Abstract
Body condition is an indicator of health, and it plays a key role in many vital processes for mammalian species. While evidence of individual body condition can be obtained, these observations provide just brief glimpses into the health state of the animal. An analytical framework is needed for understanding how health of animals changes over space and time.Through knowledge of individual health we can better understand the status of populations. This is particularly important in endangered species, where the consequences of disruption of critical biological functions can push groups of animals rapidly toward extinction. Here we built a state-space model that provides estimates of movement, health, and survival. We assimilated 30+ years of photographic evidence of body condition and three additional visual health parameters in individual North Atlantic right whales, together with survey data, to infer the true health status as it changes over space and time. We also included the effect of reproductive status and entanglement status on health. At the population level, we estimated differential movement patterns in males and females. At the individual level, we estimated the likely animal locations each month. We estimated the relationship between observed and latent health status. Observations of body condition, skin condition, cyamid infestation on the blowholes, and rake marks all provided measures of the true underlying health. The resulting time series of individual health highlight both normal variations in health status and how anthropogenic stressors can affect the health and, ultimately, the survival of individuals. This modeling approach provides information for monitoring of health in right whales, as well as a framework for integrating observational data at the level of individuals up through the health status of the population. This framework can be broadly applied to a variety of systems – terrestrial and marine – where sporadic observations of individuals exist.
Highlights
Long-term studies of body condition and survival of individual animals have provided critical insight into many different aspects of animal ecology [1,2]
The model assimilates aerial and vessel survey information, locations of identified individual right whales, photographic evidence of health status across several health parameters comprised of ordinal classes, and prior knowledge
Movement At the population level, we have estimated the paths between regions taken by adult males (Figure 5), adult females (Figure 6), and unknown gender adults
Summary
Long-term studies of body condition and survival of individual animals have provided critical insight into many different aspects of animal ecology [1,2]. Ecologists are left trying to piece together the many likely paths that may connect the previous sighting with the current sighting. These paths could be spatial, i.e., where the animal was in the previous time periods. The inability to reconstruct the pathway that leads to the current observed health state can hamper management, especially for species for which the survival of single individuals is of great importance [8]. We build a model to address two hidden processes in individual animals: changing health, and movement. We use estimates of these processes to infer individual survival
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