top of page

Disentangling sea lions

For a while now I have been involved in a project on entangled sea lions. Sea lion entanglements are brutal.

Imagine getting a packing strap, or a hard plastic fishing line, stuck around your neck when you are 4 years old, and there is no way to get it off so it just stays there and you have to deal with it while it limits your movement. As you grow older and larger, the entanglement does not stretch, which means it digs deeper and deeper until it cuts through all the skin, muscle and even your throat and trachea. It is horrendous to even contemplate, but it is the fate of many sea lions each year.

Sunbathing California sea lion
Sunbathing California sea lion

Supported by a NOAA Prescott grant, The Marine Mammal Center (TMMC) and the National Marine Mammal Lab (NOAA Fisheries) have been involved in an effort to (1) better understand the scope of the problem and (2) disentangle wild sea lions. I got involved in this project as a co-lead with Tenaya Norris, and have been both analyzing a 10-year dataset on rescued entangled sea lions and joining in field work. While the analyses are an important part of the work (it's necessary to understand where entanglements occur, which animals are affected, and whether there have been trends over the years), the more exciting part of this work is definitely going out to find and rescue entangled sea lions. For more details on the project, see the description on this page.

Young elephant seal
Young elephant seal

Last year a team of TMMC and NOAA people went out for a 10-day disentanglement trip to San Miguel island, an important breeding/pupping location off the California coast. The island is gorgeous, still wild with hardly any people allowed, and so many California sea lions, elephant seals, fur seals and island foxes. (plus we got a ride to the island in a US Coast Guard helicopter, on my birthday!)

The goal was to find and rescue as many entangled sea lions as possible, and we worked our a**es off to make the best of our limited time there. While the project results are pending, we recently published a "feature story" for NOAA and TMMC presenting the project and the field work. Below you can find this feature story that was first published here. Stay tuned for all results, planned to be published by the end of the year.

An Entangled Web: Research Collaboration Unravels Causes and Consequences of Sea Lion Entanglements

We are crawling on a sandy beach on San Miguel Island off the coast of California, making sure the wind is not at our backs. Human scent would likely spook the sleeping California sea lions in front of us—about 300 of them. One is our target. Twenty feet to our left an elephant seal watches us with open eyes, head up and ready to charge to defend her pup if the team gets too close. We move away to respect her space. We carry large, strong nets, and we remain alert and ready to respond if our target moves. The team leader halts and we get ready, watching her fingers signal a countdown – 3.…2…1…GO!

Rescued California sea lion, with GPS transmitter tag to monitor movements after release
Rescued California sea lion, with GPS transmitter tag to monitor movements after release. NMFS Permit 16078-02. Photo credit Jeff Harris.

We jump up and sprint towards the target, which startles all the sea lions and causes a chaotic run towards safety in the ocean. They are surprisingly fast, even on land! The sea lions look similar, but the target animal still stands out: the 1-inch wide gash encircling its neck with the plastic gillnet in the middle of it is hard to miss. Can we catch it before it reaches the water?

Marine mammal entanglements in fishing gear such as gillnets and fishing line, and marine debris, including packing straps, can cause serious injuries. It also kills hundreds to thousands of marine mammals every year. Young animals are particularly vulnerable to injuries from entanglements. As they grow, the netting gets tighter and tighter. It slices through fur, skin, blubber, muscle, and eventually bone. Incredibly, some sea lions suffer from painful and debilitating entanglements for years.

Gear removed from entangled California sea lions rescued by The Marine Mammal Center; packing straps, top, gillnets, bottom, and fishing hook and line, center.
Gear removed from entangled California sea lions rescued by The Marine Mammal Center; packing straps, top, gillnets, bottom, and fishing hook and line, center. Photo credit: Boone Saunders

While this certainly harms the entangled animals, what does it mean for the species in the long term? While NOAA Fisheries has gathered some information through stock assessments, many important questions remain unanswered:

  • How many entanglements occur each year?

  • Are there hotspots where they happen frequently?

  • Are there peak periods?

  • Has the problem worsened over time?

  • To what extent do entanglements impact marine mammal health?

  • How do animals recover after the entangling material is removed?

  • Are certain groups of animals at higher risk?

We need to know more about marine mammal entanglements to guide conservation and mitigation efforts. We want to answer those questions, while also actively disentangling sea lions. It’s part of a project led by The Marine Mammal Center in Sausalito, California and NOAA Fisheries’ Marine Mammal Laboratory in Seattle, Washington. The work is supported by a John H. Prescott Marine Mammal Rescue Assistance Grant from NOAA Fisheries Marine Mammal Health and Stranding Response Program.

Around 45 percent of the California sea lion population breeds on San Miguel Island. The island is part of Channel Islands National Park off the coast of Southern California. The Park is surrounded by the Channel Islands National Marine Sanctuary. It is a crucial refuge for seals and sea lions, and is home to many other unique animals including the endemic Channel Islands fox. You can find California sea lions sleeping, breeding, and pupping there alongside northern elephant seals, northern fur seals, Pacific harbor seals, threatened Guadalupe fur seals, and Steller sea lions.

Since the 1970s, the California sea lions on the island have been the focus of a long-term research program led by NOAA Fisheries. It monitors changes in population size, health, condition, and survival, providing important insights for conservation. For instance, the research has revealed how changes in oceanographic conditions affect food availability and survival. For the past decade the team has removed entangling gear from sea lions and documented the cause of the entanglement. This motivated a larger project aimed specifically at understanding how entanglement affects the health and population of California sea lions.



bottom of page