Abstract

Sick, injured, or orphaned sea lion pups stranding prior to six months of age, when still maternally dependent, present challenges for marine mammal wildlife rehabilitators.¹ Frequent handling for medical care and multiple daily feedings generates concerns of imprinting, habituation, or risk of altered behavior.^1,2 Publications on post-release movement and survival for sea lion pups stranding prior to six months of age are limited, and stranded neonate and early weaned pups may be recommended for permanent managed care rather than release.^3,4 Limited capacity in managed care facilities has prompted marine mammal wildlife rehabilitators to explore rehabilitation techniques that foster early nutritional independence and limit human contact with the goal of returning animals to their natural environment. The objective of this project was to evaluate post-release movement and survival of rehabilitated sea lion pups stranding prior to six months of age to determine if return to the natural environment is advisable for this age class.

Twenty California sea lion (Zalophus californianus) and two Steller sea lion (Eumetopius jubatus) pups were rescued, rehabilitated, and released between 2018 and 2022. The ages of stranded California sea lion (CSL) pups ranged from one day to almost six months of age. The ages of the two Steller sea lion pups were estimated to be five days and four weeks. Animals were rehabilitated at multiple facilities, and efforts were focused on achieving early nutritional independence, minimizing human contact, and providing social context. All animals received conditional release approval from National Oceanic and Atmospheric Administration/National Marine Fisheries Service (NOAA/NMFS) and were instrumented with SPOT 6 satellite-linked tags (Wildlife Computers). The pups were released in April following their birth year in accordance with NOAA conditional release requirements and observations of the normal weaning period.⁵ Satellite-linked tracking utilized satellite data collection and location for transmitting platforms (Argos) and animal movements were analyzed using R and adehabitat for R software.^6,7

Location transmissions ranged from three to 183 days. Eighty percent (16/20) of CSL pups were tracked for more than 30 days, 45% (9/20) were tracked for more than 90 days, and 30% (6/20) were tracked for more than 140 days. Tag failure occurred on two pups which were spotted alive and in good condition after transmissions had ceased. The CSL pups navigated to and from island and mainland locations, frequented established sea lion sites, and traveled in the open ocean for up to six days before returning to shore. The Steller sea lion pups were tracked for 51 and 78 days and also travelled to established Steller sea lion sites.

These findings demonstrate that sea lion pups stranding during a period of maternal dependency and prior to nutritional independence can be rehabilitated and released with an expectation of near-term survival and integration with conspecifics at established animal sites. These findings will help inform wildlife rehabilitators and managers dealing with sick, injured, or abandoned pups and potentially provide a model for rehabilitation and conservation management of other otariid populations should they become threatened.

Acknowledgements

This project could not have been completed without support from the dedicated staff and volunteers of The Marine Mammal Center, Channel Islands Marine & Wildlife Institute, California Wildlife Center, the Marine Mammal Care Center Los Angeles, Pacific Marine Mammal Center, SeaWorld San Diego, the Sonance Foundation, John and Marcia Booth, Amber Becerra, and The Annenberg Foundation: Metabolic Studios.

*Presenting author

Literature Cited

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2.  Lynn BL, Reichmuth C, Shusterman RJ, Gulland FMD. Filial imprinting in a Steller sea lion (Eumetopius jubatus). Aquatic Mammals. 2010;36(1):79–83.

3.  Lander ME, Gulland FMD. Rehabilitation and post-release monitoring of Steller sea lion pups raised in captivity. Marine Mammals. 2003;31(4):1047–1053.

4.  Tuomi, P. Challenges in the rehabilitation of a lone Steller sea lion pup (Eumetopius jubatus) In: IAAAM 34th Annual Conference Proceedings. Waikoloa, HI; 2003:196–200.

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6.  R Core Team. R: a language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2022. https://www.R-project.org.

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