Michael B. Bennett

Biology, ecology and conservation of the Mobulidae

The Mobulidae are zooplanktivorous elasmobranchs comprising two recognized species of manta rays (Manta spp.) and nine recognized species of devil rays (Mobula spp.). They are found circumglobally in tropical, subtropical and temperate coastal waters. Although mobulids have been recorded for over 400 years, critical knowledge gaps still compromise the ability to assess the status of these species. On the basis of a review of 263 publications, a comparative synthesis of the biology and ecology of mobulids was conducted to examine their evolution, taxonomy, distribution, population trends, movements and aggregation, reproduction, growth and longevity, feeding, natural mortality and direct and indirect anthropogenic threats. There has been a marked increase in the number of published studies on mobulids since c. 1990, particularly for the genus Manta, although the genus Mobula remains poorly understood. Mobulid species have many common biological characteristics although their ecologies appear to be species-specific, and sometimes region-specific. Movement studies suggest that mobulids are highly mobile and have the potential to rapidly travel large distances. Fishing pressure is the major threat to many mobulid populations, with current levels of exploitation in target fisheries unlikely to be sustainable. Advances in the fields of population genetics, acoustic and satellite tracking, and stable-isotope and fatty-acid analyses will provide new insights into the biology and ecology of these species. Future research should focus on the uncertain taxonomy of mobulid species, the degree of overlap between their large-scale movement and human activities such as fisheries and pollution, and the need for management of inter-jurisdictional fisheries in developing nations to ensure their long-term sustainability. Closer collaboration among researchers worldwide is necessary to ensure standardized sampling and modelling methodologies to underpin global population estimates and status.

Plasma steroid hormone profiles and reproductive biology of the epaulette shark, Hemiscyllium ocellatum.

Examination of the reproductive biology of the oviparous epaulette shark, Hemiscyllium ocellatum, was conducted on a wild population. Male sharks were found to reach maturity at between 55-60 cm total length (TL) and female sharks mature around 55 cm TL. Blood samples collected from mature male and female sharks were analyzed for sex steroid hormones to examine seasonal hormone patterns. Plasma samples were analyzed via radioimmunoassay techniques with female samples measured for estradiol, progesterone, and androgen concentrations, and male samples measured for androgen concentrations. Male androgen concentrations showed a single broad peak from July to October with maximum hormone concentrations (60 ng/ml) occurring in August. Male androgen concentrations were lowest in December-February (<20 ng/ml), and appeared to correlate with reproductive activity and water temperature. Female androgen concentrations were an order of magnitude lower than those for males and showed peaks in June (6 ng/ml) and December (8 ng/ml). Estradiol concentrations in females peaked during the months of September-November (0.5 ng/ml) coinciding with the egg laying period. Progesterone concentrations ranged up to 0.5 ng/ml prior to the mating season. Observations of ova size and egg production showed eggs develop in pairs and ova are ovulated at a size of 25-27 mm. Females lay eggs from August to January. Males were observed with swollen claspers from July through December, with the highest amount of sperm storage in the epididymis occurring between August through November. Our observations indicate that epaulette sharks in the waters near Heron Island mate from July through December. J. Exp. Zool. 284:586-594, 1999.

Morphometric and ultrastructural comparison of the olfactory system in elasmobranchs: the significance of structure-function relationships based on phylogeny and ecology.

This study investigated the relationship between olfactory morphology, habitat occupancy, and lifestyle in 21 elasmobranch species in a phylogenetic context. Four measures of olfactory capability, that is, the number of olfactory lamellae, the surface area of the olfactory epithelium, the mass of the olfactory bulb, and the mass of the olfactory rosette were compared between individual species and groups, comprised of species with similar habitat and/or lifestyle. Statistical analyses using generalized least squares phylogenetic regression revealed that bentho‐pelagic sharks and rays possess significantly more olfactory lamellae and larger sensory epithelial surface areas than benthic species. There was no significant correlation between either olfactory bulb or rosette mass and habitat type. There was also no significant difference between the number of lamellae or the size of the sensory surface area in groups comprised of species with similar diets, that is, groups preying predominantly on crustaceans, cephalopods, echinoderms, polychaetes, molluscs, or teleosts. However, some groups had significantly larger olfactory bulb or rosette masses than others. There was little evidence to support a correlation between phylogeny and morphology, indicating that differences in olfactory capabilities are the result of functional rather than phylogenetic adaptations. All olfactory epithelia exhibited microvilli and cilia, with microvilli in both nonsensory and sensory areas, and cilia only in sensory areas. Cilia over the sensory epithelia originated from supporting cells. In contrast to teleosts, which possess ciliated and microvillous olfactory receptor types, no ciliated olfactory receptor cells were observed. This is the first comprehensive study comparing olfactory morphology to several aspects of elasmobranch ecology in a phylogenetic context. J. Morphol., 2008.

Reproductive ecology of the reef manta ray Manta alfredi in southern Mozambique

The application of a photographic identification methodology using the unique ventral surface markings (natural spot patterns) of an observed population in southern Mozambique enabled many aspects of the reproductive ecology of reef manta rays Manta alfredi to be examined. The region encompassing the study site was identified as a mating ground for M. alfredi based on observations of mating events and fresh mating scars on females. The distribution of these pectoral fin scars was highly biased and indicated a strong lateralized behavioural trait, with 99% of these scars occurring only on the left pectoral fin. No other elasmobranch has been reported to display behavioural lateralization. The study region also acts as a birthing ground, with individuals typically giving birth in the austral summer period after a gestation of c. 1 year. Reproductive periodicity in M. alfredi was most commonly biennial, but a few individuals were pregnant in consecutive years, confirming an annual ovulatory cycle. The production of a single pup appears to be the normal situation, although observations in the wild as well as during opportunistic dissections of individuals killed by fisheries revealed that two pups are conceived on occasion. Many aspects of the study have contributed to the limited baseline data currently available for this species and have highlighted the potential need for more conservative conservation strategies.

Distribution, site affinity and regional movements of the manta ray, Manta alfredi (Krefft, 1868), along the east coast of Australia

Despite the increasing tourism interest worldwide for the manta ray, Manta alfredi, very little is known about its biology and ecology. Knowledge of its distribution and movement patterns is important for conservation purposes. Here we describe the distribution, site visitation and movements of M. alfredi along the east coast of Australia. Photographic identification techniques were used to identify individual manta rays at three study sites: Lady Elliot Island, North Stradbroke Island and Byron Bay. Of 388 M. alfredi individuals identified at Lady Elliot Island, 187 (48%) were subsequently re-identified at least once at the same site. In total, 31 individuals were identified at both Lady Elliot Island and North Stradbroke Island (,380km to the south) and 4 at both Lady Elliot Island and Byron Bay (,500km to the south). Manta alfredi was present all year around at Lady Elliot Island, although in higher numbers in winter, and was mainly observed at North Stradbroke Island and Byron Bay from mid-spring to mid-autumn. This is the first report of seasonal movements and site affinity forM. alfredi ineastern Australian waters and emphasises the value of photographic identification for monitoring the occurrence of individuals.

Stable isotope and signature fatty acid analyses suggest reef manta rays feed on demersal zooplankton.

Assessing the trophic role and interaction of an animal is key to understanding its general ecology and dynamics. Conventional techniques used to elucidate diet, such as stomach content analysis, are not suitable for large threatened marine species. Non-lethal sampling combined with biochemical methods provides a practical alternative for investigating the feeding ecology of these species. Stable isotope and signature fatty acid analyses of muscle tissue were used for the first time to examine assimilated diet of the reef manta ray Manta alfredi, and were compared with different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). Stable isotope δ15N values confirmed that the reef manta ray is a secondary consumer. This species had relatively high levels of docosahexaenoic acid (DHA) indicating a flagellate-based food source in the diet, which likely reflects feeding on DHA-rich near-surface and epipelagic zooplankton. However, high levels of ω6 polyunsaturated fatty acids and slightly enriched δ13C values in reef manta ray tissue suggest that they do not feed solely on pelagic zooplankton, but rather obtain part of their diet from another origin. The closest match was with demersal zooplankton, suggesting it is an important component of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to the horizontal and vertical movement patterns of this giant planktivore. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs.

The origin and evolution of the surfactant system in fish: Insights into the evolution of lungs and swim bladders

Several times throughout their radiation fish have evolved either lungs or swim bladders as gas‐holding structures. Lungs and swim bladders have different ontogenetic origins and can be used either for buoyancy or as an accessory respiratory organ. Therefore, the presence of air‐filled bladders or lungs in different groups of fishes is an example of convergent evolution. We propose that air breathing could not occur without the presence of a surfactant system and suggest that this system may have originated in epithelial cells lining the pharynx. Here we present new data on the surfactant system in swim bladders of three teleost fish (the air‐breathing pirarucu Arapaima gigas and tarpon Megalops cyprinoides and the non‐air‐breathing New Zealand snapper Pagrus auratus). We determined the presence of surfactant using biochemical, biophysical, and morphological analyses and determined homology using immunohistochemical analysis of the surfactant proteins (SPs). We relate the presence and structure of the surfactant system to those previously described in the swim bladders of another teleost, the goldfish, and those of the air‐breathing organs of the other members of the Osteichthyes, the more primitive air‐breathing Actinopterygii and the Sarcopterygii. Snapper and tarpon swim bladders are lined with squamous and cuboidal epithelial cells, respectively, containing membrane‐bound lamellar bodies. Phosphatidylcholine dominates the phospholipid (PL) profile of lavage material from all fish analyzed to date. The presence of the characteristic surfactant lipids in pirarucu and tarpon, lamellar bodies in tarpon and snapper, SP‐B in tarpon and pirarucu lavage, and SPs (A, B, and D) in swim bladder tissue of the tarpon provide strong evidence that the surfactant system of teleosts is homologous with that of other fish and of tetrapods. This study is the first demonstration of the presence of SP‐D in the air‐breathing organs of nonmammalian species and SP‐B in actinopterygian fishes. The extremely high cholesterol/disaturated PL and cholesterol/PL ratios of surfactant extracted from tarpon and pirarucu bladders and the poor surface activity of tarpon surfactant are characteristics of the surfactant system in other fishes. Despite the paraphyletic phylogeny of the Osteichthyes, their surfactant is uniform in composition and may represent the vertebrate protosurfactant.

Multi-year validation of photographic identification of grey nurse sharks, Carcharias taurus, and applications for non-invasive conservation research

Captive and wild Carcharias taurus were used to assess whether spots present on their flanks were suitable as natural tags for individual shark recognition. Photographic images of seven captive sharks taken at monthly intervals for 14 months and at 3 years after the start of the study indicated that spot numbers, positions and sizes did not change. Eighty-nine wild sharks were photographically re-captured at least once subsequent to their initial image-capture; fourteen were re-photographed at least 23 months subsequent to their initial image-capture and a single individual after 14 years. Unique physical marks (e.g. partial fin loss) on six wild sharks were used to validate the pattern recognition process by providing unambiguous identification of individuals independently of their spots. Preliminary visual identification data on the eastern Australian C. taurus population show how spatial and temporal information on individual sharks can be collected without recourse to conventional tagging to address key questions about this species’ ecology and population biology.

Age does not influence the bone response to treadmill exercise in female rats.

PURPOSE Because it is believed that bone may respond to exercise differently at different ages, we compared bone responses in immature and mature rats after 12 wk of treadmill running. METHODS Twenty-two immature (5-wk-old) and 21 mature (17-wk-old) female Sprague Dawley rats were randomized into a running (trained, P = 10 immature, 9 mature) or a control group (controls, P = 12 immature, 12 mature) before sacrifice 12 wk later. Rats ran on a treadmill five times per week for 60-70 min at speeds up to 26 m.min. Both at baseline and after intervention, we measured total body, lumbar spine, and proximal femoral bone mineral, as well as total body soft tissue composition using dual-energy x-ray absorptiometry (DXA). After sacrificing the animals, we measured dynamic and static histomorphometry and three-point bending strength of the tibia. RESULTS Running training was associated with greater differences in tibial subperiosteal area, cortical cross-sectional area, peak load, stiffness, and moment of inertia in immature and mature rats (P < 0.05). The trained rats had greater periosteal bone formation rates (P < 0.01) than controls, but there was no difference in tibial trabecular bone histomorphometry. Similar running-related gains were seen in DXA lumbar spine area (P = 0.04) and bone mineral content (BMC; P = 0.03) at both ages. For total body bone area and BMC, the immature trained group increased significantly compared with controls (P < 0.05), whereas the mature trained group gained less than did controls (P < 0.01). CONCLUSION In this model, where a similar physical training program was performed by immature and mature female rats, we demonstrated that both age groups were sensitive to loading and that bone strength gains appeared to result more from changes in bone geometry than from improved material properties.

Growth Hormone Is Permissive for Skeletal Adaptation to Mechanical Loading

The Lewis dwarf (DW) rat was used as a model to test the hypothesis that growth hormone (GH) is permissive for new bone formation induced by mechanical loading in vivo. Adult female Lewis DW rats aged 6.2 ± 0.1 months (187 ± 18 g) were allocated to four vehicle groups (DW), four GH treatment groups at 32.5 μg/100 g body mass (DWGH1), and four GH treatment groups at 65 μg/100 g (DWGH2). Saline vehicle or GH was injected intraperitoneally (ip) at 6:30 p.m. and 6:30 a.m. before mechanical loading of tibias at 7:30 a.m. A single period of 300 cycles of four‐point bending was applied to right tibias at 2.0 Hz, and magnitudes of 24, 29, 38, or 48N were applied. Separate strain gauge analyses in 5 DW rats validated the selection of loading magnitudes. After loading, double‐label histomorphometry was used to assess bone formation at the periosteal surface (Ps.S) and endocortical surface (Ec.S) of tibias. Comparing left (unloaded) tibias among groups, GH treatment had no effect on bone formation. Bone formation in tibias in DW rats was insensitive to mechanical loading. At the Ec.S, mechanically induced lamellar bone formation increased in the DWGH2 group loaded at 48N (p < 0.05), and no significant increases in bone formation were observed among other groups. The percentage of tibias expressing woven bone formation (Wo.B) at the Ps.S was significantly greater in the DWGH groups compared with controls (p < 0.05). We concluded that GH influences loading‐related bone formation in a permissive manner and modulates the responsiveness of bone tissue to mechanical stimuli by changing thresholds for bone formation.