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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.

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.

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.

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.

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.