Age structures and reproductive patterns of two species of sea snake, Lapemis hardwickii Grey (1836) and Hydrophis elegans (Grey 1842), incidentally captured by prawn trawlers in northern Australia

Abstract

Lapemis hardwickiiand Hydrophis elegans caught by prawn trawlers reach at least 6.7 and 8.9 years of age respectively.Most L.hardwickii sampled were 2—4 years of age,and most H.elegans were 3—5 years of age. Female L.hardwickii and H.elegans appear to reach sexual maturity after 2 years and minimum snout—vent lengths of approximately 76 and 120 cm respectively.The reproductive cycles of L.hardwickii and H.elegans are similar:mating occurs between early May and the end of July;ovulation during August —September;and gestation during September—December and September—February respectively.L.hardwickii and H.elegans produce approximately 8.5 and 12.7 offspring per clutch respectively.However,female L.hardwickii breed annually whereas female H.elegans only breed every 2—3 years.The mean annual reproductive outputs of L. hardwickii (8.4 offspring per year)and H.elegans (7.5)are thus similar. Sea snakes appear to be less fecund and more susceptible to trawler-induced effects than most by-catch taxa,and should be a focus of future strategies to ameliorate the ecological effects of prawn trawling in northern Australia.