The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions

Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). 1. Harbor seals remained submerged for 82-92% of the time at swimming speeds below 1.2 m.s-1. At higher speeds, including simulated speeds above 1.4 m.s-1, the percentage of time spent submerged decreased, and was inversely related to body weight. In contrast, the percentage of time spent submerged did not change with speed for sea lions swimming from 0.5 m.s-1 to 4.0 m.s-1. 2. During swimming, harbor seals showed a distinct breathhold bradycardia and ventilatory tachycardia that were independent of swimming speed. Average heart rate was 137 beats.min-1 when swimming on the water surface and 50 beats.min-1 when submerged. A bimodal pattern of heart rate also occurred in sea lions, but was not as pronounced as in the seals. 3. The weighted average heart rate (WAHR), calculated from measured heart rate and the percentage time spent on the water surface or submerged, increased linearly with swimming speed for both species. The graded increase in heart rate with exercise load is similar to the response observed for terrestrial mammals. 4. The rate of oxygen consumption increased exponentially with swimming speed in both seals and sea lions. The minimum cost of transport calculated from these rates ranged from 2.3 to 3.6 J.m-1.kg-1, and was 2.5-4.0 times the level predicted for similarly-sized salmonids. Despite different modes of propulsion and physiological responses to swimming, these pinnipeds demonstrate similar transport costs.     

Costs of swimming measured at optimum speed: scale effects, differences between swimming styles, taxonomic groups and submerged and surface swimming

1. Data on swimming energy expenditure of 30 submerged and nine surface swimmers, covering different swimming styles and taxonomic groups, are selected from the literature. 2. The costs of transport at the optimum speed are compared and related to body mass and Re numbers. 3. Fish and turtles use relatively less and most surface swimmers slightly more energy than the other submerged swimmers; man and mink are poorly adapted to swimming. 4. The metabolic rate in W at optimum speed is approximately equal to the body mass in kg for fish and turtles and three times the mass figure for the other submerged swimmers.     

Diving behaviour and energetics in breeding little penguins (Eudyptula minor)

We present data on the diving behaviour and the energetics of breeding little penguins in Tasmania, Australia. Using an 18 m long still water canal in conjunction with respirometry, we determined the energy requirements while diving. Using electronic devices measuring dive depth or swimming speed, we investigated the foraging behaviour at sea. Cost of Transport was calculated to be minimal at the speed the birds prefer at sea (1.8 m/s) and averaged 11.1 J/kg/m (power requirements at that speed: 20.0 W/kg). Metabolic rate of little penguins resting in water was found to be 8.5 W/kg. The externally-attached devices had no significant influence on the energy expenditure.
Foraging trips can be divided into four distinct phases with different diving behaviours. A mean of 500 dives was executed per foraging trip lasting about 18 hours with 60% of this time being spent swimming. The total distance travelled averaged 73 km per day, although foraging range was about 12km. Mean swimming speed of little penguins at sea was 1.8 m/s, maximum swimming speed was 3.3 m/s. More than 50% of all dives had maxima not exceeding 2 m. Maximum depth reached was 27 m. Mean dive duration was 21 s. There were inter-sex differences in diving behaviour as well as changes in foraging behaviour over the breeding period. Aerobic dive limits (ADL) in the wild were estimated between 42 and 50 s. From the swim canal experiments we derived an ADL of 44 s. Total oxygen stores were calculated to be 45 ml O₂/kg. Only 2% of all dives exceeded the ADL. FMRs at sea were calculated to be between 1280 and 1500 kJ/kg/d according to chick size. The yearly food requirements of a breeding little penguin amount to 114 kg.     

Swimming speed, respiration rate, and estimated cost of transport in adult killer whales

The physiology of free-ranging cetaceans is difficult to study and as a consequence, data on the energetics of these animals are limited. To better understand the energetic cost of swimming in killer whales, total cost of transport ( COT ) was estimated from swimming speeds and respiration rates from wild adult northern resident killer whales ( Orcinus orca ) and reported values of oxygen consumption in captive whales. Respiration rate (breaths per minute) was positively correlated with swimming speed (meters per second), while mass-specific COT (Joules per kilogram per meter) decreased with speed. Lack of data on very fast-swimming animals hindered assessment of the exact speed at which COT was minimal. However, minimum mass-specific COT for killer whales in the present study approached those predicted by a previously published allometric equation for marine mammals, and corresponded to "optimal" swimming speeds of 2.6–3 m/s. Interestingly, the observed average swimming speed (1.6 m/s) was lower than predicted optimal swimming speed. Finally, females with dependent calves had higher respiration rates than females without calves. These findings could be due to synchronous breathing with calves or could result from increased costs of lactation and swimming with a calf in echelon formation. Consequently, females with calves may have much greater COT at optimal swimming speeds than females without calves.     

流速对细鳞裂腹鱼游泳行为及能量消耗影响的研究

通过自制密封的鱼类游泳实验装置, 研究了流速对细鳞裂腹鱼游泳行为和能量消耗的影响。结果显示,细鳞裂腹鱼的摆尾频率随游泳速度的变化有明显的变化规律, 摆尾频率随着流速的增加而显著性的增加,而摆尾幅度有减小趋势, 差异性不显著。结果还表明, (26±1) ℃时, (10.60±0.54) cm 细鳞裂腹鱼的相对临界游泳速度为(11.5±0.5) BL/s, 绝对临界游泳速度为(110.28±2.02) cm/s。测定的相对临界流速较其他的鲤科鱼大,是对生存水流环境(流速0.5—1.5m/s)适应性的表现。这一结果表明鱼类的游泳能力是能够训练的。运动代谢率与相对流速的关系为, AMR = 93.08e(0.307v) + 314.33, R2= 0.994; 单位距离能耗与流速的指数关系为COT =28e (-1.03V) +6.05, R2= 0.998。流速达到8 BL/s 时, 裂腹鱼耗氧率开始下降, 从流速7 BL/s 时, (1245.57±90.97 )mg O2/(kg·h)最大, 下降到(978.78±189.38) mg O2/(kg·h)。1—7 BL/s 流速范围内, 裂腹鱼单位时间内的耗氧率随着游泳速度的增加而增加, 而且随着游泳速度的增加, 单位距离能耗(COT)逐渐减少, 最小能耗在6 倍体长流速, 0.68 m/s 时, 为(6.00±1.57) J/(kg·m), 其能量利用效率最大。       

Non-intrusive monitoring of otters (Lutra lutra) using infrared technology

Remote, non-intrusive monitoring of elusive mammals remains problematic, particularly in running waters. The utility of using submerged infrared counters for monitoring non-intrusively the activity of Eurasian otters Lutra lutra was assessed in three tributaries of the River Dee (Beltie, Cattie, Feardar; Scotland) during 2003–2004. Otters passing through the infrared counters were strongly nocturnal and displayed a bimodal diel activity pattern. Seasonal activity indices varied fourfold between tributaries and peaked during the salmonid breeding season. The median time elapsing between consecutive night visits was 2.02±0.79 days and did not differ between tributaries. The median head–body length of adult otters was estimated at 75.0±1.1 cm, whereas median upstream swimming speed was calculated at 0.97±0.01 m s⁻¹. Minimum census estimates revealed the activity of at least two adults in the Beltie, two adults and three juveniles in the Cattie, and two adults with one juvenile in the Feardar. Our study indicates that, under suitable conditions, infrared technology can be used effectively to examine non-intrusively the activity of free-ranging otters in running waters, offering some advantages over previous, more intrusive techniques that relied on the collection of spraints, the use of radioisotopes or the tracking of marked individuals.     

亚成体巨须裂腹鱼游泳能力及活动代谢研究

以野生雅鲁藏布江巨须裂腹鱼(Schizothorax macropogon)为对象,通过自制的鱼类游泳实验装置,测定了4个温度(5、10、15和18℃)梯度下亚成体巨须裂腹鱼的临界游泳速度(Ucrit)及流速变化对耗氧率的影响,并通过摄像记录分析了不同游泳速度下的游泳行为。野生亚成体巨须裂腹鱼的临界游速随着温度的变化呈近似线性的递增趋势(P<0.001),4个温度下的绝对临界游速(Ucrit-a)分别为(0.88±0.07)、(1.09±0.07)、(1.24±0.15)和(1.49±0.15)m/s;若以单位时间内游过的体长倍数(BL/s)表示,相对临界游速(Ucrit-r)分别为(3.96±0.21)、(4.4±0.16)、(4.9±0.18)和(5.35±0.14)BL/s。根据不同温度及流速下耗氧率的变化情况,采用非线性拟合得到了4个温度梯度下耗氧率与游泳速度关系的幂函数模型(P<0.05)。模型表明耗氧率随游泳速度的增大而增加,且温度越高耗氧率随游泳速度的变化越显著。4个温度下的速度指数分别为2.4、2.6,2.8及3.1,表明有氧运动的效率随温度升高有所降低。在自然水温条件下(5—9℃),摆尾频率(TBF)与流速的关系呈线性正相关(P<0.001),而运动步长(Ls)的变化与流速没有显著关系,出现由高至低再升高的三个阶段。录像分析表明在流速逐渐增加的过程中,巨须裂腹鱼采用了三种不同的游泳方式,以实现降低能量消耗的目的。研究可为鱼道等过鱼设施的设计提供参考,对数量日益减少的巨须裂腹鱼保护具有较大的意义。     

Empirical analysis of the influence of swimming pattern on the net energetic cost of swimming in fishes

We tested the hypothesis that the energetics of swimming in a flume accurately represent the costs of various spontaneous movements using empirical relationships between fish swimming costs, weight, and speed for three swimming patterns: (1) 'forced swimming' corresponded to movements adopted by fish forced to swim against a unidirectional current of constant velocity; (2) 'directed swimming' was defined as quasi-rectilinear movements executed at relatively constant speeds in a stationary body of water and (3) 'routine swimming' was characterized by marked changes in swimming direction and speed. Weight and speed explained between 76% (routine swimming) and 80% (forced swimming) of net swimming cost variability. Net costs associated with different swimming patterns were compared using ratios of model predictions (swimming cost ratio; SCR) for various weight and speed combinations. Routine swimming was the most expensive swimming pattern (SCR for routine and forced swimming =6.4 to 14.0) followed by directed (SCR for directed and forced swimming =0.9 to 2.8), and forced swimming. The magnitude of the difference between the net costs of forced and spontaneous swimming increases with movement complexity and decreases as fish weight increases.     

Running energetics of the North American river otter: do short legs necessarily reduce efficiency on land?

Semi-aquatic mammals move between two very different media (air and water), and are subject to a greater range of physical forces (gravity, buoyancy, drag) than obligate swimmers or runners. This versatility is associated with morphological compromises that often lead to elevated locomotor energetic costs when compared to fully aquatic or terrestrial species. To understand the basis of these differences in energy expenditure, this study examined the interrelationships between limb morphology, cost of transport and biomechanics of running in a semi-aquatic mammal, the North American river otter. Oxygen consumption, preferred locomotor speeds, and stride characteristics were measured for river otters (body mass=11.1 kg, appendicular/axial length=29%) trained to run on a treadmill. To assess the effects of limb length on performance parameters, kinematic measurements were also made for a terrestrial specialist of comparable stature, the Welsh corgi dog (body mass=12.0 kg, appendicular/axial length=37%). The results were compared to predicted values for long legged terrestrial specialists. As found for other semi-aquatic mammals, the net cost of transport of running river otters (6.63 J kg(-1)min(-1) at 1.43 ms(-1)) was greater than predicted for primarily terrestrial mammals. The otters also showed a marked reduction in gait transition speed and in the range of preferred running speeds in comparison to short dogs and semi-aquatic mammals. As evident from the corgi dogs, short legs did not necessarily compromise running performance. Rather, the ability to incorporate a period of suspension during high speed running was an important compensatory mechanism for short limbs in the dogs. Such an aerial period was not observed in river otters with the result that energetic costs during running were higher and gait transition speeds slower for this versatile mammal compared to locomotor specialists.     

Swimming behaviour of upriver migrating sea lamprey assessed by electromyogram telemetry

The main subject of this study was the swimming behaviour of upriver migrating sea lamprey, Petromyzon marinus , with particular focus on identification of their swim strategies to overcome areas of difficult passage. A biotelemetry technique (electromyogram telemetry) was used to register muscle activity of the tagged animals. In the 2005 spawning season, five adult sea lampreys were surgically tagged and released in the field. Before release, electromyogram (EMG) records were calibrated with the P. marinus swimming speed in a swim tunnel. Differences between ground speed and swimming speed in the wild suggest that the calibrated CEMG (coded electromyogram) transmitter output corresponds to an activity index, and cannot be properly related to actual swimming speed. This study notes the need to confirm the laboratory calibration curves, to ascertain their use in determining swimming speed of tagged fish in the wild. In 2006, in order to confirm the field results seven adult sea lampreys were tagged, calibrated in the laboratory and released in a 30-m long experimental outdoor canal. The results were similar: observed swimming speed was generally higher when compared with the swimming speed obtained with the EMG signal. In the river, when swimming through slow-flow stretches, sea lampreys maintained a constant pattern of activity, attaining an average ground speed of 0.76 BL s⁻¹ (2.5 km h⁻¹). When sea lampreys encountered rapid flow reaches they alternated between short movements ( c. 67 s) and periods of rest ( c. 99 s). In each swim bout they progressed approximately 14 m; to overcome more difficult obstacles sea lampreys increased their number of burst movements instead of longer or more violent swimming events. About 43% of the time negotiating difficult passage areas was spent in resting by attaching motionless to the substrate with their oral disk.     

The muscle twitch and the maximum swimming speed of giant bluefin tuna, Thunnus thynnus L.

Sustained swimming of bluefin tuna was analysed from video recordings made of a captive patrolling fish school [lengths (L) 1.7–3.3 m, body mass (M) 54–433 kg]. Speeds ranged from 0.6 to 1.2 L s⁻¹ (86–260 km day⁻¹) while stride length during steady speed swimming varied between 0.54 and 0.93 L. Maximum swimming speed was estimated by measuring twitch contraction of the anaerobic swimming muscle in pithed fish 5 min after death. Muscle contraction time increased from the shortest just behind the head (30–50 ms at 20% L) to the longest at the tail peduncle (80–90 ms at 80% L) (all at 28°C). A fish (L = 2.26 m) with a muscle contraction time of 50 ms at 25% L can have a maximum tail beat frequency of 10 Hz and maximum swimming speed of 15m s⁻¹ (54km h⁻¹) with a stride length of 0.65L. With a stride length of 1 L a speed of 22.6 m s⁻¹ (81.4 km h⁻¹) is possible. Power used at maximum speed was estimated for this fish at between 10 and 40 kW, with corresponding values for the drag coefficient at a Reynolds number of 4.43 × 10⁷ of 0.0007 and 0.0027.     

不同体质量和饥饿程度对红鳍东方鲀幼鱼游泳能力的影响

为了考察不同体质量和饥饿程度红鳍东方鲀(Takifugu rubripes)幼鱼的游泳能力,利用行为生态学方法测定了不同体质量(0.22—3.31 g)和饥饿天数(1d、3d、6d和9d)下红鳍东方鲀幼鱼的绝对临界游速(U_crit,cm/s)、相对临界游速(U_crit’,体长/s,BL/s)、偏好游速(U_pref,cm/s)、6个流速区域(2—36 cm/s)下停留时间百分比(P_t,%)、偏好区域平均流速(V_mean,cm/s)和总游泳距离(D_1h,m)等游泳行为指标。结果显示,体质量和饥饿显著影响红鳍东方鲀幼鱼的U_crit、U_crit’、P_t、V_mean和D_1h。随体质量增加,实验鱼的U_crit、U_pref、V_mean和D_1h均逐渐升高,而U_crit...     

Three-dimensional movements and swimming activity of a northern elephant seal

We attached a video system and data recorder to a northern elephant seal to track its three-dimensional movements and observe propulsive strokes of the hind flippers. During 6 h of recording, the seal made 20 dives and spent 90% of the time submerged. Average dive duration, maximum depth and swimming speed were 14.9 min+/-6.1 S.D., 289 m+/-117 S.D. and 1.1 m s(-1)+/-0.12 S.D., respectively. The distance swum during a dive averaged 925 m+/-339 S.D., and the average descent and ascent angles were 41 degrees +/-18 S.D. and 50 degrees +/-21 S.D., respectively. Dive paths were remarkably straight suggesting that the seal was navigating while submerged. We identified three modes of swimming based on the interval between propulsive strokes: continuous stroking; stroke-and-glide swimming; and prolonged gliding. The seal used continuous stroking from the surface to a mean depth of 20 m followed by stroke-and-glide swimming. Prolonged gliding started at a mean depth of 60 m and continued to the bottom of dives. For dives to depths of 300 m or more, 75% of the descent time was spent in prolonged gliding and 10% in stroke-and-glide swimming, amounting to 5.9-9.6 min of passive descent per dive. Average swimming speed varied little with swimming mode and was not a good indicator of propulsive effort. It appears that the seal can use prolonged gliding to reduce the cost of transport and increase dive duration. Energetically efficient locomotion may help explain the long and deep dives that routinely exceed the theoretical aerobic dive limit in this species.     

Estimating Carrying Capacity for Sea Otters in British Columbia

ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km² and 2.53 otters/km² for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km²) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.     

Energetics of swimming by the ferret: consequences of forelimb paddling.

The domestic ferret (Mustela putorius furo) swims by alternate strokes of the forelimbs. This pectoral paddling is rare among semi-aquatic mammals. The energetic implications of swimming by pectoral paddling were examined by kinematic analysis and measurement of oxygen consumption. Ferrets maintained a constant stroke frequency, but increased swimming speed by increasing stroke amplitude. The ratio of swimming velocity to foot stroke velocity was low, indicating a low propulsive efficiency. Metabolic rate increased linearly with increasing speed. The cost of transport decreased with increasing swimming speed to a minimum of 3.59+/-0.28 J N(-1) m(-1) at U=0.44 m s(-1). The minimum cost of transport for the ferret was greater than values for semi-aquatic mammals using hind limb paddling, but lower than the minimum cost of transport for the closely related quadrupedally paddling mink. Differences in energetic performance may be due to the amount of muscle recruited for propulsion and the interrelationship hydrodynamic drag and interference between flow over the body surface and flow induced by propulsive appendages.     

Energetics of swimming by the ferret: consequences of forelimb paddling

The domestic ferret (Mustela putorius furo) swims by alternate strokes of the forelimbs. This pectoral paddling is rare among semi-aquatic mammals. The energetic implications of swimming by pectoral paddling were examined by kinematic analysis and measurement of oxygen consumption. Ferrets maintained a constant stroke frequency, but increased swimming speed by increasing stroke amplitude. The ratio of swimming velocity to foot stroke velocity was low, indicating a low propulsive efficiency. Metabolic rate increased linearly with increasing speed. The cost of transport decreased with increasing swimming speed to a minimum of 3.59+/-0.28 J N(-1) m(-1) at U=0.44 m s(-1). The minimum cost of transport for the ferret was greater than values for semi-aquatic mammals using hind limb paddling, but lower than the minimum cost of transport for the closely related quadrupedally paddling mink. Differences in energetic performance may be due to the amount of muscle recruited for propulsion and the interrelationship hydrodynamic drag and interference between flow over the body surface and flow induced by propulsive appendages.     

Status,trends, and equilibrium abundance estimates of the translocated sea otter population in Washington State

Sea otters (Enhydra lutris kenyoni) historically occurred in Washington State, USA, until their local extinction in the early 1900s as a result of the maritime fur trade. Following their extirpation, 59 sea otters were translocated from Amchitka Island, Alaska, USA, to the coast of Washington, with 29 released at Point Grenville in 1969 and 30 released at La Push in 1970. The Washington Department of Fish and Wildlife has outlined 2 main objectives for sea otter recovery: a target population level and a target geographic distribution. Recovery criteria are based on estimates of population abundance, equilibrium abundance (K), and geographic distribution; therefore, estimates of these parameters have important management implications. We compiled available survey data for sea otters in Washington State since their translocation (1977–2019) and fit a Bayesian state-space model to estimate past and current abundance, and equilibrium abundance at multiple spatial scales. We then used forward projections of population dynamics to explore potential scenarios of range recolonization and as the basis of a sensitivity analysis to evaluate the relative influence of movement behavior, frontal wave speed, intrinsic growth, and equilibrium density on future population recovery potential. Our model improves upon previous analyses of sea otter population dynamics in Washington by partitioning and quantifying sources of estimation error to estimate population dynamics, by providing robust estimates of K, and by simulating long-term population growth and range expansion under a range of realistic parameter values. Our model resulted in predictions of population abundance that closely matched observed counts. At the range-wide scale, the population size in our model increased from an average of 21 independent sea otters (95% CI = 13–29) in 1977 to 2,336 independent sea otters (95% CI = 1,467–3,359) in 2019. The average estimated annual growth rate was 12.42% and varied at a sub-regional scale from 6.42–14.92%. The overall estimated mean K density of sea otters in Washington was 1.71 ± 0.90 (SD) independent sea otters/km² of habitat (1.96 ± 1.04 sea otters/km², including pups), and estimated densities within the current range correspond on average to 87% of mean sub-regional equilibrium values (range = 66–111%). The projected value of K for all of Washington was 5,287 independent sea otters (95% CI = 2,488–8,086) and 6,080 sea otters including pups (95% CI = 2,861–9,300), assuming a similar range of equilibrium densities in currently un-occupied habitats. Sensitivity analysis of simulations of sea otter population growth and range expansion suggested that mean K density estimates in currently occupied sub-regions had the largest impact on predicted future population growth (r² = 0.52), followed by the rate of southward range expansion (r² = 0.26) and the mean K density estimate of currently unoccupied sub-regions to the south of the current range (r² = 0.04). Our estimates of abundance and sensitivity analysis of simulations of future population abundance and geographic range help determine population status in relation to population recovery targets and identify the most influential parameters affecting future population growth and range expansion for sea otters in Washington State.     

Filter-feeding and cruising swimming speeds of basking sharks compared with optimal models: they filter-feed slower than predicted for their size

Movements of six basking sharks (4.0-6.5 m total body length, L(T)) swimming at the surface were tracked and horizontal velocities determined. Sharks were tracked for between 1.8 and 55 min with between 4 and 21 mean speed determinations per shark track. The mean filter-feeding swimming speed was 0.85 m s(-1) (+/-0.05 S.E., n=49 determinations) compared to the non-feeding (cruising) mean speed of 1.08 m s(-1) (+/-0.03 S.E., n=21 determinations). Both absolute (m s(-1)) and specific (L s(-1)) swimming speeds during filter-feeding were significantly lower than when cruise swimming with the mouth closed, indicating basking sharks select speeds approximately 24% lower when engaged in filter-feeding. This reduction in speed during filter-feeding could be a behavioural response to avoid increased drag-induced energy costs associated with feeding at higher speeds. Non-feeding basking sharks (4 m L(T)) cruised at speeds close to, but slightly faster ( approximately 18%) than the optimum speed predicted by the Weihs (1977) [Weihs, D., 1977. Effects of size on the sustained swimming speeds of aquatic organisms. In: Pedley, T.J. (Ed.), Scale Effects in Animal Locomotion. Academic Press, London, pp. 333-338.] optimal cruising speed model. In contrast, filter-feeding basking sharks swam between 29 and 39% slower than the speed predicted by the Weihs and Webb (1983) [Weihs, D., Webb, P.W., 1983. Optimization of locomotion. In: Webb, P.W., Weihs, D. (Eds.), Fish Biomechanics. Praeger, New York, pp. 339-371.] optimal filter-feeding model. This significant under-estimation in observed feeding speed compared to model predictions was most likely accounted for by surface drag effects reducing optimum speeds of tracked sharks, together with inaccurate parameter estimates used in the general model to predict optimal speeds of basking sharks from body size extrapolations.     

Energetics of foraging and locomotion in the platypus Ornithorhynchus anatinus

We measured the energy requirements of platypuses foraging, diving and resting in a swim tank using flow-through respirometry. Also, walking metabolic rates were obtained from platypuses walking on a conventional treadmill. Energy requirements while foraging were found to depend on water temperature, body weight and dive duration and averaged 8.48 W kg(-1). Rates for subsurface swimming averaged 6.71 W kg(-1). Minimal cost of transport for subsurface swimming platypuses was 1.85 J N(-1)m(-1) at a speed of 0.4 m s(-1). Aerobic dive limit of the platypus amounted to 59 s. Metabolic rate of platypuses resting on the water surface was minimal with 3.91 W kg(-1) while minimal RMR on land was 2.08 W kg(-1). The metabolic rate for walking was 8.80 W kg(-1) and 10.56 W kg(-1) at speeds of 0.2 m s(-1) and 0.3 m s(-1), respectively. A formula was derived, which allows prediction of power requirements of platypuses in the wild from measurements of body weight, dive duration and water temperature. Platypuses were found to expend energy at only half the rate of semiaquatic eutherians of comparable body sizes during both walking and diving. However, costs of transport at optimal speed were in line with findings for eutherians. These patterns suggest that underwater locomotion of semiaquatic mammals have converged on very similar efficiencies despite differences in phylogeny and locomotor mode.     

Burst swimming speeds of mackerel, Scomber scombrus L.

Burst swimming speeds were measured in mackerel 0.275–0.380 m long by filming newly caught fish, first released into a large shore-sited tank, using a high-speed cine camera and real time TV camera. The highest speed was 5.50 m s⁻¹ or 18 body length per second ( b.l . s⁻¹) in a 0.305 m long mackerel at 12° C. The recorded maximum tail beat frequency of 18 Hz agrees well with 19 Hz predicted from the measured contraction time of 0.026 s for the anterior lateral swimming muscle. The stride length was close to 1 B.L.; the power, calculated from the drag, was 4.53 W, and, calculated from the muscle used, was 5.07 W; all suggesting that the mackerel is swimming close to its physiological limit.