97 research outputs found
Mechanical challenges to freshwater residency in sharks and rays
Major transitions between marine and freshwater habitats are relatively infrequent, primarily as a result of major physiological and ecological challenges. Few species of cartilaginous fish have evolved to occupy freshwater habitats. Current thought suggests that the metabolic physiology of sharks has remained a barrier to the diversification of this taxon in freshwater ecosystems. Here, we demonstrate that the physical properties of water provide an additional constraint for this species-rich group to occupy freshwater systems. Using hydromechanical modeling, we show that occurrence in fresh water results in a two- to three-fold increase in negative buoyancy for sharks and rays. This carries the energetic cost of lift production and results in increased buoyancy-dependent mechanical power requirements for swimming and increased optimal swim speeds. The primary source of buoyancy, the lipidrich liver, offers only limited compensation for increased negative buoyancy as a result of decreasing water density; maintaining the same submerged weight would involve increasing the liver volume by very large amounts: 3- to 4-fold in scenarios where liver density is also reduced to currently observed minimal levels and 8-fold without any changes in liver density. The first data on body density from two species of elasmobranch occurring in freshwater (the bull shark Carcharhinus leucas, Muller and Henle 1839, and the largetooth sawfish Pristis pristis, Linnaeus 1758) support this hypothesis, showing similar liver sizes as marine forms but lower liver densities, but the greatest negative buoyancies of any elasmobranch studied to date. Our data suggest that the mechanical challenges associated with buoyancy control may have hampered the invasion of freshwater habitats in elasmobranchs, highlighting an additional key factor that may govern the predisposition of marine organisms to successfully establish in freshwater habitats
How large should whales be?
The evolution and distribution of species body sizes for terrestrial mammals
is well-explained by a macroevolutionary tradeoff between short-term selective
advantages and long-term extinction risks from increased species body size,
unfolding above the 2g minimum size induced by thermoregulation in air. Here,
we consider whether this same tradeoff, formalized as a constrained
convection-reaction-diffusion system, can also explain the sizes of fully
aquatic mammals, which have not previously been considered. By replacing the
terrestrial minimum with a pelagic one, at roughly 7000g, the terrestrial
mammal tradeoff model accurately predicts, with no tunable parameters, the
observed body masses of all extant cetacean species, including the 175,000,000g
Blue Whale. This strong agreement between theory and data suggests that a
universal macroevolutionary tradeoff governs body size evolution for all
mammals, regardless of their habitat. The dramatic sizes of cetaceans can thus
be attributed mainly to the increased convective heat loss is water, which
shifts the species size distribution upward and pushes its right tail into
ranges inaccessible to terrestrial mammals. Under this macroevolutionary
tradeoff, the largest expected species occurs where the rate at which
smaller-bodied species move up into large-bodied niches approximately equals
the rate at which extinction removes them.Comment: 7 pages, 3 figures, 2 data table
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Prey-mediated behavioral responses of feeding blue whales in controlled sound exposure experiments
Behavioral response studies provide significant insights into the nature, magnitude, and consequences of changes in animal behavior in response to some external stimulus. Controlled exposure experiments (CEEs) to study behavioral response have faced challenges in quantifying the importance of and interaction among individual variability, exposure conditions, and environmental covariates. To investigate these complex parameters relative to blue whale behavior and how it may change as a function of certain sounds, we deployed multi-sensor acoustic tags and conducted CEEs using simulated mid-frequency active sonar (MFAS) and pseudo-random noise (PRN) stimuli, while collecting synoptic, quantitative prey measures. In contrast to previous approaches that lacked such prey data, our integrated approach explained substantially more variance in blue whale dive behavioral responses to mid-frequency sounds (rÂČ = 0.725 vs. 0.14 previously). Results demonstrate that deep-feeding whales respond more clearly and strongly to CEEs than those in other behavioral states, but this was only evident with the increased explanatory power provided by incorporating prey density and distribution as contextual covariates. Including contextual variables increases the ability to characterize behavioral variability and empirically strengthens previous findings that deep-feeding blue whales respond significantly to mid-frequency sound exposure. However, our results are only based on a single behavioral state with a limited sample size, and this analytical framework should be applied broadly across behavioral states. The increased capability to describe and account for individual response variability by including environmental variables, such as prey, that drive foraging behavior underscores the importance of integrating these and other relevant contextual parameters in experimental designs. Our results suggest the need to measure and account for the ecological dynamics of predatorâprey interactions when studying the effects of anthropogenic disturbance in feeding animals.This is the publisherâs final pdf. The published article is copyrighted by the Ecological Society of America and can be found at: http://esajournals.onlinelibrary.wiley.com/hub/journal/10.1002/%28ISSN%291939-5582/Keywords: foraging behavior, disturbance, whales, controlled exposure experiment, prey, behavioral respons
Scaling of oscillatory kinematics and Froude efficiency in baleen whales
High efficiency lunate-tail swimming with high-aspect-ratio lifting surfaces has evolved in many vertebrate lineages, from fish to cetaceans. Baleen whales (Mysticeti) are the largest swimming animals that exhibit this locomotor strategy, and present an ideal study system to examine how morphology and the kinematics of swimming scale to the largest body sizes. We used data from whale-borne inertial sensors coupled with morphometric measurements from aerial drones to calculate the hydrodynamic performance of oscillatory swimming in six baleen whale species ranging in body length from 5 to 25 m (fin whale, Balaenoptera physalus; Bryde\u27s whale, Balaenoptera edeni; sei whale, Balaenoptera borealis; Antarctic minke whale, Balaenoptera bonaerensis; humpback whale, Megaptera novaeangliae; and blue whale, Balaenoptera musculus). We found that mass-specific thrust increased with both swimming speed and body size. Froude efficiency, defined as the ratio of useful power output to the rate of energy input (Sloop, 1978), generally increased with swimming speed but decreased on average with increasing body size. This finding is contrary to previous results in smaller animals, where Froude efficiency increased with body size. Although our empirically parameterized estimates for swimming baleen whale drag were higher than those of a simple gliding model, oscillatory locomotion at this scale exhibits generally high Froude efficiency as in other adept swimmers. Our results quantify the fine-scale kinematics and estimate the hydrodynamics of routine and energetically expensive swimming modes at the largest scale
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Using accelerometers to determine the calling behavior of tagged baleen whales
Low-frequency acoustic signals generated by baleen whales can
propagate over vast distances, making the assignment of calls to
specific individuals problematic. Here, we report the novel use of
acoustic recording tags equipped with high-resolution accelerometers
to detect vibrations from the surface of two tagged fin whales that
directly match the timing of recorded acoustic signals. A tag deployed
on a buoy in the vicinity of calling fin whales and a recording from a
tag that had just fallen off a whale were able to detect calls
acoustically but did not record corresponding accelerometer signals
that were measured on calling individuals. Across the hundreds of
calls measured on two tagged fin whales, the accelerometer
response was generally anisotropic across all three axes, appeared
to depend on tag placement and increased with the level of received
sound. These data demonstrate that high-sample rate accelerometry
can provide important insights into the acoustic behavior of baleen
whales that communicate at low frequencies. This method helps
identify vocalizing whales, which in turn enables the quantification of
call rates, a fundamental component of models used to estimate
baleen whale abundance and distribution from passive acoustic
monitoring.Keywords: Whale, Acceleration, Acoustic
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Acoustic and foraging behavior of a Bairdâs beaked whale, Berardius bairdii, exposed to simulated sonar
Beaked whales are hypothesized to be particularly sensitive to anthropogenic noise, based on previous
strandings and limited experimental and observational data. However, few species have been studied in
detail. We describe the underwater behavior of a Bairdâs beaked whale (Berardius bairdii) from the first
deployment of a multi-sensor acoustic tag on this species. The animal exhibited shallow (23 ± 15 m max
depth), intermediate (324 ± 49 m), and deep (1138 ± 243 m) dives. Echolocation clicks were produced with
a mean inter-click interval of approximately 300 ms and peak frequency of 25 kHz. Two deep dives included
presumed foraging behavior, with echolocation pulsed sounds (presumed prey capture attempts) associated
with increased maneuvering, and sustained inverted swimming during the bottom phase of the dive. A
controlled exposure to simulated mid-frequency active sonar (3.5-4 kHz) was conducted 4 hours after tag
deployment, and within 3 minutes of exposure onset, the tagged whale increased swim speed and body
movement, and continued to show unusual dive behavior for each of its next three dives, one of each type.
These are the first data on the acoustic foraging behavior in this largest beaked whale species, and the first
experimental demonstration of a response to simulated sonar
Why whales are big but not bigger : physiological drivers and ecological limits in the age of ocean giants
This research was funded in part by grants from the National Science Foundation (IOS-1656676, IOS-1656656; OPP-1644209 and 07-39483), the Office of Naval Research (N000141612477), and a Terman Fellowship from Stanford University. All procedures in USA were conducted under approval of the National Marine Fisheries Service (Permits 781-1824, 16163, 14809, 16111, 19116, 15271, 20430), Canada DFO SARA/MML 2010-01/SARA-106B, National Marine Sanctuaries (MULTI-2017-007), Antarctic Conservation Act (2009-014, 2015-011) and institutional IACUC committee protocols. Fieldwork, data collection and data processing for M. densirostris were funded by the Office of Naval Research grants N00014-07-10988, N00014-07-11023, N00014-08-10990, N00014-18-1-2062, and 00014-15-1-2553, and the U.S. Strategic Environmental Research and Development Program Grant SI-1539. PLT gratefully acknowledges funding from funding the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland). MASTS is funded by the Scottish Funding Council (HR09011) and contributing institutions.The largest animals are marine filter feeders, but the underlying mechanism of their large size remains unexplained. We measured feeding performance and prey quality to demonstrate how whale gigantism is driven by the interplay of prey abundance and harvesting mechanisms that increase prey capture rates and energy intake. The foraging efficiency of toothed whales that feed on single prey is constrained by the abundance of large prey, whereas filter-feeding baleen whales seasonally exploit vast swarms of small prey at high efficiencies. Given temporally and spatially aggregated prey, filter feeding provides an evolutionary pathway to extremes in body size that are not available to lineages that must feed on one prey at a time. Maximum size in filter feeders is likely constrained by prey availability across space and time.PostprintPeer reviewe
Avoidance responses of minke whales to 1â4 kHz naval sonar
The SOCAL project was funded by the US Navy Chief of Naval Operations Environmental Readiness Division and US Office of Naval Research. The 3S project was funded by the Norwegian Ministry of Defence, the US Office of Naval Research, the Netherlands Ministry of Defence and DGA French Ministry of Defence. The MOCHA project was funded by the US Office of Naval Research. Tyack received funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions.Minke whales are difficult to study and little information exists regarding their responses to anthropogenic sound. This study pools data from behavioural response studies off California and Norway. Data are derived from four tagged animals, of which one from each location was exposed to naval sonar signals. Statistical analyses were conducted using Mahalanobis distance to compare overall changes in parameters summarising dive behaviour, avoidance behaviour, and potential energetic costs of disturbance. Our quantitative analysis showed that both animals initiated avoidance behaviour, but responses were not associated with unusual dive behaviour. In one exposed animal the avoidance of the sonar source included a 5-fold increase in horizontal speed away from the source, implying a significant increase in metabolic rate. Despite the different environmental settings and exposure contexts, clear changes in behaviour were observed providing the first insights into the nature of responses to human noise for this wide-ranging species.PostprintPeer reviewe
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Multiple-stage decisions in a marine central-place forager
Air-breathing marine animals face a complex set of physical challenges associated with diving that affect the decisions of how to optimize feeding. Baleen whales (Mysticeti) have evolved bulk-filter feeding mechanisms to efficiently feed on dense prey patches. Baleen whales are central place foragers where oxygen at the surface represents the central place and depth acts as the distance to prey. Although hypothesized that baleen whales will target the densest prey patches anywhere in the water column, how depth and density interact to influence foraging behaviour is poorly understood. We used multi-sensor archival tags and active acoustics to quantify Antarctic humpback whale foraging behaviour relative to prey. Our analyses reveal multi-stage foraging decisions driven by both krill depth and density. During daylight hours when whales did not feed, krill were found in deep high-density patches. As krill migrated vertically into larger and less dense patches near the surface, whales began to forage. During foraging bouts, we found that feeding rates (number of feeding lunges per hour) were greatest when prey was shallowest, and feeding rates decreased with increasing dive depth. This strategy is consistent with previous models of how air-breathing diving animals optimize foraging efficiency. Thus, humpback whales forage mainly when prey is more broadly distributed and shallower, presumably to minimize diving and searching costs and to increase feeding rates overall and thus foraging efficiency. Using direct measurements of feeding behaviour from animal-borne tags and prey availability from echosounders, our study demonstrates a multi-stage foraging process in a central place forager that we suggest acts to optimize overall efficiency by maximizing net energy gain over time. These data reveal a previously unrecognized level of complexity in predatorâprey interactions and underscores the need to simultaneously measure prey distribution in marine central place forager studies.This is the publisherâs final pdf. The published article is copyrighted by The Royal Society and can be found at: http://rsos.royalsocietypublishing.org/Keywords: diving, predator-prey interactions, foraging decision
Effect of fortification of fresh cow milk with coconut milk on the proximate composition and yield of warankashi, a traditional cheese
Cheese is a concentrated dairy product produced by acid or rennet coagulation or curdling of milk, stirring and heating the curd, draining off the whey, collecting and pressing the curd. The effect of partial substitution of fresh cow milk with coconut milk on the yield and proximate composition of cheese was examined. Extracted coconut milk was mixed with fresh raw cow milk at varying proportions of 5%: 95%, 10%: 90%, 15%: 85%, 20%: 80%, 25%:75%, 70%: 30% and the control (0%:100%) to produce cheese. The control and the partially substituted cheeses were stored in a refrigerator and examined for sensory quality, percentage yield, total titrable acidity, and proximate analysis. The yield of cheese showed significant (p< 0.05) decrease from 26.71% (control sample) to 13.55% as the level of coconut milk increased. The total titrable acidity of cheese was found to be between the ranges of 0.20% - 0.29% which displayed a significant increase from 0.20% - 0.29%. The protein content of the cow-coconut cheese blends showed a significant difference (p<0.05) and an increase of 14.05%-15.33% (at 5%-30% substitution of coconut milk), with the control sample having 13.75%. There was also an increase in fat content from 9.20% - 9.64% (5% - 30% substitution of coconut milk, with the control sample having 8.94%. There was a decrease in the carbohydrate content of the cheese blends which ranged between 8.23% -2.82%, with the control sample having 9.60%. There was a significant decrease (p<0.05) in the ash content of the cow-coconut cheese blends, with the control sample having 1.02%. Significant difference (p<0.05) was observed in the colour, aroma, taste, texture, and overall acceptability as influenced by varying proportions of added coconut milk. The blend with 5% coconut milk and 95% cow milk was most acceptable by panellists. The work showed the potential of coconut as an alternative source of milk in cheese making with improved nutritional value and consumer acceptability
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