Estimating Finite Rate of Population Increase for Sharks Based on Vital Parameters

Abstract

The vital parameter data for 62 stocks, covering 38 species, collected from the literature, including parameters of age, growth, and reproduction, were log-transformed and analyzed using multivariate analyses. Three groups were identified and empirical equations were developed for each to describe the relationships between the predicted finite rates of population increase (λ’) and the vital parameters, maximum age (Tmax), age at maturity (Tm), annual fecundity (f/Rc)), size at birth (Lb), size at maturity (Lm), and asymptotic length (L∞). Group (1) included species with slow growth rates (0.034 yr-1 < k < 0.103 yr-1) and extended longevity (26 yr < Tmax < 81 yr), e.g., shortfin mako Isurus oxyrinchus, dusky shark Carcharhinus obscurus, etc.; Group (2) included species with fast growth rates (0.103 yr-1 < k < 0.358 yr-1) and short longevity (9 yr < Tmax < 26 yr), e.g., starspotted smoothhound Mustelus manazo, gray smoothhound M. californicus, etc.; Group (3) included late maturing species (Lm/L∞ ≧ 0.75) with moderate longevity (Tmax < 29 yr), e.g., pelagic thresher Alopias pelagicus, sevengill shark Notorynchus cepedianus. The empirical equation for all data pooled was also developed. The λ’ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis. The predictability was further validated by an independent data set of three species. The empirical equations developed in this study not only reduce the uncertainties in estimation but also account for the difference in life history among groups. This method therefore provides an efficient and effective approach to the implementation of precautionary shark management measures.

Development and testing of a Bayesian population model for the bigeye thresher shark, Alopias superciliosus, in an area subset of the western North Pacific

“…Comparing the results from the current study with previous demographic analysis of the Pacific bigeye thresher population (Cortés, ; Chen &Yuan, 2006; Liu, Chin, Chen & Chang, ) highlights the importance of uncertainty in model structure and life history parameters. Our estimates of finite population growth rate( λ ) are generally similar to those reported by previous studies (Table ).…”

“…The results from the demographic model indicated that bigeye threshers can only support very limited fishing mortality; thus, the present findings emphasise the importance of reducing fishing pressure for this species. Moreover, it has been shown that long-lived species with a low rate of natural mortality and low fecundity (like most shark species) cannot sustain high levels of fishing pressure (Chen & Yuan, 2006;Cortés, 2008;Cortés et al, 2010;Liu et al, 2015). Therefore, the present estimate of catch at size could be used to represent the utilisation of bigeye thresher stock in the northeastern Taiwan waters.…”

Maximum intrinsic rate of population increase in sharks, rays, and chimaeras: the importance of survival to maturity

“…3). While our study did not explore the relationship between relative maturation (the α mat /α max ratio) and r max values among species, a negative relationship between relative maturation and intrinsic rate of population increase has been previously pointed out in sharks (Liu et al, 2015) and skates (Barnett et al, 2013).…”

Possible female philopatry of the smooth hammerhead shark Sphyrna zygaena revealed by genetic structure patterns

“…Ecological and anthropogenic events contribute to changes in the size of natural populations. S. tiburo presents a higher rate of population increase in the estuaries of the Florida Panhandle (Cortés & Parsons, ) than S. lewini (Liu et al ., ; Smith et al ., ), which agrees with their levels of mitochondrial genetic diversity (Castillo‐Olguín et al ., ; Escatel‐Luna et al ., ; Nance et al ., ). In the NMP, S. zygaena has historically been one of two most abundant sphyrnids fished, but there are fewer catch records for this species compared with S. lewini as S. zygaena presents a primarily pelagic distribution while the fisheries in the NMP are mainly coastal, artisanal fishery (Bizzarro et al ., , ; Cartamil et al ., ; Pérez‐Jiménez, ; Saldaña‐Ruiz et al ., ; Smith et al ., ).…”