Figure - available from: PLOS ONE
This content is subject to copyright.
External and schematic (dorsal cutaway) views showing position of paired racks of 300 serial baleen plates between tongue and lips In dorsal cutaway view with oral roof removed (bottom of figure), blue arrows indicate direction of water flow though and around baleen filtering apparatus in life as well as in experimental flow tank trials and computational modeling calculations (hypothetical but predicted from data of current study and previously published experiments [3, 5]). Water can flow anteroposteriorly (AP) within mouth along the tongue (APT channel) or the lip (APL channel). Filtered water exits the mouth via paired posterior openings (PO). Oropharyngeal opening which leads to esophagus lies near oral floor caudal to the tongue root. Dashed red box indicate the approximate location of the shortened mini-rack studied in a previous flow tank study [9]; dotted green box shows the system under consideration in this paper.
Source publication
Balaenid whales feed on large aggregates of small and slow-moving prey (predominantly copepods) through a filtration process enabled by baleen. These whales exhibit continuous filtration, namely, with the mouth kept partially opened and the baleen exposed to oncoming prey-laden waters while fluking. The process is an example of crossflow filtration...
Citations
... Over the past three decades, a large body of experimental and modelling studies have investigated the flow dynamics through baleen (Braithwaite 1983, Jensen et al. 2017, Mayo et al. 2001, Werth and Potvin 2016, 2024, Potvin and Werth 2017, Vandenberg et al. 2023, Werth 2004, 2013, Werth et al. 2019, 2024, Zhu et al. 2020a, 2020b. Still poorly understood, however, are the relationships linking filter geometry, porosity, and flow strength past and through realistic renditions of the entire baleen system, as driven by the ambient pressure inside and outside the oropharyngeal cavity. ...
... The red arrows and labels indicate anatomical directions and planes/sections; sagittal divides the animal into left and right halves, transverse or cross-section divides anterior (cranial) from posterior (caudal). Figure credits: Potvin and Werth (2017) and NOAA (top and middle, respectively); and WHOI (bottom). such links will help to further clarify filtration performance in extant whales as well as its evolution in ancestral mysticetes (Werth and Beatty 2023, and references cited). ...
... Unfortunately, the accuracy of this approach has so far been handicapped by the lack of realistic anatomical and morphological information on the geometry of the oropharyngeal cavity, as well as the actual mat porosity distribution within the baleen system. In balaenids, simplified, rectangular geometries of both cavity and baleen plates have been used to focus on the relevant fluid dynamics of CFF (Werth and Potvin 2016, Potvin and Werth 2017, Zhu et al. 2020a, 2020b. (Low-resolution CFD simulations of more realistic oral cavity models was reported in McGregor 2010). ...
Baleen plates of filter-feeding whales are longitudinally fibrous, separating where eroded medially into mats of fringes due to friction from water, prey, and the tongue. The fringes end up spreading-out, in other words suffusing, over the comb-like structure of the baleen assemblage. This study examined the relationships between mat morphology and the hydrodynamics it generates. Samples collected from nine rack locations on a bowhead whale (Balaena mysticetus) and fin whale (Balaenoptera physalus) were investigated with a new technique of mat porosity determination in a flume setting. Porosity was measured in the range of 5–20% and 8–37% in the bowhead and fin whale samples respectively. These were largest ventrally in both species, while remaining somewhat insensitive to the flume’s water speed. A new hydrodynamical model of the through-mat currents was used to estimate speeds of 0.15–3.0 cm/s and mat permeabilities of the order of 10−13 m2, depending on the applied pressure. Finally, and relative to samples collected near the entrance of the mouth, these trends were quantitatively similar in both species. With tongue- and flow-based erosion as the main mechanism for mat creation in all extant mysticetes, our analysis suggests baleen-generated filtration as having emerged early in their evolution.
... Fortunately, the past two decades have witnessed an explosive rise in the application of new techniques and technologies, many long used in other fields of science, ushering in a new era for our understanding of mysticete feeding, and particularly of baleen filtration, both in specific details and general outline. Examples of these new techniques and studies notably include but are not limited to hypothesis-based laboratory experiments (e.g., Lambertsen, 1983;Werth, 2013), tag data (Goldbogen et al., 2017a), photogrammetry (e.g., Lambertsen et al., 1989), aerial drones (Werth et al., 2019b), engineering methods (Lambertsen et al., 2005), computational fluid dynamics (Zhu et al., 2020a, Zhu et al., 2020b, morphometrics (Werth et al., 2018a), histology (e.g., Werth et al., 2018b), mathematical modeling (Potvin et al., 2009;Potvin and Werth, 2017), and physical modeling (Werth, 2004). ...
... The resulting scoop-like head can comprise a third of the length of a balaenid's plump body. After flowing through the center of the mouth, water flows laterally through each rack, then through a gutter-like fold, the orolabial sulcus, between the lip and lateral rack surface (Lambertsen et al., 1989;Potvin and Werth, 2017). In addition to laterally supporting and constraining the baleen racks, the lips may be especially important in generating and modifying flow regimes (Werth et al., 2018a;Werth et al., 2019b); their positioning should be the focus of further flow experiments and field observations. ...
... In addition to laterally supporting and constraining the baleen racks, the lips may be especially important in generating and modifying flow regimes (Werth et al., 2018a;Werth et al., 2019b); their positioning should be the focus of further flow experiments and field observations. The balaenid tongue may preferentially direct flow toward either rack (Werth, 2007;Werth and Crompton, 2023); it also, without moving, sets up a flow regime that channels flow toward each rack (Potvin and Werth, 2017;. Balaenids typically swim at about 0.7-1.0 ...
Recent findings have greatly improved our understanding of mysticete oral filtration, and have upended the traditional view of baleen filtration as a simple process. Flow tank experiments, telemetric tag deployment on whales, and other lab and field methods continue to yield new data and ideas. These suggest that several mechanisms arose from ecological, morphological, and biomechanical adaptations facilitating the evolution of extreme body size in Mysticeti. Multiple lines of evidence strongly support a characterization of baleen filtration as a conceptually dynamic process, varying according to diverse intraoral locations and times of the filtration process, and to other prevailing conditions. We review and highlight these lines of evidence as follows. First, baleen appears to work as a complex metafilter comprising multiple components with differing properties. These include major and minor plates and eroded fringes (AKA bristles or hairs), as well as whole baleen racks. Second, it is clear that different whale species rely on varied ecological filtration modes ranging from slow skimming to high-speed lunging, with other possibilities in between. Third, baleen filtration appears to be a highly dynamic and flow-dependent process, with baleen porosity not only varying across sites within a single rack, but also by flow direction, speed, and volume. Fourth, findings indicate that baleen (particularly of balaenid whales and possibly other species) generally functions not as a simple throughput sieve, but instead likely uses cross-flow or other tangential filtration, as in many biological systems. Fifth, evidence reveals that the time course of baleen filtration, including rate of filter filling and clearing, appears to be more complex than formerly envisioned. Flow direction, and possibly plate and fringe orientation, appears to change during different stages of ram filtration and water expulsion. Sixth, baleen’s flexibility and related biomechanical properties varies by location within the whole filter (=rack), leading to varying filtration conditions and outcomes. Seventh, the means of clearing/cleaning the baleen filter, whether by hydraulic, hydrodynamic, or mechanical methods, appears to vary by species and feeding type, notably intermittent lunging versus continuous skimming. Together, these and other findings of the past two decades have greatly elucidated processes of baleen filtration, and heightened the need for further research. Many aspects of baleen filtration may pertain to other biological filters; designers can apply several aspects to artificial filtration, both to better understand natural systems and to design and manufacture more effective synthetic filters. Understanding common versus unique features of varied filtration phenomena, both biological and artificial, will continue to aid scientific and technical understanding, enable fruitful interdisciplinary partnerships, and yield new filter designs.
... Many entanglements include rope wrapped through an individual whale's baleen rack (Sharp et al. 2019). Balaenid whales' buccal anatomy creates hydrodynamic flow while swimming, creating a hydrau lic circuit that increases flow over the baleen rack (Werth 2004, Werth & Potvin 2016, Potvin & Werth 2017. The extent to which entangling rope disrupting the baleen rack interferes with this flow has not previously been considered as posing an issue for foraging NARWs; however, oral entanglement has been hypothesized to interfere with a critical hydrostatic oral seal in bowhead and right whales (Lambertsen et al. 2005). ...
Without substantive reduction in anthropogenic trauma, Critically Endangered North Atlantic right whales Eubalaena glacialis (NARWs) risk extinction. Decreasing population size is attributable to 2 main issues besides vessel collision: entanglement in fishing gear and changes in food availability due to ecosystem changes in the face of climate disruption. Both can affect NARW energetics, leading to reduced body condition, decreased reproductive success of individuals, and deterioration of overall population health. To measure the impact of these stressors and their interaction, energetic costs associated with entanglement and starvation were incorporated in a bioenergetics model, established for a generic female right whale. We compared models for a NARW living now, one from 2 decades ago, when the species’ abundance was increasing at approximately 2% yr ⁻¹ , and a southern right whale (SRW) from a population increasing at approximately 6% yr ⁻¹ . Parameter uncertainty associated with daily estimates of energy income, basal metabolic rate, and possible influences of baleen rack disruption from entanglement was so great that differences between the 3 generic right whale females were indistinguishable. Therefore, we included a stunted whale in the model. It was also indistinguishable from our first 3 model whales. Further, it made robust predictions of NARW energy budgets, let alone the impact of specific stressors of varying intensity, impossible. The capacity of bioenergetic modeling to inform conservation management of NARWs will be substantially enhanced by resolving these parameter uncertainties.
... Unlike fish, which use gills to filter prey, baleen plates with the fringes layer are the key filter part of balaenid whales [22,23]. The feeding channel of balaenid whale is a parallel channel, including inlet channel, parallel transverse channel and outlet channel [24,25]. This is a new structure, which can provide important guidance for the design of new bionic filter. ...
... At present, the research methods of balaenid whales mainly include multi-sensor tag [26,27], flume experiment [24,28,29] and fluid dynamics modeling [25,[30][31][32]. These studies have undeniably advanced the understanding of balaenid whales. ...
Solid-liquid separation is widely used in daily life and practical engineering. Traditional industrial filters are prone to clogging, but this rarely occurs in filter-feeding organisms. Inspired by the filter feeding mechanism of balaenid whales and considering the local grooves in the fringes layer, a new bionic filter is produced by 3D printing technology through the bionic design of the parallel channels inside the mouth of balaenid whales. At the same time, a test platform composed of the bionic filter, peristaltic pump, fluid pulse rectifier and water tank is built to carry out the fluid flow pattern dyeing and particle filtration experiments. It is found that fluid separation occurs near the groove structure and local vortices are generated. The vortex control filtration mechanism makes the particles in the front grooves tend to accumulate on the left side, which has a certain anti-clogging effect. Moreover, the increase of flow velocity leads to the enhancement of vortices, which makes the accumulation effect on the left more obvious. This study initially practices the bionic application from biological model to engineering design, and the vortex control anti-clogging filtration mechanism proposed in the study has a wide range of application prospects and values.
... In virtually all fishes, waterflows generated by suction are essential for transporting food inside the buccal cavity (Labarbera, 1984;Potvin and Werth, 2017;Wainwright et al., 2015). During suction feeding, the three-dimensional (3D) waterflow patterns toward the fish's mouth have been particularly well studied (Day et al., 2007;Nauwelaerts et al., 2008;Skorczewski et al., 2012;van Leeuwen, 1984). ...
Virtually all fishes rely on flows of water to transport food to the back of their pharynx. While external flows that draw food into the mouth are well described, how intra-oral water flows manage to deposit food at the esophagus entrance remains unknown. In theory, the posteriorly moving water must, at some point, curve laterally and/or ventrally to exit through the gill slits. Such flows would eventually carry food away from the esophagus instead of toward it. This apparent paradox calls for a filtration mechanism to deviate food from the suction-feeding streamlines. To study this gap in our fundamental understanding of how fishes feed, we developed and applied a new technique to quantify three-dimensional patterns of intra-oral water flows in vivo . We combined stereoscopic high-speed x-ray videos to quantify skeletal motion (XROMM) with 3D x-ray particle tracking (XPT) of neutrally buoyant spheres of 1.4 mm in diameter. We show, for carp ( Cyprinus carpio ) and tilapia ( Oreochromis niloticus ), that water tracers displayed higher curvatures than food tracers, indicating an inertia-driven filtration. In addition, tilapia also exhibited a 'central jet' flow pattern, which aids in quickly carrying food to the pharyngeal jaw region. When the food was trapped at the branchial basket, it was resuspended and carried more centrally by periodical bidirectional waterflows, synchronized with head-bone motions. By providing a complete picture of the suction-feeding process and revealing fundamental differences in food transport mechanisms among species, this novel technique opens a new area of investigation to fully understand how most aquatic vertebrates feed.
... Among these filter feeders, balaenid whales (right, Eubalaena spp. and bowhead, Balaena mysticetus) have gigantic bodies (8-15 m) (Potvin and Werth, 2017) but they feed on aggregations of tiny calanoid copepods (1-3 mm) (van der Hoop JM et al., 2019), which has special bionic applications and significances. The dorsal cutaway diagram of the balaenid whale filter feeding is shown in Fig. 1a. ...
... The dorsal cutaway diagram of the balaenid whale filter feeding is shown in Fig. 1a. The flow channels inside the oral cavity mainly consist of three parts, namely, the anteroposterior flow channels along with the tongue (the APT channel) and lip (the APL channel), and the mediolateral flow channel between the intra baleen plates (the IB channel) (Potvin and Werth, 2017;Zhu et al., 2020a). When foraging, balaenid whales continuously swim forward to make the mixture of copepods and water flow directly into their oral cavities. ...
... The study of the filter feeding biomechanics and hydrodynamics associated with balaenid whales can guide the design of new filtration systems that reduce clogging and increase the service life. Previous studies have promoted our understanding of balaenid whales' filter feeding mechanisms, mainly by multi-sensor tags (Simon et al., 2009;van der Hoop JM et al., 2019), flume experiments (Werth, 2012;Werth, 2013;Werth and Potvin, 2016) and theoretical modeling (Potvin and Werth, 2017;Zhu et al., 2020b;Zhu et al., 2020a). The multi-sensor tags approach, usually combined with the depth recorder, the inertial sensor, the accelerometer sensor, and so on, mainly reveals the locomotion and foraging mechanism of balaenid whales. ...
Solid-liquid separation is a key link in environmental chemical and process engineering, including water purification, pollution treatment, etc. Traditional industrial filters are often clogged and damaged because they cannot be cleaned or replaced in time. Filter-feeders, on the other hand, are rarely clogged. Therefore, it is of great significance to draw bionic inspiration from biological filtration to guide the design of traditional filters. In this study, a computational fluid dynamics (CFD) and discrete element method (DEM) coupled model is adopted to investigate the filtering mechanism in balaenid whale feeding. In this model, DEM is used for the particle and the Navier-Stokes equation is used for the fluid. The effects of particle space and shape, as well as particle-particle/wall interaction, are considered. Then, the model is validated by comparing some crucial information with the theoretical results of previous literature. Finally, the effects of four key parameters on the filter feeding characteristics are analyzed, including the fringe layer permeability, prey incident direction, size and shape. The results show that the large permeability, random incidence direction, large size and real irregular shape all lead to more particle collisions. Besides, the captured prey is prone to form an uneven, backward aggregation trend. The large permeability and size make the trend of posterior aggregation more obvious. However, there are no significant differences in the number of the captured prey at each location for different types of incident directions or prey shapes. But the variation of the captured prey distribution in the real shape case is not as smooth as in the simplified sphere case, which shows that the increase in collisions changes the trajectories of some particles to some extent. This study provides a new idea for bionic design in solid-liquid separation field.
... baleen filter) (Pivorunas, 1976;Werth, 2013), as shown in figure 1 (b). Previous studies (Werth, 2004;Werth and Potvin, 2016;Potvin and Werth, 2017;Zhu et al, 2020) indicate that the feeding channels of balaenid whales are made up of three channels, namely, the anteroposterior channels along the tongue (APT channel) and lip (APL channel), and the mediolateral intrabaleen channel between baleen plates (IB channel), as shown in figures 1(c) and (d). This is a typical cross-flow fil- (Zhu et al, 2020). ...
... tration because the direction of ingestion is parallel to the fringe layer. In addition, it has been recognized in the balaenid whales feeding, the ingested suspension flows in through the mouth, then the filtered water flows out through the posterior opening and the prey is carried to the oropharynx (Werth, 2004;Werth and Potvin, 2016;Potvin and Werth, 2017). However, many details of the filter feeding process remain not very clear inside the balaenid whales' oral cavity. ...
... At present, some hydrodynamic models for whale feeding are mainly simplified analytical models. Potvin and Werth (Potvin and Werth, 2017) built a theoretical model called baleen hydraulic circuit (BHC) to obtain the analytical flow velocities in the APT, APL and IB channels, as well as the pressure drop between the APT and APL channels. Despite the simplification of the structure, the BHC model analyzes the internal flow involving a full-size baleen rack for the first time. ...
Balaenid whales are giant filter feeders that feed on the dense aggregations of prey. Through their unique oral filters, they can effectively filter water out and leave prey in their mouths. In this study, a theoretical model is established to analyze the hydrodynamic filtering system in the balaenid whales suspension feeding. First, the appropriate velocity profiles in the anteroposterior and mediolateral directions are adopted to approximate the flow field in the anteroposterior channel along the tongue (APT channel). Then, a 4-stage Runge-Kutta method is used to calculate the particle trajectories and predict the corresponding filter cake profile by solving the particle motion equations. Finally, the effects of three crucial parameters, i.e., the APT channel width DT, the fringe layer permeability K, and the food particle diameter dp, are discussed. The results show that the particle trajectories consist of a series of backward-outward arcs and the food particles tend to accumulate in the posterior region of the oral cavity. The growing parabolic filter cake profiles are formed except for the case of extremely low permeability. A small DT and large K make the tendency of particle posterior aggregation obviously. So squeezing the tongue and having larger fringe layer permeability are both conducive to the swallowing process. But the change in dp has less influence on this tendency. The proposed theoretical analysis method is a fast and low-cost calculation method. The study on the balaenid whales' filter feeding biomechanics and hydrodynamics is helpful to guide the design of the high-efficiency bionic filters.
... The drag force acting on a NARW during foraging is greater than during travelling since openmouth feeding exposes a larger surface area to oncoming water flow, adding resistance to forward motion (Sanderson and Wassersug 1990;Potvin and Werth 2017). For a given speed, foraging increases drag by an estimated 2 to 3 times compared to travelling in NARWs (Nousek McGregor 2010;Potvin and Werth 2017). ...
... The drag force acting on a NARW during foraging is greater than during travelling since openmouth feeding exposes a larger surface area to oncoming water flow, adding resistance to forward motion (Sanderson and Wassersug 1990;Potvin and Werth 2017). For a given speed, foraging increases drag by an estimated 2 to 3 times compared to travelling in NARWs (Nousek McGregor 2010;Potvin and Werth 2017). Fdrag was thus multiplied by 2 and 3 to obtain low and high estimates of energy expended during foraging. ...
The North Atlantic right whale (Eubalaena glacialis, NARW) is an endangered cetacean which faces population decline from anthropogenic activities. Climate change may also be adding pressure on population recovery by shifting distribution of their preferred prey, Calanus copepods. The Gulf of St. Lawrence (GSL) in eastern Canada has been used as a foraging ground by a large proportion of the NARW population in recent years (at least from 2015 to present). Given the motivation to better understand NARW contemporary habitat use patterns and propose recovery measures for this population, we used a mechanistic modeling approach to predict areas that hold foraging potential in the GSL. We first assessed the overall annual energetic costs incurred by an adult female NARW in one of three reproductive states, and determined the theoretical prey densities required to sustain energy demand. We used a 12-year data set describing the abundance and three-dimensional distribution of late-stage Calanus copepods in the GSL coupled to a foraging bioenergetics model to identify potentially suitable foraging areas for NARW. Results show interannual variations in the spatial distribution and quantity of suitable habitat, with a decreasing amount of habitat available for resting, pregnant and lactating females, respectively. Suitable prey densities for foraging NARW were found in nearly all areas of the GSL that were surveyed for copepods, in one year or another, with a greater frequency of suitable prey densities identified in the southern GSL. Yearly maps of suitable foraging habitat for NARW were superimposed to identify areas that showed temporal persistence; the southern GSL (from Shediac Valley east to the Magdalen Islands) had suitable prey densities for all three reproductive states in most (≥ 6) years of the study period. For resting and pregnant females, other potential areas of foraging importance included offshore of Chaleurs Bay as well as the southern slope of the Laurentian Channel north of the Magdalen Islands. These findings highlight areas where NARWs may occur based on habitat modelled foraging value, and emphasize the need to survey offshore, under-studied regions in the GSL to better characterize NARW occurrence and habitat use patterns.
... This is especially true of lunge feeding in rorqual (groove throated) whales of Balaenopteridae , in which up to 100,000 L of seawater can be filtered in 15-30 s, with peak pressures reaching 800-1000 kPa (Werth 2013;Werth et al. 2018b). Continuous filtration of bowhead (Balaena mysticetus) and right whales (Eubalaena spp.) of Balaenidae is a slower, steady-state phenomenon, but likewise involves impressive hydrodynamic forces and flows (Werth and Potvin 2016;Potvin and Werth 2017). ...
Baleen, a unique oral α-keratin, has flat cortical layers enclosing hollow horn tubules. Baleen grows continuously to replace erosive loss from feeding-related wear. This is essential for maintaining efficient filtration over a whale’s long life history. Baleen fragments are seen in stomach contents and feces. We focused on fin (Balaenoptera physalus) and bowhead whales (Balaena mysticetus), but examined eleven mysticete species. Histological features including variably sized tubules plus differential growth along plate axes (growing faster along the medial fringed edge) and between plates of a rack (central plates growing faster than others) relate to baleen strength and flexibility. Sheet-like cortical layers provide strength and probably hinder erosive shedding, whereas medullary (tubular/intertubular) keratin provides flexibility and likely promotes shedding. To calculate amounts of grown/lost baleen, we considered both erosive wear and basal growth, recognizing that each plate represents several years of growth. We estimate average annual loss of 70–100,000 cm2 (20–40,000 cm3) of baleen in balaenids and 25–50,000 cm2 (7–14,000 cm3) in balaenopterids. Baleen growth rates depend on age, size, and other life history parameters; the most reliable calculations come from morphometric data with plate dimensions measured along full racks. We argue that baleen turnover has been under-rated and baleen growth rates underestimated in the published literature. Baleen turnover maintains filter integrity/porosity, while gut passage possibly clears gastrointestinal tracts of endoparasites. Large volumes of shed keratin hold potential ecological consequences by providing food for microbial decomposers and detritivores throughout ocean ecosystems, especially in polar regions where most mysticete feeding occurs.
... While the relative effort required for each of these foraging modes has not before been quantified, surface feeding should be more energetically costly due to increased wave drag when swimming at the surface (Blake, 2009). Similarly, we hypothesize that swim effort while ram filtration feeding, both at the surface and at depth, is more energetically costly than regular swimming due to resistance from water passing through the filter as well as increased drag from the open mouth (Vogel, 1994;Potvin and Werth, 2017). Indeed, increases in effort have been noted while foraging in two previous ram filtration kinematic feeding studies, in species as diverse as anchovies (Carey and Goldbogen, 2017) and baleen whales (van der Hoop et al., 2019). ...
Whale sharks (Rhincodon typus Smith 1828) - the largest extant fish species - reside in tropical environments, making them an exception to the general rule that animal size increases with latitude. How this largest fish thrives in tropical environments that promote high metabolism but support less robust zooplankton communities has not been sufficiently explained. We used open-source inertial measurement units (IMU) to log 397 hours of whale shark behavior in Yucatan, Mexico, at a site of both active feeding and intense wildlife tourism. Here we show that the strategies employed by whale sharks to compensate for the increased drag of an open mouth are similar to ram-feeders five orders of magnitude smaller and one order of magnitude larger. Presumed feeding constituted 20% of the total time budget of four sharks, with individual feeding bouts lasting up to 11 consecutive hrs. Compared to normal, sub-surface swimming, three sharks increased their stroke rate and amplitude while surface feeding, while one shark that fed at depth did not demonstrate a greatly increased energetic cost. Additionally, based on time-depth budgets, we estimate that aerial surveys of shark populations should consider including a correction factor of 3 to account for the proportion of daylight hours that sharks are not visible at the surface. With foraging bouts generally lasting several hours, interruptions to foraging during critical feeding periods may represent substantial energetic costs to these endangered species, and this study presents baseline data from which management decisions affecting tourist interactions with whale sharks may be made.
