Demographic Analysis of the Crocodile Shark Pseudocarcharias kamoharai from the Tropical Southwestern Atlantic Ocean

The crocodile (Pseudocarcharias kamoharai) is a small oceanic shark belonging to the Lamnidae family. It is caught incidentally in longline fisheries directed to tuna (Thunnus spp.) and swordfish (Xiphias gladius). The species has no commercial importance being totally discarded without catch records. An usual practice is discarding the specimens without jaws, which leads to death. Population studies on the crocodile shark are essential for determining the species conservation status which is the objective of this study through demographic analyses that use deterministic and stochastic models employing age-based and stage-based approaches. Samples of the crocodile shark were collected throughout the South Atlantic Ocean, allowing the input parameters (age at first maturity, longevity, fecundity and natural mortality) to be estimated for the construction of life history tables (LHT). Those parameters were randomly taken from their respective probability distributions, considering the uncertainty in estimates derived from Monte Carlo Simulations. Each scenario was executed 1000 times with varying input vital rates for the estimation of demographic parameters (net reproductive rate, R0; mean generation length, G; and intrinsic rate of population increase, r). For age-(AB) and stage-based (SB) matrices, the elasticities were estimated. Age at first maturity of females is 5 years, with recruitment to fisheries beginning on this same age; 57.6% of the stock is made up of adults. The scenarios reveal that the exploitation leads to a significant reduction in population for the three models (LHT = AB = -5.8%/year and SB = -11.3%/year). If we use only natural mortality in scenarios, the population continue to decrease LHT = AB = -1.9%/year and SB = -5.9%/year). The SB matrix was not an appropriate model to be used because of the short longevity of species (13 years) leading to overestimations of values of the annual decrease. The lack of catch and fishery data does not allow the estimation of fishing mortality. However, the LHT data and elasticities of AB model with natural mortalities showed that the combination of low survival rate of juveniles and low fecundity (0.94 females per year) renders the species highly vulnerable to fisheries, indicating that the P. kamoharai population off Brazil can be near the overexploitation.