is most likely occurring, although recent releases of carp into the ponds in another possibility.

The fate of the introduced fish varied depending on what species they were. Perch and tench were released back into the ponds after captures as they are classified as sports fish. Koi carp and mosquitofish are classified as unwanted organisms and were humanely destroyed with an anaesthetic overdose (benzocaine), and retained for further analysis.

year: 2007

title: Variability of physical and biological parameters in Lake Taupo: Bio-fish survey 2004-5

authors: Hamilton, David P.

abstract: This project was initiated by the Lakes and Waterways Action Group (LWAG) in response to declining water quality of Lake Taupo (Gibbs, 2004). Information was sought on variability of physical and biological parameters across different parts of the lake particularly in relation to use of only one profiling site (Station A) or three profiling sites (Stations A, B, and C) used in previous studies (e.g. Gibbs, 2004). Furthermore, the Taupo District Council (TDC) has a concern that some taste and odour problems (e.g. geosmin) experienced in its water supply may be due to cyanobacteria that accumulate in the near-shore region where water supply intakes are located. The TDC also sought information about variability of phytoplankton biomass across Lake Taupo.

The objective of this study was to carry out a series of BIO-FISH transects of Lake Taupo, to observe the variability of temperature, chlorophyll a, dissolved oxygen and conductivity.

text: Variability of physical and biological parameters in Lake Taupo: Bio-fish survey 2004-5 This project was initiated by the Lakes and Waterways Action Group (LWAG) in response to declining water quality of Lake Taupo (Gibbs, 2004). Information was sought on variability of physical and biological parameters across different parts of the lake particularly in relation to use of only one profiling site (Station A) or three profiling sites (Stations A, B, and C) used in previous studies (e.g. Gibbs, 2004). Furthermore, the Taupo District Council (TDC) has a concern that some taste and odour problems (e.g. geosmin) experienced in its water supply may be due to cyanobacteria that accumulate in the near-shore region where water supply intakes are located. The TDC also sought information about variability of phytoplankton biomass across Lake Taupo.

The objective of this study was to carry out a series of BIO-FISH transects of Lake Taupo, to observe the variability of temperature, chlorophyll a, dissolved oxygen and conductivity.

year: 2005-12

title: Waitangi Soda Springs alum dosing – bioavailability of aluminium 2013

authors: Ling, Nicholas

abstract: Continuous alum dosing of the Waitangi Soda Springs at Lake Rotoehu commenced in 2010 to reduce inflows of dissolved reactive phosphorus to Lake Rotoehu. Analyses of bioaccumulation in the tissues of kōura and goldfish from Lake Rotoehu were undertaken on animals collected in September 2013 to determine the bioavailability and bioaccumulation of aluminium. Comparative analyses were undertaken on kōura and goldfish collected from Lakes Rotorua and Rotoiti. Lake Rotoehu kōura and goldfish showed slightly elevated aluminium concentrations in the gills indicating enhanced exposure to aluminium but little evidence for significant bioaccumulation in tissues.

text: Waitangi Soda Springs alum dosing – bioavailability of aluminium 2013 Continuous alum dosing of the Waitangi Soda Springs at Lake Rotoehu commenced in 2010 to reduce inflows of dissolved reactive phosphorus to Lake Rotoehu. Analyses of bioaccumulation in the tissues of kōura and goldfish from Lake Rotoehu were undertaken on animals collected in September 2013 to determine the bioavailability and bioaccumulation of aluminium. Comparative analyses were undertaken on kōura and goldfish collected from Lakes Rotorua and Rotoiti. Lake Rotoehu kōura and goldfish showed slightly elevated aluminium concentrations in the gills indicating enhanced exposure to aluminium but little evidence for significant bioaccumulation in tissues.

year: 2015