Ontogeny of head and caudal fin shape of an apex marine predator: The tiger shark (Galeocerdo cuvier)

How morphology changes with size can have profound effects on the life history and ecology of an animal. For apex predators that can impact higher level ecosystem processes, such changes may have consequences for other species. Tiger sharks (Galeocerdo cuvier) are an apex predator in tropical seas, and, as adults, are highly migratory. However, little is known about ontogenetic changes in their body form, especially in relation to two aspects of shape that influence locomotion (caudal fin) and feeding (head shape). We captured digital images of the heads and caudal fins of live tiger sharks from Southern Florida and the Bahamas ranging in body size (hence age), and quantified shape of each using elliptical Fourier analysis. This revealed changes in the shape of the head and caudal fin of tiger sharks across ontogeny. Smaller juvenile tiger sharks show an asymmetrical tail with the dorsal (upper) lobe being substantially larger than the ventral (lower) lobe, and transition to more symmetrical tail in larger adults, although the upper lobe remains relatively larger in adults. The heads of juvenile tiger sharks are more conical, which transition to relatively broader heads over ontogeny. We interpret these changes as a result of two ecological transitions. First, adult tiger sharks can undertake extensive migrations and a more symmetrical tail could be more efficient for swimming longer distances, although we did not test this possibility. Second, adult tiger sharks expand their diet to consume larger and more diverse prey with age (turtles, mammals, and elasmobranchs), which requires substantially greater bite area and force to process. In contrast, juvenile tiger sharks consume smaller prey, such as fishes, crustaceans, and invertebrates. Our data reveal significant morphological shifts in an apex predator, which could have effects for other species that tiger sharks consume and interact with. J. Morphol. 277:556–564, 2016. © 2016 Wiley Periodicals, Inc.     

Body Form and Locomotion in Sharks

A revised interpretation of the mode of action of the heterocercaltail in sharks shows that the upturned tail axis tends to producea thrust directed downwards behind the centre of balance ofthe fish and thus gives a moment turning the head upwards. Thisis countered in two ways—by the rotation of the tail alongits longitudinal axis during each lateral beat, and throughthe action of the ventral hypochordal lobe. The shape of thetail and the mode of action of the tail in all sharks so farconsidered reflects a balance between these three factors, inall of them the net effect being the production of a forwardthrust from the tail that passes directly through the centreof balance of the fiish. There is normally therefore no tendencyfor the fish to turn around the centre of balance in a sagittalplane but there is a net sinking effect that is countered bythe planning effect of the pectoral fins and the ventral surfaceof the head. A study of 56 species of sharks shows that the tail is constructedaccording to a remarkably consistent common plan, the extremesbeing the high angled rather symmetrical tail of pelagic sharkssuch as hums, Lamna and Rhincodon and the straight tails ofbenthic sharks such as Ginglymostoma in which a ventral hypochordallobe is absent. When the general body shape of sharks, includingthe position of insertion of the median and paired fins andthe pattern of growth of fin surface areas is considered, theuniformity of the shark body plan and locomolor function isfurther emphasised. Four patterns of body form in sharks are recognised: 1) Thefast swimming pelagic sharks and the whale sharks have a tailwith a high aspect ratio, a conical head, a lateral fluke onthe caudal peduncle. 2) The generalised sharks typified by theCarcharhinidae, have lower heterocercal angles, a flattenedventral surface on the head and lack the caudal fluke. 3) Thedemersal sharks typified by the catsharks (Scyliorhinidae) havea very low, almost straight tail. The ventral hypochordal lobeis absent and the first dorsal fin is posterior in position.4) The squalomorph sharks are distinct in the absence of theanal fin, presence of a marked epicaudal lobe in the tail andoften an elevated insertion of the pectorals. The anal and second dorsal fins are always the smallest finsand the pectorals grow at the fastest rate. In general thereis an inverse relationship between size and rale of growth ofall fins and the ventral surface of the head. In hammerheadsthe growth data confirms that the head has a significant planingaction in swimming. The pectoral, second dorsal and anal finsshow an extreme constancy of position of insertion in all sharksstudied. The locomotor mechanism of sharks is adapted for anefficient cruising swimming but at the same time, the potentialinstability in the sagittal plan allows for the production ofturning moments that are used in attack and feeding.     

Anatomy and muscle activity of the dorsal fins in bamboo sharks and spiny dogfish during turning maneuvers

Stability and procured instability characterize two opposing types of swimming, steady and maneuvering, respectively. Fins can be used to manipulate flow to adjust stability during swimming maneuvers either actively using muscle control or passively by structural control. The function of the dorsal fins during turning maneuvering in two shark species with different swimming modes is investigated here using musculoskeletal anatomy and muscle function. White‐spotted bamboo sharks are a benthic species that inhabits complex reef habitats and thus have high requirements for maneuverability. Spiny dogfish occupy a variety of coastal and continental shelf habitats and spend relatively more time cruising in open water. These species differ in dorsal fin morphology and fin position along the body. Bamboo sharks have a larger second dorsal fin area and proportionally more muscle insertion into both dorsal fins. The basal and radial pterygiophores are plate‐like structures in spiny dogfish and are nearly indistinguishable from one another. In contrast, bamboo sharks lack basal pterygiophores, while the radial pterygiophores form two rows of elongated rectangular elements that articulate with one another. The dorsal fin muscles are composed of a large muscle mass that extends over the ceratotrichia overlying the radials in spiny dogfish. However, in bamboo sharks, the muscle mass is divided into multiple distinct muscles that insert onto the ceratotrichia. During turning maneuvers, the dorsal fin muscles are active in both species with no differences in onset between fin sides. Spiny dogfish have longer burst durations on the outer fin side, which is consistent with opposing resistance to the medium. In bamboo sharks, bilateral activation of the dorsal in muscles could also be stiffening the fin throughout the turn. Thus, dogfish sharks passively stiffen the dorsal fin structurally and functionally, while bamboo sharks have more flexible dorsal fins, which result from a steady swimming trade off. J. Morphol. 274:1288–1298, 2013. © 2013 Wiley Periodicals, Inc.     

Effects of Smart Position Only (SPOT) tag deployment on white sharks Carcharodon carcharias in South Africa

We present 15 individual cases of sub-adult white sharks that were SPOT tagged in South Africa from 2003-2004 and have been re-sighted as recently as 2011. Our observations suggest SPOT tags can cause permanent cosmetic and structural damage to white shark dorsal fins depending on the duration of tag attachment. SPOT tags that detached within 12-24 months did not cause long term damage to the dorsal fin other than pigmentation scarring. Within 12 months of deployment, tag fouling can occur. After 24 months of deployment permanent damage to the dorsal fin occurred. A shark survived this prolonged attachment and there seems little compromise on the animal's long term survival and resultant body growth. This is the first investigation detailing the long term effects of SPOT deployment on the dorsal fin of white sharks.     

Oceanic sharks clean at coastal seamount

Interactions between pelagic thresher sharks (Alopias pelagicus) and cleaner wrasse were investigated at a seamount in the Philippines. Cleaning associations between sharks and teleosts are poorly understood, but the observable interactions seen at this site may explain why these mainly oceanic sharks regularly venture into shallow coastal waters where they are vulnerable to disturbance from human activity. From 1,230 hours of observations recorded by remote video camera between July 2005 and December 2009, 97 cleaner-thresher shark events were analyzed, 19 of which were interrupted. Observations of pelagic thresher sharks interacting with cleaners at the seamount were recorded at all times of day but their frequency declined gradually from morning until evening. Cleaners showed preferences for foraging on specific areas of a thresher shark's body. For all events combined, cleaners were observed to conduct 2,757 inspections, of which 33.9% took place on the shark's pelvis, 23.3% on the pectoral fins, 22.3% on the caudal fin, 8.6% on the body, 8.3% on the head, 2.1% on the dorsal fin, and 1.5% on the gills respectively. Cleaners did not preferentially inspect thresher sharks by time of day or by shark sex, but there was a direct correlation between the amount of time a thresher shark spent at a cleaning station and the number of inspections it received. Thresher shark clients modified their behavior by "circular-stance-swimming," presumably to facilitate cleaner inspections. The cleaner-thresher shark association reflected some of the known behavioral trends in the cleaner-reef teleost system since cleaners appeared to forage selectively on shark clients. Evidence is mounting that in addition to acting as social refuges and foraging grounds for large visiting marine predators, seamounts may also support pelagic ecology by functioning as cleaning stations for oceanic sharks and rays.     

Scaling of fast-start performance and its thermal dependence in mummichog Fundulus heteroclitus

Fast-start predator-escape performance and its sensitivity to temperature (24, 30, and 36°C) were evaluated in mummichog Fundulus heteroclitus across a range of body sizes spanning YOY to adult (35–68 mm standard length). Mummichogs exhibit isometry of body dimensions and areas of the dorsal and anal fins but negative allometry of the caudal fin area. These scaling relationships are consistent with observed decreases in fast-start angular velocities with increasing body size. Linear velocity, on the contrary, does not vary with size, and both large and small mummichogs are capable of traversing similar distances in a given amount of time. In addition, temperature influences fast-start performance in similar ways over the size range, though the magnitude of the effect varies with size for some performance measures. In general, fast-start performance increases with test temperature, but mummichogs acclimated to warmer temperatures exhibit lower performance at each test temperature. Altogether, our results suggest that mummichogs across the adult size range may suffer decreases in their predator-escape performance as increasing sea temperatures combine with short-term temperature fluctuations in the estuaries these fish occupy.     

Correlated evolution of body and fin morphology in the cichlid fishes

Body and fin shapes are chief determinants of swimming performance in fishes. Different configurations of body and fin shapes can suit different locomotor specializations. The success of any configuration is dependent upon the hydrodynamic interactions between body and fins. Despite the importance of body–fin interactions for swimming, there are few data indicating whether body and fin configurations evolve in concert, or whether these structures vary independently. The cichlid fishes are a diverse family whose well‐studied phylogenetic relationships make them ideal for the study of macroevolution of ecomorphology. This study measured body, and caudal and median fin morphology from radiographs of 131 cichlid genera, using morphometrics and phylogenetic comparative methods to determine whether these traits exhibit correlated evolution. Partial least squares canonical analysis revealed that body, caudal fin, dorsal fin, and anal fin shapes all exhibited strong correlated evolution consistent with locomotor ecomorphology. Major patterns included the evolution of deep body profiles with long fins, suggestive of maneuvering specialization; and the evolution of narrow, elongate caudal peduncles with concave tails, a combination that characterizes economical cruisers. These results demonstrate that body shape evolution does not occur independently of other traits, but among a suite of other morphological changes that augment locomotor specialization.     

Function of dorsal fins in bamboo shark during steady swimming

To gain insight into the function of the dorsal fins in white-spotted bamboo sharks (Orectolobiformes: Hemiscyillidae) during steady swimming, data on three-dimensional kinematics and electromyographic recordings were collected. Bamboo sharks were induced to swim at 0.5 and 0.75 body lengths per second in a laminar flow tank. Displacement, lag and angles were analyzed from high-speed video images. Onset, offset, duration, duty cycle and asynchrony index were calculated from three muscle implants on each side of each dorsal fin. The dorsal fins were displaced more laterally than the undulating body. In addition, the dorsal tips had larger lateral displacement than the trailing edges. Increased speed was accompanied by an increase in tail beat frequency with constant tail beat amplitude. However, lateral displacement of the fins and duration of muscle bursts remained relatively constant with increased speed. The range of lateral motion was greater for the second dorsal fin (mean 33.3°) than for the first dorsal fin (mean 28.4°). Bending within the fin was greater for the second dorsal fin (mean 43.8°) than for the first dorsal fin (mean 30.8°). Muscle onset and offset among implants on the same side of each dorsal fin was similar. Three-dimensional conformation of the dorsal fins was caused by interactions between muscle activity, material properties, and incident flow. Alternating bilateral activity occurred in both dorsal fins, further supporting the active role of these hydrofoils in thrust production during steady swimming. The dorsal fins in bamboo sharks are capable of thrust production during steady swimming and do not appear to function as stabilizing structures.     

Performance of iSharkFin in the identification of wet dorsal fins from priority shark species

The past decade has seen a considerable rise in international concern regarding the conservation status of sharks and rays. The demand for highly prized shark commodities continues to fuel the international trade and gives fisheries incentive to use these resources, which have a low intrinsic capability to recover. Recognising the urgency for regulation, many countries voted to include more shark and ray species in the Appendices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, the identification of fins in fisheries landings before they enter international trade is a major limitation for CITES compliance. This study reports the current performance of the iSharkFin system, a machine learning technology which aims to allow users to identify the species of a wet shark dorsal fin from its image. Photographs of 1147 wet dorsal fins from 39 shark species, collected in 12 countries, were used to train the algorithm over a four-year period. As new cohorts of images were used to test the performance of the learning algorithm, the accuracy of species assignments of known specimens was variable but did increase, reaching 85.3% and 59.1% at genus and species level respectively. The accuracy in predicting CITES-listed sharks versus unlisted sharks was 94.0% based on the 39 species currently represented in the baseline. Our results suggest that if supplied with high data inputs for specific fisheries assemblages and accompanied by user training, iSharkFin has promise for site-specific development as a rapid field identification tool in fisheries monitoring, and as a screening tool alongside traditional field morphology to detect potential CITES specimens for fisheries compliance and enforcement.     

The Species and Origin of Shark Fins in Taiwan’s Fishing Ports,Markets, and Customs Detention: A DNA Barcoding Analysis

The increasing consumption of shark products, along with the shark’s fishing vulnerabilities, has led to the decrease in certain shark populations. In this study we used a DNA barcoding method to identify the species of shark landings at fishing ports, shark fin products in retail stores, and shark fins detained by Taiwan customs. In total we identified 23, 24, and 14 species from 231 fishing landings, 316 fin products, and 113 detained shark fins, respectively. All the three sample sources were dominated by Prionace glauca, which accounted for more than 30% of the collected samples. Over 60% of the species identified in the fin products also appeared in the port landings, suggesting the domestic-dominance of shark fin products in Taiwan. However, international trade also contributes a certain proportion of the fin product markets, as four species identified from the shark fin products are not found in Taiwan’s waters, and some domestic-available species were also found in the customs-detained sample. In addition to the species identification, we also found geographical differentiation in the cox1 gene of the common thresher sharks (Alopias vulpinus), the pelagic thresher shark (A. pelagicus), the smooth hammerhead shark (Sphyrna zygaena), and the scalloped hammerhead shark (S. lewini). This result might allow fishing authorities to more effectively trace the origins as well as enforce the management and conservation of these sharks.     

Gauging the Threat: The First Population Estimate for White Sharks in South Africa Using Photo Identification and Automated Software

South Africa is reputed to host the world’s largest remaining population of white sharks, yet no studies have accurately determined a population estimate based on mark-recapture of live individuals. We used dorsal fin photographs (fin IDs) to identify white sharks in Gansbaai, South Africa, from January 2007 – December 2011. We used the computer programme DARWIN to catalogue and match fin IDs of individuals; this is the first study to successfully use the software for white shark identification. The programme performed well despite a number of individual fins showing drastic changes in dorsal fin shape over time. Of 1682 fin IDs used, 532 unique individuals were identified. We estimated population size using the open-population POPAN parameterisation in Program MARK, which estimated the superpopulation size at 908 (95% confidence interval 808–1008). This estimated population size is considerably larger than those described at other aggregation areas of the species and is comparable to a previous South African population estimate conducted 16 years prior. Our assessment suggests the species has not made a marked recovery since being nationally protected in 1991. As such, additional international protection may prove vital for the long-term conservation of this threatened species.     

Blue shark Prionace glauca fin-to-carcass-mass ratios in Spain and implications for finning ban enforcement

This study examines the processing of fins from blue sharks Prionace glauca caught by the Spanish longline fleet and landed in Vigo, Spain, and implications of these practices for enforcing the E.U. ban on shark finning, which relies on a maximum fin-to-carcass-mass ratio. Two major sources of variability in fin-to-carcass ratios are quantified and discussed: (1) the fin set (type and number of fins retained from each shark) and (2) the cutting method used to separate fins from carcasses. The significant differences in fin-to-carcass-mass ratios between fin sets or cutting procedure demonstrates that the ratio limit is problematic and, conclusively, in order to facilitate proper enforcement, fishermen should be required to land all sharks with the fins still naturally attached to the bodies.     

Dorsal fin in the white shark, Carcharodon carcharias: a dynamic stabilizer for fast swimming

Transverse sections of the skin in the dorsal fin of the white shark, Carcharodon carcharias, tiger shark, Galeocerdo cuvier, and spotted raggedtooth shark, Carcharias taurus, show large numbers of dermal fiber bundles, which extend from the body into the fin. The bundles are tightly grouped together in staggered formation (not arranged in a straight line or in rows). This arrangement of dermal fibers gives tensile strength without impeding fiber movement. Tangential sections indicate that the fibers in all three species are strained and lie at angles in excess of 60 degrees . Of the three species investigated the dermal fibers in C. carcharias are the most densely concentrated and extend furthest distally along the dorsal fin. The overall results indicate that the dorsal fin of C. carcharias functions as a dynamic stabilizer and that the dermal fibers are crucial to this role. The fibers work like riggings that stabilize a ship's mast. During fast swimming, when the problems of yaw and roll are greatest, hydrostatic pressure within the shark increases and the fibers around the body, including in the dorsal fin, become taut, thereby stiffening the fin. During slow swimming and feeding the hydrostatic pressure is reduced, the fibers are slackened, and the muscles are able to exert greater bending forces on the fin via the radials and ceratotrichia. In C. carcharias there is a trade-off for greater stiffness of the dorsal fin against flexibility.     

Characterization of the pelagic shark‐fin trade in north‐central Chile by genetic identification and trader surveys

Shark fins have become a highly valued commodity with the major Asian fin‐trade centres supplied from global sources, including Chile. With growing concerns about the resilience of shark populations to heavy fishing pressure, there is a need for better information on shark landings to aid management efforts. In the widespread absence of shark landing records especially by species, monitoring the fin trade has been proposed as a way to assess species exploitation levels. Here, the first species assessment of the Chilean shark‐fin trade was provided. The goals of this study were to (1) determine the species composition and relative species proportion of sharks utilized in the fin trade, (2) determine the relationship between fin trader market names and species and (3) assess trader accuracy in identifying shark fin species based on fin photographs. Fins were analysed from two different fin drying facilities (n = 654) (secaderos) and two fin‐storage warehouses (n = 251). In contrast to official government landing records that only document four species in the landings, molecular species identification of the fins demonstrated that at least 10 pelagic shark species are present in the north‐central Chilean shark fin trade: Alopias superciliosus, Alopias vulpinus, Carcharhinus obscurus, Galeorhinus galeus, Isurus oxyrinchus, Isurus paucus, Lamna nasus, Prionace glauca, Sphyrna lewini, Sphyrna zygaena. The species composition of the fins from the secaderos was P. glauca (83·9%), I. oxyrinchus (13·6%), L. nasus (1·7%) and A. superciliosus (0·2%). There was generally good agreement between market names and single shark species for the trade categories ‘Azulejo’, ‘Tiburon’, ‘Tintorera’, ‘Cola de zorro’ and ‘Martillo’. In contrast, the market category ‘Carcharhinus’ consisted of a mixture of at least five species. The molecular results also identified two species (S. lewini and I. paucus) not previously recorded in Chilean waters. The fin identification survey given to nine regional traders demonstrated that they were highly accurate in recognizing pictures of fins from P. glauca and I. oxyrinchus. The overall strong concordance between market categories and fins from single species and the trader accuracy in survey fin identification suggests that monitoring the Chilean fin trade by market names will provide a reasonably accurate picture of the volume of sharks landed by species.     

Trophic ecology of juvenile bull sharks (Carcharhinus leucas) in the Coyote estuary,Costa Rica

Bull shark (Carcharhinus leucas) is a near-threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81–103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ¹⁵N and δ¹³C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest.     

Pectoral fin morphology of batoid fishes (Chondrichthyes: Batoidea): Explaining phylogenetic variation with geometric morphometrics

The diverse cartilaginous fish lineage, Batoidea (rays, skates, and allies), sister taxon to sharks, comprises a huge range of morphological diversity which to date remains unquantified and unexplained in terms of evolution or locomotor style. A recent molecular phylogeny has enabled us to confidently assess broadscale aspects of morphology across Batoidea. Geometric morphometrics quantifies the major aspects of shape variation, focusing on the enlarged pectoral fins which characterize batoids, to explore relationships between ancestry, locomotion and habitat. A database of 253 specimens, encompassing 60 of the 72 batoid genera, reveals that the majority of morphological variation across Batoidea is attributable to fin aspect‐ratio and the chordwise location of fin apexes. Both aspect‐ratio and apex location exhibit significant phylogenetic signal. Standardized independent linear contrast analysis reveals that fin aspect‐ratio can predict locomotor style. This study provides the first evidence that low aspect‐ratio fins are correlated with undulatory‐style locomotion in batoids, whereas high aspect‐ratio fins are correlated with oscillatory locomotion. We also show that it is phylogeny that determines locomotor style. In addition, body‐ and caudal fin‐locomotors are shown to exhibit low aspect‐ratio fins, whereas a pelagic lifestyle correlates with high aspect‐ratio fins. These results emphasize the importance of phylogeny in determining batoid pectoral fin shape, however, interactions with other constraints, most notably locomotor style, are also highlighted as significant. J. Morphol. 275:1173–1186, 2014. © 2014 Wiley Periodicals, Inc.     

Natural or Artificial? Habitat-Use by the Bull Shark,Carcharhinus leucas

Background

Despite accelerated global population declines due to targeted and illegal fishing pressure for many top-level shark species, the impacts of coastal habitat modification have been largely overlooked. We present the first direct comparison of the use of natural versus artificial habitats for the bull shark, Carcharhinus leucas, an IUCN ‘Near-threatened’ species - one of the few truly euryhaline sharks that utilises natural rivers and estuaries as nursery grounds before migrating offshore as adults. Understanding the value of alternate artificial coastal habitats to the lifecycle of the bull shark is crucial for determining the impact of coastal development on this threatened but potentially dangerous species.

Methodology/Findings

We used longline surveys and long-term passive acoustic tracking of neonate and juvenile bull sharks to determine the ontogenetic value of natural and artificial habitats to bull sharks associated with the Nerang River and adjoining canals on the Gold Coast, Australia. Long-term movements of tagged sharks suggested a preference for the natural river over artificial habitat (canals). Neonates and juveniles spent the majority of their time in the upper tidal reaches of the Nerang River and undertook excursions into adjoining canals. Larger bull sharks ranged further and frequented the canals closer to the river mouth.

Conclusions/Significance

Our work suggests with increased destruction of natural habitats, artificial coastal habitat may become increasingly important to large juvenile bull sharks with associated risk of attack on humans. In this system, neonate and juvenile bull sharks utilised the natural and artificial habitats, but the latter was not the preferred habitat of neonates. The upper reaches of tidal rivers, often under significant modification pressure, serve as nursery sites for neonates. Analogous studies are needed in similar systems elsewhere to assess the spatial and temporal generality of this research.     

Tail growth tracks the ontogeny of prehensile tail use in capuchin monkeys (Cebus albifrons and C. apella)

Physical anthropologists have devoted considerable attention to the structure and function of the primate prehensile tail. Nevertheless, previous morphological studies have concentrated solely on adults, despite behavioral evidence that among many primate taxa, including capuchin monkeys, infants and juveniles use their prehensile tails during a greater number and greater variety of positional behaviors than do adults. In this study, we track caudal vertebral growth in a mixed longitudinal sample of white-fronted and brown capuchin monkeys (Cebus albifrons and Cebus apella). We hypothesized that young capuchins would have relatively robust caudal vertebrae, affording them greater tail strength for more frequent tail-suspension behaviors. Our results supported this hypothesis. Caudal vertebral bending strength (measured as polar section modulus at midshaft) scaled to body mass with negative allometry, while craniocaudal length scaled to body mass with positive allometry, indicating that infant and juvenile capuchin monkeys are characterized by particularly strong caudal vertebrae for their body size. These findings complement previous results showing that long bone strength similarly scales with negative ontogenetic allometry in capuchin monkeys and add to a growing body of literature documenting the synergy between postcranial growth and the changing locomotor demands of maturing animals. Although expanded morphometric data on tail growth and behavioral data on locomotor development are required, the results of this study suggest that the adult capuchin prehensile-tail phenotype may be attributable, at least in part, to selection on juvenile performance, a possibility that deserves further attention.     

Vertical Movement Patterns and Ontogenetic Niche Expansion in the Tiger Shark,Galeocerdo cuvier

Sharks are top predators in many marine ecosystems and can impact community dynamics, yet many shark populations are undergoing severe declines primarily due to overfishing. Obtaining species-specific knowledge on shark spatial ecology is important to implement adequate management strategies for the effective conservation of these taxa. This is particularly relevant concerning highly-mobile species that use wide home ranges comprising coastal and oceanic habitats, such as tiger sharks, Galeocerdo cuvier. We deployed satellite tags in 20 juvenile tiger sharks off northeastern Brazil to assess the effect of intrinsic and extrinsic factors on depth and temperature usage. Sharks were tracked for a total of 1184 d and used waters up to 1112 m in depth. The minimum temperature recorded equaled 4°C. All sharks had a clear preference for surface (< 5 m) waters but variability in depth usage was observed as some sharks used mostly shallow (< 60 m) waters whereas others made frequent incursions into greater depths. A diel behavioral shift was detected, with sharks spending considerably more time in surface (< 10 m) waters during the night. Moreover, a clear ontogenetic expansion in the vertical range of tiger shark habitat was observed, with generalized linear models estimating a ~4-fold increase in maximum diving depth from 150- to 300-cm size-classes. The time spent in the upper 5 m of the water column did not vary ontogenetically but shark size was the most important factor explaining the utilization of deeper water layers. Young-of-the-year tiger sharks seem to associate with shallow, neritic habitats but they progressively move into deeper oceanic habitats as they grow larger. Such an early plasticity in habitat use could endow tiger sharks with access to previously unavailable prey, thus contributing to a wider ecological niche.