Why They Become Stranded

Animals on the Beach

The rocky and sandy shoreline is part of the natural habitat for a seal or a sea lion and healthy animals come ashore to rest, get warm, or to breed and have their pups. Any pinniped suspected of being sick or injured should be left alone until experienced personnel can assess the animal.

Malnutrition in Young Animals

Young seals and sea lions often become stranded shortly after being weaned. Weaning occurs when the young animal no longer nurses from its mother. At that time the pup must catch fish on its own. If it canít catch enough fish or if the appropriate sized fish arenít available within the animalís range, an energy deficit develops and malnutrition results.

Between the months of March and June, many young California sea lions, Northern elephant seals, and Harbor seal pups become stranded. It is not uncommon for young stranded animals to have multiple health problems such as malnutrition, pneumonia and parasitism. If untreated, malnutrition eventually leads to hypoglycemia, seizures, unconsciousness, and death.

Northern elephant seal pups (Mirounga angustirostris) are born in late December through January. They nurse for approximately 30 days before being abruptly weaned. After weaning, they undergo a period of fasting for several weeks while they mature physiologically. The pups then enter the ocean to begin hunting for food. Beginning in late February to early March, those pups that are not successful at hunting for their food arrive at MMCC LA malnourished and dehydrated.

Parasitism

In young animals, parasites can be transmitted through milk,  skin, or through fish and invertebrates they ingest. Older animals that are chronically ill or that have compromised immune systems often have heavy parasite burdens. Several different species of parasites are commonly found in pinnipeds and they survive in the lungs, stomach, intestinal tract, liver, muscle and, occasionally, in the brain. 

Parasites induce tissue damage and inflammation, disrupt blood flow, predispose the animal to bacterial infections and may, ultimately, result in the death of the animal.

Traumatic Injuries & Bacterial / Viral Infections

Traumatic injuries occur as a result of natural injuries such as bites from other sea lions, falling in and around rocks, sting ray barbs, shark bites, or from unnatural causes such as fishing line entanglement, fish hooks, bullets, and gaff and knife wounds. These injuries can produce mechanical injury to the body by breaking bones, lacerating tissue, disrupting blood supply, or causing nerve damage. In addition to the traumatic injury, bacterial infections may subsequently develop. If treated early in the course of events, many bacterial infections can be eliminated and, given time, the traumatic injury may also resolve.

Cookie cutter sharks (Isistius brasiliensis) prey on fish and some marine mammals. They grow to 2-3 feet in length and are slow swimmers and deep water dwellers. They are named for the circular bites they take out of their prey. It is not uncommon in the fall months to admit a few deep diving elephant seals with these superficial wounds. The wounds usually heal well once the animalís overall health improves.

Ratfish (Hydrolagus colliei) grow to a maximum of about 3 feet and inhabit Northern California waters as well as the colder, deeper waters in Southern California. They are rarely seen in less than 100 feet of water in Southern California. They can be distinguished by their lack of scales and the venomous spine at the base of the dorsal fin. Northern elephant seals are occasionally admitted due to injury from these spines but more commonly sustain injury from sting ray barbs.

Bat rays (Holorhinus californicus) often bury themselves in the sand on the ocean floor to catch unsuspecting prey. When pinnipeds startle the rays they may also encounter the rayís defensive barb located at the base of the tail. These barbs can pass through subcutaneous tissue without causing permanent damage.  However, if the animal is struck near the eyes or face or if the barb migrates to deeper structures, significant trauma can result. In the animal below, the barb entered the side of the neck and migrated through the joint at the base of the neck causing severe septic arthritis in the atlanto-occipital joint in one of the most severe injuries seen in a sea lion by a sting ray barb.

Harmful Algal Blooms

Domoic acid is a naturally occurring neurotoxin produced by several species of unicellular algae. It is responsible for the conditions called Amnesic Shellfish Poisoning and Domoic Acid Poisoning and has implications for both animal and human health.

When the algae (Pseudonitzschia spp) and the toxin are consumed by smaller schooling fish, such as sardine, anchovy, or herring, or by filter feeding invertebrates, the toxin is introduced into the food chain. California sea lions are particularly sensitive to this toxin and may become disoriented, experience seizures, lapse into a coma, or die as a result. Affected adult female animals may abort or abandon their pups.

Animals that survive often have chronic brain damage and succumb at a later date. The hippocampus of the brain has a large number of glutamate receptors that bind the neurotoxin. Brain damage in this area results in memory loss (amnesia). 

Algal blooms are episodic, but when they occur, large numbers of sea lions are affected and may be encountered on beaches.

Human Interaction

This California sea lion suffered from several gunshots that punctured her left lung, creating a large air pocket (pneumothorax). The wounds healed and she recovered her normal shape and lung function.

This Guadalupe fur seal (Arctocephalus townsendi) could not capture fish because a plastic ring was wedged behind her lower teeth and under her jaw. She was suffering from severe malnutrition when she was rescued.

This sea lion became trapped in fishing line, which is a common problem. Fishing line and commercial nets don’t stretch or break and as the animal grows, the line gradually cuts into the animal’s neck which produces deep, open wounds. It may take months before an injured animal becomes so debilitated that it can be rescued and treated with surgery and wound care.


If you find an animal that appears to be disoriented, is not responsive, or is having seizures, please call a rescue agency!  Do not try to assist the animal.

You can best help MMCC LA by:

Be prepared to provide:

  • The location and condition of animal.
  • Caution: Keep your distance and observe the animal from binocular range. You are too close if the animal is watching you.
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