The morphology of euphausiid mandibles used to assess selective predation by blue whales in the southern sector of the California Current System

Nickels, Catherine F.; Sala, Linsey M.; Ohman, Mark D.

doi:10.1093/jcbiol/ruy062

Cited by 30 publications

(28 citation statements)

References 15 publications

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“…The bank feature appears to function as an outer limit for both the whales and high densities of T. spinifera, rather than a consistent site of aggregation. This covariation is in agreement with dietary analysis from fecal samples that T. spinifera is the strongly preferred prey in the CCS, followed by the more abundant, though generally smaller E. pacifica (Schoenherr 1991;Kieckhefer 1992;Croll et al 1998;Fiedler et al 1998;Croll et al 2005;Nickels et al 2018). Other euphausiid species appear incidentally in the diet when consumed with these two but are not targeted (Nickels et al 2018).…”

Section: Euphausiid Association With Nmbsupporting

confidence: 85%

“…In the central California region, blue whales feed mostly on Thysanoessa spinifera and to a much lesser extent Euphausia pacifica, to a lower size limit of approximately 10 mm (Croll et al 1998). A similar strong dietary preference of blue whales for larger T. spinifera has recently been documented in the southern California region (Nickels et al 2018). The whales' restricted choice of prey items limits the food resources available to blue whales and may serve to structure whale distributions.…”

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confidence: 92%

“…The density of blue whales is maximal in summer and decreases in fall, but blue whales are rare or absent from the southern CCS in winter and spring (Campbell et al 2015). Blue whales are typically obligate predators on euphausiids (Schoenherr 1991;Croll et al 2005;Nickels et al 2018). In the central California region, blue whales feed mostly on Thysanoessa spinifera and to a much lesser extent Euphausia pacifica, to a lower size limit of approximately 10 mm (Croll et al 1998).…”

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confidence: 99%

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The euphausiid prey field for blue whales around a steep bathymetric feature in the southern California current system

Nickels

Sala

Ohman

2018

Limnology & Oceanography

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Euphausiids are important prey for many marine organisms and often occur in patchy aggregations. Euphausiid predators, such as blue whales, may become concentrated in the vicinity of these aggregations. We investigated an area called Nine Mile Bank (NMB) near San Diego, California, defined by an area of steep bathymetry, to determine whether the frequent whale sightings in that locality can be explained by the distribution of euphausiids across the bank and by the vertical distribution of euphausiids in the water column. Thysanoessa spinifera, the strongly preferred blue whale prey euphausiid in this area, was consistently more abundant on the bank or inshore of it than offshore. In contrast, Euphausia pacifica, a minor blue whale prey item, was much more abundant and distributed across the study region. Adults of both species were concentrated in a stratum corresponding to the feeding depth of blue whales. Other euphausiids that form a negligible part of the blue whale diet also showed no association with NMB. Both blue whales and their primary prey species Thysanoessa spinifera were more abundant on or inshore of the bank than offshore, suggesting that the bank may serve as an offshore limit of high prey abundance that helps to concentrate blue whales.

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Section: Euphausiid Association With Nmbsupporting

confidence: 85%

mentioning

confidence: 92%

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confidence: 99%

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The euphausiid prey field for blue whales around a steep bathymetric feature in the southern California current system

Nickels

Sala

Ohman

2018

Limnology & Oceanography

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“…Dynamic features such as ocean fronts (Belkin et al ) that can markedly restructure plankton communities (e.g., Landry et al ; Powell and Ohman ) and alter C export (Stukel et al ) are amenable to investigation. Responses to event‐scale perturbations, such as upwelling–downwelling, wind‐mixing, or predator passage (Nickels et al ) events can be quantified. Quasi‐Lagrangian studies that entail repeated measurements of the zooplankton over time are feasible.…”

Section: Discussionmentioning

confidence: 99%

Zooglider: An autonomous vehicle for optical and acoustic sensing of zooplankton

Ohman

Davis

Sherman

et al. 2018

Limnology & Ocean Methods

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We present the design and preliminary results from ocean deployments of Zooglider, a new autonomous zooplankton-sensing glider. Zooglider is a modified Spray glider that includes a low-power camera (Zoocam) with telecentric lens and a custom dual frequency Zonar (200 and 1000 kHz). The Zoocam quantifies zooplankton and marine snow as they flow through a defined volume inside a sampling tunnel. Images are acquired on average every 5 cm from a maximum operating depth of~400 m to the sea surface. Biofouling is mitigated using a dual approach: an ultraviolet light-emitting diode and a mechanical wiper. The Zonar permits differentiation of large and small acoustic backscatterers in larger volumes than can be sampled optically. Other sensors include a pumped conductivity, temperature, and depth unit and chlorophyll a fluorometer. Zooglider enables fully autonomous in situ measurements of mesozooplankton distributions, together with the three-dimensional orientation of organisms and marine snow in relation to other biotic and physical properties of the ocean water column. It is well suited to resolve thin layers and microscale ocean patchiness. Battery capacity supports 50 d of operations. Zooglider includes two-way communications via Iridium, permitting near-real-time transmission of data from each dive profile, as well as interactive instrument control from remote locations for adaptive sampling.

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“…Blue (Balaenoptera musculus) and fin (B. physalus) whales are the two largest species of cetaceans and both occur off the west coast of the United States (USA). Blue whales arrive seasonally beginning in the late spring-early summer and feed on aggregations of krill (Thysanoessa spinifera and Euphausia pacifica; Fiedler et al, 1998;Croll et al, 2005;Nickels et al, 2018) until the late fall-early winter when they migrate south to breeding areas off Baja California, Mexico, in the Gulf of California, and near an offshore oceanographic feature called the Costa Rica Dome (Mate et al, 1999;Bailey et al, 2010;Irvine et al, 2014). Although the seasonal movements of fin whales are less well-understood, they occur year-round off southern California (Stafford et al, 2009;Sirovic et al, 2015;Scales et al, 2017) suggesting they do not follow the typical baleen whale pattern of migrating to lower latitudes during the winter to breed and calve (see also Edwards et al, 2015;Geijer et al, 2016;Jiménez López et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Scales of Blue and Fin Whale Feeding Behavior off California, USA, With Implications for Prey Patchiness

et al. 2019

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Intermediate-duration archival tags were attached to eight blue whales (Balaenoptera musculus; four females, three males, one of unknown sex), and five fin whales (B. physalus; two females, one male, two of unknown sex) off southern California, USA, in summer 2014 and 2015. Tags logged 1-Hz data from tri-axial accelerometers, magnetometers, and a depth sensor, while acquiring Fastloc GPS locations. Tag attachment duration ranged from 18.3 to 28.9 d for blue whales and 4.9-16.0 d for fin whales, recording 1,030-4,603 dives and 95-3,338 GPS locations per whale across both species. Feeding lunges (identified from accelerometer data) were used to characterize "feeding bouts" (i.e., sequences of feeding dives with <60 min of consecutive non-feeding dives), within-bout behavior, and to examine the spatial distribution of feeding effort. Whales fed near the tagging locations (Point Mugu and San Miguel Island) for up to 7 d before dispersing as far south as Ensenada, Mexico, and north to Cape Mendocino, California. Dispersal within southern California waters differed by sex in both species with males undertaking offshore, circuitous excursions, while females remained more coastal, suggesting that movement patterns on the feeding grounds may not be exclusively related to energy gain. Feeding bout characteristics were similar for both species, with the median bout having 24 dives and lasting 3.3 h for blue whales (n = 242), and 19 dives while lasting 2.7 h for fin whales (n = 59). Bout duration was positively correlated with the number of feeding lunges per dive within a bout for both species, suggesting whales left poor-quality prey patches quickly but fed intensively for up to 34.9 h when prey was abundant. Feeding bouts occurred further apart as the distance from shore increased, but there was no corresponding difference in the number of feeding lunges per dive, suggesting the whales were feeding at the same rate throughout their range, but that prey was more dispersed in offshore waters. This may be evidence of two feeding strategies, with spatially aggregated foraging around highly localized, topographically forced upwelling centers nearshore, and more dispersed foraging in larger areas of elevated, but patchy, productivity offshore.

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The morphology of euphausiid mandibles used to assess selective predation by blue whales in the southern sector of the California Current System

Cited by 30 publications

References 15 publications

The euphausiid prey field for blue whales around a steep bathymetric feature in the southern California current system

The euphausiid prey field for blue whales around a steep bathymetric feature in the southern California current system

Zooglider: An autonomous vehicle for optical and acoustic sensing of zooplankton

Scales of Blue and Fin Whale Feeding Behavior off California, USA, With Implications for Prey Patchiness

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