BACKGROUND:Global aquatic environments are changing profoundly as a result of human actions; consequently, so too are the ways in which organisms are distributing themselves through space and time. Our ability to predict organism and community responses to these alterations will be dependent on knowledge of animal movements, interactions, and how the physiological and environmental processes underlying them shape species distributions. These patterns and processes ultimately structure aquatic ecosystems and provide the wealth of ecosystem services upon which humans depend. Until recently, the vast size, opacity, and dynamic nature of the aquatic realm have impeded our efforts to understand these ecosystems. With rapid technological advancement over the past several decades, a suite of electronic tracking devices (e.g., acoustic and satellite transmitters) that can remotely monitor animals in these challenging environments are now available. Aquatic telemetry technology is rapidly accelerating our ability to observe animal behavior and distribution and, as a consequence, is fundamentally altering our understanding of the structure and function of global aquatic ecosystems. These advances provide the toolbox to define how future global aquatic management practices must evolve.

Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about the spatial and temporal scales of their habitat use and associated ecological role. In this study, we employed passive acoustic telemetry to investigate the residency patterns and migration dynamics of 18 adult bull sharks (195–283 cm total length) tagged in southern Mozambique for a period of between 10 and 22 months. The majority of sharks (n = 16) exhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709 km (mean  = 533 km) with eight of these sharks returning to the study site. During migration, individuals exhibited rates of movement between 2 and 59 km.d−1 (mean  = 17.58 km.d−1) and were recorded travelling annual distances of between 450 and 3760 km (mean  = 1163 km). Migration towards lower latitudes primarily took place in austral spring and winter and there was a significant negative correlation between residency and mean monthly sea temperature at the study site. This suggested that seasonal change is the primary driver behind migration events but further investigation is required to assess how foraging and reproductive activity may influence residency patterns and migration. Results from this study highlight the need for further understanding of bull shark migration dynamics and suggest that effective conservation strategies for this vulnerable species necessitate the incorporation of congruent trans-boundary policies over large spatial scales.

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Ebert, D. A., Compagno, L. J. V., and Cowley, P. D. 2008. Aspects of the reproductive biology of skates (Chondrichthyes: Rajiformes: Rajoidei) from southern Africa. – ICES Journal of Marine Science, 65: 81–102. New information is presented on the reproductive biology of 22 southern African skate species. Sex ratios for most species were relatively even. Sexual dimorphic differences in disc shape were evident in all species, but the total length (LT) to disc width (D) relationship was significantly different in only three species, and the LT to weight (W) relationship significant in just five species. Sexual dimorphism relative to maximum total length (LTmax) was absent in all but the two largest species. Males and females of the same species grow to a similar LTmax except those whose LTmax is >1.5 m LT. Size at first and 50% (LT50) sexual maturity was approximately the same for both sexes in all but the two largest species. First maturity occurred at >60% of LTmax for all species for which sufficient data were available, and most (n = 18) matured at >75% LTmax. The large size at maturity relative to LTmax suggests that growth slows or is partially suspended following sexual maturity. The egg cases of 15 species are described, and a key to their identification is presented. Egg cases in utero were observed throughout the year suggesting that most species reproduce year-round.

This study presents information on the reproductive biology of five southern African catshark species: Apristurus microps, A. saldanha, Apristurus sp., Galeus polli, and Scyliorhinus capensis. They were caught between Walvis Bay, Namibia, and Cape Agulhas, South Africa, from 50 to 1016 m deep. The reproductive mode of four species was oviparous, whereas G. polli exhibited aplacental viviparity. Males of all species attained first maturity slightly larger than females, and males of the four oviparous species attained a larger LTmax than females. The length at 50% maturity was similar for males and females in most species. All species matured at an LT > 75% of LTmax except for male Apristurus spp. and female G. polli, which matured at 71.2% and 68.8%, respectively, of LTmax. The egg case of A. microps has minute tendrils, whereas those of S. capensis were quite long, suggesting different egg-laying habitats. Fecundity in G. polli ranged from 5 to 13, and litter size increased in relation to increased female length. Embryos of G. polli were large, each measuring approximately 30% of female LT. Neonates of G. polli were common and appear to have a demersal lifestyle; those of the four oviparous species were entirely absent from the study. Gravid A. microps were found in summer and winter, indicating a protracted breeding cycle, but reproductively active S. capensis were caught only in winter. Prior to this study, reproductive information on these catsharks was largely lacking.