Records of the Australian redclaw crayfish Cherax quadricarinatus (von Martens, 1868) on the island of Puerto Rico

Abstract

The redclaw crayfish, Cherax quadricarinatus (von Martens, 1868), a tropical freshwater crayfish endemic to Northern Australia and Southern Papua New Guinea, was introduced to the island of Puerto Rico in the late 1990’s. Redclaw has established populations within man-made reservoirs and ponds across the island, where impoundments have impeded the migration and recruitment of native decapods, potentially opening niche space for the redclaw. We present a case study focused on documenting the presence/ absence, sex ratio, size class, and standing stock biomass of redclaw populations from six reservoirs (Carraízo, Cidra, Carite, Güajataca, El Guineo, Dos Bocas), as well as from various holding ponds of an aquaculture facility (Caribe Fisheries) located near the town of Lajas in the southwestern part of the island where the crayfish are considered pests. Crayfish were detected in 5 out of the 7 sample locations (Carraízo, Cidra, Carite, Güajataca, and Caribe Fisheries). A total of N = 150 crayfish were caught during sampling, with 91% being adults (N = 136) and sex counts resulting in a 0.81 male to female ratio. Standard Carapace Length (SCL) ranged from 16 mm (Güajataca) to 82 mm (Carraízo). No significant difference in SCL was found between adult males (48.32 mm ± 1.62 SE) and females (48.17 mm ± 1.47 SE) (F(1,134) = 0.81, P = 0.37), as well as between SCL in M:F ratio among sample sites (F(4,134) = 0.84, P = 0.50). However, a significant difference in total mean SCL among sample sites was found (F(4,134)= 16.96, P < 0.0001). A post-hoc Tukey-Kramer test indicated that individuals in Carraízo, located close to the area of initial redclaw introduction into the headwaters of the Loiza River, had the largest mean SCL (61.38 mm). Mean standing stock biomass per individual ranged from 1.46 g (Güajataca) to 9.71 g (Carraízo). These biomass estimates provide the first insight into the energy supplements that redclaw provides to higher trophic levels (e.g. predatory fish) in these reservoirs. Furthermore, with populations of native decapods having been completely extirpated from most impounded watersheds, introduced redclaw could fill in the empty niche space by processing organic matter and by providing a direct consumption item to recreational fish species. This could reestablish the missing links in the cycling of nutrients and transfer of energy within reservoirs.