Reproductive biology and age determination of the blind shark, Brachaelurus waddi

Despite an increase in elasmobranch research in general, the knowledge of small benthic shark species is still sparse. Commonly, species not targeted in commercial fisheries and of limited economic value are rarely the focus of research and often assumed to be relatively resilient to increased mortality rates. However, many of these species inhabit areas which are exposed to significant impact from anthropogenic perturbation such as fishing, coastal development, dredging and pollution. It is therefore important to collect information on these less studied species regarding basic biology, life history strategies, ecology and demography as well as their place and function in the ecosystem. This study was conducted from July 2011 to September 2013 and investigated the basic biology and life history of the blind shark, Brachaelurus waddi, a small benthic shark endemic to the east coast of Australia. A total of 180 blind sharks were obtained from a commercial trap fishery operating off the Central Coast of New South Wales. Vertebral band counts were used to estimate age and growth parameters for B. waddi, whilst Marginal Increment Analysis (MIA) and edge analysis (EA) was used to validate the growth band deposition rate. The von Bertalanffy growth function (VBGF) and linear regression were used to estimate growth rates. Assuming an annual growth band deposition, maximum age for both males and females was 19 years. The VBGF produced growth estimates for males that indicated slow growth, L∞ 1112 mm and k=0.03 years-1. Female length-at-age data did not provide any reliable growth estimates. Importantly, the MIA and EA, proved to be less reliable for B. waddi, indicating that growth bands may not be deposited annually. Length and age at maturity was determined for males whilst length at maturity was determined for females. Reproductive periodicity, including gestation time and vitellogenic period was determined for females. Sex-ratio of pups, and length at birth were estimated as well as litter size. Female B. waddi matured at a smaller TL than males (L50 females; 495 mm TL, L50 males; 581 mm TL), which is contrary to most shark species. Age at maturity for males was estimated to between 7.3-13.9 years (L50-L95). Females displayed consecutive growth of follicles and embryos, each lasting one year, with a likely yearlong resting phase. B. waddi has a reproductive cycle that it, at least, biennial and more likely triennial. Litter size ranged from three to nine (mean=6.6) embryos per female and length at birth was approximately 175-209 mm TL.