Scaling of maneuvering performance in baleen whales: larger whales outperform expectations.

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.

Erratum to: Simulated maternal stress reduces offspring aerobic swimming performance in Pacific salmon.

[This corrects the article DOI: 10.1093/conphys/coz095.].

Simulated maternal stress reduces offspring aerobic swimming performance in Pacific salmon.

Pacific salmon routinely encounter stressors during their upriver spawning migration, which have the potential to influence offspring through hormonally-mediated maternal effects. To disentangle genetic vs. hormonal effects on offspring swimming performance, we collected gametes from three species of Pacific salmon (Chinook, pink and sockeye) at the end of migration and exposed a subset of eggs from each female to cortisol baths to simulate high levels of maternal stress. Fertilised eggs were reared to fry and put through a series of aerobic swim trials. Results show that exposure to cortisol early in development reduces maximum oxygen consumption while swimming, and decreases aerobic scope in all three species. Resting oxygen consumption did not differ between cortisol and control treatment groups. We also examined several metrics that could influence aerobic performance, and found no differences between treatment groups in haematocrit%, haemoglobin concentration, heart mass, citrate synthase activity or lactate dehydrogenase activity. Though it was not the focus of this study, an interesting discovery was that pink salmon had a higher MO2max and aerobic scope relative to the other species, which was supported by a greater haematocrit, haemoglobin, a larger heart and higher CS activity. Some management and conservation practices for Pacific salmon focus efforts primarily on facilitating adult spawning. However, if deleterious effects of maternal stress acquired prior to spawning persist into the next generation, consideration will need to be given to sub-lethal effects that could be imparted onto offspring from maternal stress.

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator.

Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes' cst model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during prey-scarce winters.