6 results for Powrie, Warrick

  • Boat electrofishing survey of five Waitakere City ponds

    Hicks, Brendan J.; Brijs, Jeroen; Bell, Dudley G.; Powrie, Warrick (2007)

    Report
    University of Waikato

    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.

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  • Boat electrofishing survey of the upper Turitea Reservoir, Palmerston North.

    Hicks, Brendan J.; Brijs, Jeroen; Bell, Dudley G.; Ling, Nicholas; Blair, Jennifer Marie; Powrie, Warrick (2009)

    Report
    University of Waikato

    The upper Turitea Reservoir is a 12-ha reservoir that supplies water to the city of Palmerston North (Figure 1). It was constructed in 1957 and is located in the foothills of the Tararua Ranges at 40.43208°S, 175,67669°E. The 2,300 hectare catchment area is comprised mainly of native forest with a small section of pine forest bordering the northern end of the reservoir. The reservoir is contained by a 39-m high concrete gravity arch dam.

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

    Brijs, Jeroen; Hicks, Brendan J.; Powrie, Warrick (2009)

    Report
    University of Waikato

    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.

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  • Boat electrofishing of the Waikato River upstream and downstream of the Huntly Power Station: spring 2010

    Hicks, Brendan J.; Baker, Cindy F.; Tana, Raymond; Powrie, Warrick; Bell, Dudley G. (2010-11)

    Report
    University of Waikato

    The objective of this investigation was to evaluate fish abundance and community composition upstream and downstream of the Huntly Power Station discharge by boat electrofishing in order to contribute to effects assessment of the thermal discharge. This limited sampling suggests that koi carp had the greatest biomass of any fish species, and were aggregated immediately downstream of the Huntly Power Station. Previous work would suggest that a single electrofishing pass catches about half of the fish present. The method is known to under-sample eels and catfish, but is a robust semiquantitative tool to estimate relative fish abundance.

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  • Comparison of injuries to New Zealand rock lobsters (Jasus edwardsii) caused by hand versus snare collection

    Powrie, Warrick; Tempero, Grant Wayne (2009)

    Journal article
    University of Waikato

    Following the prohibition in New Zealand of lobster snares in late 2005, we undertook research to compare the frequency and extent of injuries to rock lobsters (Jasus edwardsii) (Hutton) caused by recreational SCUBA divers using lobster snares compared with hand collection. Rock lobsters were sampled between January 2006 and October 2006 from multiple dive sites around the North Island of New Zealand. Of the 124 rock lobsters caught, 20.9% were in a soft shell state. Female rock lobsters constituted 43.5% of the catch, but only one was carrying eggs. Female mean tail width was 72.2 mm; male mean tail width was 71.9 mm. We found that hand collection caused significantly more injuries than snare collection, to both soft shell and hard shell animals. Hand collection also resulted in more major injuries, with 18% of hard shell animals and 31% of soft shell animals losing two or more limbs. We recommend that the prohibition on the use of rock lobster snares be lifted, as their use appears to significantly reduce injury and stress to rock lobsters in recreational dive areas, and increase the survival of undersized individuals released after capture.

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  • Invasive fish survey of Lake Arapuni by boat electrofishing

    Tempero, Grant Wayne; Powrie, Warrick; Kim, Brian (2017)

    Report
    University of Waikato

    A boat electrofishing survey of Lake Arapuni was conducted on 2 February 2017 by the University of Waikato to investigate anecdotal reports of koi carp (Cyprinus carpio) presence in the lake. Nine 10-minute electrofishing transects were conducted around the littoral zone of the lake. This resulted in a total distance fished of 3.35 km and a total area fished of 1.34 ha. A total of 100 fish were captured, comprising three species: brown bullhead catfish (Ameiurus nebu/osus), goldfish {Carassius auratus) and rudd {Scardinius erythrophthalmus); in addition, eels (Anguilla sp.) were observed but not captured. Total captured fish biomass was 14.8 kg {11. 7 kg/ha) with goldfish being the most abundant species (86 individuals), accounting for most of the biomass (86.8%). Rudd were the next most abundant species with nine individuals captured (1.0 kg/ha) followed by catfish (five individuals; 0.4 kg/ha). Rudd and catfish boat electrofishing biomass estimates should be regarded as minimal as capture rates for benthic species (catfish) and juveniles (rudd) are often lower than those of adult pelagic species. The reduced capture efficiency of benthic species is due to their preference for depths beyond the extent of the electrofishing field (approximately 2 m in extent from the anode), in addition benthic species are more likely to be missed by netters due to their reduced visibility. The smaller size (150 mm FL), many of which were highly coloured and had markings similar to those of koi carp. It is likely that these larger coloured goldfish were mistaken for koi carp in previous sightings, especially as adult goldfish form small aggregations similar to those of koi carp. If koi carp are present in Lake Arapuni they are likely to be at biomass levels too low to mount viable control or eradication programmes given the large area and depth of the lake.

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