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Backing up from negative stimuli: A back-thrust mechanism during escape-like response in wild sevengill sharks (Notorynchus cepedianus)
Abstract
Broadnose sevengill sharks (Notorynchus cepedianus) show great interest for bait and
display a repertoire of movements while engaging with it. A novel back-thrust mechanism
is described in wild sevengill sharks by which individuals back up from a negative
stimulus while interacting with baited video stations. This mechanism initiates
upon head contact with the device that functions as a negative stimulus eliciting a
startle escape-like response. By heavily flipping pectoral fins and curving the body,
sharks increase hydrodynamic resistance, backing up from the negative stimulus.
Once backed up, sharks performed the common C-shaped double-bend escape maneuver
described for sharks. Sharks also used the same back-thrust mechanism as a
repositioning maneuver, but not as part of a startle response. The quantification of
the turning rate indicated context-dependent variation in velocity and confirmed that
the majority of withdrawals corresponded to slow escape-like motions. In general,
an elongated body and individual flipping control of pectoral fins allowed for great
maneuverability and lateral flexure. Sharks exhibited great tolerance to one another
during double and triple encounters. The implications for grouping and social hunting
of the species are briefly discussed based on past evidence and the movement
behavior, gregarious interactions, and body markings observed in the present study.
This work highlights the importance of studies in the natural environment and the
use of complementary approaches to investigate the broader range of locomotor
aspects of different shark species.
... Recent strategic planning in Argentina, Brazil and Uruguay provides a framework for a collaborative regional protection network, focusing on essential habitats and enhancing awareness and fishing regulations to improve conservation efforts (Cuevas et al. 2021), as promoting good fishing practices may not suffice (Lucifora et al. 2009). Similarly, N. cepedianus shows marked site fidelity and seasonal use of Patagonian bays, coves and estuaries (Cedrola et al. 2009;Irigoyen et al. 2019Irigoyen et al. , 2018Jaureguizar et al. 2024;Lucifora, Menni, and Escalante 2005b), with notable dependence on nursery areas (Jaureguizar et al. 2023) and gregarious behaviour (De Wysiecki, Trobbiani, and Irigoyen 2021). Decade-long research in northern Patagonia highlights the importance of Caleta Valdés, an aggregation site used year-round for feeding with peak abundance in late spring and early summer Funes et al. 2024;Irigoyen et al. 2018). ...
This study investigates the spatial overlap in habitat use among four key predatory species—school shark ( Galeorhinus galeus ), broadnose sevengill shark ( Notorynchus cepedianus ), copper shark ( Carcharhinus brachyurus ) and sand tiger shark ( Carcharias taurus )—along the Argentine coast to identify important areas for joint management. Leveraging habitat suitability predictions for these predators, we generated annual and seasonal maps to identify significant regions of habitat overlap. Notably, the coastal zone between the Uruguayan and northern Argentine coasts emerged as crucial for developing fishery management and conservation strategies for these four species. Historical catch data also identified important zones for recreational fishing and potential nursery sites, stressing the need for targeted management of the coastal area between Punta Rasa and Mar del Plata (36.3°–38° S). This highlights the necessity of comprehensive fishing regulations with stronger enforcement in the unregulated provincial waters of Chubut and Santa Cruz, as well as the Uruguayan coast. Our findings underscore the importance of integrating species‐specific ecological data in designing marine protected areas and conservation strategies tailored to the unique life history and movement patterns of these sharks. Additionally, the study emphasizes the need for adaptive, multijurisdictional management strategies to accommodate the migratory nature of these species across provincial and national waters. The implications of these findings are discussed within the context of current chondrichthyan policy in Argentina, presenting a foundational basis for informing future management strategies aimed at sustaining shark populations in the Southwest Atlantic.
... Las técnicas de vídeo submarino se han aplicado con éxito a una amplia variedad de objetivos (Cappo et al. 2007;Mallet and Pelletier 2014), incluidos el monitoreo de peces de arrecife (Willis and Babcock 2000;Gardner and Struthers 2012;Trobbiani and Venerus 2015;Trobbiani et al. 2021), tiburones (Brooks et al. 2011;Irigoyen et al. 2018b;De Wysiecki et al. 2021), carroñeros de aguas profundas (Priede et al. 1990) e invertebrados epibentónicos (Stokesbury et al. 2004;Trobbiani 2019), así como el estudio de hábitats (Carbines and Cole 2009;Tran 2013;Trobbiani 2019). Estos estudios utilizaron gran variedad de configuraciones de cámaras (individuales o estéreo vídeo) montadas en estaciones remotas fijas (con o sin cebo) o conectadas a dispositivos móviles (vehículos operados a distancia o ROV, trineos y cámaras de deriva) (Cappo et al. 2007;Mallet and Pelletier 2014;Trobbiani and Venerus 2015;Trobbiani and Irigoyen 2016). ...
Clams belonging to the genus Panopea, part of
the Hiatellidae family, are distributed in temperate seas and represent valuable fishing resources in most of the
regions where they inhabit. These bivalves tend to aggregate on sandy and/or muddy substrates, exhibiting
temporal variations in their abundance, or more precisely, in their detectability. Traditionally, monitoring
of panopea populations has relied on autonomous diving, which poses safety limitations in terms of depth
and duration of diving. In this study, we evaluated the efficacy of the low-cost remote video method known
as ‘Toki’ for evaluating and monitoring Panopea abbreviata in the San Matías Gulf. Abundance observations
were analyzed using generalized additive mixed models, incorporating temperature, depth, sampling date,
and image quality as covariates. We observed a differential paern in the abundance of P. abbreviata, with
peaks occurring during October and May, in contrast to previous reports for other species within the same
genus. Notably, the variation in abundance exceeded that reported for the same species in previous studies.
In agreement with prior research, we found significantly higher densities of P. abbreviata on sandy substrates.
‘Toki’ proved to be an effective tool, enabling the coverage of extensive areas effortlessly and within a short
timeframe. Its key advantages include accessibility to greater depths and minor time constraints than associated
with diving, especially at depths below 25 m. Moreover, this technique provides a permanent record that can be
subsequently utilized for additional purposes. It is worth noting that the entire procedure was conducted from
a small boat, using manual operations, resulting in relatively low costs and enhanced operational convenience.
Nevertheless, diving can serve as a complementary technique for intensive tasks in confined areas.
... Underwater videos have won wide acceptance for the study of marine life in recent years (Mallet, Pelletier, 2014;Whitmarsh et al., 2016;2018). Remote video techniques make it possible to collect information on how species relate to their habitat and to analyse their populations in a non-destructive way, including the patterns and processes that may drive them, such as feeding or reproduction (Trobiani et al., 2018(Trobiani et al., , 2021Irigoyen et al., 2018;Branconi et al., 2019;De Wysiecki et al., 2020). This technique is widely used for the analysis of richness, relative abundance, population monitoring, habitat preferences and fish behaviour in marine and freshwater bodies (Cappo et al., 2003;Sheehan et al., 2010;Ebner et al., 2014;King et al., 2017). ...
The aim of this study was to evaluate the performance of Underwater Video Stations (UVS) to detect caddisfly larvae (Trichoptera), estimate density in a lake, as well as to evaluate its effectiveness in tracking larvae. For this, were deployed UVS. Recording a total of 3120 minutes of video were analysed, of which 968 min were used for abundance analysis. Finally, caddisfly larvae were tracked using the Tracker software, which recorded the velocity of everyone in mm/s. This work successfully put into practice a novel sampling methodology for this insect group. The technique was implemented quickly, easily, and inexpensively and is highly scalable for the monitoring of aquatic invertebrates. Remote video stations are a potential tool for use in the field of population monitoring and studies of personality and behaviour in the natural habitat.
How to cite this article: Fernández M.V., Trobbiani G. 2023. Video stations, a potential low-cost tool to monitoring invertebrates. A pilot study with Limnephilidae (Trichoptera) // Invert.
This study reports the first records of cowsharks (Hexanchidae) in the Galápagos Islands, in particular Notorynchus cepedianus and Hexanchus griseus, observed between depths of 210 and 418 m on footage from free‐falling autonomous deep‐ocean cameras. These sightings provide new information on the habitat preferences and range distribution for N. cepedianus and the first records of H. griseus in Ecuadorian waters. The findings support the formulation of regional conservation strategies for these large apex predator species and highlight the limited biological knowledge of Galápagos' deep‐water ecosystems.
Conservation and management measures for large mobile sharks are more effective when information on migratory patterns and environmental cues are known. In the absence of long-term monitoring data or tracking programs, available information is based on occasional catch or sighting records from a variety of sources, usually constrained in space and time. This study demonstrates the utility of developing temporally explicit habitat suitability (HS) models to infer the migratory pattern of large mobile sharks. Bimonthly presence-only HS models (MaxEnt algorithm) were developed for the broadnose sevengill shark (Notorynchus cepedianus) in the southwest Atlantic based on an exhaustive collection of data records and ecologically relevant predictors. The six final models showed good predictive power and were evaluated with independent data. A migratory pattern characterized by two main displacements was inferred from the models. We show that HS models can be applied as a no-cost, desk-based alternative to infer broadscale movements of large mobile sharks. This methodology is relevant as an important first step toward informing management plans in data-poor and financially limited regions or regions under urgent conservation need.
Apex predators play an important role in structuring food webs and are thus key components of healthy, stable ecosystems. While the loss of apex predators has been shown to disrupt ecosystems and trigger trophic cascades, the introduction of novel apex predators to functionally intact systems is less well understood. False Bay, South Africa, is an aggregation site for both white (Carcharodon carcharias) and broadnose sevengill sharks (Notorynchus cepedianus) which together fulfill the role of coastal apex predators. However, since 2009, their position at the top of the food chain has been subverted by the increased presence of killer whales (Orcinus orca) in False Bay. These super predators are known to specialize on certain prey species, and up until 2015 were only documented preying on marine mammals within False Bay. However, in 2015 and 2016 we documented two events in which killer whales preyed upon broadnose sevengill sharks, using a specialized feeding method in which only the liver of each shark was consumed. Although selective feeding on shark liver by killer whales is established, this is the first record of killer whale predations on sevengill sharks in False Bay, and the first documentation of a novel feeding technique, in which killer whales used force applied to the pectoral fins of each shark to rupture the pectoral girdle and thereby access the liver. These predation events resulted in the prolonged absence of sevengill sharks from what is the largest known aggregation site for this species globally, which remained abandoned for up to a month. We briefly review the literature on killer whale behavior, dietary specialization, and population delineation globally and locally, and hypothesize that the novel predations on broadnose sevengill sharks in False Bay are possibly indicative of the arrival of a different sub‐group or ecotype of killer whale in the bay, which habitually feeds on sharks. Due to the unique predatory niche occupied by sevengill sharks in False Bay, the increased presence of these particular killer whales in False Bay could have profound impacts throughout the ecosystem.
Fish pectoral fins move in complex ways, acting as control surfaces to affect force balance during swimming and maneuvering. Though objectively less dynamic than their actinopterygian relatives, shark pectoral fins undergo complex conformational changes and movements during maneuvering. Asynchronous pectoral fin movement is documented during yaw turning in at least two shark species but the three-dimensional (3D) rotation of the fin about the body axes is unknown. We quantify the 3D actuation of the pectoral fin base relative to the body axes. We hypothesized that Pacific spiny dogfish rotate pectoral fins with three degrees of freedom relative to the body during volitional turning. The pectoral fin on the inside of the turn is consistently protracted, supinated and depressed. Additionally, turning angular velocity increased with increasing fin rotation. Estimated drag on the fin increased and the shark decelerated during turning. Based on these findings, we propose that Pacific spiny dogfish uses drag-based turning during volitional swimming. Post-mortem muscle stimulation revealed depression, protraction and supination of the pectoral fin through stimulation of the ventral and cranial pterygoideus muscles. These data confirm functional hypotheses about pectoral fin musculature and suggest that Pacific spiny dogfish actively rotate pectoral fins to facilitate drag-based turning.
This article has an associated First Person interview with the first author of the paper.
Background
Sevengill sharks are common inhabitants of estuaries and coastal areas and particularly abundant in San Francisco Bay (SFB). There is limited knowledge about the level of residency and migratory movements of this species. We describe the degree of residence of sevengill sharks in SFB and nearby locations, using ultrasonic tags and automated listening stations.
Results
Sevengills showed a high degree of residency in SFB, particularly to the Golden Gate (GG) area where they have a strong site preference, both seasonally and inter-annually. Site fidelity was also the highest at the GG. In sharks with deployment times longer than 300 days, we found that > 80% of visits of all mature males were at GG, 80% of visits of a single mature female occurred there, > 85% of visits of most juvenile males, and > 70% of visits of most juvenile females. At GG, sharks moved into the range of the receiver day and night without a strong preference for a particular time of the day, which implies movements up and down the area day and night. At most other locations within the bay, sharks were present during daytime hours, while at Point Reyes during nighttime hours. Sharks moved into SFB during early spring and summer, and moved out of SFB to Point Reyes during late spring and fall. Three sevengill sharks migrated roughly 800 km southeastward along the coastline from SFO, one making three trips back and forth between the sites.
Conclusions
There was strong evidence of residency of sharks within SFB, and sharks repeatedly returned to the same region of the bay with some sharks making long-distance movements.
Positioned at the intersection of the head, body and forelimb, the pectoral girdle has the potential to function in both feeding and locomotor beha-viours—although the latter has been studied far more. In ray-finned fishes, the pectoral girdle attaches directly to the skull and is retracted during suction feeding, enabling the ventral body muscles to power rapid mouth expansion. However, in sharks, the pectoral girdle is displaced caudally and entirely separate from the skull (as in tetrapods), raising the question of whether it is mobile during suction feeding and contributing to suction expansion. We measured three-dimensional kinematics of the pectoral girdle in white-spotted bamboo sharks during suction feeding with X-ray reconstruction of moving morphology, and found the pectoral girdle consistently retracted about 118 by rotating caudoventrally about the dorsal scapular processes. This motion occurred mostly after peak gape, so it likely contributed more to accelerating captured prey through the oral cavity and pharynx, than to prey capture as in ray-finned fishes. Our results emphasize the multiple roles of the pectoral girdle in feeding and locomotion, both of which should be considered in studying the functional and evolutionary morphology of this structure. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
Animals exhibit various physiological and behavioural strategies for minimizing travel costs.
Fins of aquatic animals play key roles in efficient travel and, for sharks, the functions of dorsal
and pectoral fins are considered well divided: the former assists propulsion and generate
lateral hydrodynamic forces during turns and the latter generates vertical forces that offset
sharks’ negative buoyancy. Here we show that great hammerhead sharks drastically
reconfigure the function of these structures, using an exaggerated dorsal fin to generate lift by
swimming rolled on their side. Tagged wild sharks spend up to 90% of time swimming at roll
angles between 50° and 75°, and hydrodynamic modelling shows that doing so reduces
drag—and in turn, the cost of transport—by ~10% compared with traditional upright
swimming. Employment of such a strongly selected feature for such a unique purpose raises
interesting questions about evolutionary pathways to hydrodynamic adaptations, and our
perception of form and function.
Underwater video techniques are increasingly used in marine ecology studies. Technological progress regarding video cameras, sensors (such as sounders), battery life and information storage make these techniques now accessible to a majority of users. However, diver-based underwater visual censuses, and catch and effort data, remain the most commonly used for observing coastal biodiversity and species. In this paper, we review the underwater video techniques that have been developed since the 1950s to investigate and/or monitor coastal biodiversity. Techniques such as remote underwater video, whether baited or not, diver-operated video and towed video are described, along with corresponding applications in the field. We then analyse the complementary of techniques, first from studies comparing video techniques with other observation techniques, whether video-based or not, and second by documenting their respective cost efficiencies. These findings are discussed with respect to current challenges in monitoring and investigating coastal biodiversity. Video should be more often considered and used, either in addition to or as an alternative to diver-based, fishing and acoustic techniques, as it may be particularly suited for monitoring coastal biodiversity in a variety of areas and on larger scales than hitherto and within an ecosystem-based approach to management and conservation.
Studies on the feeding behaviour of large predatory sharks are inherently problematic because of the size of the animals, the difficulty in observing and handling them and the risks to the investigator. Observations on the feeding behaviour of the sevengill shark Notorynchus cepedianus over a seven-year period revealed this species to display at least four distinct foraging strategies. A particular strategy, or a combination of two or more, was employed depending on the size and type of prey being subdued. The four primary factors that appear to influence prey selection were prey size, availability and density, and scavenging. The behaviour of a prey species influences the predator's foraging and hunting behaviour. The success of the sevengill shark as an apical predator can be attributed, in part, to the feeding strategies it employs to subdue prey.
Post hoc and planned comparison procedures for interpreting chi-square contingency-table test results, not currently discussed in most standard textbooks, are presented. A planned comparison procedure that simplifies the tedious process of partitioning a contingency table by creating single-degree-of-freedom contrasts through a regression-based approach is proposed. Importantly, these post hoc methods supplement the analysis of standardized residuals by reporting the percentage contribution for each cell to the overall chi-square statistic (relative contribution) and to the percentage of variance shared by the two factors (absolute contribution). Both methods can be readily incorporated into existing statistical packages such as SAS or SPSS. The equivalence of the percentage contribution method to the more common standardized residual method is also presented along with an example of a typical application.
Quantifying the feeding ecology of marine predators is essential for understanding their trophic interactions and their potential regulatory effects in marine ecosystems. I quantified the feeding ecology of 2 related predators that overlap only in part in spatial distribution: the coastal broadnose Notorynchus cepedianus and the deepwater sharpnose Heptranchias perlo sevengill sharks. I found the following: These 2 shark species have different diet specialisation patterns, but show similarities in their prey handling mode. N. cepedianus has a generalised diet, whereas H. perlo shows high specialisation and lower prey diversity. For both shark species, small, medium and large individuals use different strategies for handling different prey groups. H. perlo preys largely on deepwater teleosts, mainly Lepidorhynchus denticulatus, with larger individuals (901 to 1365 mm total length, TL) also consuming high proportions of large predatory teleosts of the families Gempylidae and Trichiuridae. N. cepedianus has a diverse diet. Small individuals (≤900 mm TL) prey largely on teleosts and secondarily on chondrichthyans. Medium individuals (901 to 1520 mm TL) prey primarily on chondrichthyans and secondarily on teleosts. Chondrichthyans (mainly Mustelus antarcticus) are also the main prey of large N. cepedianus (>1700 mm TL), but this group also shows a greater preference (than small and medium individuals) for fur seals. Despite the overall differences in dietary composition and the minimal overlap in spatial distribution, the 2 shark species consume prey that migrate from deep to coastal waters (ommastrephid squid and gempylid fish).
Broadnose sevengill sharks Notorynchus cepedianus caught in a recreational fishery during a 3 yr period in Anegada Bay, Argentina were examined. Monthly variations in abundance were found, with the highest mean abundance in April. Neonates and juveniles were common in the study area, indicating that Anegada Bay is a nursery area of N. cepedianus. Male and female sizes at maturity were 170 and 224 cm total length (TL), respectively, similar to other studied regions. Liver size was sexually dimorphic, with adult females having larger livers, which might allow for the maximization of oocyte size/number. Individuals < 100 cm TL fed mainly on teleosts, sharks 100 to 170 cm TL consumed mainly cartilaginous fishes and less teleosts, and sharks > 170 cm fed mostly on cartilaginous fishes and marine mammals. All size groups preyed on marine mammals, which may be a result of the local availability of small calves of La Plata River dolphins Pontoporia blainvillei. Possibly, the pattern of habitat use of Anegada Bay by P. blainvillei is affected by N. cepedianus. The proportion of individuals with prey within the stomach was negatively correlated with TL. As indicated by prey remains found within stomachs (most were in pieces) and by the location of the fishing hook in sharks (most were hooked in the mouth), N. cepedianus extensively handles its prey with the mouth before swallowing it, which is consistent with previous observations. Anegada Bay may be an important area for conservation of N. cepedianus in the SW Atlantic given the high abundance of juveniles and subadults.
The sevengill shark Notorynchus cepedianus is a large, common species of most coastal temperate waters that has often been overlooked as an important marine predator. It is a eurytrophic predator that optimizes the available resources. Analysis of sevengill shark stomachs from four different regions off southern Africa reveal that chondrichthyan, teleost and marine mammal species were the major prey categories and lead to the conclusion that the sevengill is an apex predator in that nearshore marine ecosystem. Other than the great white shark, the sevengill shark has no trophic equivalents in those areas where it occurs, particularly among carcharhinoids.
The study describes the annual cycle of southern elephant seals for the increasing colony of Península Valdés, and compares it to the haul-out pattern reported for stable or decreasing sub-Antarctic colonies of the species. Data were collected during censuses of the entire colony (nine breeding seasons, two moulting seasons and one autumn–winter haul-out), monthly surveys of coastline and mark-recapture of pups. Pup production during the study period grew from 12 113 to 14 621 animals (1995–2003). Most relevant events of the cycle were similar for all colonies studied, independent of the geographical location, size or population trend. Compared with other locations where southern elephant seals breed and moult, distinct features for Península Valdés were: i) breeding occurs earlier in the spring, and ii) most adult females reproduce and moult in the same colony. The increasing number of animals ashore was correlated with the expansion in pup production. Population trends and stability of demographic events could be related to a consistent physical environment (ocean fronts) during foraging phases of the annual cycle.
The diet of the broadnose sevengill shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correlation with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.
On 21 December 1998, four killer whales (an adult male, two females or immature males, and one juvenile) attacked a group of sevengill sharks (Notorhynchus cepedianus) off the coast of Caleta Malaspina, Chubut, Argentina. Persecution, catches, and tossing behavior were performed by the two females or immature males in the inlet. Next day, carcasses of several sharks were found on the beach adjacent to the attack area. Seven of them were intact and sized approximately 2.5 m in length. The presence of complete sevengill shark carcasses on the beach suggests that they were attempting to avoid capture by the killer whales by stranding on the beach. Attacks on sevengills by killer whales in Caleta Malaspina are frequent in some years, especially from mid-December to mid-January when the sevengill seems to use the inlet as a nursery ground. The observation of the same male feeding both on pin-nipeds in Peninsula Valdes and on sharks in Caleta Malaspina may indicate that at least some groups in the Southwestern Atlantic could regularly feed on both fish and marine mammals. This is the first report of an attack of killer whales on sharks off the coast of Patagonia, and the first report of toss-ing behavior in sharks.
The detailed movements of 32 acoustically tagged broadnose sevengill shark Notorynchus cepedianus were documented in and around north-east Pacific Ocean estuarine embayments from 2005 to 2007. Arrangements of passive acoustic receivers allowed analysis of movement at several spatial scales, with sex and size examined as possible factors influencing the pattern and timing of these movements. Notorynchus cepedianus exhibited a distinctly seasonal pattern of estuary use over three consecutive years, entering Willapa Bay in the spring, residing therein for extended periods of time during the summer and dispersing into nearshore coastal habitats and over the continental shelf during the autumn. Notorynchus cepedianus within Willapa Bay showed spatio-temporal patterns of segregation by size and sex, with males and small females using peripheral southern estuary channels early in the season before joining large females, who remained concentrated in central estuary channels for the entire season. Individuals displayed a high degree of fidelity not only to Willapa Bay (63% were documented returning over three consecutive seasons), but also to specific areas within the estuary, showing consistent patterns of site use from year to year. Cross-estuary movement was common during the summer, with most fish also moving into an adjacent estuarine embayment for some extent of time. Most winter and autumn coastal detections of N. cepedianus were made over the continental shelf near Oregon and Washington, U.S.A., but there were also examples of individuals moving into nearshore coastal habitats further south into California, suggesting the feasibility of broad-scale coastal movements to known birthing and nursery grounds for the species. These findings contribute to a better understanding of N. cepedianus movement ecology, which can be used to improve the holistic management of this highly mobile apex predator in regional ecosystems.
Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator's movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey's decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill shark Notorynchus cepedianus and its main prey, the Gummy shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with the presence of oscillatory behaviour and burst speed events suggest that N. cepedianus are nocturnal foragers, but may opportunistically attack prey they happen to encounter during the day.
This study quantified the electrosensitivity of a euryhaline elasmobranch, the Atlantic stingray (Dasyatis sabina) across a range of salinities. Specimens from a permanent freshwater (FW) population in the St Johns River system, FL, USA, were compared with stingrays from the tidally dynamic Indian River Lagoon in east Florida, USA. Behavioral responses of stingrays to prey-simulating electric stimuli were quantified in FW (0 p.p.t., rho=2026 Omega cm), brackish (15 p.p.t., rho=41 Omega cm) and full strength seawater (35 p.p.t., rho=19 Omega cm). This study demonstrated that the electrosensitivity of D. sabina is significantly reduced in FW. In order to elicit a feeding response, stingrays tested in FW required an electric field 200-300x greater than stingrays tested in brackish and saltwater (median FW treatments=1.4 microV cm(-1), median brackish-saltwater treatments=6 nV cm(-1)), and the maximum orientation distance was reduced by 35.2%, from 44.0 cm in the brackish and saltwater treatments to 28.5 cm in FW. The St Johns River stingrays did not demonstrate an enhanced electrosensitivity in FW, nor did they exhibit reduced sensitivity when introduced to higher salinities. Stingrays from both populations responded similarly to the prey-simulating stimulus when tested at similar salinities, regardless of their native environment. The reduction in electrosensitivity and detection range in FW is attributed to both an environmental factor (electrical resistivity of the water) and the physiological function of the ampullary canals. The plasticity of this sensory system to function across such a wide environmental range demonstrates its adaptive significance.
Electromyography (EMG) and cinematography revealed a rapid, vibration-evoked startle response in intact larval lampreys. Vibratory stimuli produce simultaneous contraction of both sides of the body, and the response is lost after labyrinthectomy. Midbody EMGs exhibit a stimulus-response latency of 26.5 +/- 4.2 ms. Direct stimulation of the otic capsules, using an electrically driven probe applied to a semi-intact preparation, first evokes a volley of giant axon spikes in the spinal cord followed by the bilateral trunk response.
While most actinopterygian fishes perform C-start or S-start behaviors as their primary startle responses, many elongate species instead use a withdrawal movement. Studies of withdrawal have focused on the response to head-directed or nonspecific stimuli. During withdrawal, the animal moves its head back from the stimulus, often resulting in several tight bends in the body. In contrast to C-start or S-start behaviors, withdrawal to a head stimulus generally does not involve a subsequent propulsive stage of movement. We examined intraspecific diversity in withdrawal behavior and muscle activity patterns of the rope fish, Erpetoichthys calabaricus, in response to stimulation of the head and the tail. In addition, we describe the anatomy of the Mauthner cells and their axon caps, structures that are generally absent in species with a withdrawal startle. We recorded high-speed video (250 Hz) and electromyograms (EMGs) from 12 electrodes in the axial muscle during the behavioral response. We used Bodian silver staining techniques to visualize Mauthner cell and axon cap morphology. We found that E. calabaricus responds with a withdrawal to both head and tail stimulation. Tail stimulation elicits a stronger kinematic and muscle activity response than head stimulation. While withdrawal movement generally constitutes the entire response to head stimuli, withdrawal was followed by propulsive movements when the tail was stimulated, suggesting that withdrawal can both act alone and serve as the first stage of a propulsive startle. Unexpectedly, bilaterality of muscle activity was variable for responses to both head and tail stimuli. In addition, we were surprised to find that E. calabaricus has a distinct axon cap associated with its Mauthner cell. These data suggest that the withdrawal response is a more diverse functional system than has previously been believed.
Sharks are among the oldest vertebrate lineages in which their success has been attributed to their diversity in body shape and locomotor design. In this study, we investigated the diversity of body forms in extant sharks using landmark-based geometric morphometric analyses on nearly all the known (ca. 470) extant sharks. We ran three different analyses: the ‘full body,' ‘precaudal body,’ and ‘caudal fin' analyses. Our study suggests that there are two basic body forms in sharks, a ‘shallow-bodied’ form (Group A) and ‘deep-bodied’ form (Group B), where all sharks essentially have one basic caudal fin design of a heterocercal tail despite some specializations. We found that swimming modes in sharks are highly correlated with body forms where Group A sharks are predominantly anguilliform swimmers and Group B sharks are represented by carangiform and thunniform swimmers. The majority of Group A sharks are found to be benthic whereas pelagic forms are relatively common among Group B sharks. Each of the two superorders of sharks, Squalomorphii and Galeomorphii, must have gone through complex evolutionary history where each superorder contains both Group A sharks and Group B sharks, possibly involving parallel evolution from one group to the other or at least one episode of evolutionary reversal.
The study of fish escape responses has provided important insights into the accelerative motions and fast response times of these animals. In addition, the accessibility of the underlying neural circuits has made the escape response a fundamental model in neurobiology. Fish escape responses were originally viewed as highly stereotypic all-or-none behaviours. However, research on a wide variety of species has shown considerable taxon-specific and context-dependent variability in the kinematics and neural control of escape. In addition, escape-like motions have been reported: these resemble escape responses kinematically, but occur in situations that do not involve a response to a threatening stimulus. This Review focuses on the diversity of escape responses in fish by discussing recent work on: (1) the types of escape responses as defined by kinematic analysis (these include C- and S-starts, and single- versus double-bend responses); (2) the diversity of neuromuscular control; (3) the variability of escape responses in terms of behaviour and kinematics within the context of predator-prey interactions; and (4) the main escape-like motions observed in various species. Here, we aim to integrate recent knowledge on escape responses and highlight rich areas for research. Rapidly developing approaches for studying the kinematics of swimming motion both in the lab and within the natural environment provide new avenues for research on these critical and common behaviours.
The habitat use, seasonality and demography of the broadnose sevengill shark Notorynchus cepedianus were investigated in central Patagonia, where a data gap exists for the species. Catch and effort and video‐derived indices indicated high relative abundance of sharks during warm months. Video stations revealed differences in the spatial use by sharks, being more frequently observed in the inner section of the bay. Complementary tagging efforts evidenced both a seasonal residence pattern and site fidelity between consecutive warm seasons. Juveniles outnumbered adults, which suggests that they may use the study area as a secondary nursing ground. Evidence from spontaneous regurgitation further suggests that prey abundance may be driving the seasonal occurrence of sharks in the region. This study allows for a more comprehensive understanding of the population structure and dynamics of sevengill sharks in the Southwest Atlantic.
Abstract in Spanish is available with online material.
While post-release mortality estimates have been conducted on a range of shark species, the short-term sub-lethal effects of capture, handling and release are poorly known and have been mostly investigated in controlled conditions. In addition, the widely accepted notion that immediate post-release active swimming is an indicator of shark condition has never been tested. This study assessed the effects of deck exposure by analysing post-release behaviour of two species of shark, the draughtboard (Cephaloscyllium laticeps) and the piked spurdog (Squalus megalops) in-situ using a remote-operated-vehicle and in a replicated experiment in controlled conditions. In total, 67 sharks were caught with demersal fish trawls and commercial longlines and subjected to different deck exposures and release environments. Tailbeat rates of deck-exposed sharks were significantly lower than the control sharks, but this effect differed between in-situ and experimental environments. Results indicate that capture has species-specific effects, that post-release effects may last longer than 5 min, and that controlled experiments may not be reliable indicators of post-release effects. Immediate post-release swimming was not a good predictor of post-release behaviour, suggesting capture and release fisheries may have significant sub-lethal effects on some species of shark, and that limiting capture or handling time may reduce post-release effects.
Gaining insight on how species relate to the environment and other members of the trophic community is critical for their management. This study investigated habitat use, seasonal patterns of abundance and population structure of the broadnose sevengill shark Notorynchus cepedianus in the marine temperate environment of a northern Patagonian bay (Argentina). We expected N. cepedianus to exhibit strong seasonality in the bay driven by the seasonal occurrence of important marine mammal prey. However, an alternative or complementary hypothesis could be related to the possibility that N. cepedianus uses the area seasonally as mating grounds. To explore these hypotheses a suite of baited remote underwater video stations and catch and effort data indices were used to estimate the seasonal relative abundance of the species inside the bay. Reproductive hormone levels were employed to determine reproductive status and maturity stages of the population. Results indicated that N. cepedianus uses the bay year-round, showing a peak of abundance during spring when the species aggregates, likely for feeding and mating purposes. Male and female sizes at maturity occurred at 170 and 190 cm of total length, respectively. Contrary to other studies in the Southwest Atlantic, population composition remained similar throughout the seasons, with adults dominating over juveniles and adult females prevailing in the population at all times. Considering the historical abundance decline recently reported for the species, protection and enforcement within protected areas across the Southwest Atlantic must remain of high priority in government initiatives.
Baited remote underwater video systems (BRUVS) are increasingly used to study fish communities, biomass, and animal behaviour. Due to the abundance of BRUVS data, there are many analysis methods. The most commonly used method for analysis of BRUV data is MaxN which refers to the maximum number of individuals observed of a species in a single frame of a video. Here, we present a novel method for BRUVS analysis that involves identifying and counting distinct individuals (MaxIND) to quantify the accuracy of MaxN. Individual oriental bluespotted maskray (Neotrygon orientalis) and the bluespotted fantail ray (Taeniura lymma) were identified on BRUVS by spot patterns, tail characteristics, and sex at three sites in Malaysian Borneo. We demonstrated that MaxIND gave abundances that were 2.4 and 1.1 times higher than MaxN for N. orientalis and T. lymma, respectively. These differences between methods were consistent for each species between sites regardless of the presence of marine reserves. However, differences in abundance estimates from MaxN to MaxIND were apparent between species, indicating that correction factors need to be developed on a species basis to better estimate true abundance. While identifying individuals is time consuming, it provides improved accuracy and information about populations. We therefore recommend the use of MaxIND when rare and endangered species are present, in high density populations, and for behavioural analyses.
The locomotor performance of dogfish during escape responses was observed by means of high-speed video. Dogfish show C-type escape responses that are comparable with those shown previously in teleosts. Dogfish show high variability of turning rates of the anterior part of the body (head to centre of mass), i.e. with peak values from 434 to 1023 deg. s - 1 . We suggest that this variability may be due to the presence of two types of escape manoeuvres, i.e. responses with high and low turning rates, as previously found in a teleost species. Fast responses (i.e. with high maximum turning rates, ranging between 766 and 1023 deg. s - 1 ) showed significantly higher locomotor performance than slow responses (i.e. with low maximum turning rates, ranging between 434 and 593 deg. s - 1 ) in terms of distance covered, speed and acceleration, although no differences were found in the turning radius of the centre of mass during the escape manoeuvres. The existence of two types of escape responses would have implications in terms of both neural control and muscular activation patterns. When compared with literature data for the locomotor performance of bony fishes, dogfish showed relatively low speed and acceleration, comparable turning rates and a turning radius that is in the low part of the range when compared with teleosts, indicating relatively high manoeuvrability. The locomotor performance observed in dogfish is consistent with their morphological characteristics: (1) low locomotor performance associated with low thrust developed by their relatively small posterior depth of section and (2) relatively high manoeuvrability associated with their high flexibility.
To investigate the biochemical effects of capture and restraint on sharks, 17 serum constituents were measured in three species (bonnethead shark Sphyrna tiburo, blacktip shark Carcharhinus limbatus, and bull shark C. leucas) after gill-net capture. The relative degree of capture effects on each animal was judged using an index of behavioral response devised for use in tag−recapture studies. Serum from each shark was assayed for glucose, creatinine, uric acid, sodium, chloride, potassium, inorganic phosphate, total and ionized calcium, total protein, albumin, globulin, alkaline phosphatase, lactate, lactate dehydrogenase, aspartate aminotransferase, and total iron. In addition, hematocrit was measured from whole blood for each shark. When correlated with the relative degree of capture effects, there were significant intraspecific changes in the concentration of potassium, lactate, inorganic phosphate, uric acid, alkaline phosphatase, aspartate aminotransferase, total and ionized calcium, and glucose. Significant interspecific differences in the concentration of sodium, chloride, potassium, total protein, albumin, globulin, lactate dehydrogenase, aspartate aminotransferase, ionized calcium, alkaline phosphatase, and glucose in minimally stressed animals also were observed. The study suggests that the deleterious effects of gill-net capture and restraint probably involve respiratory and metabolic acidosis and hypoglycemia as well as cellular damage. Species-specific and individual differences in the mortality of sharks caught in gill nets are likely related to an animal's respiratory physiology and degree of struggling upon capture as well as to the extent of net entanglement around the gill area.
SUMMARY Fast-start kinematics and performance were determined for Etheostoma caeruleum, Cottus cognatus, Notropis cornutus, Lepomis macrochirus, Perca flavescens, Salmo gairdneri and a hybrid Esox sp. at an acclimation and test temperature of 15 °C. Normal three-stage kinematic patterns were observed for all species. Fast-start movements were similar in all species, except Lepomis, which had slightly higher amplitudes than expected for its length. The duration of kinematic stages was a major variable among the seven species but was a linear function of length. Acceleration rates were not functions of size. Maximum acceleration rates ranged from 22-7 to 39-5 m. s~s with mean rates from 6-i to 12*3 m.s~2, averaged to the completion of kinematic stage 2. Maximum velocity and distance covered in each fast-start stage varied among species but were related to length. Fast-start performance depended primarily on compromise between muscle mass as a percentage of body mass, and lateral body and fin profile. Optimal profiles provide large depth distant from the centre of mass to maximize thrust, and anterior depth enhancement to minimize recoil. The body form of Lepomis is considered optimal for multiple swimming modes.
Fast-starts are brief, sudden accelerations used by fish during predator-prey encounters. The kinematics and performance of fish during fast-start manoeuvres have received a lot of attention since they may determine the outcome of predator-prey interactions in terms of feeding success or survival. We will discuss recent progress on (1) the kinematics of escape responses and feeding strikes, (2) the fast-start performance of species with different body morphologies and from different habitats, and (3) the functional significance of fast-start kinematics and performance within the context of predator-prey interactions.
Combining movement behaviour with other ecological information of predators and their prey is
essential for an adequate understanding of ecosystem dynamics. The movement patterns of broadnose
sevengill sharks, Notorynchus cepedianus , were monitored with acoustic and satellite technology in
coastal areas of southeast Tasmania, Australia. Individuals were tagged in two habitats (Norfolk Bay and
the Derwent Estuary) for which we had ecological information such as diet, population structure and
abundance. Notorynchus cepedianus showed seasonal site fidelity in the use of the coastal habitats. The
general pattern was for sharks to exit coastal areas over winter and females to return the following
spring and males in summer. Their movement into these coastal areas coincided with high seasonal
abundance of their known prey species during summer, suggesting feeding site fidelity. Individuals
tagged in two coastal areas showed low spatial and dietary overlap, suggesting localized site fidelity and
fine spatial scale resource partitioning. This has rarely been reported for large mobile predators. Both
satellite and acoustic methods showed that males make northerly migrations during winter to distances
of at least 1000 km. The combined use of tracking, diet and abundance information demonstrated that
N. cepedianus are likely to exert significant predation pressure on prey inhabiting these areas during
summer. Overall, this study highlights the benefit of complementing movement data with other
ecological information to understand the habitat use of large mobile predators and their potential
influences on ecosystem structure and function.
A bstract
Daily counts of Southern sea lions ( Otaria byronia ) made at Punta Norte, Argentina, during four consecutive breeding seasons (1980–1984) yielded similar results in the time of the reproductive events. Males and females began to arrive during the second week of December. Males reached peak numbers (100–110) between 15 and 21 January. Females reached maximum numbers (300–350) at the end of January. About 380–430 pups were born between December 20 and February 2, and 70–80 percent of births occurred between 10 and 25 January. Copulations peaked during the third week of January. The sex ratio of adult males to adult females at peak season fluctuated from 1:3.7 to 1:4.2. By the first week of February, coinciding with the maximum number of young males (25–50), 90 percent of the adult males had abandoned the area and the number of females fluctuated greatly. Since 1980 the number of females and pups has shown a slight increase, particularly during the 1983–1984 breeding season.
Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigated their locomotory function to determine if pectoral fin function during both benthic station-holding and pelagic swimming differs from fin function described previously in leopard sharks, Triakis semifasciata. We used three-dimensional kinematics and digital particle image velocimetry (DPIV) to quantify pectoral fin function in five white-spotted bamboo sharks, C. plagiosum, during four behaviors: holding station on the substrate, steady horizontal swimming, and rising and sinking during swimming. During benthic station-holding in current flow, bamboo sharks decrease body angle and adjust pectoral fin angle to shed a clockwise fluid vortex. This vortex generates negative lift more than eight times that produced during open water vertical maneuvering and also results in an upstream flow that pushes against the posterior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and at a negative dihedral angle during steady horizontal swimming, promoting maneuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockwise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive lift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substrate and to enhance stability when swimming in the water column. J. Morphol. 249:195–209, 2001. © 2001 Wiley-Liss, Inc.
The escape behaviour of solitary herring (Clupea harengus L.) startled by a sound stimulus was observed by means of high-speed video-filming. The results were compared with data from
a previous study on the escape behaviour of schooling herring. Escape responses were divided into “away responses” and “towards
responses” according to the orientation of the C-bend of the body relative to the stimulus. The proportion of away responses
was smaller for solitary than for schooling herring. In solitary herring, the subsequent escape trajectories of fish making
initial away responses showed a bimodal pattern of distribution, with modes at 130 and 180° from the stimulus. Trajectories
following towards responses, however, were mainly within the semicircle directed at the stimulus, and their pattern of distribution
differed from that of away responses. This result contrasts with observations on schooling herring, whose trajectories following
both initial away and towards responses are directed away from the stimulus. In addition, we measured the response latency,
defined as the interval of time between stimulus presentation and the first detectable movement of the fish. Solitary herring
showed a higher proportion of short-latency responses (latency <50 ms) than schooling herring. Different behaviours appear
to be exhibited by herring depending on whether they are solitary or within a school. We hypothesize that schooling may raise
the threshold for initiation of fast escape responses, giving longer latencies and slower responses which are more appropriate
in their directionality and reduce the possibility of collisions with neighbours. In addition, we suggest that schooling behaviour
enhances the directionality and co-ordination of the escape response of the whole school, possibly increasing the probability
of surviving a predator attack.
The large size, high trophic level and wide distribution of Hexanchiformes (cow and frilled sharks) should position this order as important apex predators in coastal and deep-water ecosystems. This review synthesizes available information on Hexanchiformes, including information not yet published, with the purpose of evaluating their conservation status and assessing their ecological roles in the dynamics of marine ecosystems. Comprising six species, this group has a wide global distribution, with members occurring from shallow coastal areas to depths of c. 2500 m. The limited information available on their reproductive biology suggests that they could be vulnerable to overexploitation (e.g. small litter sizes for most species and suspected long gestation periods). Most of the fishing pressure exerted on Hexanchiformes is in the form of commercial by-catch or recreational fishing. Comprehensive stock and impact assessments are unavailable for most species in most regions due to limited information on life history and catch and abundance time series. When hexanchiform species have been commercially harvested, however, they have been unable to sustain targeted fisheries for long periods. The potentially high vulnerability to intense fishing pressure warrants a conservative exploitation of this order until thorough quantitative assessments are conducted. At least some species have been shown to be significant apex predators in the systems they inhabit. Should Hexanchiformes be removed from coastal and deep-water systems, the lack of sympatric shark species that share the same resources suggests no other species would be capable of fulfilling their apex predator role in the short term. This has potential ecosystem consequences such as meso-predator release or trophic cascades. This review proposes some hypotheses on the ecology of Hexanchiformes and their role in ecosystem dynamics, highlighting the areas where critical information is required to stimulate research directions.
During predator–prey encounters, a high locomotor performance in unsteady manoeuvres (i.e. acceleration, turning) is desirable for both predators and prey. While speed increases with size in fish and other aquatic vertebrates in continuous swimming, the speed achieved within a given time, a relevant parameter in predator–prey encounters, is size independent. In addition, most parameters indicating high performance in unsteady swimming decrease with size. Both theoretical considerations and data on acceleration suggest a decrease with body size. Small turning radii and high turning rates are indices of manoeuvrability in space and in time, respectively. Manoeuvrability decreases with body length, as minimum turning radii and maximum turning rates increase and decrease with body length, respectively. In addition, the scaling of linear performance in fish locomotion may be modulated by turning behaviour, which is an essential component of the escape response. In angelfish, for example, the speed of large fish is inversely related to their turning angle, i.e. fish escaping at large turning angles show lower speed than fish escaping at small turning angles. The scaling of unsteady locomotor performance makes it difficult for large aquatic vertebrates to capture elusive prey by using whole-body attacks, since the overall manoeuvrability and acceleration of small prey is likely to be superior to that of large predators. Feeding strategies in vertebrate predators can be related to the predator–prey length ratios. At prey–predator ratios higher than approximately 10−2, vertebrate predators are particulate feeders, while at smaller ratios, they tend to be filter feeders. At intermediate ratios, large aquatic predators may use a variety of feeding methods that aid, or do not involve, whole body attacks. Among these are bubble curtains used by humpback whales to trap fish schools, and tail-slapping of fish by delphinids. Tail slapping by killer whales is discussed as an example of these strategies. The speed and acceleration achieved by the flukes of killer whales during tail slaps are higher and comparable, respectively, to those that can be expected in their prey, making tail-slapping an effective predator behaviour.
Escape responses are used by most fish species in order to avoid predation. Escape responses include a number of behavioral and kinematic components, such as responsiveness, reaction distance, escape latency, directionality, and distance-derived performance. All of these components can contribute to escape success. Work on the context-dependent variability has focused on reaction distance, and suggests that this component is largely determined by the relative cost and benefits of escaping (economic hypothesis). For example, reaction distance was found to depend on many factors related to perceived risk and cost of escaping, such as the attack speed and size of the predators, the proximity to refuges, and engagement in other activities (e.g., feeding). Evidence from many behavioral, kinematic, and physiological studies suggest that performance in other components of the escape response is also not always maximized. For example, escape latencies may increase in the presence of schooling neighbors, and escape speed is higher in fish that have been subject to higher predation pressure. In addition, all escape components are further modulated by the effect of environmental factors. Variability in escape components can be interpreted by using both ultimate and proximate explanations, for example, the effect of stimulus strength on escape latency can be interpreted as the triggering neural threshold varying with stimulus strength (proximate explanation) and high intensity stimuli representing higher risk to the prey (ultimate explanation). An integrative approach is suggested for a full, ecologically relevant, assessment of escape performance in fish.
Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size-matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r(2) values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non-vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming.
Fast-starts are brief, sudden accelerations used by fish during predatorprey encounters. The kinematics and performance of fish during fast-start manoeuvres have received a lot of attention since they may determine the outcome of predatorprey interactions in terms of feeding success or survival. We will discuss recent progress on (1) the kinematics of escape responses and feeding strikes, (2) the fast-start performance of species with different body morphologies and from different habitats, and (3) the functional significance of fast-start kinematics and performance within the context of predatorprey interactions.
The startle response is a model system for examining the neural basis of behavior because of its relatively simple neural circuit organization and kinematic pattern. In fishes, the two primary types of startle behavior differ in their initial movements. In the C-start type of startle, the fish bends into a C shape, while the S-start involves an S-shaped body bend. Although considerable research has focused on determining how the C-start is generated neurally, S-start neurobiology has not been examined. I quantify the kinematics and electromyographic patterns of the initial movements of the C-start and S-start behaviors of the muskellunge (Esox masquinongy) to test three hypotheses for how the S-start is generated. (i) The S-start is generated by the same motor neural circuit as the C-start, but passive bending of the tail causes the body to take on an S shape. (ii) The S-start is generated by the same motor neural circuit as undulatory swimming. (iii) The S-start is generated by an independent neural mechanism from that used either in the C-start or in undulatory swimming. Results from kinematics and muscle activity patterns support the third hypothesis. In the muskellunge, the S-start is a high-performance startle behavior with peak angular velocity and peak angular acceleration of its initial bending comparable with those of the C-start and higher than would be expected for undulatory swimming. The S-start motor pattern, however, is distinct from the C-start motor pattern in having simultaneous muscle activity anteriorly on one side of the body and posteriorly on the opposite side. In contrast, the C-start is characterized by simultaneous unilateral muscle activity along the full length of the body. Alternative models are proposed for S-start neural circuit organization involving reticulospinal and local control of muscle activity.
The peculiar head morphology of hammerhead sharks has spawned a variety of untested functional hypotheses. One of the most intuitively appealing ideas is that the anterior foil acts, as in canard-winged aircraft, to increase maneuverability. We tested this hypothesis by determining whether juveniles of two hammerhead species (Sphyrna tiburo and S. lewini) turn more sharply, more often, and with greater velocity than a juvenile carcharhinid shark (Carcharhinus plumbeus). Although the hammerheads were more maneuverable, further investigation revealed that they do not roll their body during turns, suggesting that the cephalofoil does not act as a steering wing. We also show that hammerhead sharks demonstrate greater lateral flexure in a turn than carcharhinids, and that this flexibility may be due to cross sectional shape rather than number of vertebrae.
Elasmobranch phylogeny: a mitochondrial estimate based on 595 species
- G J Naylor
- J N Caira
- K Jensen
- K A Rosana
- N Straube
- C Lakner
Naylor, G. J., Caira, J. N., Jensen, K., Rosana, K. A., Straube, N., & Lakner,
C. (2012). Elasmobranch phylogeny: a mitochondrial estimate based
on 595 species. In J. Carrier, J. Musick, & M. Heithaus (Eds.), Biology
of sharks and their relatives (pp. 125-151). CRC Press.
Biology of sharks and their relatives
- G. J. Naylor
- J. N. Caira
- K. Jensen
- K. A. Rosana
- N. Straube
- C. Lakner