“A dynamic state model of migratory behavior and physiology to assess the consequences of environmental variation and anthropogenic disturbance on marine vertebrates”

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Enrico Pirotta, Marc Mangel, Daniel P. Costa, Bruce Mate, Jeremy Goldbogen, Daniel M. Palacios, Luis Huckstadt, Elizabeth A. McHuron, Lisa Schwarz, and Leslie New (Feb 2018)

The DOI is https://dx.doi.org/10.1086/695135

Dynamic state modeling offers new insights into the migratory behavior and physiology of baleen whales

The interplay of physiology, behavior and the environment sheds light on the migration of large marine vertebrates and the potential effects of environmental and human disturbance

Animals that migrate between their feeding and breeding grounds are subject to intense physiological pressure. On the feeding grounds, they must acquire a large portion of the energy they need to cover their travel and reproductive costs, before returning to the breeding grounds where they may exhaust the accumulated resources. This paper explores the mechanisms underlying this complex trade-off and suggests hypotheses on the processes driving migratory behavior, with blue whales as an example.

Researchers at Washington State University, in collaboration with colleagues from the University of California Santa Cruz, Oregon State University, and Stanford University, have combined their expertise and available data on the ecology, feeding behavior, movements, energetics, and reproduction of migrating blue whales to develop a model describing a female’s optimal behavior over time. They find that migration emerges from the animals tracking the seasonal variability of prey in their range, while having to return to the breeding grounds. The results also show that female blue whales must feed on the breeding grounds to sustain the large costs of lactation, while pregnancy is energetically less costly.

The authors then use the model to demonstrate how environmental changes could disproportionately affect reproductive success depending on how whales react and adjust to a perturbed environment. They also predict that the impact of localized, acute disturbance from human activities depends on how whales change their behavior, while chronic, but weaker, disturbances are expected to have limited short-term effects on reproduction. Blue whale migration appears to balance access to sufficient food resources with the constraints of reproduction. The proposed approach could be applied to other migratory species to disentangle similar trade-offs.


Abstract

Integrating behavior and physiology is critical to formulating new hypotheses on the evolution of animal life-history strategies. Migratory capital breeders acquire most of the energy they need to sustain migration, gestation and lactation before parturition. Therefore, when predicting the impact of environmental variation on such species, a mechanistic understanding of the physiology of their migratory behavior is required. Using baleen whales as a model system, we developed a dynamic state variable model that captures the interplay among behavioral decisions, energy, reproductive needs and the environment. We applied the framework to blue whales (Balaenoptera musculus) in the Eastern North Pacific Ocean, and explored the effects of environmental and anthropogenic perturbations on female reproductive success. We demonstrate the emergence of migration to track prey resources, enabling us to quantify the trade-offs among capital breeding, body condition, and metabolic expenses. We predict that periodic climatic oscillations affect reproductive success less than unprecedented environmental changes do. The effect of localized, acute anthropogenic impacts depended on whales’ behavioral response to the disturbance; chronic, but weaker, disturbances had little effect on reproductive success. Because we link behavior and vital rates by modeling individuals’ energetic budgets, we provide a general framework to investigate the ecology of migration and assess the population consequences of disturbance, while identifying critical knowledge gaps.

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