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Oral | Posters


Oral Presentations

 

 

Day: 3, Session: 2, Talk: 1

Development of Mass Production Hatchery Technology for Cherax quadricarinatus

CLIVE JONES and Colin Valverde

Aquaculture production of redclaw (Cherax quadricarinatus) in Australia, has never reached the high level projections made in the 1990’s. This can be attributed to a range of factors, but the most significant is the supply of seedstock. One of the most positive aquaculture characteristics of redclaw is its bearing of offspring in adult form, obviating the requirement for larval rearing, as is necessary for most successfully commercialised aquaculture species. Among other positive characteristics, this was seen as the most significant and methods for pond-based, mass production of juvenile redclaw were devised and implemented by industry. This relied on natural reproduction, and natural productivity in the pond to support the survival and growth of the juveniles. Mean productivity was reported as 63.2 juveniles produced per berried female, and a harvest density of 24.6 juveniles per m2. Under suitable, summer photoperiod and temperature conditions, three consecutive crops of juveniles could be produced per year. Such managed pond production of seed stock for redclaw production was applied by industry with some success, but it soon became evident that productivity was too low and the practice occupied valuable pond space that would be more profitably applied to growout. An alternative production method for the supply of lobster juvenile redclaw was conceived by an innovative redclaw farmer, Colin Valverde, utilising artificial egg incubators, that had been successfully applied to freshwater crayfish species in Europe. The putative advantages of artificial egg incubation include savings of space, water and energy, minimising egg loss, control over the period of embryogenesis, known parentage for genetic selection and prevention of transmission of disease from parent to offspring. The primary advantages were initially for its application to genetic selection and for generating specific pathogen free stock. However, an even greater benefit became apparent, that this approach could support mass production of seedstock. The system that formed the basis of the that developed in Australia for redclaw was based primarily on the Hemputin™ incubator from Finland used for Pacifastacus leniusculus and Astacus astacus. Its design was modified to suit the specific requirements of redclaw and greater production volumes. The procedures and equipment have evolved, providing a foundation for more consistent and greater production of seed. The juvenile crayfish produced by the hatchery have generally moulted twice since hatching and are referred to as stage 3 juveniles or craylings. A hatchery supply of craylings provides the opportunity for farmers to stock an exact quantity of uniform size crayfish into growout ponds, which in turn enables calculation of likely survival, growth and biomass at the end of the production cycle. The Valverde hatchery system can generate tens of thousands of craylings per batch and is scalable. However there are production issues to be resolved including year round supply of eggs to the hatchery and management of egg health. This paper will detail the development of the Valverde hatchery system, and the challenges to see it develop into fully commercial production that can support expansion of the redclaw farming industry.


 

Poster Presentations

 

 

POSTER 56

Assessing Rarity Patterns in Crayfish at Multiple Spatial Scales Using Scale-area Curves

JOHN W. JOHANSEN, Hayden T. Mattingly, Christopher A. Taylor and Guenter A. Schuster

Identification of at-risk species often relies mostly on range size, particularly for poorly studied species. Although this provides a relatively efficient method for identifying species of conservation concern, it may lead to an inaccurate assignment of conservation status. For example, many species occupy small native ranges but are locally abundant and temporally stable. Additionally, extinction processes operate at different spatial-scales. Scale-area curves provide a framework that examines rarity at multiple spatial scales, and thus, can lead to development of more impactful conservation strategies. Using a well-vetted database of Alabama crayfish collections, we used measures of area of occupancy to construct scale-area curves and assess rarity patterns for lotic crayfishes at two spatial scales: 1 km2 and 100 km2. Area of occupancy (AOO) is a measure of range size that varies depending on the spatial-scale of interest. For each species, AOO was estimated by counting the number of occupied cells in nested grids at increasing user-defined areas. In addition to AOO, the degree of range fragmentation was determined for each species from the slope of the scale-area curve at each spatial scale. Principle components analysis was used to identify scale-specific patterns of rarity. For example, at the 1 km2 spatial scale, we identified 5 groups of species based on AOO and degree of range fragmentation while at the 100 km2 scale six groups were identified. At the 1 km2 scale, several state imperiled species (S2) had higher levels of fragmentation than many critically imperiled species (S1). This indicates the lower ranked (S2) species may actually be more susceptible to loss of local populations due to increased range fragmentation. Accordingly, understanding metapopulation dynamics and maintaining habitat connectivity should be a priority for this subset of state imperiled (S2) species. This demonstrates the need to examine multiple variables and spatial scales in prioritizing species of conservation concern, particularly for those species that lack basic biological and ecological data beyond range size.

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