Increase In Swimming Speed Research Articles

Volitional Swimming Kinematics of Blacktip Sharks, Carcharhinus limbatus, in the Wild

Recent work showed that two species of hammerhead sharks operated as a double oscillating system, where frequency and amplitude differed in the anterior and posterior parts of the body. We hypothesized that a double oscillating system would be present in a large, volitionally swimming, conventionally shaped carcharhinid shark. Swimming kinematics analyses provide quantification to mechanistically examine swimming within and among species. Here, we quantify blacktip shark (Carcharhinus limbatus) volitional swimming kinematics under natural conditions to assess variation between anterior and posterior body regions and demonstrate the presence of a double oscillating system. We captured footage of 80 individual blacktips swimming in the wild using a DJI Phantom 4 Pro aerial drone. The widespread accessibility of aerial drone technology has allowed for greater observation of wild marine megafauna. We used Loggerpro motion tracking software to track five anatomical landmarks frame by frame to calculate tailbeat frequency, tailbeat amplitude, speed, and anterior/posterior variables: amplitude and frequency of the head and tail, and the body curvature measured as anterior and posterior flexion. We found significant increases in tailbeat frequency and amplitude with increasing swimming speed. Tailbeat frequency decreased and tailbeat amplitude increased as posterior flexion amplitude increased. We found significant differences between anterior and posterior amplitudes and frequencies, suggesting a double oscillating modality of wave propagation. These data support previous work that hypothesized the importance of a double oscillating system for increased sensory perception. These methods demonstrate the utility of quantifying swimming kinematics of wild animals through direct observation, with the potential to apply a biomechanical perspective to movement ecology paradigms.

Field Testing of Biohybrid Robotic Jellyfish to Demonstrate Enhanced Swimming Speeds.

Biohybrid robotic designs incorporating live animals and self-contained microelectronic systems can leverage the animals’ own metabolism to reduce power constraints and act as natural chassis and actuators with damage tolerance. Previous work established that biohybrid robotic jellyfish can exhibit enhanced speeds up to 2.8 times their baseline behavior in laboratory environments. However, it remains unknown if the results could be applied in natural, dynamic ocean environments and what factors can contribute to large animal variability. Deploying this system in the coastal waters of Massachusetts, we validate and extend prior laboratory work by demonstrating increases in jellyfish swimming speeds up to 2.3 times greater than their baseline, with absolute swimming speeds up to 6.6 ± 0.3 cm s−1. These experimental swimming speeds are predicted using a hydrodynamic model with morphological and time-dependent input parameters obtained from field experiment videos. The theoretical model can provide a basis to choose specific jellyfish with desirable traits to maximize enhancements from robotic manipulation. With future work to increase maneuverability and incorporate sensors, biohybrid robotic jellyfish can potentially be used to track environmental changes in applications for ocean monitoring.

Acute effects of acetaminophen on the developmental, swimming performance and cardiovascular activities of the African catfish embryos/larvae (Clarias gariepinus)

Acetaminophen is a widely used analgesic that has been detected in many water bodies with few reports concerning its potential toxicity to fish. This study sought to assess the developmental, swimming performance and cardiovascular activities of embryo/larvae catfish (Clarias gariepinus) exposed to acetaminophen. The Organization for Economic Development (OECD) Fish Embryo Acute Toxicity Test (OECD 236) was employed. Fertilized embryo were exposed to different concentrations of acetaminophen (0, 0.5, 1, 10 µg/L) for 96 h. Hatching rates of the embryo were observed to decrease with increasing concentrations of acetaminophen. Fish embryo exposed to acetaminophen displayed varying levels of teratogenic effects at different levels of development in a dose-dependent manner. The results also showed a significant (p < 0.05) dose-dependent increase in swimming speed and movement patterns in fish larvae exposed to acetaminophen, with distance travelled in larvae exposed to the highest concentration of acetaminophen (10 µg/L) about eight (8) times the distance travelled by the control larvae, indicating that acetaminophen-induced erratic swimming behaviour in the catfish species. Cardiotoxicity was evident, with a significant reduction in heartbeat rate with increasing concentrations of acetaminophen. The results showed that exposure to acetaminophen resulted in teratogenic, neurotoxic and cardiotoxic effects in embryo/larvae of Clarias gariepinus. The findings suggest that acetaminophen which has recently been detected in many water bodies could potentially impact on survival of aquatic life, especially catfish.

Behavioral and physiological responses of Daphnia magna to salicylic acid

Salicylic acid (SA), a metabolite of acetylsalicylic acid is a monohydroxybenzoic acid a common non-steroidal analgesic and anti-inflammatory drug (NSAID) frequently detected in various aquatic ecosystems at concentrations up to 19.50 μg L−1 in surface waters near livestock farms and 59.6 μg L−1 in wastewaters. Little is known on the effects of short-term exposure of freshwater crustaceans to salicylic acid. Therefore, the aim of our study was to determine the effects of SA at concentrations of 5 μg L−1, 500 μg L−1, 5 mg L−1, 50 mg L−1 and 500 mg L−1 on the behavior (swimming speed, swimming height, distance travelled) and physiological endpoints (heart rate, mandible movement) of Daphnia magna exposed for 24 h, 48 h and 72 h. The results showed that SA inhibited the swimming speed, swimming height and distance travelled, heart rate and mandible movement at 5 mg L−1, 50 mg L−1 and 500 mg L−1 when compared to the control. On the other hand, SA at 5 μg L−1 and 500 μg L−1 transiently increased swimming speed and distance travelled after 24 h of the exposure, except for swimming height. Behavioral and physiological disturbances were observed much earlier than lethality. Our study showed SA at environmental levels may be an ecotoxicological agent imparing behavior and physiology of freshwater crustaceans.

Heart rates of Atlantic salmon Salmo salar during a critical swim speed test and subsequent recovery.

In this study, heart rate (HR) bio-loggers were implanted in the abdominal cavity of 12 post-smolt Atlantic salmon Salmo salar weighing 1024 ± 31 g and acclimated to 12°C sea water. One week after the surgical procedure, a critical swim speed (Ucrit ) test was performed on tagged and untagged conspecifics, whereafter tagged fish were maintained in their holding tanks for another week. The Ucrit was statistically similar between tagged and untagged fish (2.67 ± 0.04 and 2.74 ± 0.05 body lengths s-1 , respectively) showing that the bio-logger did not compromise the swimming performance. In the pre-swim week, a diurnal cycle was apparent with HR peaking at 65 beats min-1 during the day and approaching 40 beats min-1 at night. In the Ucrit test, HR increased approximately exponentially with swimming speed until a plateau was reached at the final speed before fatigue with a maximum of 85.2 ± 0.7 beats min-1 . During subsequent recovery tagged fish could be divided into a surviving group (N = 8) and a moribund group (N = 4). In surviving fish HR had fully recovered to pre-swim levels after 24 h, including reestablishment of a diurnal HR cycle. In moribund fish HR never recovered and remained elevated at c. 80 beats min-1 for 4 days, whereafter they started dying. We did not identify a proximal cause of death in moribund fish, but possible explanations are discussed. Tail beat frequency (TBF) was also measured and showed a more consistent response to increased swimming speeds. As such, when exploring correlations between HR, TBF and metabolic rates at different swimming speeds, TBF provides better predictions. On the contrary, HR measurements in free swimming fish over extended periods of time are useful for other purposes such as assessing the accumulative burden of various stressors and recovery trajectories from exhaustive exercise.

Foraging strategy mediates ectotherm predator-prey responses to climate warming.

Climate warming and species traits interact to influence predator performance, including individual feeding and growth rates. However, the effects of an important trait-predator foraging strategy-are largely unknown. We investigated the interactions between predator foraging strategy and temperature on two ectotherm predators: an active predator, the backswimmer Notonecta undulata, and a sit-and-wait predator, the damselfly Enallagma annexum. In a series of predator-prey experiments across a temperature gradient, we measured predator feeding rates on an active prey species, zooplankton Daphnia pulex, predator growth rates, and mechanisms that influence predator feeding: body speed of predators and prey (here measured as swimming speed), prey encounter rates, capture success, attack rates, and handling time. Overall, warming led to increased feeding rates for both predators through changes to each component of the predator's functional response. We found that prey swimming speed strongly increased with temperature. The active predator's swimming speed also increased with temperature, and together, the increase in predator and prey swimming speed resulted in twofold higher prey encounter rates for the active predator at warmer temperatures. By contrast, prey encounter rates of the sit-and-wait predator increased fourfold with rising temperatures as a result of increased prey swimming speed. Concurrently, increased prey swimming speed was associated with a decline in the active predator's capture success at high temperatures, whereas the sit-and-wait predator's capture success slightly increased with temperature. We provide some of the first evidence that foraging traits mediate the indirect effects of warming on predator performance. Understanding how traits influence species' responses to warming could clarify how climate change will affect entire functional groups of species.

Influence of stroke rate on coordination and sprint performance in elite male and female swimmers.

This study investigated the effects of gender and the manipulation of the preferred stroke rate on swimming performance and arm coordination in elite front crawl swimmers. Nineteen swimmers performed a dual task, that is, imposed stroke rate and maximal speed. They swam nine 25-m trials at maximal speed twice: one trial at the preferential stroke rate, one trial at maximal stroke rate and seven trials at stroke rates between 41 and 59 cycles/min imposed by an Aquapacer. Stroke rate, arm stroke phases, and arm coordination were computed from an inertial measurement unit on each forearm and one on the sacrum. Time on the 25-m was recorded to assess swimming speed. Results indicated that the error between the imposed and performed stroke rates was lowest at the preferred stroke rate for women. An increase in stroke rate led to an increase in swimming speed and the index of coordination, but these changes could be influenced by the preferred stroke rate. Individual analysis revealed that some swimmers exhibited higher flexibility (larger range of stroke rate) around their preferred stroke rate. This stroke rate flexibility appeared more functional in swimmers who reached higher speeds when swimming at the maximal stroke rate than at the preferred stroke rate.

Minor effects of dietary methylmercury on growth and reproduction of the sheepshead minnow Cyprinodon variegatus and toxicity to their offspring

Methylmercury (MeHg) is a neurotoxic compound that is found in virtually all fish and biomagnifies in aquatic food webs. Although MeHg concentrations in marine and estuarine fish are often elevated, the impacts of MeHg on marine and estuarine fish have largely been understudied. To evaluate the impact of dietary MeHg on marine fish reproduction and effects on their offspring, female juvenile sheepshead minnows (Cyprinodon variegatus) at three months of age were experimentally exposed to MeHg-contaminated diets for two months and then paired with Hg-free males for spawning. Egg production, hatching success of embryos, time to hatching, survival of larvae, growth of larvae and swimming behavior of larvae were determined. Selenium (Se) was also measured and Se/Hg molar ratios were calculated to assess whether Se reduced MeHg toxicity. MeHg had no significant impact on fish reproduction or on survival and growth of larvae. Larvae produced by MeHg-exposed mothers had concentrations of Hg about 1 ppm (dry wt), or about 12% of that in the muscle of their mothers and consistently displayed 6–15% increased swimming speed relative to controls; the ecological significance of this moderate effect on swimming speed requires further study. The Se/Hg molar ratios in these fish, which were >1 in controls (adults and larvae) and MeHg-exposed larvae but <1 in Hg-exposed adults, did not correlate with MeHg effects. The sheepshead minnow, at a low trophic level, appears to have a high tolerance of MeHg; however, it can pass MeHg to higher trophic levels in marine ecosystems where upper level predators have MeHg concentrations sometimes exceeding US FDA safety limits of 1 ppm wet wt.

Correlation of Bone Density in Semi‐Aquatic and Aquatic Animals with Ecological and Dietary Specializations

A successful transition from a terrestrial to an aquatic environment requires the acquisition of unique adaptations that fit the distinct habitat. Pachyosteosclerosis is a combination of pachyostosis (thickening of cortical bone) and osteosclerosis (thickening of medullary bone). This accumulation of bone increases the density and weight of the animals that exhibit these characters. Pachyosteosclerosis is commonly found in aquatic and semiaquatic animals such as sirenians (sea cows), odobenids (walruses), otariids (sea lions), phocids (true seals) and cetaceans (whales). Increased bone density occurred early in the transition from a terrestrial to a marine environment, present before many of the other morphological characters such as flukes, flippers and fins and behavioral characters such as oscillatory swimming associated with aquatic life appear. Pachyosteosclerosis helps to counteract buoyancy, allowing taxa to remain submerged longer in order to feed while expending little energy. This is clearly demonstrated in sirenians, which are known to feed on sea grasses in shallow waters near the coastline. In most other aquatic mammals, such as modern cetaceans, pachyosteosclerosis is followed by an osteoporosis‐like bone lightening for increased swimming speeds that allows for the active hunting of fast‐moving prey. Pinnipeds live in a wide range of habitats (from cold to warm waters, from marine to fresh water) and demonstrate varying feeding mechanisms, ranging from filter feeding to bottom feeding to catching fast prey. Increased bone density is seen in multiple species of seals in different geological ages from the Miocene (~ 23mya) to present. The morphological and ecological significance for seals with thicker bones is that they swim slower and hunt in shallower water, while seals with lighter bones swim faster and hunt fast moving prey. Bone microstructural disparity allows different species of seals to successfully live in sympatric habitats due to their ecological and dietary specializations. Bone density is one vital character that can be used to predict the specific ecological niche and feeding preference for pinnipeds. Some early hominids, such as Homo erectus, have been shown to have increased density in the bones also. These heavier, thicker bones would make it easier for early Homo to hunt in coastal waters for littoral food sources and would compensate for the lack of stability from bipedalism.Support or Funding InformationFunding Provided by Torres Advanced Enterprise Solutions LLC and Just‐Julian Fellowship

Neuromodulatory Selection of Motor Neuron Recruitment Patterns in a Visuomotor Behavior Increases Speed.

Animals generate locomotion at different speeds to suit their behavioral needs. Spinal circuits generate locomotion at these varying speeds by sequential activation of different spinal interneurons and motor neurons. Larval zebrafish can generate slow swims for prey capture and exploration by activation of secondary motor neurons and much faster and vigorous swims during escape and struggle via additional activation of primary motor neurons. Neuromodulators are known to alter the motor output of spinal circuits, but their precise role in speed regulation is not wellunderstood. Here, in the context of optomotor response (OMR), an innate evoked locomotor behavior, we show that dopamine (DA) provides an additional layer to regulation of swim speed in larval zebrafish. Activation of D1-like receptors increases swim speed during OMR in free-swimming larvae. By analyzing tail bend kinematics in head-restrained larvae, we show that the increase in speed is actuated by larger tail bends. Whole-cell patch-clamp recordings from motor neurons reveal that, during OMR, typically only secondary motor neurons are active, whereas primary motor neurons are quiescent. Activation of D1-like receptors increases intrinsic excitability and excitatory synaptic drive in primary and secondary motor neurons. These actions result in greater recruitment of motor neurons during OMR. Our findings provide an example of neuromodulatory reconfiguration of spinal motor neuron speed modules where members are selectively recruited and motor drive is increased to effect changes in locomotor speed. VIDEO ABSTRACT.

Dynamics of Swimmers in Fluids with Resistance

Micro-swimmers such as spermatozoa are able to efficiently navigate through viscous fluids that contain a sparse network of fibers or other macromolecules. We utilize the Brinkman equation to capture the fluid dynamics of sparse and stationary obstacles that are represented via a single resistance parameter. The method of regularized Brinkmanlets is utilized to solve for the fluid flow and motion of the swimmer in 2-dimensions when assuming the flagellum (tail) propagates a curvature wave. Extending previous studies, we investigate the dynamics of swimming when varying the resistance parameter, head or cell body radius, and preferred beat form parameters. For a single swimmer, we determine that increased swimming speed occurs for a smaller cell body radius and smaller fluid resistance. Progression of swimmers exhibits complex dynamics when considering hydrodynamic interactions; attraction of two swimmers is a robust phenomenon for smaller beat amplitude of the tail and smaller fluid resistance. Wall attraction is also observed, with a longer time scale of wall attraction with a larger resistance parameter.

A novel cylindrical overlap-and-fling mechanism used by sea butterflies.

The clap-and-fling mechanism is a well-studied, unsteady lift generation mechanism widely used by flying insects and is considered obligatory for tiny insects flying at low to intermediate Reynolds numbers, Re However, some aquatic zooplankters including some pteropod (i.e. sea butterfly) and heteropod species swimming at low to intermediate Re also use the clap-and-fling mechanism. These marine snails have extremely flexible, actively deformed, muscular wings which they flap reciprocally to create propulsive force, and these wings may enable novel lift generation mechanisms not available to insects, which have less flexible, passively deformed wings. Using high-speed stereophotogrammetry and micro-particle image velocimetry, we describe a novel cylindrical overlap-and-fling mechanism used by the pteropod species Cuvierina atlantica In this maneuver, the pteropod's wingtips overlap at the end of each half-stroke to sequentially form a downward-opening cone, a cylinder and an upward-opening cone. The transition from downward-opening cone to cylinder produces a downward-directed jet at the trailing edges. Similarly, the transition from cylinder to upward-opening cone produces downward flow into the gap between the wings, a leading edge vortex ring and a corresponding sharp increase in swimming speed. The ability of this pteropod species to perform the cylindrical overlap-and-fling maneuver twice during each stroke is enabled by its slender body and highly flexible wings. The cylindrical overlap-and-fling mechanism observed here may inspire the design of new soft robotic aquatic vehicles incorporating highly flexible propulsors to take advantage of this novel lift generation technique.

Chemotaxis and cyclic‐di‐GMP signalling control surface attachment of Escherichia coli

Attachment to surfaces is an important early step during bacterial infection and during formation of submerged biofilms. Although flagella-mediated motility is known to be important for attachment of Escherichia coli and other bacteria, implications of motility regulation by cellular signalling remain to be understood. Here, we show that motility largely promotes attachment of E. coli, including that mediated by type 1 fimbriae, by allowing cells to reach, get hydrodynamically trapped at and explore the surface. Inactivation or inhibition of the chemotaxis signalling pathway improves attachment by suppressing cell reorientations and thereby increasing surface residence times. The attachment is further enhanced by deletion of genes encoding the cyclic diguanosine monophosphate (c-di-GMP)-dependent flagellar brake YcgR or the diguanylate cyclase DgcE. Such increased attachment in absence of c-di-GMP signalling is in contrast to its commonly accepted function as a positive regulator of the sessile state. It is apparently due to the increased swimming speed of E. coli in absence of YcgR-mediated motor control, which strengthens adhesion mediated by the type 1 fimbriae. Thus, both signalling networks that regulate motility of E. coli also control its engagement with both biotic and abiotic surfaces, which has likely implications for infection and biofilm formation.

Investigating the Effects of Different LED Wavelengths on Aggregation and Swimming Behavior of Chub Mackerel (Scomber japonicus)

Efficient fish aggregation systems are essential for catching chub mackerel (Scomber japonicus), which is a major target of purse seine fisheries in South Korea. To aid the development of such systems, this study used a Dual frequency IDentification SONar acoustic camera and a visual camera to investigate the effects of light emission diode (LED) aggregation systems of different light wavelengths on the frequency of occurrence and swimming behavior of chub mackerel. The experiment was performed using 50 individuals in a circular tank (diameter, 6.0 m × height, 1.5 m). The LED aggregation systems emitted blue light (454 nm), white light (545 nm + 560 nm), yellow light (596 nm), and red light (634 nm). At night, initial swimming speed increased in response to the four LED systems, and stabilized over time. Frequency of occurrence was highest under blue light, followed by yellow light, white light, and red light, in this order, and, according to wavelength at daytime and at nighttime, it was highest under blue light. The swimming speed of the mackerel school showed an increasing trend over time for all LED aggregation systems, and, for blue light, there was a large, rapid increase in swimming speed.

Humpback Whale Movements and Behavior in Response to Whale-Watching Vessels in Juneau, AK

The whale watching industry in Juneau, Alaska relies primarily on the presence of North Pacific humpback whales (Megaptera novaeangliae). To meet demands from the rapidly growing tourism industry, the number of whale watching vessels in this region has tripled over the last 18 years. As a result, increased vessel presence could have negative effects on humpback whales, ranging from short-term behavioral disturbance to long-term impacts. The current humpback whale viewing regulations are outdated and may not be as effective as they were 18 years ago, when both the whale watching industry and humpback whale population were smaller. The present study assessed how humpback whale movement and behavioral patterns were affected by (1) vessel presence and number of vessels present, and (2) time spent in the presence of vessels. The study also determined how humpback whale behavioral state transitions were affected by vessel presence. A total of 201 humpback whale focal follows were conducted during summer 2016 and 2017. Based on linear mixed effects models, whales in the presence (vs. absence) of vessels exhibited 38.9% higher deviation in linear movement (p = 0.001), 6.2% increase in swimming speed (p = 0.047) and a 6.7% decrease in inter-breath intervals (IBI) (p = 0.025). For each additional vessel present, deviation increased by 6.2% (p = 0.022) and IBI decreased by 3.4% (p = 0.001). As time spent in the presence of vessels increased, respiration rate increased (p = 0.011). Feeding and traveling humpback whales were likely to maintain their behavioral state regardless of vessel presence, while surface active humpback whales were likely to transition to traveling in the presence of vessels. These short-term changes in movement and behavior in response to whale watching vessels could lead to cumulative, long-term consequences, negatively impacting the health and predictability of the resource on which the industry relies. Current formal vessel approach regulations and voluntary guidelines should be revisited to reduce vessel pressure and mitigate potential negative effects of this growing whale watching industry.

CREATIN AS A SUPPLEMENT IN NUTRITION AND EFFECTS ON SWIMMING

The subject of the study is the effect of creatine on swimming speed. In previous studies, creatine monohydrate was thought to be an effective nutritional supplement currently available related to improving exercise results. Almost 70% of these studies report a significant improvement in exercise capacity, while in the other studies, no significant improvement in results was generally observed.The test was performed on a sample of 60 swimmers, members of the Academic Swimming Club "April 22" divided into three groups and ages from 21-25. All examinees are male and in good health. Examinees belonging to this population are at the zenith of their morphological and motor development and are well motivated to advance in swimming. The subjects were divided into three groups and engaged in recreational swimming until the application of this research.All three groups of swimmers performed a specific amount of swimming, which was accompanied by the plan for the development of swimming in recreation, with the first group of swimmers taking creatine in addition to swimming, the second group of swimmers doing fitness in addition to swimming, and the third group only swimming. The measurement was carried out at the end of May and half of June 2008 at the premises of the Recreation Center SrpskeToplice (water temperature 28 degrees C).Variablessemple referred to swimming speed at 50 m freestyle technique (both measurements and time differences) were used. Descriptive statistics indicators were used. The main objective of the study is to determine whether, with creatine ingestion, with a duration of three weeks, there are significant differences in the increase in swimming speeds compared to the training of strength and swimming training models. The results of the study, analyzed by t-test, show that the difference in swimming time of 50 m freestyle technique is statistically significant.

Consequences of temperature and temperature variability on swimming activity, group structure, and predation of endangered delta smelt

Abstract The effects of water temperature on individual and group movement behaviour in prey fish can affect ecological interactions such as competition and predation, but how variability in temperature influence fish behaviour is less understood. Of particular concern is how increased warming in tidally fluctuating estuaries may impact the native and endangered delta smelt (Hypomesus transpacificus, Osmeridae). To help address this issue, we tested the effects of increased water temperature (fluctuating [17–21°C] and warm [21°C] acclimated treatments) on juvenile delta smelt individual and group behaviour, response to chemical alarm and predator cues, as well as capacity to evade predation. In addition, predation of delta smelt was tested in the presence of a dominant invasive competitor, Mississippi silversides (Menidia beryllina, Atherinopsidae), as well as comparative predation mortality on Mississippi silversides when isolated. After 7 days of increased temperature treatments, delta smelt in the warm treatment increased swimming velocity, decreased turning angle, and altered group structure with larger inter‐individual distances compared to fish in the control (17°C) and fluctuating temperature treatments. Following conspecific and predator chemical alarm cues, delta smelt showed anti‐predator responses. Control and fluctuating treatment fish responded to conspecific cues with increased swimming speeds, decreased inter‐individual distances and near‐neighbour distances, and, after 15 min, fish recovered back to baseline behaviours. In contrast, fish in the warm treatment had not recovered after 15 min, and swimming speeds were maintained at roughly 25 cm/s, close to maximum capabilities. Fish in control and fluctuating treatments showed minimal responses to predator cues, whereas delta smelt exposed to warm conditions significantly increased swimming speeds and decreased turning angle. Predation of delta smelt by largemouth bass (Micropterus salmoides, Centrarchidae) was greatest under the warm treatment, correlating with altered behaviours of delta smelt; however, predation of Mississippi silversides was greater than delta smelt, independent of temperature. This study provides novel insight into the group behaviour of delta smelt, their response to predation, and how prolonged exposure to elevated temperature may induce negative individual and group behaviours causing alterations in predator–prey dynamics. This work highlights the importance of testing ecologically realistic temperature fluctuations in experiments as delta smelt had significantly altered responses to elevated temperature, dependent on variability of warming.

How dorsal fin sharpness affects swimming speed and economy

Multi-fin systems, like fish or fish-inspired vehicles, are governed by unsteady three-dimensional interactions between their multiple fins. In particular, dorsal/anal fins have received much attention because they are just upstream of the main thrust-producing fin: the caudal (tail) fin. We used a tuna-inspired fish model with variable fin sharpness to study the interaction between elongated dorsal/anal fins and caudal fins. We found that the performance enhancement is stronger than previously thought (15 % increase in swimming speed and 50 % increase in swimming economy) and is governed by a three-dimensional dorsal-fin-induced cross-flow that lowers the angle of attack on the caudal fin and promotes spanwise flow. Both simulations and multi-layer particle image velocimetry reveal that the cross-flow stabilizes the leading edge vortex on the caudal fin, similar to how wing strakes prevent stall during fixed-wing aircraft manoeuvres. Unlike other fin–fin interactions, this mechanism is phase-insensitive and offers a simple, passive solution for flow control over oscillating propulsors. Our results therefore improve our understanding of multi-fin flow interactions and suggest new insights into dorsal/anal fin shape and placement in fish and fish-inspired vehicles.

Fin whale singing decreases with increased swimming speed.

The attributes of male acoustic advertisement displays are often related to a performer's age, breeding condition and motivation, but these relationships are particularly difficult to study in free-ranging marine mammals. For fin whale singers, we examined the relationships between a singer's swimming speed, song duration and amount of singing. We used a unique set of fin whale singing and swimming data collected in support of the US Navy's marine mammal monitoring programme associated with the Navy's Integrated Undersea Surveillance System. A goal of the programme is to improve understanding of the potential effects of anthropogenic sound sources on baleen whale behaviours and populations. We found that as whales swam faster, some continued to sing, while others did not. If swimming speed is an indication of male stamina, then singing while swimming faster could be a display by which females and/or other males assess a singer's physical fitness and potential reproductive quality. Results have implications for interpreting fin whale singing behaviour and the possible influences of anthropogenic sounds on fin whale mating strategies and breeding success.

Upper to Lower Limb Coordination Dynamics in Swimming Depending on Swimming Speed and Aquatic Environment Manipulations.

Swimming is a challenging locomotion, involving the coordination of upper and lower limbs to propel the body forward in a highly resistive aquatic environment. During front crawl, freestyle stroke, alternating rotational motion of the upper limbs above and below the waterline, is coordinated with alternating lower limb pendulum actions. The aim of this study was to investigate the upper to lower limbs coordination dynamics of eight male elite front crawlers while increasing swimming speed and disturbing the aquatic environment (i.e.,pool vs. flume). Upper to lower limb frequency ratios, coordination, coupling strength, and asymmetry were computed from data collected by inertial measurement units. Significant speed effect was observed, leading to transitions from 1∶1 to 1∶3 frequency ratios (1∶3 overrepresented), whereas 1∶2 frequency ratio was rarely used. Flume swimming led to a significant lower coupling strength at low speeds and higher asymmetries, especially at the highest speeds, probably related to the flume dynamic environment.