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Growth & Morphometrics

Molting Dynamics

2010 brought an end to our 7 year documentation of the molting patterns of California sea lions of different age and sex classes.  We completed the study with our juvenile sea lions finally arriving at adulthood.  The data has been partially processed and analyzed for the capstone project of one of our graduates, Heather Yeager and the remainder was completed by another student, Tiana Hanna. California sea lion molting appears to occur as follows: The front and rear flippers molt first, followed by the ventral surface (starting at the midline and forming a “Y” pattern as the molt moves to the sides of the body and the ventral surface).  Molt progresses around the sides of the body to the dorsal surface; the head begins to molt, followed by the neck and chest.  The timing of the molt seems to be correlated with age. There is often a second partial molt in older males, which as yet has not been reported elsewhere and we postulate may be related to recovering disturbed surface fur after mating season. Analysis found air and water temperatures were not significant factors for determining the timing of the molt in sea lions.  The average rate of change of daylight per day and monthly photoperiod were somewhat reliable factors to predict molt, however they were not more effective than using a calendar to predict the onset of molt.


Whisker Growth

Partnering with University of California, Santa Cruz graduate student, Liz McHuron, we measured pinniped vibrissae using 1.2 of our California Sea Lions (Zalophus californianus) to see the whisker growth dynamics using photogrammetry.  Each month we took several calibrated photos of our animals whiskers to monitor growth and loss of whiskers.  Stable isotope analysis of vibrissae can provide a temporal record of foraging behavior in pinnipeds, and is one of the few methods available to measure individual behavior over a relatively long time period. Despite the increasing use of this method, an understanding of vibrissal growth dynamics are lacking for most pinniped species, yet are necessary for appropriate study design and interpretation of isotope data.  This study provided the first measurements of growth rates and growth and shedding patterns in spotted seals (Phoca largha) and California sea lions (Zalophus californianus) using photogrammetry. The work was published in 2016:


McHuron, EA, Walcott, SM, Zeligs, J, Skrovan, S, Costa, DP, Reichmuth, C. 2016. Whisker growth dynamics of two North Pacific pinnipeds: implications for determining foraging ecology from stable isotope analysis. Marine Ecology Progress Series 554: 213-224. Read it here

Sea Lion Growth and Development

Starting in early 2001, 2 juvenile male and 2 juvenile female sea lions participated in monthly length measurements for our on-going, long term morphometrics data collection. Those efforts comprised a long term study on growth dynamics in California sea lions, contrasting male and female development that ended in 2013.  This study has restarted with two new juvenile females starting in 2016.