Eight Years of Freshwater Crayfish (Paranephrops Zealandicus(White))

Freshwater Crayfish 25(1):7–12, 2020 RESEARCH ARTICLE ISSN: 2076-4324 (Print), 2076-4332 (Online) https://doi.org/10.5869/fc.2020.v25-1.007 Eight Years of Freshwater Crayfish Paranephrops( zealandicus (White)) Harvest from One New Zealand Pond: Comments on the Resulting Population Structure John Hollows,1,* Thomas Song 1 and Callum Kyle 1 1 Ernslaw One Ltd., Invermay, Private Bag 50034, Mosgiel 9053, New Zealand. *Corresponding Author.— [email protected] ABSTRACT ARTICLE INFO A 100 m2 forestry pond was stocked with 65 crayfish (Paranephrops zealandicus (White, 1847)), weighing Article History: approximately 35 g, in 2010. Sampling was undertaken at the end of each growing season (March - Submitted: 28 OCT 2019 April) from 2012 to 2019. All crayfish > 45 g were harvested from the population; from 2015 between Accepted: 24 MAR 2020 1.84 kg and 3.65 kg of crayfish < 45 g were harvested (11 to 24% of the < 45 g population). In 2014, refuge Published Online: 15 APR 2020 (Cytisus scoparius) for the crayfish was added to the pond. The following year there was a noticeable Published Print: 30 APR 2020 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, Keywords: but there was a corresponding increase in total biomass and biomass of crayfish > 45 g. Crayfish biomass biomass; ranged from 2.76 kg (2012) to 17.71 kg (2017). Harvests of crayfish > 45 g ranged from 1.1 kg (2012) crayfish; to 3.98 kg (2019) and for crayfish < 45 g from 1.84 kg (2018) to 3.65 kg (2016). Our findings suggest density; that habitat modification and harvesting a range of crayfish size classes can increase total biomass, but not harvest; necessarily the biomass of larger crayfish. Paranephrops; refuge; Copyright © 2020 by The Author(s). Published by the International Association of Astacology. This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. INTRODUCTION challenges in developing Paranephrops crayfish as an aquaculture species (Hammond et al. 2006). One approach suggested to New Zealand freshwater crayfish (Paranephrops spp.) have improve production and biomass is to increase refuge for the been investigated as an aquaculture species for many years (de crayfish (Hollows 2016). Refuge type has been demonstrated to Jong 2010; Jones 1981; Lawrence et al. 2006a; Shaddock 1976; have a significant effect on harvestable biomass, mainly through Hollows 2016). However, a freshwater crayfish industry has not increased survival in ponds (Jones and Ruscoe 2001). In natural developed despite this research (de Jong 2010). Limited research streams, Parkyn et al. (2009) found that increased refuge was funding for the intensification of freshwater crayfish farming associated with a higher abundance and biomass of P. planifrons. may partly explain this lack of development (Hammond et al. Lawrence et al. (2006b) noted that while doubling the amount of 2006; Hollows 2016; Lovett 2014). By comparison significant refuge increased the number of juvenile crayfish, it did not result government funding has been made available for Australian in increased numbers of market-sized crayfish. redclaw (Cherax quadricarinatus (von Martens)) (Stevenson et al. 2013) and marron (Cherax tenuimanus (Smith)) (Luckers 2015) Environmental factors need to be considered in an aquaculture research, and this industry is significantly more advanced in its setting as they can affect population dynamics, such as growth rates, intensification and production techniques. reproduction, and survival in crayfish populations. For example, water chemistry is an important determinant for successful New Zealand freshwater crayfish farming methods are mostly crayfish growth (Lowery 1988) and should be considered when extensive (de Jong 2010), with many ponds. These ponds are not attempting to increase production. Calcium is an essential element supplied with artificial food and are typically visited once or twice to all crustacea (Hessen et al. 1991), and slow or incomplete a year (Hollows 2016). This farming approach may be attributed recalcification due to lower calcium levels in the water can make to economics as Paranephrops spp. are slow growing, taking freshwater crustaceans more vulnerable to predation (Stein 1977) two to three years to produce a crayfish of approximately 50 g and cannibalism (Dick 1995). Improved moult survival rates (Jones 1981; Hollows 2016). Furthermore, their low fecundity, have been noted with higher levels of calcium for Paranephrops slow growth rates and cannibalistic nature indicate there are many zealandicus (White) (Hammond 2006) and Procambarus clarkii 7 8 Freshwater Crayfish Volume 25, Number 1 results from this approach to date have been inconclusive and questions remain as to its value (Froese et al. 2016). This paper discusses the results of eight consecutive years of P. zealandicus harvest from a small pond in New Zealand and the implications of modifying habitat, water chemistry and reducing crayfish biomass on population dynamics in an extensive aquaculture setting. METHODS A 100 m2 earthen pond in Dusky Forest, West Otago, New Zealand (-45.817611, 169.164472, WGS84, was used for this study. The pond receives water from rain and overland runoff and is isolated from any other ponds or flowing water sources. In 2010, there was no cover/refuge in the middle areas of the pond, with overhanging riparian vegetation providing the only Figure 1. Total crayfish biomass (kg), biomass (kg) of crayfish < 45 g in shelter for the crayfish. In June 2014, refuge was added to the pond weight and harvest biomass (kg) of crayfish > 45 g and < 45 g in weight in the form of recently cut broom (Cytisus scoparius (L.) Link), for P. zealandicus 2012 to 2019. an exotic leguminous shrub. This was placed in the middle of the pond approximately one metre from any bank and covered an area (Girard) (Bretonne et al. 1969). Furthermore, crayfish growth of approximately 52 m2. and survival during moulting has been demonstrated to be In June 2018, eight kg of dissolved lime (Daltons Big Value significantly higher with elevated pH inAustropotamobius pallipes Garden Lime made from ground limestone rock) was added to the (Lereboullet) when reared under laboratory conditions (Haddaway pond. Calcium and pH levels in the water were measured prior to et al. 2013). Water temperature is another determinant of crayfish the addition of lime, and measured again approximately 10 months growth (Whitmore 1997; Hammond 2006); differences in water later. temperature may influence growth, survival and/or reproductive The pond was stocked with 65 ~26 g P. zealandicus in 2010 output. Ten degrees Celsius has been suggested as a minimum (33 males and 32 females). The pond was harvested once at the for P. zealandicus growth to occur in natural streams (Whitmore end of each summer growing season (March – April) from 2012 to 1997). New Zealand’s temperate climate results in long periods 2019. A harvest event consisted of eight fyke nets set for 48 hours when water temperature does not exceed 10 degrees (Hollows (baited with salmon intestines), followed by three harvest events 2016). using a large dip net, undertaken at 10-minute intervals. Under extensive crayfish farming models, all large crayfish are All crayfish were measured; those > 45 g were removed, while harvested, and small crayfish and berried females are returned to all small crayfish and berried females were returned to the pond the pond. The implication of this harvest strategy on Paranephrops (2012 to 2014). A proportion of crayfish < 45 g were also removed spp. production is not fully understood and has not been previously during the 2015 to 2019 sampling. The number of eggs under each researched in an aquaculture setting. In many finfish and crustacean berried female was estimated and recorded for each year. fisheries, it has been reported that the harvesting of the largest specimens from a population may result in earlier onset of sexual RESULTS maturity, less overall fecundity in a population, and less harvest yield (Huner et al. 2015; Kuparinen and Merilä 2007). An example Total biomass of crayfish increased steadily up to 2014, then of this was reported in Australia, where the practice of removing exhibited a greater annual increase starting in 2015, following the addition of refuge in 2014. This peaked at 14.95 kg in 2017 large crayfish (Cherax albidus Clark) and leaving small crayfish (range 2.76 kg (2012) to 17.7 kg (2017) (Figure 1). The biomass and berried females to grow resulted in high density populations of of crayfish < 45 g ranged from 0.385 g (2012) to 14.95 kg (2017). small crayfish, and possible genetic selection for slower growing crayfish (Lawrence et al. 2006a). Furthermore, it was suggested There was a decrease in all crayfish measures in 2018 (Figure that this harvest model may lead to a sex bias towards females, as 1). This occurred after 3.65 kg of crayfish < 45 g was harvested males are more likely to be caught. Over time, this would result in in 2016 (36% of the < 45 g population) (Figure 1), compared to greater numbers of berried females and high densities of juvenile the ~1.9 kg harvested in other years (~11 to 23% of the < 45 g crayfish (Lawrence et al. 2006a). The balanced harvest model was population) (Figure 1). put forward as a way of maintaining increased yields and reducing The biomass of crayfish < 45 g removed from the population skewed size-class distributions in a population (Garcia et al. 2012). each year ranged from 1.84 kg (2018) to 3.65 kg (2016) (Figure 1). This model requires mortality to be spread over the widest range of The biomass of crayfish > 45 g (range 1.1 in 2012 to 3 kg in 2018) species and sizes in an ecosystem, thereby maintaining ecosystem did not increase proportionally as total biomass increased (range composition akin to an unharvested environment.

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