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Given the effects of harmful algal blooms (HABs) on human and wildlife health, understanding how domoic acid (DA) is accumulated and transferred through food webs is critical for recognizing the most affected marine communities and predicting ecosystem effects. This study combines stable isotopes of carbon (δ13C) and nitrogen (δ15N) from bulk muscle tissue with DA measurements from viscera to identify the foraging strategies of important DA vectors and predators in Monterey Bay, CA. Tissue samples were collected from 27 species across three habitats in the summer of 2018 and 2019 (time periods without prominent HABs). Our results highlight an inshore-offshore variation in krill δ13C values and DA concentrations ([DA]; ppm) in anchovies indicating differences in coastal productivity and DA accumulation. The narrow overlapping isotopic niches between anchovies and sardines suggest similar diets and trophic positions, but striking differences in [DA] indicate a degree of specialization, thus, resource partitioning. In contrast, krill, market squid, and juvenile rockfish accumulated minimal DA and had comparatively broad isotopic niches, suggesting a lower capacity to serve as vectors because of potential differences in diet or feeding in isotopically distinct locations. Low [DA] in the liver of stranded sea lions and their generalist foraging tendencies limits our ability to use them as sentinels for DA outbreaks in a specific geographic area. Collectively, our results show that DA was produced a few kilometers from the coastline, and anchovies were the most powerful DA vector in coastal-pelagic zones (their DA loads exceeded the 20 ppm FDA regulatory limits for human consumption), while mussels did not contain detectable DA and only reflect in situ DA, δ13C, and δ15N values. Our study demonstrates the efficacy of combining multiple biogeochemical tracers to improve HAB monitoring efforts and identify the main routes of DA transfer across habitats and trophic levels.

We read ‘Whistling is metabolically cheap for communicating bottlenose dolphins ( Tursiops truncatus )’ by [Pedersen et al. (2020)][1] and were concerned to see how our results ([Noren et al., 2013][2]; [Holt et al., 2015][3]) were presented. This was especially surprising, given our previous

Toothed whales use echolocation to sense their environment and capture prey. However, their reliance on acoustic information makes them vulnerable to sound exposure. Odontocetes modify echolocation signals in response to ambient noise levels, yet the metabolic cost of producing and modifying echolocation signals are unknown. Studies on bats found that the metabolic cost of producing echolocation signals and modifying sonar parameters is high. Unlike terrestrial mammals, however, the conservation of oxygen is paramount for odontocetes that echolocate underwater on a breath-hold. Flow-through respirometry was used to determine the metabolic costs of producing and modifying echolocations signals in two trained bottlenose dolphins ( Tursiops truncatus ) that produced echolocation clicks with variable sound energy levels. Unlike bats, the metabolic cost of echolocation was negligible in dolphins. On average, the metabolic rate of submerged dolphins producing clicks was 1.1 times greater than the metabolic rate of submerged, silent dolphins. Similar to bats, the metabolic cost of producing echolocation signals increased significantly with acoustic energy in dolphins. Yet, for the sound energy levels produced, metabolic rates of dolphins producing clicks were within the range of metabolic rates measured when the dolphins were silent. These results can be used to better understand some of the energetic costs associated with dolphin foraging behavior as well as assess the relative energetic impacts of different delphinid behavioral responses to anthropogenic disturbance.

The mechanism by which odontocetes produce sound is unique among mammals. To gain insight into the physiological properties that support sound production in toothed whales, we examined myoglobin content ([Mb]), non-bicarbonate buffering capacity (β), fiber-type profiles, and myosin heavy chain expression of vocal musculature in two odontocetes: the bottlenose dolphin (Tursiops truncatus; n = 4) and the harbor porpoise (Phocoena phocoena; n = 5). Both species use the same anatomical structures to produce sound, but differ markedly in their vocal repertoires. Tursiops produce both broadband clicks and tonal whistles, while Phocoena only produce higher frequency clicks. Specific muscles examined in this study included: (1) the nasal musculature around the phonic lips on the right (RNM) and left (LNM) sides of the head, (2) the palatopharyngeal sphincter (PPS), which surrounds the larynx and aids in pressurizing cranial air spaces, and (3) the genioglossus complex (GGC), a group of muscles positioned ventrally within the head. Overall, vocal muscles had significantly lower [Mb] and β than locomotor muscles from the same species. The PPS was predominately composed of small diameter slow-twitch fibers. Fiber-type and myosin heavy chain analyses revealed that the GGC was comprised largely of fast-twitch fibers (Tursiops: 88.6%, Phocoena: 79.7%) and had the highest β of all vocal muscles. Notably, there was a significant difference in [Mb] between the RNM and LNM in Tursiops, but not Phocoena. Our results reveal shared physiological characteristics of individual vocal muscles across species that enhance our understanding of key functional roles, as well as species-specific differences which appear to reflect differences in vocal capacities.

Recovery of cetacean carcasses provides data on levels of human-caused mortality, but represents only a minimum count of impacts. Counts of stranded carcasses are negatively biased by factors that include at-sea scavenging, sinking, drift away from land, stranding in locations where detection is unlikely, and natural removal from beaches due to wave and tidal action prior to detection. We estimate the fraction of carcasses recovered for a population of coastal bottlenose dolphins (Tursiops truncatus), using abundance and survival rate data to estimate annual deaths in the population. Observed stranding numbers are compared to expected deaths to estimate the fraction of carcasses recovered. For the California coastal population of bottlenose dolphins, we estimate the fraction of carcasses recovered to be 0.25 (95% CI = 0.20– 0.33). During a 12 yr period, 327 animals (95% CI = 253–413) were expected to have died and been available for recovery, but only 83 carcasses attributed to this population were documented. Given the coastal habits of California coastal bottlenose dolphins, it is likely that carcass recovery rates of this population greatly exceed recovery rates of more pelagic dolphin species in the region.

In 2007, the apparent increase in the number of harbor porpoises (Phocoena phocoena) stranding along the central California coast compared to the number of strandings the previous year resulted in the declaration of an Unusual Mortality Event by the National Marine Fisheries Service. A statistically significant increase in strandings occurred in 2008 and 2009, with more than twice the mean annual number of strandings documented per year in the previous decade occurring each year, but then strandings decreased in 2010. No single cause of mortality explained all the strandings, and there were no significant changes in age class or sex of strandings in 2008 and 2009. Trauma, including interspecific aggression and fisheries interactions, was the most common cause of death, and blunt force trauma increased significantly in August through October of 2008 and 2009. Domoic acid toxicosis was documented for the first time in this species. Although the cause of death for many strandings was unidentified, the increase in strandings in 2008-2009 reflects an increase in blunt trauma rather than an epizootic of disease.

Cetaceans produce different types of sounds that vary according to behavioral context. They also modify their acoustic signals in response to noise. The metabolic costs of producing social sounds and clicks were recently measured in two bottlenose dolphins using flow-through respirometry methods. For both sound types, metabolic rates significantly increased as vocal effort increased, illustrating a modest cost of vocal modification. Using these data, metabolic costs can be extrapolated to more typical (higher) values of free-ranging dolphins and compared among sound types. However, cost comparisons are complicated by important differences in methodology and the acoustic energy output between sound type trials. In this investigation, existing data are analyzed specifically to scale and compare costs with these differences taken into account. Total metabolic cost of sound production was calculated above baseline values in ml O2 and related to vocal effort in dB re 1 μPa2s (adjusted to on-axis source levels) on a per trial basis. Results reveal that clicks are produced at smaller costs compared to whistles. These findings are consistent with the observation that whistles require higher intranasal air pressure during sound generation and allow estimates of the costs of responses across a range of behavioral contexts and disturbance scenarios.

Cetacean responses to marine anthropogenic activities include changes in acoustic behavior, surface active behavior, dive behavior, direction of travel, and behavioral activity states. Behavioral effects have been observed in several field studies involving both observational and controlled exposure experiments. However, the consequences of these behavioral responses are often difficult to quantify in biological currencies. Previous work has empirically measured the energetic consequences of many of these behavioral responses that may have acute or chronic energetic consequences including our ONR-supported work on the metabolic costs of communicative sound and click production, and the metabolic costs of changes in vocal behavior in bottlenose dolphins that are consistent with vocal modification. The current investigation involves two separate but related studies that will address energetic costs of behavioral responses to anthropogenic disturbance, including acoustic effects, in odontocetes. The first study will address, in a comparative framework, metabolic costs of sound production and vocal modification across different sound types and odontocete species. The second component of the investigation will address cumulative energetic costs of behavioral responses to disturbance. These analyses will provide quantitative information that will be particularly useful to incorporate into models such as the Population Consequence of (Acoustic) Disturbance (PCAD/PCoD) as well as provide input data for environmental assessments/impact statements and other permit processes involving anthropogenic activities that have the potential to impact marine mammals.

SUMMARYIn Atlantic bottlenose dolphins Tursiops truncatus, both the thickness and lipid content of blubber vary across ontogeny and across individuals of differing reproductive and nutritional status. This study investigates how these changes in blubber morphology and composition influence its thermal properties. Thermal conductivity (W m–1deg.–1, where deg. is °C) and thermal insulation(m2 deg. W–1) of dolphin blubber were measured in individuals across an ontogenetic series (fetus through adult, N=36),pregnant females (N=4) and emaciated animals (N=5). These thermal properties were determined by the simultaneous use of two common experimental approaches, the heat flux disc method and the standard material method. Thickness, lipid and water content were measured for each blubber sample. Thermal conductivity and insulation varied significantly across ontogeny. Blubber from fetuses through sub-adults was less conductive(range=0.11–0.13±0.02 W m–1deg.–1) than that of adults (mean=0.18 W m–1deg.–1). The conductivity of blubber from pregnant females was similar to non-adult categories, while that of emaciated animals was significantly higher (0.24 ± 0.04 W m deg.–1) than all other categories. Blubber from sub-adults and pregnant females had the highest insulation values while fetuses and emaciated animals had the lowest. In nutritionally dependant life history categories, changes in blubber's thermal insulation were characterized by stable blubber quality (i.e. conductivity)and increased blubber quantity (i.e. thickness). In nutritionally independent animals, blubber quantity remained stable while blubber quality varied. A final, unexpected observation was that heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface, a pattern not observed in control materials. This apparent ability to absorb heat, coupled with blubber's fatty acid composition, suggest that dolphin integument may function as a phase change material.

Many animals produce louder, longer or more repetitious vocalizations to compensate for increases in environmental noise. Biological costs of increased vocal effort in response to noise, including energetic costs, remain empirically undefined in many taxa, particularly in marine mammals that rely on sound for fundamental biological functions in increasingly noisy habitats. For this investigation, we tested the hypothesis that an increase in vocal effort would result in an energetic cost to the signaler by experimentally measuring oxygen consumption during rest and a 2 min vocal period in dolphins that were trained to vary vocal loudness across trials. Vocal effort was quantified as the total acoustic energy of sounds produced. Metabolic rates during the vocal period were, on average, 1.2 and 1.5 times resting metabolic rate (RMR) in dolphin A and B, respectively. As vocal effort increased, we found that there was a significant increase in metabolic rate over RMR during the 2 min following sound production in both dolphins, and in total oxygen consumption (metabolic cost of sound production plus recovery costs) in the dolphin that showed a wider range of vocal effort across trials. Increases in vocal effort, as a consequence of increases in vocal amplitude, repetition rate and/or duration, are consistent with behavioral responses to noise in free-ranging animals. Here, we empirically demonstrate for the first time in a marine mammal, that these vocal modifications can have an energetic impact at the individual level and, importantly, these data provide a mechanistic foundation for evaluating biological consequences of vocal modification in noise-polluted habitats.

SUMMARYElephant movement patterns in relation to surface water demonstrate that they are a water-dependent species. Thus, there has been interest in using surface water management to mitigate problems associated with localized elephant overabundance. However, the physiological mechanisms underlying the elephant's water dependence remain unclear. Although thermoregulation is likely an important driver, the relationship between thermoregulation, water use and climate has not been quantified. We measured skin surface temperature of and cutaneous water loss from 13 elephants (seven African, 3768±642 kg; six Asian, 3834±498 kg) and determined the contribution of evaporative cooling to their thermal and water budgets across a range of air temperatures (8–33°C). We also measured respiratory evaporative water loss and resting metabolic heat production on a subset of elephants (N=7). The rate of cutaneous evaporative water loss ranged between 0.31 and 8.9 g min−1 m−2 for Asian elephants and 0.26 and 6.5 g min−1 m−2 for African elephants. Simulated thermal and water budgets using climate data from Port Elizabeth, South Africa, and Okaukuejo, Namibia, suggested that the 24-h evaporative cooling water debt incurred in warm climates can be more than 4.5 times that incurred in mesic climates. This study confirms elephants are obligate evaporative coolers but suggests that classification of elephants as water dependent is insufficient given the importance of climate in determining the magnitude of this dependence. These data highlight the potential for a physiological modeling approach to predicting the utility of surface water management for specific populations.

SummaryBottlenose dolphins (Tursiops truncatus) produce various communicative sounds that are important for social behavior, maintaining group cohesion, and coordinating foraging. For example, whistle production increases during disturbances, such as separations of mother/calf pairs and vessel approaches. It is clear that acoustic communication is important to the survival of these marine mammals, yet the metabolic cost of producing whistles and other socials sounds and the energetic consequences of modifying these sounds in response to both natural and anthropogenic disturbance are unknown. We used flow-through respirometry to determine if the metabolic cost of sound production could be quantified in two captive dolphins producing social sounds (whistles and squawks). On average, we found that metabolic rates measured during two-min periods of sound production were 1.2 times resting values. Up to 7 min were required for metabolism to return to resting values following vocal periods. The total metabolic cost (over resting values) of the two-min vocal period plus required recovery period (163.3 to 2995.9 ml O2 or 3,279.6 to 60,166.7 J) varied by individual as well as by mean duration of sounds produced within the vocal period. Observed variation in received cumulative sound energy levels of vocalizations was not related to total metabolic costs. Furthermore, our empirical findings did not agree with previous theoretical estimates of the metabolic cost of whistles. This study provides the first empirical data on the metabolic cost of sound production in dolphins which can be used to estimate metabolic costs of vocal responses to environmental perturbations in wild dolphins.

Many species respond to increases in environmental noise by increasing the amplitude, duration, and/or repetition rate of their vocalizations. Potential costs of noise-induced vocal modifications include increased energetic costs but no empirical data in marine mammals exist. This study’s objective was to compare the metabolic costs of communicative sounds produced by captive bottlenose dolphins (N = 2) under two conditions (low- and high-amplitude vocalization trials) to assess energetic costs of vocal responses to noise. An experimental trial consisted of a 10-min rest period to determine resting metabolic rate, followed by a two-minute vocalization period, and concluded with another 10-min rest period to measure recovery. Open-flow respiratory was used to measure oxygen consumption during each trial component. Vocalizations were recorded using a calibrated hydrophone for analysis. Both dolphins tended to produce longer vocalizations during high-amplitude trials. Thus, metabolic rates were related to to...

Several studies have shown that cetaceans respond to the physical presence and/or acoustic emissions from marine vessels. For example, cetaceans perform surface-active behaviors (SABs) in response to an increase in the number of and/or close approaches by vessels (Lusseau 2006; Noren et al. 2009; Williams et al. 2002, 2009). SABs are often performed in bouts of one or more behaviors performed sequentially, and the majority of SABs provide both visual and acoustic signals that are important to social marine mammals. Indeed, the use of sound is essential to the survival and reproduction of cetaceans (National Research Council 2003), and because of this, anthropogenic sound exposure in marine mammals is a concern. Individuals may compensate for increased vessel noise by changing the amplitude (Holt et al. 2009; Scheifele et al. 2005), duration (Foote et al. 2004), repetition rate, and/or frequency of the sounds they produce.

In Atlantic bottlenose dolphins (Tursiops truncatus) the thickness and lipid content of blubber (the integument's specialized hypodermis) varies across ontogeny and with reproductive and nutritional state. Because the integument comprises up to 25% of total body mass in this species, ontogenetic changes in its lipid content may influence whole body buoyancy. The density and volume of the integument were measured and its buoyancy calculated across an ontogenetic series of dolphins and in pregnant and emaciated adults (total n = 45). Regional differences between the metabolically labile trunk integument and the structural tailstock integument were also investigated. Mean densities of both trunk and tailstock integument were similar across life history categories (trunk = 1,040.7 ± 14.1 kg/m 3 ; tailstock = 1,077.1 ± 21.2 kg/m 3 ) and were statistically similar to the density of seawater (1,026 kg/m 3 ). The mean buoyant force of integument from the trunk (—1.01 ± 1.74 N) and tailstock (—0.30 ± 0.21 N) did not vary significantly across ontogeny. In contrast, pregnancy and emaciation did influence the integument's buoyancy, which ranged between 9 N and —45 N in these categories. Although neutral during growth, the integument's contribution to whole body buoyancy can be influenced by an individual's reproductive and nutritional status.

Dolphins produce many types of sounds known to have distinct qualities and functionalities. Whistles, which function in social contexts, are much longer in duration and require close to twice the intranasal air pressure to produce relative to biosonar click production. Thus, it is predicted that whistle production would be energetically more costly but this prediction is complicated by the fact that clicks are generated at much higher signal intensities. We used flow-through respirometry methods to measure metabolic costs of social sound and click production in two bottlenose dolphins. For all signal types, metabolic rates were related to the energy content of the signals produced. When metabolic costs were compared for equal energy sound generation, clicks were produced at negligible costs relative to resting and at a fraction of the cost of social sound production. However, while the performed repetition rates during click production were similar to field measurements, those of social sounds were much h...