Triakis

Abstract: Patterns of red muscle strain and activation were examined at three positions along the body (0.42, 0.61 and 0.72 L, where L is total body length) and correlated with simultaneous measurements of midline kinematics during steady swimming (approx. 1.0 L s(-1)) in the leopard shark Triakis semifasciata. Analysis of lateral displacement along the body indicates that the leopard shark is a subcarangiform swimmer. Longitudinal variation in red muscle strain was observed with strain amplitudes ranging from +/-3.9% in the anterior, +/-6.6% in the mid, to +/-4.8% in the posterior body position. Strain was in-phase with local midline curvature. In addition, strain amplitude calculated from a bending beam model closely matched strain measured using sonomicrometry at all three body positions. There is a high degree of similarity in red muscle activation patterns along the body between the leopard shark and many fish species, in that the onset of activation occurs during muscle lengthening while offset occurs during muscle shortening. However, we found no significant longitudinal variation in the EMG/strain phase relationship and duty cycles, with onset of muscle activation occurring at 51.4-61.8 degrees and offset at 159.7-165.2 degrees (90 degrees is peak length). This consistent pattern of activation suggests that red muscle along the entire length of the body contributes to positive power production. Thus, sharks such as Triakis may have no regional specialization in red muscle function like that seen in many teleosts, which may indicate that the evolution of differential muscle function along the body occurred after the divergence of cartilaginous and bony fishes.

Abstract: The presence of a C-type natriuretic peptide (CNP) has been reported in the brain of mammals, birds, amphibians and teleost fishes, mostly as a 22-residue peptide (CNP-22). In the present study, we attempted to isolate natriuretic peptides from an elasmobranch, Triakis scyllia, using a chick rectum-relaxant assay, and different molecular forms of CNP were found in the brain and heart. Only CNP-22 was recovered from the brain, as is the case in other vertebrates. A large amount of prohormone (proCNP or CNP-115) and small amounts of its C-terminal peptides (CNP-38 and CNP-39) were isolated from the atrium and ventricle, however. No CNP-22 was recovered from the heart. Natriuretic peptides other than CNP were not isolated from Triakis heart and brain by the rectum-relaxant assay. The 22 residues at the C-terminal region of proCNP, i.e. CNP-22, were well conserved when Triakis and mammals were compared, although the sequence homology of the N-terminal segment of proCNP was very low. Not only was CNP-22 identical but the N-terminal segments of proCNP were also quite similar when Triakis and another elasmobranch, Scyliorhinus canicula, were compared. These data suggest that, in elasmobranchs, CNP is a primary hormone in the natriuretic peptide family, and also that CNP is processed differently in the brain and heart.

Abstract: The demography, spatial distribution, and movement patterns of leopard sharks (Triakis semifas- ciata) aggregating near the head of a submarine canyon in La Jolla, California, USA, were investigated to resolve the causal explanations for this and similar shark aggre- gations. All sharks sampled from the aggregation site (n0140) were sexually mature and 97.1 % were female. Aerial photographs taken during tethered balloon surveys revealed high densities of milling sharks of up to 5470 sharks ha −1 . Eight sharks were each tagged with a continuous acoustic transmitter and manually tracked without interruption for up to 48 h. Sharks exhibited strong site-fidelity and were generally confined to a divergence (shadow) zone of low wave energy, which results from wave refraction over the steep bathymetric contours of the submarine canyon. Within this diver- gence zone, the movements of sharks were strongly localized over the seismically active Rose Canyon Fault. Tracked sharks spent most of their time in shallow water (≤2 m for 71.0 % and ≤10 m for 95.9 % of time), with some dispersing to deeper (max: 53.9m) andcooler (min: 12.7 °C) water after sunset, subsequently returning by sunrise. These findings suggest multiple functions of this aggregation and that the mechanism controlling its formation, maintenance, and dissolution is complex and rooted in the sharks' variable response to numerous confounding environmental factors.

Abstract: The spotted gully shark, Triakis megalopterus, was sampled op- portunistically over a 12-year period from catches of shore and ski-boat fish- ermen using hooks and lines. Most specimens (89.6%) were taken from rocky reefs less than 10 m deep, 8% were caught at 11-20 m, and only 2.4% were recorded from waters more than 20 m deep. The reproductive biology of 35 males and 87 females was examined. The spotted gully shark exhibits apla- cental viviparity. Size at 50% maturity for males is ca. 1320 mm total length (TL) and for females ca. 1450 mm TL. Maximum sizes recorded here were 1520 mm TL for males and 2075 mm TL for females. Gestation appears to last 19-21 months. The female repro- ductive cycle may be 2-3 years, depend- ing on the time between pregnancies. The sex ratio of embryos was found to be 1:1 but the postpartum male:female ratio was 1:2.5. Size at birth was esti- mated to be 420-450 mm TL. The smallest free-swimming individual re- corded was 576 mm TL. Number of embryos per pregnancy ranged between 5 and 15, with a mean of 9.7. A total of 110 stomachs were examined in the feed- ing study. Diet changed with increase in shark size. Small sharks (<1 m) preyed mainly on Cape rock crabs, Plagusia chabrus (78% of mass), whereas sharks of 1-1.4 m preyed largely on Cape rock crabs (48%) and cephalopods (33%). Te- leosts were more important for sharks larger than 1.4 m (54%); most of these prey were associated with rocky reefs.