Abstract
In the last decade, thousands of satellite-relayed data loggers (SRDLs) have been deployed, providing large datasets on marine predator movement patterns at sea and their diving behaviour. However, the latter is in a highly summarised, low-resolution form, from which it is difficult to make the sorts of important behavioural inferences that are possible from higher-resolution datasets (such as detection of likely foraging events). The main objective of this study was to develop a simple, but accurate tool to detect and quantify within-dive foraging periods in low-resolution dives. Two southern elephant seals were fitted with a head-mounted time depth recorder (TDR) (recording depth at 1 Hz) and an accelerometer (recording 3 axes of acceleration at 16 Hz) from which prey capture attempts were estimated (PrCA), and a Weddell seal was also fitted with a TDR (1 Hz).The resulting high-resolution dive profiles were used to: (1) calculate an accurate index of foraging effort based on the detection of vertical sinuosity switches (i.e. huntinghighres time); (2) produce an SRDL-equivalent low-resolution dataset using a broken stick algorithm; and (3) from each low-resolution dive calculate a set of candidate foraging effort indices. Huntinglowres time, which is the total time spent in decreased vertical velocity segments of the dive, was the foraging effort index that best correlated with huntinghighres time. Huntinghighres mode of SES dives (highly sinuous parts of high-resolution dives) was associated with 77 % of total PrCA. In comparison, Huntinglowres segments of SES dives were associated with 68 % of PrCA as well as with four times more PrCA than transitlowres segments. We found a low-resolution index which indicates foraging activity within a highly summarised dive profile and which identified most PrCA, despite degraded information transmitted by SLDRs. Used in combination with other measurements of the in situ environment, the huntinglowres index could be used in numerous integrated marine ecology studies, such as habitat use studies that are crucial to facilitate more effective conservation.
Highlights
In the last decade, thousands of satellite-relayed data loggers (SRDLs) have been deployed, provid‐ ing large datasets on marine predator movement patterns at sea and their diving behaviour
We found a low-resolution index which indicates foraging activity within a highly summarised dive pro‐ file and which identified most prey capture attempts (PrCA), despite degraded information transmitted by SLDRs
General diving behaviour The time depth recorder (TDR) recorded the diving behaviour of two SES for 72 and 73 days from November to January 2011
Summary
Thousands of satellite-relayed data loggers (SRDLs) have been deployed, provid‐ ing large datasets on marine predator movement patterns at sea and their diving behaviour. The latter is in a highly summarised, low-resolution form, from which it is difficult to make the sorts of important behavioural inferences that are possible from higher-resolution datasets (such as detection of likely foraging events). Predators perceive and react to environmental heterogeneity in ways that maximise resource acquisition [1, 2] These reactions are manifested through changes in their movement characteristics (e.g. direction, speed, sinuosity) that are likely to reflect the presence, or Heerah et al Anim Biotelemetry (2015) 3:42. Several hours of diving behaviour data can be summarised into bins of summarised information on depth, duration or time submerged
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