Population variables and life-history characteristics of the alligator pipefish Syngnathoides biaculeatus, in Papua New Guinea

Population structure and life-history variables of the widely distributed alligator pipefish Syngnathoides biaculeatus were characterized in Bootless Bay, Papua New Guinea over the course of 11 months. There was little evidence of seasonality with four focal populations showing no significant change in abundance. Similarly, the sex ratio remained 1:1 for all but 1 month. Reproductive males carrying eggs (148-278 mm in total length, L-T) were found in all months. Brood size was significantly, positively related to male L-T for newly laid broods only. Maximum observed brood size was 351 and mean +/- s.d. brood size was 238 +/- 57 for newly laid broods. Juveniles and males showed no change in mean L-T over the year while slightly smaller females were captured in November 2006 and September 2007. Males were significantly longer than females so von Bertalanffy growth coefficients were estimated separately for each sex: males L-infinity = 285 mm, K = 0.82 year(-1) and females L-infinity = 261 mm, K = 1.10 year(-1). These estimates suggest that this species grows rapidly and has a short-life span. In the context of growing concern about overexploitation of syngnathids, a rapid growth rate combined with year round reproductive activity suggests that the tropical S. biaculeatus may be relatively resilient with regard to fishing pressure.