Life histories of two deep-water Australian endemic elasmobranchs: Argus skate Dipturus polyommata and eastern spotted gummy shark Mustelus walkeri

Two Australian endemic elasmobranchs, the Argus skate Dipturus polyommata and the eastern spotted gummy shark Mustelus walkeri, were collected from the by-catch of a prawn Melicertus plebejus trawl fishery off Queensland. Age and growth parameters were estimated from growth band counts in vertebral sections of 220 D. polyommata and 44 M. walkeri. Dipturus polyommata males and females had an observed maximum age of 10 years and reached maximum sizes of 369 and 371 mm total length (L_T), respectively. Mustelus walkeri lived longer, with the oldest female aged 16 years and measuring 1050 mm stretched total length (L_ST), and oldest male aged 9 years and 805 mm L_ST. Dipturus polyommata grew relatively fast with a von Bertalanffy growth completion parameter of k = 0·208 year⁻¹ with males reaching maturity at 4·0 years (c. 278 mm L_T) and females at 5·1 years (c. 305 mm L_T). Mustelus walkeri grew more slowly with k = 0·033 year⁻¹ with males estimated to mature at 7–9 years (670–805 mm L_ST) and females at 10–14 years (833–1012 mm L_ST). Length at birth inferred from neonate D. polyommata was 89–111 mm L_T while for M. walkeri it was estimated to be 273 L_ST based on the value of L₀ from the von Bertalanffy growth model. Both species appeared to have continuous reproductive cycles and low fecundity with an average ovarian fecundity of eight follicles for D. polyommata and a litter size of five to seven pups for M. walkeri. Based on these life-history traits, D. polyommata is more resilient to fishing pressure than M. walkeri.