Despite their enormous size, whales make their living as voracious predators. To catch their much smaller, more maneuverable prey, they have developed several unique locomotor strategies that require high energetic input, high mechanical power output and a surprising degree of agility. To better understand how body size affects maneuverability at the largest scale, we used bio-logging data, aerial photogrammetry and a high-throughput approach to quantify the maneuvering performance of seven species of free-swimming baleen whale. We found that as body size increases, absolute maneuvering performance decreases: larger whales use lower accelerations and perform slower pitch-changes, rolls and turns than smaller species. We also found that baleen whales exhibit positive allometry of maneuvering performance: relative to their body size, larger whales use higher accelerations, and perform faster pitch-changes, rolls and certain types of turns than smaller species. However, not all maneuvers were impacted by body size in the same way, and we found that larger whales behaviorally adjust for their decreased agility by using turns that they can perform more effectively. The positive allometry of maneuvering performance suggests that large whales have compensated for their increased body size by evolving more effective control surfaces and by preferentially selecting maneuvers that play to their strengths.

1. The relative energetic benefits of foraging on one type of prey rather than another are not easily measured, particularly for large free-ranging predators. Nonetheless, assumptions about preferred and alternative prey are frequently made when predicting how a predator may impact its environment, adapt to environmental change or interact with human activities. 2. We developed and implemented a process-based model to investigate the potential energetic benefit (PEB) of in situ foraging opportunities in rorqual whales. The model integrates and evaluates the energetic importance of measured prey patch characteristics (prey distribution, energy content and predator avoidance) and predator characteristics (morphometrics, foraging tactics and feeding rates). We applied the model to test the assumption that hatchery-released juvenile salmon are an 'easy meal' for humpback whales compared to more common prey: herring and krill. 3. In 11 out of the 13 foraging situations considered, whales were found to be feeding in a manner where net energy gain was greater than the energetic costs of non-foraging swimming. Humpback whale PEB for hatchery-released juvenile salmon fell within the range of the PEB for krill and herring but varied by species, from relatively high PEB for chum salmon to relatively low for coho salmon. Our model provides behavioural insight as well, indicating that shallow feeding may be more important for reducing energy expenditure through slower lunge speeds than for increasing prey capture. The model also provides a means of identifying prey patch characteristics, with prey aggregation playing the largest role in determining PEB despite being a poor overall proxy for PEB, supporting the use of the complex model framework. 4. Modelling approaches are especially valuable where they can use reasonable assumptions to substitute for lack of reliable observations, thereby integrating a range of interacting factors into a single framework. Additionally, because process-based models can be used to make predictions outside the range of previously observed conditions, they will be increasingly useful in a changing climate.

AbstractResource partitioning is an important process driving habitat use and foraging strategies in sympatric species that potentially compete. Differences in foraging behavior are hypothesized to contribute to species coexistence by facilitating resource partitioning, but little is known on the multiple mechanisms for partitioning that may occur simultaneously. Studies are further limited in the marine environment, where the spatial and temporal distribution of resources is highly dynamic and subsequently difficult to quantify. We investigated potential pathways by which foraging behavior may facilitate resource partitioning in two of the largest co‐occurring and closely related species on Earth, blue (Balaenoptera musculus) and humpback (Megaptera novaeangliae) whales. We integrated multiple long‐term datasets (line‐transect surveys, whale‐watching records, net sampling, stable isotope analysis, and remote‐sensing of oceanographic parameters) to compare the diet, phenology, and distribution of the two species during their foraging periods in the highly productive waters of Monterey Bay, California, USA within the California Current Ecosystem. Our long‐term study reveals that blue and humpback whales likely facilitate sympatry by partitioning their foraging along three axes: trophic, temporal, and spatial. Blue whales were specialists foraging on krill, predictably targeting a seasonal peak in krill abundance, were present in the bay for an average of 4.7 months, and were spatially restricted at the continental shelf break. In contrast, humpback whales were generalists apparently feeding on a mixed diet of krill and fishes depending on relative abundances, were present in the bay for a more extended period (average of 6.6 months), and had a broader spatial distribution at the shelf break and inshore. Ultimately, competition for common resources can lead to behavioral, morphological, and physiological character displacement between sympatric species. Understanding the mechanisms for species coexistence is both fundamental to maintaining biodiverse ecosystems, and provides insight into the evolutionary drivers of morphological differences in closely related species.

Humpback whales Megaptera novaeangliae are filter feeders that use discrete lunges to effectively capture densely aggregated prey. The objective of this research was to examine how foraging humpback whales in Southeast Alaska responded to varying prey patch densities and depths. Digital acoustic recording tags (DTAGs; n = 6) were deployed and focal follows were conducted on foraging whales in Sitka Sound, Alaska in September 2012. Prey density was recorded around tagged whales using a Simrad EK60 scientific echosounder and ground-truthed with net tows. Lunges were identified from peaks in jerk in the accelerometer signal, and krill were identified from echosounder data using decibel differencing. Lunge depth was 111 +/- 9 m (mean +/- SD) for the shallowest diving whale (foraging past sunset) and 144 +/- 7 (mean +/- SD) m for the deepest diving whale (foraging diurnally). Ninety-five percent of lunges occurred within a 300 m and 30 min spatio-temporal buffer of krill, indicating that tagged whales fed on krill. Generalized additive mixed model (GAMM) results for spatio-temporally integrated prey and lunge data indicated that mean volume backscattering strength, a proxy for krill density, and krill depth significantly affected the occurrence of a lunge (density: p = 0.006, depth: p < 0.001). Whales fed in the densest region of the krill layer, where mean volume backscatter was -57 dB (range: -50 to -81 dB re 1 m(-1) at 120 kHz). By targeting the densest prey layer, whales maximized their energetic gain by capturing the most prey with each lunge.

The coastal upwelling ecosystem near Monterey Bay, California, is a productive yet variable ecosystem and an important foraging area for many mobile apex predators, such as marine mammals. Long-term studies are necessary to better understand how wide-ranging predators respond to temporal environmental variability; however, few of these studies exist. We conducted monthly shipboard line-transect surveys in Monterey Bay from 1997 to 2007. We identified 22 species of marine mammals, and calculated monthly and annual densities for the 12 most commonly sighted (focal) species. Species richness remained relatively constant (mean richness +/- SE: 13.7 +/- 0.396 species yr(-1)) from 1997 to 2006. Focal species were most evenly distributed (Shannon's equitability, E-H = 0.820) but least dense (mean density +/- SE: 0.0598 +/- 0.0141) during the anomalous upwelling conditions of 2005, and least even (1997 E-H = 0.413; 1998 E-H = 0.407) but dense (mean density +/- SE: 1997: 0.433 +/- 0.177; 1998: 0.438 +/- 0.169 ind. km(-2)) during the 1997/1998 El Nino event. There were no statistically significant differences in the densities of marine mammal species between warmer and cooler years. The community and species-specific responses of marine mammals to warm-water years differed depending on the mechanism of oceanographic variability. During the 1997/1998 El Nino (a basin-wide event), marine mammals aggregated in nearshore areas, such as Monterey Bay, with relatively greater productivity than offshore regions, whereas during anomalous upwelling conditions of 2005 (a more localized oceanographic event), marine mammals redistributed away from Monterey Bay to areas less affected by the anomaly.