Extremely high conservation in the untranslated Region as well as the coding region of CNP mRNAs throughout elasmobranch species

C-type natriuretic peptide (CNP) is a crucial osmoregulatory hormone in elasmobranchs, participating in salt secretion and drinking. In contrast to teleosts and tetrapods in which the NP family is composed of a group of structurally related peptides, we have shown that CNP is the sole NP in sharks. In the present study, CNP cDNAs were cloned from four species of batoids, another group of elasmobranchs. The cloned batoid CNP precursors contained a plausible mature peptide of 22 amino acid residues that is identical to most shark CNP-22s, but five successive amino acids were consistently deleted in the prosegment compared with shark precursors, supporting the diphyletic classification of sharks and rays. In addition, molecular phylogenetic trees of CNP precursors were consistent with a diphyletic interpretation. Except for the deletion, the nucleotide and deduced amino acid sequences of the CNP cDNAs are extremely well-conserved among all elasmobranch species, even between sharks and rays. Surprisingly, high conservation is evident not only for the coding region, but also for the untranslated regions. It is most likely that the high conservation is due to the low nucleotide substitution rate in the elasmobranch genome, and high selection pressure. The 3′-untranslated region of the elasmobranch CNP cDNAs contained three to six repeats of the ATTTA motif that is associated with the regulation of mRNA stability and translation efficiency. Alternative polyadenylation sites were also found; the long 3′-untranslated region contains a core of ATTTA motifs while the short form has only one or no ATTTA motif, indicating that the post-transcriptional modification of mRNA is important for regulation of CNP synthesis. These characteristics in the 3′-untranslated region were conserved among all elasmobranch CNP cDNAs. Since CNP has been implicated as a fast-acting hormone to facilitate salt secretion from the rectal gland, the conserved 3′-untranslated region most likely contributes to rapid regulation of CNP synthesis in elasmobranchs in response to acute changes in internal and external environments.

Osmoregulation in elephant fish Callorhinchus Milii (Holocephali), with special reference to the rectal gland

Osmoregulatory mechanisms in holocephalan fishes are poorly understood except that these fish are known to conduct urea-based osmoregulation as in elasmobranchs. We, therefore, examined changes in plasma parameters of elephant fish Callorhinchus milii, after gradual transfer to concentrated (120%) or diluted (80%) seawater (SW). In control fish, plasma Na and urea concentrations were about 300 mmol l^–1 and 450 mmol l^–1, respectively. These values were equivalent to those of sharks and rays, but the plasma urea concentration of elephant fish was considerably higher than that reported for chimaeras, another holocephalan. After transfer to 120% SW, plasma osmolality, urea and ion concentrations were increased, whereas transfer to 80% SW resulted in a fall in these parameters. The rises in ion concentrations were notable after transfer to 120% SW, whereas urea concentration decreased predominantly following transfer to 80% SW. In elephant fish, we could not find a discrete rectal gland. Instead, approximately 10 tubular structures were located in the wall of post-valvular intestine. Each tubular structure was composed of a putative salt-secreting component consisting of a single-layered columnar epithelium, which was stained with an anti-Na⁺,K⁺-ATPase serum. Furthermore, Na⁺,K⁺-ATPase activity in the tubular structures was significantly increased after acute transfer of fish to concentrated SW (115%). These results suggest that the tubular structures are a rectal gland equivalent, functioning as a salt-secreting organ. Since the rectal gland of elephant fish is well developed compared to that of Southern chimaera, the salt-secreting ability may be higher in elephant fish than chimaeras, which may account for the lower plasma NaCl concentration in elephant fish compared to other chimaeras. Since elephant fish have also attracted attention from a viewpoint of genome science, the availability of fish for physiological studies will make this species an excellent model in holocephalan fish group.

Osmoregulation in elephant fish, CALLORHYNCHUS MILLII (HOLOCEPHALI)

Osmoregulatory mechanisms in holocephalan fishes are unknown except that they conduct urea-based osmoregulation as in elasmobranchs. We, therefore, examined changes in plasma parameters of elephant fish, Callorhynchus millii, after gradual transfer to concentrated (120%) or diluted (80%) seawater (SW). In control fish, plasma Na and urea concentrations were about 300mM and 450mM, respectively. These values were equivalent to those of sharks and rays, but the plasma urea concentration of elephant fish was considerably higher than that reported for chimaeras, another holocephalan. After transfer to 120% SW, the plasma Na concentration markedly increased, while a conspicuous decrease in plasmaurea concentration was observed following transfer to 80% SW. In elephant fish, we could not find a discrete rectal gland. Instead, approximately 10 tubular structures were located in the wall of post-valvular intestine. Each tubular structure was composed of a putative salt-secreting component consisting of a single-layered columnar epithelium, which was stained with anti-Na+,K±ATPase serum. It is most likely that the tubular structures in the posterior intestine represent a primitive form of the rectal gland in elephant fish. In addition, we have identified two C-type natriuretic peptides (CNPs) from the heart and brain of elephant fish, which may contribute to the control of NaCl excretion from the rectal gland of elephant fish as it does in elasmobranchs.

Microscopic modifications of the female reproductive tissues of Mustelus antarcticus

The ovarian follicles and oviducal glands have structural organisations similar to other chondrichthyans. Sperm are stored in the oviducal gland of all maturing and mature animals throughout the year and throughout pregnancy. Microscopic features of the uterine epithelium suggest nutrients are supplied to developing embryos without placenta formation.

Using omeprazole to link the components of the post-prandial alkaline tide in the spiny dogfish, Squalus acanthias

After a meal, dogfish exhibit a metabolic alkalosis in the bloodstream and a marked excretion of basic equivalents across the gills to the external seawater. We used the H⁺, K⁺-ATPase pump inhibitor omeprazole to determine whether these post-prandial alkaline tide events were linked to secretion of H⁺ (accompanied by Cl^–) in the stomach. Sharks were fitted with indwelling stomach tubes for pretreatment with omeprazole (five doses of 5mg omeprazole per kilogram over 48 h) or comparable volumes of vehicle (saline containing 2% DMSO) and for sampling of gastric chyme. Fish were then fed an involuntary meal by means of the stomach tube consisting of minced flatfish muscle (2% of body mass) suspended in saline (4% of body mass total volume). Omeprazole pretreatment delayed the post-prandial acidification of the gastric chyme, slowed the rise in Cl^– concentration of the chyme and altered the patterns of other ions, indicating inhibition of H⁺ and accompanying Cl^– secretion. Omeprazole also greatly attenuated the rise in arterial pH and bicarbonate concentrations and reduced the net excretion of basic equivalents to the water by 56% over 48h. Arterial blood CO₂ pressure and plasma ions were not substantially altered. These results indicate that elevated gastric H⁺ secretion (as HCl) in the digestive process is the major cause of the systemic metabolic alkalosis and the accompanying rise in base excretion across the gills that constitute the alkaline tide in the dogfish.

Unusual suspects : a newspaper's coverage of a scuba diving rescue and journalism's role in narrating Australia

Brisbane’s Courier-Mail newspaper ran a fantastic story a couple of years ago about a couple left at sea behind by their tour boat, after going scuba diving. The story suggested American diver Allyson Dalton and her British partner Richard Neely ignored advice when they ventured away from a lagoon where the tour boat was anchored. But the focus was on how Neely and Dalton survived by treading water for 19 hours at Paradise Reef, part of Queensland’s Great Barrier Reef, not so much (yet) on how fortunate they were not to be attacked by sharks. It would not be long, however, before that old journalistic maxim that implores practitioners to ‘question every assertion, doubt every claim’ shaped the reportage into an extended narrative about chequebook journalism, credibility, and culpability.

The scuba dive rescue story analysis presented here reflects contemporary journalism’s role in the formation of ideas about cultural value and character, and in more complex determinations of who gets a participatory stake in the formation of national narratives. As such, the article concludes with some signposts toward a critical approach to journalism-centred studies of culture in Australia.

The diving behaviour of green turtles undertaking oceanic migration to and from Ascension Island: dive durations, dive profiles and depth distribution

Satellite telemetry was used to record the submergence duration of green turtles (Chelonia mydas) as they migrated from Ascension Island to Brazil (N=12 individuals) while time/depth recorders (TDRs) were used to examine the depth distribution and dive profiles of individuals returning to Ascension Island to nest after experimental displacement (N=5 individuals). Satellite telemetry revealed that most submergences were short (<5 min) but that some submergences were longer (>20 min), particularly at night. TDRs revealed that much of the time was spent conducting short (2–4 min), shallow (approximately 0.9–1.5 m) dives, consistent with predictions for optimisation of near-surface travelling, while long (typically 20–30 min), deep (typically 10–20 m) dives had a distinctive profile found in other marine reptiles. These results suggest that green turtles crossing the Atlantic do not behave invariantly, but instead alternate between periods of travelling just beneath the surface and diving deeper. These deep dives may have evolved to reduce silhouetting against the surface, which would make turtles more susceptible to visual predators such as large sharks.

Convergent evolution in locomotory patterns of flying and swimming animals

Locomotion is one of the major energetic costs faced by animals and various strategies have evolved to reduce its cost. Birds use interspersed periods of flapping and gliding to reduce the mechanical requirements of level flight while undergoing cyclical changes in flight altitude, known as undulating flight. Here we equipped free-ranging marine vertebrates with accelerometers and demonstrate that gait patterns resembling undulating flight occur in four marine vertebrate species comprising sharks and pinnipeds. Both sharks and pinnipeds display intermittent gliding interspersed with powered locomotion. We suggest, that the convergent use of similar gait patterns by distinct groups of animals points to universal physical and physiological principles that operate beyond taxonomic limits and shape common solutions to increase energetic efficiency. Energetically expensive large-scale migrations performed by many vertebrates provide common selection pressure for efficient locomotion, with potential for the convergence of locomotory strategies by a wide variety of species.

Environmental context explains Lévy and Brownian movement patterns of marine predators

An optimal search theory, the so-called Lévy-flight foraging hypothesis1, predicts that predators should adopt search strategies known as Lévy flights where prey is sparse and distributed unpredictably, but that Brownian movement is sufficiently efficient for locating abundant prey2, 3, 4. Empirical studies have generated controversy because the accuracy of statistical methods that have been used to identify Lévy behaviour has recently been questioned5, 6. Consequently, whether foragers exhibit Lévy flights in the wild remains unclear. Crucially, moreover, it has not been tested whether observed movement patterns across natural landscapes having different expected resource distributions conform to the theory’s central predictions. Here we use maximum-likelihood methods to test for Lévy patterns in relation to environmental gradients in the largest animal movement data set assembled for this purpose. Strong support was found for Lévy search patterns across 14 species of open-ocean predatory fish (sharks, tuna, billfish and ocean sunfish), with some individuals switching between Lévy and Brownian movement as they traversed different habitat types. We tested the spatial occurrence of these two principal patterns and found Lévy behaviour to be associated with less productive waters (sparser prey) and Brownian movements to be associated with productive shelf or convergence-front habitats (abundant prey). These results are consistent with the Lévy-flight foraging hypothesis1, 7, supporting the contention8, 9 that organism search strategies naturally evolved in such a way that they exploit optimal Lévy patterns.

Asynchrony and regional differences in the reproductive cycle of the greenback stingaree Urolophus viridis from south-eastern Australia

Determining the periodicity of the reproductive cycle in chondrichthyan species when the population is recruiting asynchronously, as found for Urolopus viridis, can be problematic. The reproductive cycle generally requires distinguishable trends in reproductive indices across the population. The present study utilised other similar and sympatric urolophid species with synchronous reproductive cycles. Through data collected in the present study and comparisons of maximum total length (TL), periodicity of egg and embryo in utero, ovarian cycles, largest ovarian follicle diameter, and matrotrophic contribution (percentage increase from egg to embryo after maternal histotroph supplement) from similar studies, an annual reproductive cycle can be hypothesised. Sampling across two separate regions of Lakes Entrance (LE) and Western Bass Strait (WBS), U. viridis also showed regionality in several of the reproductive indices. Maximum TL and mass for females, mean size-at-birth, and female size-at-maturity and size-at-maternity in LE were markedly smaller than in WBS. In both regions litter size (1–2) increased with TL, with an exception of one female in WBS producing a litter of 3 which could be attributed to the larger TL. The implication of U. viridis producing such few young annually is they have the lowest biological productivity of any urolophid species in south-eastern Australia.

Protected species use of a coastal marine migratory corridor connecting marine protected areas

The establishment of protected corridors linking the breeding and foraging grounds of many migratory species remains deficient, particularly in the world's oceans. For example, Australia has recently established a network of Commonwealth Marine Reserves, supplementing existing State reserves, to protect a wide range of resident and migratory marine species; however, the routes used by mobile species to access these sites are often unknown. The flatback marine turtle (Natator depressus) is endemic to the continental shelf of Australia, yet information is not available about how this species uses the marine area. We used a geospatial approach to delineate a coastal corridor from 73 adult female flatback postnesting migratory tracks from four rookeries along the north-west coast of Australia. A core corridor of 1,150 km length and 30,800 km2 area was defined, of which 52 % fell within 11 reserves, leaving 48 % (of equivalent size to several Commonwealth Reserves) of the corridor outside of the reserve network. Despite limited data being available for other marine wildlife in this region, humpback whale migratory tracks overlapped with 96 % of the core corridor, while the tracks of three other species overlapped by 5-10 % (blue whales, olive ridley turtles, whale sharks). The overlap in the distribution ranges of at least 20 other marine vertebrates (dugong, cetaceans, marine turtles, sea snakes, crocodiles, sharks) with the corridor also imply potential use. In conclusion, this study provides valuable information towards proposing new locations requiring protection, as well as identifying high-priority network linkages between existing marine protected areas. © 2014 Springer-Verlag Berlin Heidelberg.

Use of long-distance migration patterns of an endangered species to inform conservation planning for the world's largest marine protected area

Large marine protected areas (MPAs), each hundreds of thousands of square kilometers, have been set up by governments around the world over the last decade as part of efforts to reduce ocean biodiversity declines, yet their efficacy is hotly debated. The Chagos Archipelago MPA (640,000 km2) (Indian Ocean) lies at the heart of this debate. We conducted the first satellite tracking of a migratory species, the green turtle (Chelonia mydas), within the MPA and assessed the species' use of protected versus unprotected areas. We developed an approach to estimate length of residence within the MPA that may have utility across migratory taxa including tuna and sharks. We recorded the longest ever published migration for an adult cheloniid turtle (3979 km). Seven of 8 tracked individuals migrated to distant foraging grounds, often ≥1000 km outside the MPA. One turtle traveled to foraging grounds within the MPA. Thus, networks of small MPAs, developed synergistically with larger MPAs, may increase the amount of time migrating species spend within protected areas. The MPA will protect turtles during the breeding season and will protect some turtles on their foraging grounds within the MPA and others during the first part of their long-distance postbreeding oceanic migrations. International cooperation will be needed to develop the network of small MPAs needed to supplement the Chagos Archipelago MPA.

How small-scale variation in oyster reef patchiness influences predation on bivalves

As oyster fishing continues to degrade reef habitat along the US Atlantic coast, oyster reefs appear increasingly fragmented on small spatial scales. In outdoor mesocosms, experiments tested how consumption of representatives of 4 different bivalve guilds by each of 3 mesopredators varies between continuous and fine-scale patches of oyster reef habitat. The mesopredator that fed least (stone crab) exhibited no detectable change in consumption on any bivalve (ribbed mussel, bay scallop, hard clam, and 3 size classes of eastern oyster). Consumption of bay scallops by both blue crabs and sheepshead fish was greater in small patches than in continuous oyster reef habitat. Of the bivalve guilds tested, only the scallop possesses swimming motility sufficient to reduce predation, an escape response that would likely leave the bivalve protected within structured habitat in larger continuous oyster reefs. Sheepshead consumed more small oysters in the continuous habitat than in the fine patches, while no other predator-prey interaction exhibited differential feeding as a function of habitat patchiness. Consequently, predation by mesopredators on bivalves can vary with the scale of oyster reef patchiness, but this process may depend upon the bivalve guild. Understanding the role of habitat patchiness on fine scales may be increasingly important in view of the declines in apex predatory sharks leading to mesopredator release, and global climate change directly and indirectly enhancing stone crab abundances, thereby increasing potential predation on bivalves.

A new method for resolving uncertainty of energy requirements in large water breathers: The 'mega-flume' seagoing swim-tunnel respirometer

Body size is a key determinant of metabolic rate, but logistical constraints have led to a paucity of energetics measurements from large water-breathing animals. As a result, estimating energy requirements of large fish generally relies on extrapolation of metabolic rate from individuals of lower body mass using allometric relationships that are notoriously variable. Swim-tunnel respirometry is the 'gold standard' for measuring active metabolic rates in water-breathing animals, yet previous data are entirely derived from body masses <10 kg - at least one order of magnitude lower than the body masses of many top-order marine predators. Here, we describe the design and testing of a new method for measuring metabolic rates of large water-breathing animals: a c. 26 000 L seagoing 'mega-flume' swim-tunnel respirometer. We measured the swimming metabolic rate of a 2·1-m, 36-kg zebra shark Stegostoma fasciatum within this new mega-flume and compared the results to data we collected from other S. fasciatum (3·8-47·7 kg body mass) swimming in static respirometers and previously published measurements of active metabolic rate measurements from other shark species. The mega-flume performed well during initial tests, with intra- and interspecific comparisons suggesting accurate metabolic rate measurements can be obtained with this new tool. Inclusion of our data showed that the scaling exponent of active metabolic rate with mass for sharks ranging from 0·13 to 47·7 kg was 0·79; a similar value to previous estimates for resting metabolic rates in smaller fishes. We describe the operation and usefulness of this new method in the context of our current uncertainties surrounding energy requirements of large water-breathing animals. We also highlight the sensitivity of mass-extrapolated energetic estimates in large aquatic animals and discuss the consequences for predicting ecosystem impacts such as trophic cascades.

Examining the functional role of current area closures used for the conservation of an overexploited and highly mobile fishery species

Protecting essential habitats through the implementation of area closures has been recognized as a useful management tool for rebuilding overfished populations and minimizing habitat degradation. School shark (Galeorhinus galeus) have suffered significant stock declines in Australia; however, recent stock assessments suggest the population may have stabilized and the protection of closed nursery areas has been identified as a key management strategy to rebuilding their numbers. Young-of-The-year (YOY) and juvenile G. galeus were acoustically tagged and monitored to determine ontogenetic differences in residency and seasonal use of an important protected nursery area (Shark Refuge Area or SRA) in southeastern Tasmania. BothYOYand juvenile G. galeus showed a distinct seasonal pattern of occurrence in the SRAwith most departing the area during winter and only a small proportion of YOY (33%) and no juveniles returning the following spring, suggesting areas outside the SRA may also be important during these early life-history stages. While these behaviors confirm SRAs continue to function as essential habitat during G. galeus early life history, evidence of YOY and juveniles emigrating from these areas within their first 1-2 years and the fact that few YOY return suggest that these areas may only afford protection for a more limited amount of time than previously thought. Determining the importance of neighbouring coastal waters and maintaining the use of traditional fisheries management tools are therefore required to ensure effective conservation of G. galeus during early life history.