Validated age and growth estimates are important for constructing age-structured population dynamic models of chondrichthyan fishes, especially those which are exploited. We review age and growth studies of chondrichthyan fishes, using 28 recent studies to identify areas where improvements can be made in describing the characteristics of ageing structures (both traditional and novel) utilized to estimate ages of sharks, rays, and chimaeras. The topics identified that need consistency include the: (1) terminology used to describe growth features; (2) methods used to both verify and validate age estimates from chondrichthyan calcified structures, especially edge and marginal increment analyses; and (3) the functions used to produce and describe growth parameters, stressing the incorporation of size at birth (L 0 ) and multiple functions to characterize growth characteristics, age at maturity and longevity.

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Differences in the chemical composition of calcified skeletal structures (e.g. shells, otoliths) have proven useful for reconstructing the environmental history of many marine species. However, the extent to which ambient environmental conditions can be inferred from the elemental signatures within the vertebrae of elasmobranchs (sharks, skates, rays) has not been evaluated. To assess the relationship between water and vertebral elemental composition, we conducted two laboratory studies using round stingrays, Urobatis halleri, as a model species. First, we examined the effects of temperature (16°, 18°, 24°C) on vertebral elemental incorporation (Li/Ca, Mg/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca). Second, we tested the relationship between water and subsequent vertebral elemental composition by manipulating dissolved barium concentrations (1x, 3x, 6x). We also evaluated the influence of natural variation in growth rate on elemental incorporation for both experiments. Finally, we examined the accuracy of classifying individuals to known environmental histories (temperature and barium treatments) using vertebral elemental composition. Temperature had strong, negative effects on the uptake of magnesium (DMg) and barium (DBa) and positively influenced manganese (DMn) incorporation. Temperature-dependent responses were not observed for lithium and strontium. Vertebral Ba/Ca was positively correlated with ambient Ba/Ca. Partition coefficients (DBa) revealed increased discrimination of barium in response to increased dissolved barium concentrations. There were no significant relationships between elemental incorporation and somatic growth or vertebral precipitation rates for any elements except Zn. Relationships between somatic growth rate and DZn were, however, inconsistent and inconclusive. Variation in the vertebral elemental signatures of U. halleri reliably distinguished individual rays from each treatment based on temperature (85%) and Ba exposure (96%) history. These results support the assumption that vertebral elemental composition reflects the environmental conditions during deposition and validates the use of vertebral elemental signatures as natural markers in an elasmobranch. Vertebral elemental analysis is a promising tool for the study of elasmobranch population structure, movement, and habitat use.

Maturity and growth characteristics were estimated for Dasyatis dipterura from western Mexico, where it is a common component of artisanal elasmobranch fisheries. Median disc width at maturity was estimated as 57.3 cm for females (n = 126) and 46.5 cm for males (n = 55) respectively. Age estimates were obtained from 304 fishery-derived specimens (169 female, 135 male). An annual pattern of band-pair deposition was validated through modified centrum edge and marginal increment analyses. Gompertz, polynomial and von Bertalanffy growth models were fit to disc width and weight-at-age data. Resulting models were evaluated based on biological rationale, standard error of model estimates, and Akaike’s information criteria. Growth characteristics differed significantly between females and males. Maximum age estimates were 28 years for females and 19 years for males. Three-parameter von Bertalanffy growth models of disc width-at-age data generated the most appropriate fits and produced relatively low estimates of instantaneous growth rates for females (DW∞ = 92.4 cm, k = 0.05, t0 = –7.61, DW0 = 31.4 cm) and males (DW∞ = 62.2 cm, k = 0.10, t0 = –6.80, DW0 = 31.3 cm). These values are the lowest reported for myliobatiform stingrays and indicate slow growth rates in comparison with elasmobranchs in general.