English

Abstract

Abstract A 100 m2 forestry pond was stocked with 65 crayfish (Paranephrops zealandicus (White, 1847)), weighing approximately 35 g, in 2010. Sampling was undertaken at the end of each growing season (March - April) from 2012 to 2019. All crayfish > 45 g were harvested from the population; from 2015 between 1.84 kg and 3.65 kg of crayfish < 45 g were harvested (11 to 24% of the < 45 g population). In 2014, refuge (Cytisus scoparius) for the crayfish was added to the pond. The following year there was a noticeable increase in crayfish biomass, particularly those 45 g or less. In 2018, eight kg of lime was added to the pond. This did not greatly change the pH or calcium in the pond water when measured 10 months later, but there was a corresponding increase in total biomass and biomass of crayfish > 45 g. Crayfish biomass ranged from 2.76 kg (2012) to 17.71 kg (2017). Harvests of crayfish > 45 g ranged from 1.1 kg (2012) to 3.98 kg (2019) and for crayfish < 45 g from 1.84 kg (2018) to 3.65 kg (2016). Our findings suggest that habitat modification and harvesting a range of crayfish size classes can increase total biomass, but not necessarily the biomass of larger crayfish.