Costs and effectiveness of different methods for capturing invasive fish

Abstract

Comparisons of the effectiveness of different fishing techniques in non-wadeable habitats give insights into the relative abundance of invasive fish and native fish, which is important to provide evidence for changes in fish abundance over time. Such comparisons can also be used to determine the most effective methods to remove invasive fish. The objective of this section is to examine methods that yield the most fish for the least cost (i.e. maximise the catch per unit effort). Because comparisons are most effective when applied in a single habitat, they are best considered as case histories at one location. All costs of removal in this chapter are in $NZ. Rotenone has been applied successfully in New Zealand in small waterbodies (e.g. the 0.7 ha Lake Parkinson near Auckland—Tanner et al. 1990; Rowe & Champion 1994) and routinely by the Department of Conservation; use of rotenone to control invasive fish is not considered in this section because it is dealt with in Section 4.1. Boat electrofishing is a technique that has been applied widely in the North Island of New Zealand since 2003 (e.g. Hicks & Bell 2003; Hicks & Tempero 2013; Section 4.4), and provides a useful basis for comparing other methods as it is highly effective at capturing some fish species in non-wadeable habitats. For instance, while boat electrofishing 700 m2 of the Lake Whangape littoral margin (0.4–0.7 m deep) during the spawning season in September 2003, 24 koi carp were caught in 11 minutes, weighing 87.4 kg, with a mean fish mass of 3.64 kg and a catch rate of 349 fish/person-day or 1,271 kg/personday. The calculated population estimate of 68 carp from the single removal (24 carp), applying Equation 1 in Section 4.4, implies a biomass of 3,541 kg/ha. The electrofishing boat normally has a crew of three, so assuming a cost of $480/person-day and a time of 0.07 person-day, the capture cost was $0.38/kg. The average catch rate for koi carp across our entire data set for locations with koi carp (205 capture occasions) by boat electrofishing is 62 fish/person-day and 99 kg/person-day, suggesting an average capture cost of $4.85/kg for labour for fishing time. These costs do not take into account consumables, travel, capital costs, depreciation or maintenance.