Sea Lion Summer: Both humans and pinnipeds compete for La Jolla Cove waters at this time of year
The months of May, June and July are a popular time of year at La Jolla Cove with visitors coming in droves. But it is also a significant time of year in the life cycle of a sea lion.
According to the City of San Diego’s newly released Marine Coastal Management Plan (MCMP), “The La Jolla coastline is the first on the Southern California mainland where sea lions have hauled out in significant numbers and demonstrated viable birthing and successful nursing of pups” and in 2016, “the City documented the first viable sea lion births, with three pups being born and cared for in early and mid-June.”
For some insight into the life cycle of a California Sea Lion (to benefit La Jollans and visitors alike), the Light reached out to National Oceanic & Atmospheric Association (NOAA) fisheries research biologist Mark Lowry, and referred to the MCMP. Lowry is a member of NOAA’s California Current Marine Mammal Assessment Program staff with research interests that include aerial photographic censuses of pinnipeds at offshore rookeries, California Sea Lion diets and monitoring pinniped populations.
Adult males, at full size, weigh in at nearly 800 pounds; the females can reach up to 250 pounds. Defining features of a sea lion include large, skin covered wing-like flippers; small, external ear flaps and vocal fortitude.
“The males are always barking and it’s the conventional ‘arg, arg, arg’ sound you hear,” said Lowry. “The females can bark, but you won’t hear it in La Jolla, just in the rookeries. They make this high-pitched call, it’s how they find their pups after hunting. If a female barks, they pay attention since they don’t normally do that. It’s like a warning.”
Females can live to be 22 years old and males to 18 years old.
The sea lions at La Jolla Cove have presented what the MCMP calls typical behavior including: “resting and sleeping, sub-adult males mock fighting, females nursing pups, and two documentations of viable births (nursing for a few days with the second birth) as well as a few other nursing pups assumed born on the offshore islands.”
Lowry said a California sea lion’s breeding (birthing and mating) season runs from mid-May to July — a time when La Jolla Cove beach is densely populated by visitors and swimmers. According to MCMP, the average California Sea Lion count by month across The Cove (which, in the context of MCMP, spans from north of La Jolla Cove beach and around to Boomer Beach) was highest in June, July and August.
“Female sea lions and species of seals have what’s called delayed implantation, so when one of their eggs is fertilized, it divides a few times and then stops. Its stays dormant for two to three months, then it implants (inside the mother) and develops. That way, all the pups are born at the same time of year. By the end of June, all the pups of that season are born,” he said.
Around this time, sea lions of reproductive age begin mating habits. Depending on when the females become pregnant (mid-May versus July), the delayed implantation would last up to three months, and then the nine-month gestation period would begin.
At larger sea lion rookeries — but not formally at La Jolla Cove — it is at this time that NOAA researchers count the number of births to determine population growth patterns. La Jolla Cove is not monitored because the number of sea lions that haul out there are considered “insignificant” compared to the numbers found at rookeries.
“My research is on the rookeries offshore where there are thousands of them … (La Jolla Cove) is so small and not very significant. There are thousands of sea lions born every year in the rookeries offshore, so to have a few born in one location is not considered significant (to scientists),” he said.
Sea lions birth one pup at a time, and the females raise the pups through weaning. “The mothers give birth and the males hold territory, but two or three weeks after the pups are born, the males leave. After the breeding season they go north to Oregon, Washington and British Columbia. Only the mothers raise the pups,” he said.
The MCMP goes on to say “pups are 20 pounds or less at birth, but gain weight rapidly with the mother’s fat-rich milk. They nurse for four months to a year.” During this time, Lowry explained, the mother goes out to feed for two to six days, and then comes back to rest for one to two days then goes back out. Sea lions eat squid and small schooling fish including mackerels, anchovies and sardines.
Lowry also reported that “for the most part,” sea lions return to their place of birth to give birth, but not all of them.
Once the sea lion pups survive weaning, they are fundamentally on their own.
The next generations
Lowry said that female sea lions reach sexual maturity as early as three years old, but more frequently at four and five years old.
The males reach sexual maturity at an unknown age, but must also be what is referred to as “reproductively mature” before they can reproduce. “Male sea lions must prove they can defend the territory, so they have to be big and strong when they get to the age of reproduction. As such, they are a lot older than the females,” he said.
Once the males reach this stage, they are considered “polygynous with large socially dominant bulls holding harems of up to about 30 females” according to the MCMP.
When it comes to mating behaviors and attracting females, Lowry said males have a posture they can take where they encroach on another male’s territory to show their dominance. Otherwise not aggressive, Lowry said the only time sea lions get territorial is during the breeding season, “they will protect the territory that gives them access to adult females during the breeding season. Other times of the year, they won’t be as territorial.”
Otherwise, sea lions need to leave the water (or haul out) seven to eight hours per day to rest and regulate body temperature. However, they like to haul out with each other in huddled groups.
As a result, there have been increasing numbers of human/pinniped interactions, prompting the City to develop the MCMP.
“By developing this management plan, the City of San Diego recognizes that it shares the environment with marine animals, especially pinnipeds, which are increasing in numbers and consequently are increasingly interacting with the citizens of this coastal city, as well as with visitors from all over the world,” reads its purpose statement.
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