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
.
Marine predators face the challenge of reliably finding prey that is patchily distributed in space and time. Predators make movement decisions at multiple spatial and temporal scales, yet we have a ...limited understanding of how habitat selection at multiple scales translates into foraging performance. In the ocean, there is mounting evidence that submesoscale (i.e. less than 100 km) processes drive the formation of dense prey patches that should hypothetically provide feeding hot spots and increase predator foraging success. Here, we integrated environmental remote-sensing with high-resolution animal-borne biologging data to evaluate submesoscale surface current features in relation to the habitat selection and foraging performance of blue whales in the California Current System. Our study revealed a consistent functional relationship in which blue whales disproportionately foraged within dynamic aggregative submesoscale features at both the regional and feeding site scales across seasons, regions and years. Moreover, we found that blue whale feeding rates increased in areas with stronger aggregative features, suggesting that these features indicate areas of higher prey density. The use of fine-scale, dynamic features by foraging blue whales underscores the need to take these features into account when designating critical habitat and may help inform strategies to mitigate the impacts of human activities for the species.
Open-source technology has been increasingly used for developing low-cost animal-borne bio-loggers; however, a gap remains for a bio-logger that records both inertial movement and GPS positions. We ...address this need with the Tapered Wings Logger (TWLogger), an archival bio-logger that records high-resolution (e.g. 50 Hz) tri-axial accelerometry and magnetometry, temperature and GPS. The TWLogger can be built for 90 USD, accepts user-defined sampling parameters, and with a 500 mA h battery weighs 25 g. We provide publicly available build instructions and custom analysis scripts. Bench tests recorded 50 Hz inertial movement and 2 min GPS for 31.8±2.2 h (mean±s.d.,
=6) with GPS accuracy within 10.9±13.6 m. Field deployments on a medium-sized bird of prey in the wild achieved similar results (
=13). The customizable TWLogger has wide-ranging application across systems and thus offers a practical solution for eco-physiology applications.
In the marine environment, dynamic physical processes shape biological productivity and predator-prey interactions across multiple scales. Identifying pathways of physical-biological coupling is ...fundamental to understand the functioning of marine ecosystems yet it is challenging because the interactions are difficult to measure. We examined submesoscale (less than 100 km) surface current features using remote sensing techniques alongside ship-based surveys of krill and baleen whale distributions in the California Current System. We found that aggregative surface current features, represented by Lagrangian coherent structures (LCS) integrated over temporal scales between 2 and 10 days, were associated with increased (a) krill density (up to 2.6 times more dense), (b) baleen whale presence (up to 8.3 times more likely) and (c) subsurface seawater density (at depths up to 10 m). The link between physical oceanography, krill density and krill-predator distributions suggests that LCS are important features that drive the flux of energy and nutrients across trophic levels. Our results may help inform dynamic management strategies aimed at reducing large whales ship strikes and help assess the potential impacts of environmental change on this critical ecosystem.
Linking individual and population scales is fundamental to many concepts in ecology 1, including migration 2, 3. This behavior is a critical 4 yet increasingly threatened 5 part of the life history ...of diverse organisms. Research on migratory behavior is constrained by observational scale 2, limiting ecological understanding and precise management of migratory populations in expansive, inaccessible marine ecosystems 6. This knowledge gap is magnified for dispersed oceanic predators such as endangered blue whales (Balaenoptera musculus). As capital breeders, blue whales migrate vast distances annually between foraging and breeding grounds, and their population fitness depends on synchrony of migration with phenology of prey populations 7, 8. Despite previous studies of individual-level blue whale vocal behavior via bio-logging 9, 10 and population-level acoustic presence via passive acoustic monitoring 11, detection of the life history transition from foraging to migration remains challenging. Here, we integrate direct high-resolution measures of individual behavior and continuous broad-scale acoustic monitoring of regional song production (Figure 1A) to identify an acoustic signature of the transition from foraging to migration in the Northeast Pacific population. We find that foraging blue whales sing primarily at night, whereas migratory whales sing primarily during the day. The ability to acoustically detect population-level transitions in behavior provides a tool to more comprehensively study the life history, fitness, and plasticity of population behavior in a dispersed, capital breeding population. Real-time detection of this behavioral signal can also inform dynamic management efforts 12 to mitigate anthropogenic threats to this endangered population 13, 14).
•Acoustic monitoring reveals patterns in population-level blue whale song production•Tag-derived metrics provide behavioral context for distinct diel patterns in song•When integrated, tag and acoustic metrics reveal an acoustic signature of migration•Key to discerning timing, plasticity, and drivers of a dispersed migration
Oestreich et al. integrate long-term acoustic monitoring and tag-derived metrics to identify an acoustic signature of blue whales’ transition from foraging to migration. This finding links individual and population-level behavior in a highly dispersed population and is central to discerning timing, plasticity, and drivers of blue whale migration.
Physio-logging methods, which use animal-borne devices to record physiological variables, are entering a new era driven by advances in sensor development. However, existing datasets collected with ...traditional bio-loggers, such as accelerometers, still contain untapped eco-physiological information. Here, we present a computational method for extracting heart rate from high-resolution accelerometer data using a ballistocardiogram. We validated our method with simultaneous accelerometer-electrocardiogram tag deployments in a controlled setting on a killer whale (Orcinus orca) and demonstrate the predictions correspond with previously observed cardiovascular patterns in a blue whale (Balaenoptera musculus), including the magnitude of apneic bradycardia and increase in heart rate prior to and during ascent. Our ballistocardiogram method may be applied to mine heart rates from previously collected accelerometery data and expand our understanding of comparative cardiovascular physiology.
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.
As populations of large whales recover from whaling, species that forage and breed in coastal waters, including the humpback whale (Megaptera novaeangliae), increasingly overlap with human ...activities. This represents a potential hazard in locations worldwide subject to intensive vessel traffic, including New York, Panama City and Brisbane.
Historically, humpback whales were not considered part of San Francisco Bay's fauna, except for a few ‘lost’ whales that wandered into the estuary.
An unprecedented influx of humpback whales into highly urbanized San Francisco Bay began in 2016. Research efforts in 2016–2018 from vessels and shore resulted in 496 photo‐identification records plus 319 visual sightings. Sixty‐one individuals were photo‐identified, of which 80% (n = 49) used the bay on multiple days (range = 2 to 39), and 34% (n = 21) were resighted in successive years.
Whales photographed in San Francisco Bay were found to belong to distinct population segments listed as endangered and threatened under the U.S. Endangered Species Act.
Whales moved in and out of the bay seasonally (April–November). Habitat use patterns indicated movements farther into San Francisco Bay correlated positively with high tides.
Humpback whales were visually observed lunge feeding on northern anchovy (Engraulis mordax) at the surface. Analysis of dive patterns by three tagged whales confirmed subsurface feeding when surface feeding was not apparent.
The use of San Francisco Bay and adjacent waters by recovering populations of humpback whales exacerbates the potential for collisions with vessels, entanglement in fishing gear, and harassment by recreational vessels. The most pressing conservation concern is the risk of ship strikes, observed where humpback whales occur near active seaports.
Trophic transfer of energy through marine food webs is strongly influenced by prey aggregation and its exploitation by predators. Rapid aggregation of some marine fish and crustacean forage species ...during wind‐driven coastal upwelling has recently been discovered, motivating the hypothesis that predators of these forage species track the upwelling circulation in which prey aggregation occurs. We examine this hypothesis in the central California Current Ecosystem using integrative observations of upwelling dynamics, forage species' aggregation, and blue whale movement. Directional origins of blue whale calls repeatedly tracked upwelling plume circulation when wind‐driven upwelling intensified and aggregation of forage species was heightened. Our findings illustrate a resource tracking strategy by which blue whales may maximize energy gain amid ephemeral foraging opportunities. These findings have implications for the ecology and conservation of diverse predators that are sustained by forage populations whose behaviour is responsive to episodic environmental dynamics.
The movements of blue whales off central California, monitored through the sounds they produce, reveal that Earth's largest animals closely track a specific type of circulation. This circulation results from wind‐driven upwelling, and within this circulation the prey of blue whales form dense aggregations that greatly increase energy intake by foraging whales. The patterns of blue whale movement also reveal a key threat to this endangered species: risk of mortality from ship strikes.
We examine the dive and movement behavior of blue, fin, and humpback whales along the US West Coast in regions with high ship traffic where ship strikes have been identified as a major concern. All ...three species are known to feed in coastal waters near areas of high ship traffic. We analyzed data from 33 archival tag deployments representing over 3,000 hours of data that were attached with suction-cups or short darts for periods >24 hours and recorded depth (≥1 Hz), fast-lock GPS positions and other sensors. There were clear differences among the three species but all showed a distinct diurnal difference in diving behavior. While dive depth varied among animals based on where prey was located, whales spent a high proportion of their time closer to the surface where they would be more vulnerable to ship strikes at night than in the day. This was most pronounced for blue whales where vulnerability was twice as high at night compared to the day. We also found differences in movement patterns of whales between day and night. Movements were more localized to specific areas in the day near prey resources while at night these movements often involved directional movements (though sometimes returning to the same area). We show how in several specific areas like the Santa Barbara Channel, these differences in movements and locations translate to a very different overlap with shipping lanes at night compared to the daytime locations, which is the basis for most sighting data.
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