Similar life history traits in bull (Carcharhinus leucas) and pig-eye (C. amboinensis) sharks

Abstract

Appropriate management strategies for coastal regions require an understanding of how ecological similarities and differences among species shape ecosystem processes. Here, we tested whether morphological similarity equated to similar age and growth patterns in two common coastal sharks in northern Australia. Vertebrae of 199 pig-eye (Carcharhinus amboinensis) and 94 bull (C. leucas) sharks were sourced principally from commercial fisheries operating along the Northern Territory coastline during 2007–2009. We sectioned vertebrae to provide estimates of age of these animals. Model averaging results indicated female pig-eye sharks matured at 13 years and lived >30 years. Theoretical asymptotic length (L∞) (±s.e.) was estimated to be 2672 (±11.94) mm with a growth coefficient (k) of 0.145 year–1. Male pig-eye sharks matured slightly earlier than females (12 years) and survived >26 years. Theoretical asymptotic length for males (L∞) (±s.e.) was also smaller (2540 ± 13.056) mm and they grew faster (k = 0.161 year–1) than females. Bull sharks matured at 9.5 years and reached a maximum theoretical size (L∞) (±s.e.) of 3119 mm (±9.803) with a similar growth coefficient (k = 0.158 year–1) to pig-eye sharks. Longevity of bull sharks was estimated to be more than 27 years. Our results indicate that these patterns of high longevity and slow growth are indicative of low resilience and high susceptibility to over-exploitation of these coastal sharks.