Effects of disease on foraging behaviour and success in an individual free-ranging northern elephant seal

Rachel R Holser; Daniel E Crocker; Arina R Favilla; Taiki Adachi; Theresa R Keates; Yasuhiko Naito; Daniel P Costa

doi:10.1093/conphys/coad034

Effects of disease on foraging behaviour and success in an individual free-ranging northern elephant seal

Conserv Physiol. 2023 May 25;11(1):coad034. doi: 10.1093/conphys/coad034. eCollection 2023.

Authors

Rachel R Holser¹, Daniel E Crocker², Arina R Favilla³, Taiki Adachi^{3

4}, Theresa R Keates⁵, Yasuhiko Naito⁴, Daniel P Costa^{1

3}

Affiliations

¹ Institute of Marine Sciences, University of California Santa Cruz, 115 McAllister Way, Santa Cruz, CA, 95060, USA.
² Department of Biology, Sonoma State University, Rohnert Park, California, 94928, USA.
³ Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, California, 95064 USA.
⁴ National Institute of Polar Research, Tachikawa, Tokyo, Japan.
⁵ Department of Ocean Sciences, University of California Santa Cruz, Santa Cruz, California, 95064, USA.

Abstract

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 minutes) surface intervals coinciding with almost no foraging attempts (jaw motion) during 2 weeks of acute illness early in her post-breeding foraging trip. Elephant seals typically spend ~ 2 minutes at the surface. There were less frequent but highly extended (30-200 minutes) 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.

Keywords: Pinniped; ecophysiology; energetics; foraging; infection.