Environmental drivers of movement in a threatened seabird: insights from a mechanistic model and implications for conservation

Abstract

Aim Determining the drivers of movement of different life‐history stages is crucial for understanding age‐related changes in survival rates and, for marine top predators, the link between fisheries overlap and incidental mortality (bycatch), which is driving population declines in many taxa. Here, we combine individual tracking data and a movement model to investigate the environmental drivers and conservation implications of divergent movement patterns in juveniles (fledglings) and adults of a threatened seabird, the white‐chinned petrel (Procellaria aequinoctialis). Location South‐west Atlantic Ocean. Methods We compare the spatial distributions and movement characteristics of juvenile, breeding and non‐breeding adult petrels, and apply a mechanistic movement model to investigate the extent to which chlorophyll a concentrations (a proxy for food resources) and ocean surface winds drive their divergent distribution patterns. We also consider the conservation implications by determining the relative overlap of each life‐history stage with fishing intensity and reported fishing effort (proxies for bycatch risk). Results Naïve individuals fledged with similar flight capabilities (based on distances travelled, flight speeds and track sinuosity) to adults but differed in their trajectories. Comparison of simulations from the mechanistic model with real tracks showed that juvenile movements are best predicted by prevailing wind patterns, whereas adults are attracted to food resources on the Patagonian Shelf. The juveniles initially dispersed to less productive oceanic waters than those used by adults, and overlapped less with fishing activity; however, as they moved westwards towards South America, bycatch risk increased substantially. Main conclusions The use of a mechanistic framework provided insights into the ontogeny of movement strategies within the context of learned versus innate behaviour and demonstrated that divergent movement patterns of adults and juveniles can have important implications for the conservation of threatened seabirds.

Multiple spawning run contingents and population consequences in migratory striped bass Morone saxatilis

“…warping measures how much an entire spawning phenology trajectory must be stretched or compressed in time to match that of another fish. As such, spawning run phenologies that are alike in shape, extent, and destination, but offset in time are clustered together [51,52]; Fig 2). The iterative clustering procedure, utilizing dynamic time warping and performed with the dtw [53] and dtwclust [54] packages in R, solved for maximum within-cluster similarity and minimum between-cluster similarity.…”

“…equivalent, and does not have the requirement of equal-length time series [48]. Developed as a machine learning tool in speech recognition applications, it has received scant attention by movement ecologists [51,52]. In its application to inverted U-shaped spawning run behavior, the algorithm performed well, summarizing time series that ranged between 16 and 70 days in duration, and time series that deviated from symmetry and often showed multiple up-estuary excursions (Figs 2 and 4).…”

A bird's-eye view on turbulence: seabird foraging associations with evolving surface flow features

“…Our observed movement associations with underlying vorticity and at a distance, positive divergence, might offer some insight into the visual sensory ecology of terns, as localized and ephemeral by nature, these features could be regarded as direct cues for enhanced prey accessibility through physical accumulation. The physical environment affects signal properties and without quantifying the different kinds of information that an animal can extract information from, it is challenging to obtain a mechanistic understanding of foraging behaviour [ 53 , 54 ]. Ultimately, investigating how an animal's perceptual abilities determine how it extracts information from the environment is an essential component of their foraging ability and thus, the animal's ecological function [ 55 ].…”

Movements and diving behaviour of white‐chinned petrels: Diurnal variation and implications for bycatch mitigation

“…The major diving hotspot of white‐chinned petrels in the study overlapped with these fishing areas, confirming their susceptibility to bycatch during incubation. The majority of the South Georgia population also uses this productive region during the pre‐laying exodus and nonbreeding season (Phillips et al, 2006), and so is susceptible to bycatch for much more of the year than other procellariform species from South Georgia (Phillips et al, 2016; Clay et al, 2019; Frankish et al, 2020). Therefore, although dive capabilities (maximum depth and descent rates) may vary somewhat among seasons (Rollinson, Dilley & Ryan, 2014), recorded dive characteristics in this study provide a relevant baseline for assessing the design and implementation of effective mitigation measures in the south‐west Atlantic.…”

“…The major diving hotspot of white-chinned petrels in the study overlapped with these fishing areas, confirming their susceptibility to bycatch during incubation. The majority of the South Georgia population also uses this productive region during the pre-laying exodus and nonbreeding season (Phillips et al, 2006), and so is susceptible to bycatch for much more of the year than other procellariform species from South Georgia (Phillips et al, 2016;Clay et al, 2019;Frankish et al, 2020).…”