Enric Cortés

Life History Patterns and Correlations in Sharks

ABSTRACT This study examines life history patterns and correlations between traits related to body size, reproduction, age, and growth in sharks, using data from 230 populations representing 164 species, 19 families, and 7 orders. The analysis focused on interspecific life history variability, but intraspecific and intrapopulation variation were also considered. Interspecifically, body size correlated positively with litter size and offspring size, and a tradeoff between litter size and offspring size was found after factoring out the effects of body size. Offspring size correlated negatively with growth completion rate (K), but the correlation became positive after correcting for the effects of body size. Parental size for males and females was negatively correlated with K. Parental size and size at maturity exhibited a strong positive correlation, with sexual maturity occurring at about 75% of maximum size in both sexes. Males were 10% smaller than females and reached their maximum length 34% faster than females on average. Females tend to mature later and live longer than males, but age at maturity is reached at about 50% of maximum age in both sexes. Maximum size and empirical longevity were not significantly correlated in females, but were positively correlated in males. Size and age at maturity also exhibited a moderate positive correlation in males, especially after excluding data for Squalus acanthias. Principal component and cluster analyses were used to reflect similarities among life history traits of 40 populations from 34 species, and at least three separate life history strategies were identified.

Demographic analysis as an aid in shark stock assessment and management

Abstract The use of demographic analyses incorporating life history information on validated age and growth, reproduction, and natural mortality is proposed to gain insight into the population dynamics of sharks under a variety of scenarios and to assess their vulnerability to varying exploitation rates. This approach provides a useful framework for comparison with other currently used methods of assessment, especially those that rely only on fishery-dependent data, and thus can be helpful to stock assessments and to the rational exploitation and management of shark stocks. A review of demographic analyses of large coastal sharks on the east coast of the US indicates that the lemon and sandbar sharks have very low rates of population increase ( r −1 ) and are thus extremely vulnerable to exploitation. In contrast, one of the small coastal group species of lesser importance to the fisheries, the bonnethead shark, has some of the highest r values yet calculated for any shark. Preliminary demographic analyses using nonvalidated age estimates indicate that two other common and economically valuable large coastal species, the blacktip and dusky sharks, may also exhibit relatively slow rates of population change and be very vulnerable to overexploitation. Improved assessment of shark stocks requires increased collection of biological and fishery data, and a much better understanding of their population dynamics, especially stock–recruitment relationships.

Stock Assessment of Scalloped Hammerheads in the Western North Atlantic Ocean and Gulf of Mexico

Abstract The status of the western North Atlantic Ocean population of scalloped hammerheads Sphyrna lewini (Sphyrnidae [hammerhead sharks]) was assessed from 1981 through 2005 by using Schaefer (logistic) and Fox surplus-production models. The population declined rapidly before 1996 but began rebuilding in the late 1990s as fishing pressure decreased. The Akaike information criterion for small sample sizes—a test of goodness of fit for statistical models—indicated that the Fox model provided a slightly better fit to the data. Bootstrapped parameter values showed that in 2005 the probability of the scalloped hammerheads being overfished was greater than 95% (the population was estimated to be 45% of that which would produce the maximum sustainable yield [MSY]) and a 73% probability that overfishing was occurring (fishing mortality was approximately 129% of that associated with the MSY). The size of this population was estimated to be 17% of what it had been in 1981, that is, it has been depleted by about ...

Age and Growth of the Blacknose Shark, Carcharhinus acronotus, in the Eastern Gulf of Mexico

Age and growth of the blacknose shark, Carcharhinus acronotus, from the eastern Gulf of Mexico was estimated by counting bands on the vertebral centra from 123 individuals. Back-calculated von Bertalanffy growth functions were constructed for populations in northwest Florida and Tampa Bay, Florida. Von Bertalanffy growth function parameters for males in northwest Florida (L, = 963.1 mm FL, K = 0.59, to = -0.754 yr) were significantly different from those in Tampa Bay (L, = 801.0 mm FL, K = 0.771, to = -0.797 yr), as were those for females (L, = 1136.5 mm FL, K = 0.352, to = -1.212 yr in northwest Florida; L, = 1241.3 mm FL, K = 0.237, to = -1.536 yr in Tampa Bay). Theoretical longevity, estimated as the age at which 95% of L, is reached, varied from age 10-16 yr for females and 4.5-9.0 yr for males, depending on geographic area. The oldest sharks aged were 4.5+ yr. Centrum edge and marginal increment analyses lent support to the hypothesis that narrow dark bands are formed during winter months. Length-frequency analysis verified back-calculated size at ages 0, 1, and 2. The growth dynamics of blacknose sharks are similar to those of other relatively small, fast-growing, short-lived species of sharks.

Poor-data and data-poor species stock assessment using a Bayesian hierarchical approach

Appropriate inference for stocks or species with low-quality data (poor data) or limited data (data poor) is extremely important. Hierarchical Bayesian methods are especially applicable to small-area, small-sample-size estimation problems because they allow poor-data species to borrow strength from species with good-quality data. We used a hammerhead shark complex as an example to investigate the advantages of using hierarchical Bayesian models in assessing the status of poor-data and data-poor exploited species. The hammerhead shark complex (Sphyrna spp.) along the Atlantic and Gulf of Mexico coasts of the United States is composed of three species: the scalloped hammerhead (S. lewini), the great hammerhead (S. mokarran), and the smooth hammerhead (S. zygaena) sharks. The scalloped hammerhead comprises 70-80% of the catch and has catch and relative abundance data of good quality, whereas great and smooth hammerheads have relative abundance indices that are both limited and of low quality presumably because of low stock density and limited sampling. Four hierarchical Bayesian state-space surplus production models were developed to simulate variability in population growth rates, carrying capacity, and catchability of the species. The results from the hierarchical Bayesian models were considerably more robust than those of the nonhierarchical models. The hierarchical Bayesian approach represents an intermediate strategy between traditional models that assume different population parameters for each species and those that assume all species share identical parameters. Use of the hierarchical Bayesian approach is suggested for future hammerhead shark stock assessments and for modeling fish complexes with species-specific data, because the poor-data species can borrow strength from the species with good data, making the estimation more stable and robust.

Demography and elasticity of the diamond stingray, Dasyatis dipterura: parameter uncertainty and resilience to fishing pressure

Despite their abundance in near-shore tropical and subtropical marine environments, which support much of the world’s elasmobranch fisheries, population dynamics and impacts of fisheries on stingrays are poorly documented. Age-structured demographic models were developed using empirical estimates of fecundity, longevity and maturity to project population growth parameters and potential responses to fishing mortality of Dasyatis dipterura from the Bahia Magdalena lagoon complex, Mexico. Monte Carlo simulation was incorporated to include uncertainty in life history parameters into model projections. Six models were developed using deterministic and probabilistic approaches under unexploited and exploited (fishing mortality = 0.05 year–1) conditions. Mean annual population growth rates (λ) of 1.05–1.06 (5–6% increase), net reproductive rates of 2.3–2.4 and generation times of 14.9–16.5 years were projected from simulations. The introduction of a low fishing mortality into probabilistic models produced λ of 1.01 year–1. Elasticity analysis indicated that population growth rates for D. dipterura are more strongly influenced by the survival of juvenile and adult stages than by survival of neonates or changes in fecundity. Demographic analyses indicated that D. dipterura has a low intrinsic growth potential and limited resilience to fishing pressure. Localised depletion or population collapses are therefore likely to occur through unrestricted, unmonitored fishing effort.

Reproductive variables of Urotrygon rogersi (Batoidea: Urotrygonidae): a species with a triannual reproductive cycle in the eastern tropical Pacific Ocean.

Reproductive aspects of the round ray Urotrygon rogersi were studied based on 2005 specimens obtained in the artisanal shrimp fishery operating on the Colombian Pacific coast. Females reached greater maximum total length (L(T) ), disc width (W(D) ) and mass (M) (38·0 cm, 19·9 cm and 348 g) than males (32·5 cm, 17·0 cm and 165 g). Sex ratio of juveniles and adults was 1:1. Clasper length increased rapidly between 10·0 and 12·5 cm W(D) . The smallest mature male measured 10·5 cm W(D) and the largest immature individual 13·7 cm W(D) . Male first maturity was reached at 61·8% of maximum W(D) , and estimated W(D50) was between 11·5 and 11·8 cm. The smallest mature female measured 10·5 cm W(D) ; the size at first maturity was 52·8% of maximum W(D) , and estimated W(D50) was between 11·8 and 12·3 cm. Embryos were found in females ≥ 10·5 cm W(D) and maximum fecundity was three embryos per female (mode = 1) and varied with maternal size. Embryos were found in all months, but three birthing peaks per year were identified and a gestation period of 4-5 months estimated. Based on ovulation time, embryonic growth and parturition dates, a triannual reproductive cycle was inferred for this species, with overlapping ovarian and uterine cycles. These results suggest that U. rogersi has a reproductive strategy based on low fecundity, a rapid reproductive cycle (short ovulation and gestation time), three birth peaks per year and large embryos. This strategy probably allows U. rogersi to withstand the fishing pressure they are subject to on the Colombian Pacific coast. The results also suggest that the study area is an important nursery and reproductive area for this species.

Changes to Marine Trophic Networks Caused by Fishing

Andres F. Navia1,2, Enric Cortes3, Ferenc Jordan4, Victor H. Cruz-Escalona2 and Paola A. Mejia-Falla1 1Fundacion Colombiana Para la Investigacion y Conservacion de Tiburones y Rayas SQUALUS 2Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional 3NOAA, National Marine Fisheries Service, Panama City Laboratory 4The Microsoft Research – University of Trento COSBI, Trento 1Colombia 2Mexico 3USA 4Italy

Age and Growth of the Round Stingray Urotrygon rogersi, a Particularly Fast-Growing and Short-Lived Elasmobranch

We examined the age and growth of Urotrygon rogersi on the Colombian coast of the Eastern Tropical Pacific Ocean by directly estimating age using vertebral centra. We verified annual deposition of growth increments with marginal increment analysis. Eight growth curves were fitted to four data sets defined on the basis of the reproductive cycle (unadjusted or adjusted for age at first band) and size variables (disc width or total length). Model performance was evaluated using Akaikes Information Criterion (AIC), AIC weights and multi-model inference criteria. A two-phase growth function with adjusted age provided the best description of growth for females (based on five parameters, DW∞  =  20.1 cm, k  =  0.22 yr–1) and males (based on four and five parameters, DW∞  =  15.5 cm, k  =  0.65 yr–1). Median maturity of female and male U. rogersi is reached very fast (mean ± SE  =  1.0 ± 0.1 year). This is the first age and growth study for a species of the genus Urotrygon and results indicate that U. rogersi attains a smaller maximum size and has a shorter lifespan and lower median age at maturity than species of closely related genera. These life history traits are in contrast with those typically reported for other elasmobranchs.

Is the tiger shark Galeocerdo cuvier a coastal species? Expanding its distribution range in the Atlantic Ocean using at-sea observer data

The occurrence of tiger shark Galeocerdo cuvier in the Atlantic Ocean was assessed using at-sea observer data from multiple pelagic longline fisheries. Geographic positions of 2764 G. cuvier recorded between 1992 and 2013 and covering a wide area of the Atlantic Ocean were compared with the currently accepted distribution ranges of the species. Most records fell outside those ranges in both the Southern and Northern Hemispheres, which strongly suggests that the distribution range of G. cuvier in the open ocean is considerably larger than previously described.