Abstract

The recent unusual mortality event (UME) of pup and yearling California sea lions (Zalophus californianus; CSL; <2 years old), which began in 2013 and is ongoing, has been related to increased sea surface temperatures and decreased prey availability.^1,2 As a result, a greatly elevated number of stranded CSLs were rescued and admitted to rehabilitation centers along the California coast.³ The majority of young CSLs received by rehabilitation centers during this event were diagnosed with maternal separation and starvation. Historically, the survival rate of young, rehabilitated CSLs has been approximately 50%, with many of them dying within the first couple of weeks of rehabilitation.³ One question that remains unanswered is whether or not refeeding syndrome plays a significant role in patient survival.⁴ As a retrospective analysis, our aim was to evaluate whether the diet initiated in the first three weeks of rehab had a significant effect on the survival rate of young CSLs admitted for rehabilitation. The goal of this study was to assist in identifying an optimal feeding strategy for use in treating young CSLs during future UMEs. Data collected from 433 young CSLs admitted to The Marine Mammal Center (TMMC) in Sausalito, CA between 2014 and 2015 were utilized. We compared the survival of young CSL patients receiving Emeraid Piscivore (a semi-elemental diet formulated for piscivorous species; n=248) versus fish mash (a prepared gruel made from whole ground herring; n=185) as part of their initial diet protocol, prior to transitioning to a whole fish diet. We hypothesized that patients receiving Emeraid would have a greater survival rate compared to those receiving fish mash due to improved absorption of nutrients in a malnourished state, and the potential role of refeeding syndrome associated with higher fat diets. Preliminary data reveals that the survival of young CSLs was significantly associated with their initial diet [χ2=31.61, df=1, n=433, p<0.0001]. The survival rate of patients receiving fish mash (50.8%) was greater than those patients who received Emeraid (24.2%) as part of their initial feeding protocol. Additionally, patients receiving fish mash had a mean weight gain (5.67±6.53 kg) that was greater than that of Emeraid (2.74±5.92 kg) prior to transition to fish diet. The relationship between weight gain and survival rate in young CSLs has not been evaluated, so further investigation is warranted. Another important consideration is that the majority of patients who were started on Emeraid had presented later in 2015. It is possible that these animals were starving for longer periods of time before being rescued, resulting in a lower chance of survival. Since this was a retrospective investigation, further analysis should be implemented to determine whether the use of either feeding strategy might have been influenced by concurrent disease and other factors, and ultimately affect overall growth and survival rates. These initial findings, however, set the stage for prospective research on the nutritional requirements of rehabilitated young CSLs and highlight the importance of dietary considerations for stranded animals.

Acknowledgements

The authors thank The Marine Mammal Center staff and volunteers for caring for the animals included in this study and for their mentorship. We also thank the University of California-Davis School of Veterinary Medicine for providing the externship opportunity during which this retrospective study was initiated.

* Presenting author

Literature Cited

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3.  [NOAA Fisheries] National Oceanic and Atmospheric Administration. 2017. Washington, DC: Department of Commerce. [updated 2017 Aug 15; cited 2018 Jan 31]. Available from: www.nmfs.noaa.gov/pr/health/mmume/californiasealions2013.htm.

4.  Tang K, Van Bonn W, Ramsey J, Scott C, Sherrill M. 2012. Starvation in marine mammals: electrolyte and biochemical responses to malnutrition in California sea lions (Zalophus californianus). In: Proceedings of the IAAAM 43rd Annual Conference. The Georgia Aquarium. Atlanta, GA.