Demographics of Etmopterus lucifer (Lucifer dogfish)
This study provides the first comprehensive description of the demographics of lucifer dogfish (Etmopterus lucifer) from the Chatham Rise, New Zealand during January 2012. Lucifer dogfish is a non-QMS species commonly taken as bycatch in New Zealand deepwater trawl fisheries, where it has low commercial value and is usually discarded. Sexual maturity of females was determined by assessing the condition of the ovary and uterus, and the width of the uterus and oviducal gland. Male maturity was assessed by determining clasper and testes condition, inner clasper length, testes length, and testes weight. A sample of lucifer dogfish was aged by counting growth bands on the internal section of the dorsal fin spine (n = 97), assuming annual deposition of bands. Intra- and inter-reader bias in age estimates was estimated, but count precision was high within (CV = 12.71 %) and between reader age estimates (11.98 %). A number of growth models were fitted to the length-at-age data, including the traditional and modified Von Bertalanffy growth formula (VBGF) and four cases of the Schnute growth model. Selection of the best growth model was based on the Akaike Information Criterion (AIC). The fourth case of the Schnute growth model best represented growth. Lucifer dogfish had an estimated age and length at maturity of 10.4 years and 34.0 cm respectively for males, and 13.0 years and 41.0 cm for females. The oldest observed fish were 17 and 14 years for males and females respectively. The total mortality estimates were in the range of 0.14 to 0.35 yr ⁻¹. Lucifer dogfish fed primarily upon mesopelagic fishes, with Hector’s lanternfish (Lampanyctodes hectoris) identified as being the most common prey. Lucifer dogfish had late maturity relative to its longevity. Although sampling of the population was likely to be incomplete, and biases in age estimates may have occurred, these observed life history characteristics indicate that productivity will be low, and as a consequence, the precautionary approach should be applied, as the potential impact of commercial fishing on this species is high.