Comparing external and internal dorsal-spine bands to interpret the age and growth of the giant lantern shark, Etmopterus baxteri (Squaliformes: Etmopteridae)

The giant lantern shark, Etmopterus baxteri, is taken as bycatch of commercial fisheries that operate in deepwater off southeastern Australia. Bands on the second dorsal spine were used to obtain age estimates. The number of bands on the external surface of the spine and within the inner dentine layer increased with animal length. Most spines had more bands on the external surface, and the rate of band formation was significantly different between the external surface and the inner dentine layer. Females had a maximum of 57 external bands and 26 internal bands, while males had up to 48 external bands and 22 internal bands. Age estimates from external bands suggest maturity (A ₅₀) at 20 years for males and 30 years for females. Internal band age estimates suggest maturity at 10.5 years for males and 11.5 years for females. Although there is a large discrepancy between these two preliminary (i.e., unvalidated) age estimates, they both suggest that E. baxteri is a long-lived and late maturing species that is likely to be susceptible to over fishing.

Bad habits and prosthetic performances : negotiation of individuality and embodiment of social status in Australian shark fishing

Anthropological discussion of individuality, as a component of masculinity, has tended to focus on either the performance and championing of autonomy in the West (e.g., Kapferer) or the manner in which people in non-Western contexts become explicitly manifest through relationships with others (e.g., Strathern). In this paper, I consider an atypical example of masculine identity by describing intimate interpersonal relationships between Australian commercial shark boat skippers and their young deckhands. As in other Western fisheries (e.g., Icelandic), economic success and physical safety are promoted through synergism among fishers. In the Australian case, however, the degree of corporeal cooperation is so extreme that deckhands resemble living prostheses of their skipper, embodying their peripheral socio-productive status. I consider this bond in the context of the Australian ethos of masculinity, in which displays of "individuality" are key. However, for young deckhands, their prosthetic role can compromise their passage into manhood.

Managing shark fishermen in southern Australia : a critique

This paper analyses effects of a shift from input to output controls in Australia's Southern Shark Fishery. We show that the use of two management tools--individual transferable quotas and a "partnership approach"--was flawed and argue that primary contributing causes were the unjustified expectation that quota management would serve as a [`]technical fix' to a variety of presumed problems, the discounting of social effects and the extreme lack of stability in the organizational structure within which this fishery was situated.

Assessment of shark cartilage extract from two commercially viable species

This study provided initial evidence that extract derived from the cartilage of two commercially available Australian shark species, may potentially, be effective in the inhibition of tumour growth, whilst also showing that the species and maturity level, but not the gender of the shark, influenced the amount of extract obtained.

Reproduction and ageing of Australian holocephalans and white-fin swell shark

The holocephalans are a slow growing, long lived group with a conservative life history strategy and require similarly conservative fishery management strategies to ensure their sustainable exploitation. White-fin swell shark are relatively short lived, highly fecund and likely to be more capable of withstanding intensive fishing.

Integrating network analysis, sensor tags, and observation to understand shark ecology and behavior

Group living in animals is a well-studied phenomenon, having been documented extensively in a wide range of terrestrial, freshwater, and marine species. Although social dynamics are complex across space and time, recent technological and analytical advances enable deeper understanding of their nature and ecological implications. While for some taxa, a great deal of information is known regarding the mechanistic underpinnings of these social processes, knowledge of these mechanisms in elasmobranchs is lacking. Here, we used an integrative and novel combination of direct observation, accelerometer biologgers, and recent advances in network analysis to better understand the mechanistic bases of individual-level differences in sociality (leadership, network attributes) and diel patterns of locomotor activity in a widespread marine predator, the lemon shark (Negaprion brevirostris). We found that dynamic models of interaction based on Markov chains can accurately predict juvenile lemon shark social behavior and that lemon sharks did not occupy consistent positions within their network. Lemon sharks did however preferentially associate with specific group members, by sex as well as by similarity or nonsimilarity for a number of behavioral (nonsimilarity: leadership) and locomotor traits (similarity: proportion of time swimming "fast," mean swim duration; nonsimilarity: proportion of swimming bursts/transitions between activity states). Our study provides some of the first information on the mechanistic bases of group living and personality in sharks and further, a potential experimental approach for studying fine-scale differences in behavior and locomotor patterns in difficult-to-study organisms.

Decadal decline in demersal fish biomass coincident with a prolonged drought and the introduction of an exotic starfish

Between 1990 and 2011, Port Phillip Bay in southern Australia experienced 2 major ecological disturbances: a prolonged drought from 1997 to 2010, and the introduction of the invasive starfish, Asterias amurensis. The drought reduced land-based nitrogen inputs by 64%, and the biomass of A. amurensis in the deep centre of the bay peaked at 56% of the resident fish biomass in 2000. The impacts of these disturbances on fish were assessed using a demersal trawl time-series spanning 2 decades (1990 to 2011). The timing and spatial extent of changes to fish biomass were analysed using ANCOVA and change point analysis. During the drought, fish biomass declined by 69% in the deep centre of the bay, by 50% at intermediate depths, and showed no significant change around the shallow fringes. This spatial pattern is consistent with hydrodynamic modelling, which suggests that during the drought a greater proportion of the (lower) nitrogen input was retained near the coastal fringe. Most of the decline in fish biomass was attributed to the cumulative effects of reduced productivity during the 12 yr drought. However, declines in 3 species in the deep region were attributed to competition with A. amurensis. Each of these species exhibited high dietary overlap with A. amurensis and displayed sharp declines in biomass coinciding with the peak abundance of A. amurensis in 2000.

Immunolocalisation of sodium/proton exchanger-like proteins in the gills of elasmobranchs

Na⁺/H⁺ exchangers are integral membrane proteins that exchange Na⁺ and H⁺ across cell membranes. The Na⁺/H⁺ exchangers 2 and 3 are epithelial isoforms in mammals and contribute to acid–base homeostasis. The gills of fishes, including elasmobranchs, are also associated with acid/base balance, and are probably the primary acid/base regulatory organ. This study examines the presence of Na⁺/H⁺ exchangers 2 and 3 using immunohistochemistry and immunoblotting in the gills of four species of elasmobranchs, the banjo ray (Trygonorrhina fasciata), southern eagle ray (Myliobatis australis), the gummy shark (Mustelus antarcticus) and the Australian angel shark (Squatina australis) using heterologous antibodies. Na⁺/H⁺ exchanger 2-like immunoreactivity was observed in the gills of the banjo ray, eagle ray and angel shark. In the banjo and eagle rays, this Na⁺/H⁺ exchanger-like immunoreactivity co-localised with immunoreactivity to Na⁺/K⁺-ATPase, a marker for the mitochondrial-rich cells of fishes. Na⁺/H⁺ exchanger 3-like immunoreactivity was only observed in the gills of the angel and gummy sharks, some Na⁺/H⁺ exchanger 3-like cells also showed Na⁺/K⁺-ATPase immunoreactivity. However, immunoblotting of banjo and eagle ray gill membranes demonstrated Na⁺/H⁺ exchanger 3-like immunoreactivity, which was not consistent with the immunohistochemical results. These data demonstrate the presence of epithelial Na⁺/H⁺ exchangers 2 and 3 in the gills of elasmobranchs and a link with acid/base regulation is suggested.

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.