Zalophus californiaus
California Sea Lion
Background Information
Appearance
Zalophus Califroniaus is better known as the California Sea Lion.
California Sea Lions can range in color from a light brown, more common in females, to a chocolate brown, more common in males. Males can reach up to 7 feet in length and weigh up to 850 pounds while females can grow up to 6 feet in length and weight 220 pounds.
Like all sea lions, they have external ear flaps and large front flippers that they can walk on.
Prey
The California Sea Lion Eats a variety of small aquatic species found in upwelling areas such as:
- Sardines
- Squid
- Octopus
- Herring
- Mackerel
- Anchovies
Predators
The California Sea Lions have 2 main predators:
- The Killer Whale (Orca)
- The Great White Shark
However, the biggest threat and predator to the California Sea Lions are humans.
Southern California Population
In Southern California, the population of California Sea Lions is currently stable around 238,000.
In this data, there have been 1,823 sightings of California Sea Lions since 2012 totaling 13.3k individuals.
When we look at data we collected from the Southern California population, it appears that the population peaked in 2014 and has been declining since.
However, when we look at the number of individuals observed per trip, the population appears to be remaining stable between 3 and 4 California Sea Lions seen per trip.
This shows that there was not a huge spike in the populations in 2014, the researcher just took more research trips that year and therefore saw more individuals.
Similarly, when we look at the number of California Seal Lions observed by season, it appears that there is a large spike in the population during the summer months.
However, like the yearly distribution, when we look at the number of California Sea Lions observed each season by the number of trips taken it becomes more clear that the California Sea Lion is consistently present throughout all four seasons.
California Sea Lions are very active animals and have been observed preforming a number of different behaviors in Southern California.
Map of California Sea Lion behavior by location
California Sea Lion behaviors have been defined in order to maintain consistency for multiple observers.
- Traveling - moving from one place to another
- Hauled Out - sitting out of the water, either on land or on a buoy
- Feeding - hunting or eating of prey
- Unknown - unable to determine the behavior
- Milling - animals are at the surface with no particular directions of movement
- Thermoregulating - controlling body temperature, usually in the water with a fin in the air
- Playing - interacting with others of the species
- Logging - animals are floating at the surface of the water with no movement
Pie Chart of California Sea Lion Behaviors
As we can see from the pie chart, the most common behaviors for the California Sea Lion are traveling and hauled out.
Human Threats
There are a variety of different issues regarding the conservation of the California Sea Lions:
Entanglement: is one of the most common issues California Sea Lions face. Human produced trash, plastic pollutants, and fishing nets pollute sea lion habitat, because of this they often get caught and entangled in netting and different trash. This can hinder their growth, cause injuries that can get infected or affect eating/swimming behavior, and even choke the individual.
Human Interaction/ Human caused injuries: are another way sea lion conservation is affected. Sea Lions come to the beach to rest, breed, and give birth, but humans encroaching into their habitat forces the sea lions to look for other places to do these activities. Sea Lions can also be fed by humans, which changes their behavior and conditions them to see humans as a easy way to get food. On top of this, sea lions can be victims to shooting, as they hang around fishermen and fishing boats and are seen as a nuisance for eating the fish the fishermen want to catch.
Increase in Toxic Algae Blooms: are another threat that humans make to the sea lion population. The use of fertilizers and agricultural enhancements causes excessive run-off of nutrients such as phosphorous to go into the ocean. This increases the amount of algae blooms that are often toxic to wildlife. Not only do algae blooms decrease the oxygen saturation in the water, but they can also release toxins to the surrounding fish. These fish are then eaten by the sea lions who become sick and die.
Climate Change Impacts
Increased Sea Surface Temperatures cause a Decrease in the California Sea Lion's Prey
Reproductions in fish, can be heavily influenced by the temperatures of the surrounding water. It is often measured a sea surface temperatures (SST). Rising temperatures change underwater currents and decrease/change upwelling areas. The transition of upwelling areas causes change where important nutrients are found. This leads to important food supplies such as sardines, to die off or migrate elsewhere. This has a negative affect on the sea lion population, as sardines are one of their main sources of food. Climate change is causing a documented rise in global SST. This has resulted in a decrease in the populations of fish that California sea lions commonly prey upon.
Population of Sardines in the NE Pacific Ocean
Since 2005, the Sardine populations in the northeastern Pacific Ocean has been in a drastic decline. Sardines are one of the main food sources for the California Sea Lions.
Michelle Koopman Marine Mammals Stelle read only-Copy
The frequency that California Sea Lions have been stranded, although fluctuating, has been raising throughout California. The start of the decline in the sardine population in 2005 has been correlated with larger numbers of strandings in the following years.
