Population assessments of chondrichthyan species require several key parameters of their reproductive biology, which were estimated for Squalus megalops (Macleay, 1881). Length-at-maturity differed depending on the criterion adopted for defining maturity. In the case of males, length-at-maturity was smallest when condition of seminal vesicles was adopted as a maturity criterion. For females, length-at-maturity was smallest when the largest follicle diameter >3 mm was adopted as the criterion for maturity; this was appropriate only as an indicator of the onset of maturity. Mature males are capable of mating throughout the year. Females have a continuous asynchronous reproductive cycle. The sex ratio of embryos is 1 : 1 and litter size and near-term embryo length increase with maternal length. Females have an ovarian cycle and gestation period of two years. This was reflected in the differences found between the maturity and maternity ogives. Although all females are mature at 600 mm, only 50% of them contribute to annual recruitment each year. Hence, for chondrichthyan species with reproductive cycles of two, three or more years, if maturity ogives are used in population assessments instead of maternity ogives, the models will overestimate recruitment rates.

The large size, high trophic level and wide distribution of Hexanchiformes (cow and frilled sharks) should position this order as important apex predators in coastal and deep‐water ecosystems. This review synthesizes available information on Hexanchiformes, including information not yet published, with the purpose of evaluating their conservation status and assessing their ecological roles in the dynamics of marine ecosystems. Comprising six species, this group has a wide global distribution, with members occurring from shallow coastal areas to depths of c. 2500 m. The limited information available on their reproductive biology suggests that they could be vulnerable to overexploitation (e.g. small litter sizes for most species and suspected long gestation periods). Most of the fishing pressure exerted on Hexanchiformes is in the form of commercial by‐catch or recreational fishing. Comprehensive stock and impact assessments are unavailable for most species in most regions due to limited information on life history and catch and abundance time series. When hexanchiform species have been commercially harvested, however, they have been unable to sustain targeted fisheries for long periods. The potentially high vulnerability to intense fishing pressure warrants a conservative exploitation of this order until thorough quantitative assessments are conducted. At least some species have been shown to be significant apex predators in the systems they inhabit. Should Hexanchiformes be removed from coastal and deep‐water systems, the lack of sympatric shark species that share the same resources suggests no other species would be capable of fulfilling their apex predator role in the short term. This has potential ecosystem consequences such as meso‐predator release or trophic cascades. This review proposes some hypotheses on the ecology of Hexanchiformes and their role in ecosystem dynamics, highlighting the areas where critical information is required to stimulate research directions.

Understanding the variation in the diet of skates is crucial for determining their roles in marine ecosystems. The diet of 458 sandskates, Psammobatis extenta, from Puerto Quequén, Argentina was quantified to determine whether there was geographical, sexual, ontogenetic, and/or seasonal variation in dietary composition. Cumulative prey-diversity curves reached a stable level at ~30 stomachs and thus the sample size was large enough to describe the overall diet of the sandskate. The diet comprised a variety of small invertebrates, suggesting that the sandskate is a secondary consumer (trophic level of 3.5). The most important prey items were gammarids, shrimps and, to a lesser extent, polychaete worms. A significant correlation was found between the diets of sandskates from south-eastern Brazil and Puerto Quequén, suggesting that in both locations they used similar resources and would have similar ecological roles. No difference was found between the diets of males and females, but ontogenetic and seasonal patterns were detected. Small sandskates preyed largely on gammarids and shrimps but consumed fewer polychaetes and brachyurans than larger individuals. In summer and winter, the most important prey item by number was gammarids, whereas the consumption of shrimps peaked in autumn. This ontogenetic and seasonal pattern indicates that large and small sandskates are versatile predators that can shift their diets in response to prey abundance.

Elasmobranchs (sharks and rays) show an amazing diversity of reproductive modes and behaviors. Multiple paternity (MP) has been identified in all species where more than 1 litter has been investigated; yet neither direct nor indirect benefits from MP have been determined in elasmobranchs. This has led to the suggestion that MP in this group may simply be a product of convenience polyandry with variation in the frequency of MP driven by differences in mate encounter rates. Here, we use molecular markers to investigate polyandry and MP in 2 closely related and commercially important species of shark, Mustelus antarcticus and Mustelus lenticulatus. In total, 328 M. antarcticus embryos originating from 29 different mothers and 75 M. lenticulatus embryos originating from 19 different mothers were genotyped using 8 microsatellite loci. We find that MP occurs in both species. However, in both species, the majority of litters were sired by a single father. Our results do not support increased fecundity per se as a driver of MP. Further, our results do not suggest that high population densities with resulting high mate encounter rates generated by breeding aggregations necessarily lead to high frequencies of MP. Importantly, we note evidence of reproductive skew within polyandrous litters, which is a predicted outcome of postcopulatory mechanisms.