Metabolic rates and the energetic cost of external tag attachment in juvenile blacktip sharks Carcharhinus limbatus

This study reports on the metabolic rate of the blacktip shark Carcharhinus limbatus and the energetic costs of external tag attachment. Metabolic rates, swimming speed and tail‐beat (B_T) frequency were measured in a static respirometer with untagged animals and animals equipped with a small data logger. Tagged sharks showed significantly higher routine oxygen consumption and lower swimming speeds than untagged animals, indicating that tagging significantly affected the swimming efficiency and energetic requirements in these small sharks, and that these effects must be accounted for when interpreting telemetry data from free‐ranging individuals.     

Tag retention and survival of juvenile bighead carp implanted with a dummy acoustic tag at three temperatures

Bighead carp Hypophthalmichthys nobilis and silver carp Hypophthalmichthys molitrix (together, the bigheaded carps) are invasive fishes in North America that have resulted in substantial negative effects on native fish communities and aquatic ecosystems. Movement and behavior of adult bigheaded carps has been studied previously using telemetry, while similar studies with juvenile bigheaded carps have yet to be attempted. Recent technological advances in telemetry transmitters has increased the availability of tags sufficiently small enough to implant in juvenile carps. However, the effects of surgical implantation of telemetry tags on juvenile bigheaded carps have not been evaluated. We determined tag retention and survival associated with surgical implantation of acoustic telemetry tags into juvenile bighead carp (range 128–152 mm total length) at three temperatures (13, 18, and 23°C). In addition, we assessed the effect of surgically implanted transmitters on the fitness, defined as changes in weight or critical swimming speed, of carp implanted with transmitters. Survival was high among tagged fish (85%) with 47% of tags retained at the conclusion of the 45‐day study. No substantial decline in fitness of the fish was observed in tagged fish compared to untagged fish.     

Tag retention and mortality of adult Atlantic salmon Salmo salar gastrically tagged with different sized telemetry transmitters

A batch of 1 sea winter pre‐spawning adult Salmo salar from the Bush river in Northern Ireland, U.K., were gastrically tagged with large (13 mm diameter) and small (9 mm diameter) dummy acoustic telemetry tags alongside untagged control fish. Survival differed between control and tagged fish and the estimated probability of survival by the end of the study for control fish with no tag was 0·94, small tags was 0·90 and large tags was 0·72. Tag loss through regurgitation was slightly higher for fish tagged with larger tags than for fish tagged with smaller tags and the estimated probability of tag loss for fish with a small tag was 0·10 and for large tags was 0·14.     

Review of Elasmobranch Behavioral Studies Using Ultrasonic Telemetry with Special Reference to the Lemon Shark, Negaprion Brevirostris, Around Bimini Islands, Bahamas

A review of past behavioral ultrasonic telemetry studies of sharks and rays is presented together with previously unpublished material on the behavior of the lemon shark, Negaprion brevirostris, around the Bimini Islands, Bahamas. The review, focusing on movement behaviors of 20 shark and three ray species, reveals that elasmobranchs exhibit a variety of temporal and spatial patterns in terms of rates-of-movement and vertical as well as horizontal migrations. The lack of an apparent pattern in a few species is probably attributable to the scarcity of tracking data. Movements are probably governed by several factors, some still not studied, but data show that food, water temperature, bottom type, and magnetic gradient play major roles in a shark's decision of where and when to swim. A few species exhibit differences in behavior between groups of sharks within the same geographical area. This interesting finding warrants further research to evaluate the causes of these apparent differences and whether these groups constitute different subpopulations of the same species. The lack of telemetry data on batoids and some orders of sharks must be addressed before we can gain a more comprehensive understanding of the behavior of elasmobranch fishes. Previously unpublished data from 47 smaller and 38 larger juvenile lemon sharks, collected over the decade 1988–1998, provide new results on movement patterns, habitat selection, activity rhythms, swimming speed, rate-of-movement, and homing behavior. From these results we conclude that the lemon shark is an active predator with a strong, apparently innate homing mechanism. This species shows ontogenetic differences in habitat selection and behavior, as well as differences in movements between groups of individuals within the same area. We suggest three hypotheses for future research on related topics that will help to understand the enigmatic behavior of sharks.     

Scaling of ctenes and consequences for swimming performance in the ctenophore Pleurobrachia bachei

Ctenophores coordinate large macrociliary structures called ctenes to propel themselves through the water. The morphology and kinematics of the ctenes mediate swimming performance. We investigated morphological and kinematic factors affecting swimming performance in free‐swimming ctenophores (Pleurobrachia bachei) using high speed videography. Our morphological results showed that the relationship between body size and ctene morphology and arrangement in P. bachei were well described using linear (i.e., isometric) relationships, which suggests functional limitations of ctenes that vary among individuals of different sizes. Our kinematic results showed that isometric constraints on swimming performance can potentially be overcome by alterations in kinematics: (a) swimming speed in P. bachei increased with ctene beat frequency over a range of body lengths, and (b) the separation of ctenes into clumps of cilia allowed the ctene to increase in width during the effective stroke and decrease in width during recovery. Separation increases the surface area of the ctene during the effective stroke, likely increasing the thrust produced. The finding that ctenes are not monoliths and instead are separated into clumps of cilia has not been previously described, and we subsequently observed this trait in three other ctenophore species: Euplokamis dunlapae, Bolinopsis infundibulum, and Beroe mitrata. Flexibility in function may be a necessary corollary to isometric development of the ctenes as propulsive structures.     

The Effect of Drag and Attachment Site of External Tags on Swimming Eels: Experimental Quantification and Evaluation Tool

Telemetry studies on aquatic animals often use external tags to monitor migration patterns and help to inform conservation effort. However, external tags are known to impair swimming energetics dramatically in a variety of species, including the endangered European eel. Due to their high swimming efficiency, anguilliform swimmers are very susceptibility for added drag. Using an integration of swimming physiology, behaviour and kinematics, we investigated the effect of additional drag and site of externally attached tags on swimming mode and costs. The results show a significant effect of a) attachment site and b) drag on multiple energetic parameters, such as Cost Of Transport (COT), critical swimming speed (U_crit) and optimal swimming speed (U_opt), possibly due to changes in swimming kinematics. Attachment at 0.125 bl from the tip of the snout is a better choice than at the Centre Of Mass (0.35 bl), as it is the case in current telemetry studies. Quantification of added drag effect on COT and U_crit show a (limited) correlation, suggesting that the U_crit test can be used for evaluating external tags for telemetry studies until a certain threshold value. U_opt is not affected by added drag, validating previous findings of telemetry studies. The integrative methodology and the evaluation tool presented here can be used for the design of new studies using external telemetry tags, and the (re-) evaluation of relevant studies on anguilliform swimmers.     

How small puffers (Teleostei: Tetraodontidae) swim

 The tetraodontiform swimming mode has recently attracted attention because puffers swim very steadily and, unlike most of the other median and paired fin (MPF) swimmers, use more than one pair of fins to propel themselves through the water. To date, only one study presenting data concerning the swimming kinematics of puffers has been published, and this study dealt only with two species of large body size. In the present study, the swimming kinematics of small puffers (<6 cm TL) Tetraodon schoutedeni is described and compared to the swimming kinematics of larger puffers and boxfish. The results show that, generally, the swimming kinematics of small puffers is similar to that of larger puffers. The main differences that were found are in the synchronization of dorsal and anal fin motion, and in the motion of the pectoral fins, which complete their adduction before the dorsal and anal fins do. Maximum fin beat frequency was 18.4 Hz, much faster than that of larger puffers. At slow and median swimming speeds, dorsal fin beat amplitude increases with swimming speed and then remains constant between median and fast swimming speeds. The results confirm previous findings that puffers swim extremely steadily. Most of the differences in swimming kinematics between large and small puffers can be attributed to the size differences, but the difference in fin synchronization should be further studied to be completely understood. Received: September 27, 2002 / Revised: January 7, 2003 / Accepted: February 6, 2003     

Coastal swimming patterns of white sharks (<Emphasis Type="Italic">Carcharodon carcharias</Emphasis>) at Mossel Bay,South Africa

Between June and December 2005, active and passive acoustic telemetry was used to examine fine scale movements of 13 white sharks (Carcharodon carcharias) (ten passive, three active) at Mossel Bay. A total of 24 active trackings (ranging from 2 h to 103 h in duration) were conducted. Patterns of rate of movement (ROM), swimming linearity (LI), swimming bearing, and instantaneous swimming speed (ISS) were assessed. A conversion quotient (Q) of 1.21 between ISS and ROM (10 min sample interval) was calculated suggesting ROM is a good indicator of white shark activity. The mean ROM for tracked sharks was 0.52 m·s⁻¹, with a greatest sustained ROM of 1.33 m·s⁻¹ (4.8 km·h⁻¹). Sharks displayed greatest LI and ROM during directional travels between the three persistent aggregation sites. The majority of the shark movement was, however, non-linear as the sharks repeat patrolled at the three aggregation sites. Two of these sites were not associated with pinniped presence, and sharks typically patrolled back and forth parallel to the shore line at a comparatively low ROM which suggested resting. The third aggregation site was adjacent to Seal Island, and despite low LI, sharks displayed a high ROM, indicating high activity levels. We propose that the high ROM is related to maximising search area when patrolling to hunt Cape fur seals (Arctocephalus p. pusillus).     

Unilateral ablation of trunk superficial neuromasts increases directional instability during steady swimming in the yellowtail kingfish Seriola lalandi

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail‐beat frequency, stride length, caudal fin‐beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A₀) was significantly increased in SN‐disrupted fish compared with sham‐operated controls. In addition, the orientation of caudal fin‐tip relative to the overall swimming direction of SN‐disrupted fish was significantly deflected (two‐fold) in comparison with sham‐operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body‐wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN‐disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (L_F) s^?1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.     

Telemetry tag effects on juvenile lingcod Ophiodon elongatus movement: a laboratory and field study

This study tested the behavioural effects of tagging subyearling and yearling lingcod Ophiodon elongatus with acoustic telemetry tags in laboratory tanks and in the natural environment (Puget Sound, WA). In the laboratory, tagged individuals showed less movement and feeding behaviour soon after tagging than untagged controls. The effect dissipated after c. 1 week, presumably as the tagged O. elongatus recovered from surgery or adjusted to the presence of the tags. This dissipation enabled a field study that compared early‐tagged individuals with a long recovery period after tagging to recently‐tagged individuals with a short recovery period after tagging. Consistent with findings from the laboratory experiment, recently tagged individuals showed less movement away from three release sites in Puget Sound than early‐tagged individuals. Together, the laboratory and field results provide evidence of temporary tag effects on actual movement in the natural environment and provide a method for testing tag effects in the field. This study suggests that subyearling and yearling O. elongatus should be held for a recovery period before release. If holding after tagging is not an option, then movement data collected during the first week should be interpreted cautiously.     

Pop up satellite tags impair swimming performance and energetics of the European eel (Anguilla anguilla)

Pop-up satellite archival tags (PSATs) have recently been applied in attempts to follow the oceanic spawning migration of the European eel. PSATs are quite large, and in all likelihood their hydraulic drag constitutes an additional cost during swimming, which remains to be quantified, as does the potential implication for successful migration. Silver eels (L_T = 598.6±29 mm SD, N = 9) were subjected to swimming trials in a Steffensen-type swim tunnel at increasing speeds of 0.3–0.9 body lengths s⁻¹, first without and subsequently with, a scaled down PSAT dummy attached. The tag significantly increased oxygen consumption (MO₂) during swimming and elevated minimum cost of transport (COT_min) by 26%. Standard (SMR) and active metabolic rate (AMR) as well as metabolic scope remained unaffected, suggesting that the observed effects were caused by increased drag. Optimal swimming speed (U _opt) was unchanged, whereas critical swimming speed (U _crit) decreased significantly. Swimming with a PSAT altered swimming kinematics as verified by significant changes to tail beat frequency (f), body wave speed (v) and Strouhal number (St). The results demonstrate that energy expenditure, swimming performance and efficiency all are significantly affected in migrating eels with external tags.     

Roles of Adenylate Cyclases in Ciliary Responses of Paramecium to Mechanical Stimulation

Paramecium shows rapid forward swimming due to increased beat frequency of cilia in normal (forward swimming) direction in response to various kinds of stimuli applied to the cell surface that cause K⁺‐outflow accompanied by a membrane hyperpolarization. Some adenylate cyclases are known to be functional K⁺ channels in the membrane. Using gene‐specific knockdown methods, we examined nine paralogues of adenylate cyclases in P. tetraurelia to ascertain whether and how they are involved in the mechanical stimulus‐induced hyperpolarization‐coupled acceleration of forward swimming. Results demonstrated that knockdown of the adenylate cyclase 1 (ac1)‐gene and 2 (ac2)‐gene inhibited the acceleration of forward swimming in response to mechanical stimulation of the cell, whereas that spared the acceleration response to external application of 8‐Br‐cAMP and dilution of extracellular [K⁺] induced hyperpolarization. Electrophysiological examination of the knockdown cells revealed that the hyperpolarization‐activated inward K⁺ current is smaller than that of a normal cell. Our results suggest that AC1 and AC2 are involved in the mechanical stimulus‐induced acceleration of ciliary beat in Paramecium.     

Drag of suction cup tags on swimming animals: Modeling and measurement

Bio‐logging tags are widely used to study the behavior and movements of marine mammals with the tacit assumption of little impact to the animal. However, tags on fast‐swimming animals generate substantial hydrodynamic forces potentially affecting behavior and energetics adversely, or promoting early removal of the tag. In this work, hydrodynamic loading of three novel tag housing designs are compared over a range of swimming speeds using computational fluid dynamics (CFD). Results from CFD simulation were verified using tag models in a water flume with close agreement. Drag forces were reduced by minimizing geometric disruptions to the flow around the housing, while lift forces were reduced by minimizing the frontal cross‐sectional area of the housing and holding the tag close to the attachment surface. Hydrodynamic tag design resulted in an experimentally measured 60% drag force reduction in 5.6 m/s flow. For all housing designs, off‐axis flow increased the magnitude of the force on the tag. Experimental work with a common dolphin (Delphinus delphis) cadaver indicates that the suction cups used to attach the types of tags described here provide sufficient attachment force to resist failure to predicted forces at swimming speeds of up to 10 m/s.     

Swimming restricted foraging behavior of two zooplanktivorous fishes <Emphasis Type="Italic">Pseudorasbora parva</Emphasis> and <Emphasis Type="Italic">Rasbora daniconius</Emphasis> (Cyprinidae) in a simulated structured environment

In littoral zones of aquatic systems, submerged macrophytes have marked structural variation that can modify the foraging activity of planktivores. Swimming and feeding behavior of Pseudorasbora parva and Rasbora daniconius (Cyprinidae) on their prey Daphnia pulex and Artemia salina, respectively, was studied in a series of laboratory experiments with varying stem densities. A range of stem densities was tested for each of the two species to compare the effect of simulated macrophytes on prey attack rates and swimming speed, average stem distance (D) was measured in fish body lengths for each of the two fish species. We found that, with reducing average stem distance, the attack rate decreased in the similar trend and this trend was similar for both fish species. However, the species differed in the degree to which swimming activity was hindered at increased stem densities, and this was due to species-specific differences in the distance moved with one tail beat. Therefore, we conclude that the reductions in swimming speed with reduced average stem distance are due to the differences in fish movement per tail beat.     

Using unmanned aerial vehicle (UAV) surveys and image analysis in the study of large surface‐associated marine species: a case study on reef sharks Carcharhinus melanopterus shoaling behaviour

A novel image analysis‐based technique applied to unmanned aerial vehicle (UAV) survey data is described to detect and locate individual free‐ranging sharks within aggregations. The method allows rapid collection of data and quantification of fine‐scale swimming and collective patterns of sharks. We demonstrate the usefulness of this technique in a small‐scale case study exploring the shoaling tendencies of blacktip reef sharks Carcharhinus melanopterus in a large lagoon within Moorea, French Polynesia. Using our approach, we found that C. melanopterus displayed increased alignment with shoal companions when distributed over a sandflat where they are regularly fed for ecotourism purposes as compared with when they shoaled in a deeper adjacent channel. Our case study highlights the potential of a relatively low‐cost method that combines UAV survey data and image analysis to detect differences in shoaling patterns of free‐ranging sharks in shallow habitats. This approach offers an alternative to current techniques commonly used in controlled settings that require time‐consuming post‐processing effort.     

PIT-tagging Italian spined loach (Cobitis bilineata): Methodology,survival and behavioural effects

The Italian spined loach (Cobitis bilineata) is an elongated, small-sized (<12 cm) spined loach native to northern Italy, Slovenia and Croatia. As for loaches in general, little is known about the individual movements of this loach in nature. Passive integrated transponders (PIT-tags) are small (typically 7–32 mm), relatively cheap and allow tracking of individual fish movements and behaviour. A fundamental assumption in animal telemetry is that the performance of a tagged animal does not deviate substantially from its natural performance. Although PIT-tagged fish often display high survival and tag retention, the effect varies between species and contexts, and few studies have looked at behavioural effects of PIT-tagging. Here we demonstrate a PIT-tagging methodology for spined loaches, and compare survival, activity and provoked escape response (maximum swimming speed) between tagged and control fish. We also track tag retention in the tagged fish. Italian spined loaches tagged with 12 mm PIT-tags displayed high tag retention and no extra mortality, and no effects of tagging on activity or maximum swimming speed were observed. The tag-to-fish weight and length ratios in our study ranged from 2% to 5% and from 10% to 16%, respectively, and we conclude that PIT-tagging, within these ratios, appears suitable for Italian spined loach.     

Population variation in the thermal response to climate change reveals differing sensitivity in a benthic shark

Many species with broad distributions are exposed to different thermal regimes which often select for varied phenotypes. This intraspecific variation is often overlooked but may be critical in dictating the vulnerability of different populations to environmental change. We reared Port Jackson shark (Heterodontus portusjacksoni) eggs from two thermally discrete populations (i.e. Jervis Bay and Adelaide) under each location's present‐day mean temperatures, predicted end‐of‐century temperatures and under reciprocal‐cross conditions to establish intraspecific thermal sensitivity. Rearing temperatures strongly influenced ?O_2Max and critical thermal limits, regardless of population, indicative of acclimation processes. However, there were significant population‐level effects, such that Jervis Bay sharks, regardless of rearing temperature, did not exhibit differences in ?O_2Rest, but under elevated temperatures exhibited reduced maximum swimming activity with step‐wise increases in temperature. In contrast, Adelaide sharks reared under elevated temperatures doubled their ?O_2Rest, relative to their present‐day temperature counterparts; however, maximum swimming activity was not influenced. With respect to reciprocal‐cross comparisons, few differences were detected between Jervis Bay and Adelaide sharks reared under ambient Jervis Bay temperatures. Similarly, juveniles (from both populations) reared under Adelaide conditions had similar thermal limits and swimming activity (maximum volitional velocity and distance) to each other, indicative of conserved acclimation capacity. However, under Adelaide temperatures, the ?O_2Rest of Jervis Bay sharks was greater than that of Adelaide sharks. This indicates that the energetics of cooler water population (Adelaide) is likely more thermally sensitive than that of the warmer population (Jervis Bay). While unique to elasmobranchs, these data provide further support that by treating species as static, homogeneous populations, we ignore the impacts of thermal history and intraspecific variation on thermal sensitivity. With climate change, intraspecific variation will manifest as populations move, demographics change or extirpations occur, starting with the most sensitive populations.     

The use of an unoccupied aerial vehicle to survey shark species over sand and rocky-reef habitats in a marine protected area

Cabo Pulmo National Park was established in 1995 and has since seen a large increase in fish biomass. An unoccupied aerial vehicle (UAV) was used to survey shallow coastal habitat in which lemon sharks (Negaprion brevirostris), bull sharks (Carcharhinus leucas) and Pacific nurse sharks (Ginglymostoma unami) were recorded. Sharks were more common in the afternoon, potentially using warmer shallow areas to behaviourally thermoregulate. This study highlights UAV surveying to be a viable tool for species identification, a limitation of previous terrestrial surveys conducted in the area.     

Chemical excretions of angled bonefish Albula vulpes and their potential use as predation cues by juvenile lemon sharks Negaprion brevirostris

Bonefish Albula vulpes (n = 7) exercised to exhaustion and air exposed for 1 min as part of a catch‐and‐release angling event were found to excrete both ammonia and urea, but cortisol and lactate were below detectable levels. Urea made up a greater proportion of total nitrogen excretion from these fish at all time points following an angling event. When captive juvenile lemon sharks Negaprion brevirostris (n = 12) were exposed to a 30 s pulse of these chemicals [ammonia (500 mM), cortisol (20 µg l^?1), lactate (6 mM) or urea (3 mM)], they showed a significant reduction in the frequency of resting behaviours when exposed to ammonia and urea than when exposed to control water. It appears that products excreted by A. vulpes, particularly ammonia and urea, may provide an olfactory cue for the post‐release predation of A. vulpes by N. brevirostris during catch‐and‐release angling events.