DOI: 10.7291/d1w101
title: Data From: Effects of disease on foraging behaviour and success in an individual free-ranging northern elephant seal

description: Evaluating consequences of stressors on vital rates in marine mammals is
 of considerable interest to scientific and regulatory bodies. Many of
 these species face numerous anthropogenic and environmental disturbances.
 Despite its importance as a critical form of mortality, little is known
 about disease progression in air-breathing marine megafauna at sea.
  We examined the movement, diving, foraging behaviour, and
 physiological state of an adult female northern elephant seal (Mirounga
 angustirostris) who suffered from an infection while at sea. Comparing her
 to healthy individuals, we identified abnormal behavioural patterns from
 high-resolution biologging instruments that are likely indicators of
 diseased and deteriorating condition. We observed continuous extended
 (3–30 min) surface intervals coinciding with almost no foraging attempts
 (jaw motion) during two weeks of acute illness early in her post-breeding
 foraging trip. Elephant seals typically spend ~2 min at the surface. There
 were less frequent but highly extended (30–200 min) surface periods across
 the remainder of the trip. Dive duration declined throughout the trip
 rather than increasing. This seal returned in the poorest body condition
 recorded for an adult female elephant seal (18.3% adipose tissue;
 post-breeding trip average is 30.4%). She was immunocompromised at the end
 of her foraging trip and has not been seen since that moulting season. The
 timing and severity of the illness, which began during the end of the
 energy-intensive lactation fast, forced this animal over a tipping point
 from which she could not recover. Additional physiological constraints to
 foraging, including thermoregulation and oxygen consumption, likely
 exacerbated her already poor condition. These findings improve our
 understanding of illness in free-ranging air-breathing marine megafauna,
 demonstrate the vulnerability of individuals at critical points in their
 life-history, highlight the importance of considering individual health
 when interpreting biologging data, and could help differentiate between
 malnutrition and other causes of at-sea mortality from transmitted data.
description: Adult female diving and foraging behaviour was measured using
 biologging instruments deployed on ~20 individuals per year during the
 post-breeding trip from 2004–2020 for a total of 289 deployments. Each
 animal was sedated following standard protocols (Robinson et al., 2012)
 and equipped with a time-depth recorder (TDR) programmed to collect depth
 data at least every 8 seconds and with a satellite tag providing either
 Argos or GPS locations (Wildlife Computers, Seattle, WA, USA; Sea Mammal
 Research Unit, St. Andrews University, UK). Upon returning to shore,
 individuals were sedated again for instrument recoveries. 
 Body composition and energy gain values were calculated using
 established methods (Robinson et al., 2012). Morphometric measurements
 were collected during deployment and recovery sedations, including weight,
 blubber depths, lengths, and girths. Body composition was calculated using
 the truncated cones method (Gales and Burton, 1987) and calibrated to body
 water measurements (Webb et al., 1998). Blubber thickness was measured at
 six evenly spaced locations along the length of the body along a dorsal
 line and again along a lateral line (12 measurements total) using a
 backfat ultrasound meter (Scanoprobe, Ithaca, NY, USA) at deployment and a
 Signos handheld ultrasound (Signostics, Thebarton, AUS) at recovery. Both
 instruments have previously been used to measure blubber thickness in
 elephant seals and produce comparable data. Mass was measured each time
 animals were sedated by suspending the seal from a hanging scale using a
 tripod and sling. To determine mass upon arrival and departure from the
 colony, measured masses were corrected to account for time spent onshore
 fasting before (Simmons et al., 2010) and after measurements were
 taken. The surface area to volume ratio (SA:V) was
 calculated for post-breeding seals in 2017 using morphometrics measured at
 deployment and recovery. Each seal was represented geometrically by seven
 circular truncated cones from the ankle to the ears (divided at the same
 six locations along the length of the body where blubber thickness was
 measured) and a normal circular cone from the ears to the nose for the
 head of the seal. This method was chosen as the least likely to over- or
 underestimate the dimensions of the seal. Surface area and volume were
 calculated as the sum of the lateral surface areas and volumes,
 respectively, of each of these geometric shapes. For comparison to our
 best estimate methodology, a minimum and maximum SA:V were also calculated
 using differing geometric representations of the seal. The minimum
 estimate was calculated without the normal cone representing the head of
 the seal (only truncated cones from ankles to ears). The maximum estimate
 was calculated with the addition of normal circular cones for both the
 head (ears to nose) and tail (ankles to tail tip) to the truncated cones
 from ankles to ears.
description: The body composition and morphometric data provided are in CSV
 format.  Files included: 
 DiseaseAtSea_ForagingSuccess_PB2004-2020.csv - includes all
 foraging success metrics for post-breeding adult female elephant seals
 from 2004 to 2020 included in this paper (Mass Gain, Mass Gain Rate, %
 Mass Gain, Energy Gain, Energy Gain Rate, Departure %Adipose, Arrival
 %Adipose, Trip Duration; Table 2, Fig. 1).
 DiseaseAtSea_LengthMass_PB2013-2020.csv - includes the standard
 length and mass, measured in the field at deployment for all post-breeding
 females from 2013-2020. These data were used to produce S1. 
 DiseaseAtSea_AllMorphs_PB2017.csv - includes all morphometric
 measurements collected at deployment and recovery for post-breeding 2017
 animals.  These metrics were used to calculate surface-area-to-volume
 ratios. DiseaseAtSea_PB2017_SAV_V3.csv - contains the
 surface area and volume calculations completed using the script
 "DiseaseAtSea_SA_V_calc.R" and the data from
 DiseaseAtSea_AllMorphs_PB2017.csv.  These values were used to produce Fig.
 8. All code is available at  https://doi.org/10.5281/zenodo.7864665