Baleen whales influence their ecosystems through immense prey consumption and nutrient recycling
. It is difficult to accurately gauge the magnitude of their current or historic ecosystem role ...without measuring feeding rates and prey consumed. To date, prey consumption of the largest species has been estimated using metabolic models
based on extrapolations that lack empirical validation. Here, we used tags deployed on seven baleen whale (Mysticeti) species (n = 321 tag deployments) in conjunction with acoustic measurements of prey density to calculate prey consumption at daily to annual scales from the Atlantic, Pacific, and Southern Oceans. Our results suggest that previous studies
have underestimated baleen whale prey consumption by threefold or more in some ecosystems. In the Southern Ocean alone, we calculate that pre-whaling populations of mysticetes annually consumed 430 million tonnes of Antarctic krill (Euphausia superba), twice the current estimated total biomass of E. superba
, and more than twice the global catch of marine fisheries today
. Larger whale populations may have supported higher productivity in large marine regions through enhanced nutrient recycling: our findings suggest mysticetes recycled 1.2 × 10
tonnes iron yr
in the Southern Ocean before whaling compared to 1.2 × 10
tonnes iron yr
recycled by whales today. The recovery of baleen whales and their nutrient recycling services
could augment productivity and restore ecosystem function lost during 20th century whaling
.
Body length is one of the most important factors that influence organismal function and ecological niche. Although larger animals tend to have a suite of physiological advantages, such as lower ...mass‐specific metabolic rates and lower costs of transport, they may also experience significant limitations to unsteady locomotor performance or maneuverability because of the relative scaling of control surface areas and body mass. Rorqual whales are the largest of all animals and thus represent a unique study system for understanding how animals function at the extreme of body mass. Rorquals are characterized by an engulfment‐filtration foraging strategy facilitated by a complex set of morphological adaptations. We studied the scaling of key morphological structures related to locomotion and feeding in six rorqual species in a comparative framework. Our analyses show that most rorqual species exhibit positive allometry of both the control surfaces and body length, but the large scaling differences between these parameters suggest that larger rorquals will predictably suffer from decreased maneuverability and unsteady locomotor performance. However, we found that the dimensions of the engulfment apparatus also exhibit positive allometry, and thus engulfment capacity was relatively greater in larger rorquals. We posit that the allometric growth in the engulfment apparatus may be an adaptation that ameliorates the detrimental effects of large size on maneuverability. Our analyses also reveal significant differences in the scaling of mass‐specific engulfment capacity among rorqual species that may reflect the evolution of unique foraging behaviors and the exploitation of divergent ecological niches.
Rorqual species exhibit positive allometry of their control surfaces, engulfment apparatus, and body mass. Allometric growth and differences in the scaling of mass‐specific engulfment capacity may explain unique foraging behaviors and diverse ecological niches.
Animals are distributed relative to the resources they rely upon, often scaling in abundance relative to available resources. Yet, in heterogeneously distributed environments, describing resource ...availability at relevant spatial scales remains a challenge in ecology, inhibiting understanding of predator distribution and foraging decisions.
We investigated the foraging behaviour of two species of rorqual whales within spatially limited and numerically extraordinary super‐aggregations in two oceans. We additionally described the lognormal distribution of prey data at species‐specific spatial scales that matched the predator's unique lunge‐feeding strategy.
Here we show that both humpback whales off South Africa's west coast and blue whales off the US west coast perform more lunges per unit time within these aggregations than when foraging individually, and that the biomass within gulp‐sized parcels was on average higher and more tightly distributed within super‐group‐associated prey patches, facilitating greater energy intake per feeding event as well as increased feeding rates.
Prey analysis at predator‐specific spatial scales revealed a stronger association of super‐groups with patches containing relatively high geometric mean biomass and low geometric standard deviations than with arithmetic mean biomass, suggesting that the foraging decisions of rorqual whales may be more influenced by the distribution of high‐biomass portions of a patch than total biomass. The hierarchical distribution of prey in spatially restricted, temporally transient, super‐group‐associated patches demonstrated high biomass and less variable distributions that facilitated what are likely near‐minimum intervals between feeding events.
Combining increased biomass with increased foraging rates implied that overall intake rates of whales foraging within super‐groups were approximately double those of whales foraging in other environments. Locating large, high‐quality prey patches via the detection of aggregation hotspots may be an important aspect of rorqual whale foraging, one that may have been suppressed when population sizes were anthropogenically reduced in the 20th century to critical lows.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
Despite a recent report of high concentrations of microplastics and microfibers in the mesopelagic waters of Monterey Bay National Marine Sanctuary (MBNMS), little is known about these particles in ...surface waters. From 2017 to 2019, we sampled two nearshore and two offshore locations within MBNMS using a manta trawl and analyzed these samples for microplastics and microfibers. We found an average concentration of 1.32 ± 0.70 (SE) particles per m3. We found the highest concentration of particles closest to shore, and the lowest concentration above the remote Davidson Seamount. Fiber-like debris was more common in offshore, as compared to nearshore, sites. Overall, particles in our samples were primarily buoyant synthetic polymers, including polypropylene and polyethylene. Our results provide baseline data on the degree of microplastic and microfiber pollution in MBNMS surface waters and confirm that this pollution can be found in waters from the surface to at least 1000 m depth.
•First extensive sampling of MBNMS surface water for microplastics and microfibers (i.e., ‘particles’).•Nearshore Santa Cruz had highest concentrations (3.21particles/m3); offshore Davidson Seamount had lowest (0.26 particles/m3)•There was a higher proportion of microfibers at offshore sites compared to nearshore sites.•Polypropylene and polyethylene were most common polymers identified using FTIR.•Overall, concentrations (1.32 particles/m3) were similar to other studies of surface seawater both regionally and globally.
Breeding animals trade off maximizing energy output to increase their number of offspring with conserving energy to ensure their own survival, leading to an energetic ceiling influenced by external, ...environmental factors or by internal, physiological factors. We examined whether internal or external factors limited energy expenditure by supplementally feeding breeding black-legged kittiwakes varying in individual quality, based on earlier work that defined late breeders as low-quality and early breeders as high-quality individuals. We tested whether energy expenditure increased when food availability decreased in both low- and high-quality birds; we predicted this would only occur in high-quality individuals capable of sustaining high levels of energy expenditure. Here, we find that food-supplemented birds expended less energy than control birds because they spent more time at the colony. However, foraging trips of food-supplemented birds were only slightly shorter than control birds, implying that food-supplemented birds were limited by food availability at sea similarly to control birds. Late breeders expended less energy, suggesting that low-quality individuals may not intake the energy necessary for sustaining high-energy output. Food-supplemented birds had more offspring than control birds, but offspring number did not influence energy expenditure, supporting the idea that the birds reached an energy ceiling. Males and lighter birds expended more energy, possibly compensating for relatively higher energy intake. Chick-rearing birds were working near their maximum, with highest levels of expenditure for early-laying (high-quality) individuals foraging at sea. Due to fluctuating marine environments, kittiwakes may be forced to change their foraging behaviors to maintain the balance between reproduction and survival.
Filter‐feeding has been present for hundreds of millions of years, independently evolving in aquatic vertebrates' numerous times. Mysticete whales are a group of gigantic, marine filter‐feeders that ...are defined by their fringed baleen and are divided into two groups: balaenids and rorquals. Recent studies have shown that balaenids likely feed using a self‐cleaning, cross‐flow filtration mechanism where food particles are collected and then swept to the esophagus for swallowing. However, it is unclear how filtering is achieved in the rorquals (Balaenopteridae). Lunging rorqual whales engulf enormous masses of both prey and water; the prey is then separated from the water through baleen plates lining the length of their upper jaw and positioned perpendicular to flow. Rorqual baleen is composed of both major (larger) and minor (smaller) keratin plates containing embedded fringe that extends into the whale's mouth, forming a filtering fringe. We used a multimodal approach, including microcomputed tomography (µCT) and scanning electron microscopy (SEM), to visualize and describe the variability in baleen anatomy across five species of rorqual whales, spanning two orders of magnitude in body length. For most morphological measurements, larger whales exhibited hypoallometry relative to body length. µCT and SEM revealed that the major and minor plates break away from the mineralized fringes at variable distances from the gums. We proposed a model for estimating the effective pore size to determine whether flow scales with body length or prey size across species. We found that pore size is likely not a proxy for prey size but instead, may reflect changes in resistance through the filter that affect fluid flow.
The placement of baleen in a blue whale, with the baleen plates hanging down from the gums. Note the hairs that form the mat for filtration of prey from water. The illustration highlights the measurements taken, including the length of the plate, the thickness of the plate, the spacing between the plates and the diameter of the fringe. Illustration by California State University, Fullerton.
The considerable power needed for large whales to leap out of the water may represent the single most expensive burst maneuver found in nature. However, the mechanics and energetic costs associated ...with the breaching behaviors of large whales remain poorly understood. In this study we deployed whale-borne tags to measure the kinematics of breaching to test the hypothesis that these spectacular aerial displays are metabolically expensive. We found that breaching whales use variable underwater trajectories, and that high-emergence breaches are faster and require more energy than predatory lunges. The most expensive breaches approach the upper limits of vertebrate muscle performance, and the energetic cost of breaching is high enough that repeated breaching events may serve as honest signaling of body condition. Furthermore, the confluence of muscle contractile properties, hydrodynamics, and the high speeds required likely impose an upper limit to the body size and effectiveness of breaching whales.
The scale dependence of locomotor factors has long been studied in comparative biomechanics, but remains poorly understood for animals at the upper extremes of body size. Rorqual baleen whales ...include the largest animals, but we lack basic kinematic data about their movements and behavior below the ocean surface. Here, we combined morphometrics from aerial drone photogrammetry, whale-borne inertial sensing tag data and hydrodynamic modeling to study the locomotion of five rorqual species. We quantified changes in tail oscillatory frequency and cruising speed for individual whales spanning a threefold variation in body length, corresponding to an order of magnitude variation in estimated body mass. Our results showed that oscillatory frequency decreases with body length (∝length
) while cruising speed remains roughly invariant (∝length
) at 2 m s
We compared these measured results for oscillatory frequency against simplified models of an oscillating cantilever beam (∝length
) and an optimized oscillating Strouhal vortex generator (∝length
). The difference between our length-scaling exponent and the simplified models suggests that animals are often swimming non-optimally in order to feed or perform other routine behaviors. Cruising speed aligned more closely with an estimate of the optimal speed required to minimize the energetic cost of swimming (∝length
). Our results are among the first to elucidate the relationships between both oscillatory frequency and cruising speed and body size for free-swimming animals at the largest scale.
Cetaceans are capable of extraordinary locomotor behaviors in both water and air. Whales and dolphins can execute aerial leaps by swimming rapidly to the water surface to achieve an escape velocity. ...Previous research on spinner dolphins demonstrated the capability of leaping and completing multiple spins around their longitudinal axis with high angular velocities. This prior research suggested the slender body morphology of spinner dolphins together with the shapes and positions of their appendages allowed for rapid spins in the air. To test whether greater moments of inertia reduced spinning performance, videos and biologging data of cetaceans above and below the water surface were obtained. The principal factors affecting the number of aerial spins a cetacean can execute were moment of inertia and use of control surfaces for subsurface corkscrewing. For spinner dolphin, Pacific striped dolphin, bottlenose dolphin, minke whale and humpback whale, each with swim speeds of 6-7 m s-1, our model predicted that the number of aerial spins executable was 7, 2, 2, 0.76 and 1, respectively, which was consistent with observations. These data implied that the rate of subsurface corkscrewing was limited to 14.0, 6.8, 6.2, 2.2 and 0.75 rad s-1 for spinner dolphins, striped dolphins, bottlenose dolphins, minke whales and humpback whales, respectively. In our study, the moment of inertia of the cetaceans spanned a 21,000-fold range. The greater moments of inertia for the last four species produced large torques on control surfaces that limited subsurface corkscrewing motion and aerial maneuvers compared with spinner dolphins.
Abstract
Bio-logging devices equipped with inertial measurement units—particularly accelerometers, magnetometers, and pressure sensors—have revolutionized our ability to study animals as necessary ...electronics have gotten smaller and more affordable over the last two decades. These animal-attached tags allow for fine scale determination of behavior in the absence of direct observation, particularly useful in the marine realm, where direct observation is often impossible, and recent devices can integrate more power hungry and sensitive instruments, such as hydrophones, cameras, and physiological sensors. To convert the raw voltages recorded by bio-logging sensors into biologically meaningful metrics of orientation (e.g., pitch, roll and heading), motion (e.g., speed, specific acceleration) and position (e.g., depth and spatial coordinates), we developed a series of MATLAB tools and online instructional tutorials. Our tools are adaptable for a variety of devices, though we focus specifically on the integration of video, audio, 3-axis accelerometers, 3-axis magnetometers, 3-axis gyroscopes, pressure, temperature, light and GPS data that are the standard outputs from Customized Animal Tracking Solutions (CATS) video tags. Our tools were developed and tested on cetacean data but are designed to be modular and adaptable for a variety of marine and terrestrial species. In this text, we describe how to use these tools, the theories and ideas behind their development, and ideas and additional tools for applying the outputs of the process to biological research. We additionally explore and address common errors that can occur during processing and discuss future applications. All code is provided open source and is designed to be useful to both novice and experienced programmers.
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