Age And Feeding Of Oceanic Whitetip Shark,Carcharhinus Longimanus,in The Central And Eastern Pacific Ocean Inferred By Vertebrae

The oceanic whitetip shark,Carcharhinus longimanus,is a highly migratory apex predator.Due to its complex movement patterns and habitat division,the information on the habitat use of this endangered species was still limited,and it is difficult to make the implementation of species protection and management.Microchemistry of vertebrae is a powerful auxiliary method for studying the habitat of elasmobranchs.In this study,samples from 87 individuals（43 males and 44 females）were used to estimate the age,growth,and maturity parameters of sharks retained by longline fisheries in the Central and Eastern Pacific.And 25 oceanic whitetip sharks were used to evaluate the potential ontogenetic differences in feeding habits and niche width between sexes by stable isotopic.13 individuals’retrospective chemical elements signatures of vertebrae were tested by using ablation-inductively coupled plasma mass spectrometry and isotope ratio mass spectrometer.Characterized of elemental signatures and stable isotopes values in vertebrae,encompassing complete life histories,were used to verify sharks’habitat distribution.Using Ba:Ca,Mn:Ca,Sr:Ca,Mg:Ca,Li:Ca,and Zn:Ca ratios along vertebral transects to explore age-related movement patterns.（1）Back-calculation was used because of the low number of juveniles and a multimodel framework with corrected Akaike’s information criterion for small sample size was used to estimate the growth parameters.The linear regression relationship was the best fit for the relationship between the radius of the vertebrae and the total length.The von Bertalanffy growth model provided the best fit for the observed data of combined sexes and back-calculation data of females,and the Gompertz growth model provided the best fit for the back-calculation data of males.The parameter estimates for males were as follows:asymptotic length（L_∞）=330.8 cm;growth coefficient（k）=0.05/a;and the age when the length would theoretically be t₀=–5.84 a.For females,the parameter estimates were as follows:L_∞=363 cm;k=0.08/a;and constant(g_Gom)=1.49.The maximum age was estimated to be 14 a for males and 16 a for females,with a calculated longevity of 25.8 and 28.4 a,respectively.Males matured at 8.8±1.2 a and191±9.1 cm,whereas females matured at 8.6±1.2 a and 173±12.9 cm.（2）Results showed that C.longimanus had a wide range ofδ¹³C values（-18.1～-12.3‰）andδ¹⁵N values（8.9～14.8‰）.However,males and females had similar trophic positions with large niche overlap at similar growth stages.Both sexes had increasingδ¹³C values but relatively constantδ¹⁵N values along the vertebrae.These results indicated that male and female C.longimanus may share similar prey and have complex movement patterns.（3）The results revealed that C.longimanus from two sampling reigns have similar nurseries and movement connectivity.And they may experience reproductive or feeding migration or more complex habitat shift.These results provide evidence to support the conservation and management of this species and highlight the applicability of vertebral chemistry as a tool for characterising shark life-history traits.