The West Coast of the United States has experienced a marked increase in the number of California Sea Lion pups stranded on beaches across southern and central California during the first four months of 2015. The sight of distressed marine life along our shores is an emotive topic for those of us who enjoy spending time on the water. Most paddlers have a deep appreciation for the ocean and the marine life dependent on a healthy ecosystem in order to survive. As word of the strandings began to filter through the stand up paddling community in Southern California, SUP Examiner decided to look into the situation and report back to the paddling public.
This is the second installment in a three-part series examining California Sea Lions and the increased number of pup strandings in 2015.
What is Causing the Increase in Sea Lion Pup Strandings?
The [U.S.] National Oceanic and Atmospheric Administration (NOAA) declared an El Niño in early March 2015. El Niño events have previously resulted in elevated numbers of marine mammal strandings. This is believed to be a result of the availability of prey and physiological stress on the animals. Scientists at NOAA have reported the ocean current off California is experiencing warmer temperatures than normal this spring, possibly as a result of the El Niño. The change in ocean temperature effects type of fish found in the region which in turn has a butterfly effect on the California Sea Lion population in terms of the availability of prey. This phenomenon is believed to be the most likely reason behind the increase in pup strandings this year.
The increase in strandings of California Sea Lion pups has been primarily seen in from San Diego County north to Santa Barbara County. According to NOAA, they began to receive reports of an increase in strandings in December 2014 / January 2015. During the first three months of this year, the number of strandings was over 20 times the annual average number of strandings, based on records from 2004 – 2015.
As a result of the drastic increase in strandings, officials from the Working Group on Marine Mammal Unusual Mortality Events has declared an Unusual Mortality Event is affecting the California Sea Lion population based on the following criteria:
- A marked increase in the magnitude or a marked change in the nature of morbidity, mortality or strandings when compared with prior records;
- A temporal change in morbidity, mortality or strandings is occurring;
- Affected animals exhibit similar or unusual pathological findings, behavior patterns, clinical signs or general physical condition, e.g. blubber thickness.
Based on their holistic analysis of California Sea Lion strandings, the Working Group determined the stranding rates in 2014 did not return to a baseline after the last Unusual Mortality Event in 2013, therefore the current situation affecting pups should be considered one continuous Unusual Mortality Event from 2013-2015.
The decreased availability of prey can produce a situation where California Sea Lion mothers are unable to produce enough milk to adequately care for their pups, leading to premature weaning. Pups are 100% dependent on their mothers for the first six months and are typically not fully weaned until 11 months. Based on the information we received from NOAA and the Marine Mammal Care Center in San Pedro, California, were the mothers to have difficulty finding food this could produce a scenario where the pups may try to find food on their own before they are fully capable of doing so, resulting in starvation.
The increase in the number of strandings is not the only factor that stands out to scientists monitoring the population of California Sea Lions. The fact the increase was first observed from January – March is unusual because it occurred when the pups were still quite young. In a normal year, marine mammal care centers typically begin reporting stranded pups in May and June around the time when the pups are expected to be independent from their mother’s care. The strandings in 2013 disproportionately affected Southern California. Based on our analysis of the current situation, a similar pattern is playing out.
Part Three of this series will take a look at the role of the Marine Mammal Rescue Centers and what stand up paddlers can do to help.