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Transcript: Sea Lion Strandings – The View from the Rookery

Announcer: Welcome to On the Line, a NOAA Fisheries podcast.

Rich Press: For a few months now, sea lion pups have been stranding on the coast of Southern California. So many have washed up, emaciated and exhausted that marine mammal care centers can scarcely hold them all. But while most people first notice the pups on the beach, their desperate plight began on the Channel Islands, which are about 25 miles offshore of Santa Barbara. Those islands are home to the sea lion rookeries where the pups are born and where they spend their first year of life.

Sharon Melin is a wildlife biologist with the NOAA Fisheries National Marine Mammal Laboratory, and she recently returned from three weeks of fieldwork on the Channel Islands. She went there to weigh sea lion pups and collect other data on the population. And, in fact, she does this every year, though what she saw this year was a very different sight from what she saw in years past.

I understand that you just got back from San Miguel Island, which is one of the Channel Islands, and it's a major sea lion rookery, is that correct?

Sharon Melin: Yes, that's right.

Rich Press: And so what were you doing there?

Sharon Melin: Well, this last trip was a three week trip. We were following up on the condition of California sea lion pups given this large stranding event that's going on along the coast. So I was out there weighing pups. We captured 50 pups that have long-term marks on them. And we – so we know their weight from September and then again in February, and now again in March. And we're trying to keep track of their weight gain and their growth, which is largely influenced by environmental conditions that their mother is experiencing, because right now they're still depending on their mother.

So basically, they're reflecting their difficulties finding food out in the environment. They don't wean until the following April. So they're with their mother almost a full year. And so they're basically still dependent on her during this period of time. And so their growth is a reflection of her condition, as well as their own.

Rich Press: So you said that you were weighing them. What have you found?

Sharon Melin: Well, they are still not growing. So basically, since September of last year, so pups were about three months on their first time that we weighed them, and from that time until now, until March, they basically haven't grown at all. Their growth rates have been very, very, very low, 0.01 kilograms per day, which is – normally it's 0.07. So it's a lot less than it should be. And they're in very poor condition. Those that have survived to this point are in very poor condition.

Rich Press: So they're starving. Is that what you're saying?

Sharon Melin: Some of them are definitely starving. Those that are surviving and they're sort of just hanging on, they're sort of right at that cusp of starving. And then there are a lot of animals that are literally starving to death. And a lot of those animals are eventually leaving the rookeries, and those are the animals that are washing up on shore. They're the ones that finally decide they just have to go to try to find food, but they're too little and they're not – they don't have any foraging skills, and so they get out there in the ocean and they just can't survive. And so they end up washing ashore.

Rich Press: You said that the condition of the pups reflects the fact that the mothers are having difficulty finding food. So what's going on?

Sharon Melin: Well, there has been – and you possibly have heard of this in the press recently. They've been calling it the warm blob. Warm pools of water extending hundreds of miles off shore from Baja all the way up to the Gulf of Alaska. So it's a huge, huge warm pool and it's been persistent. So it's been there since last April. And so that warm water basically has caused a displacement of most of the prey for California sea lions. And so they're having to travel farther, dive deeper in order to find food. And for females, it's not as much of a problem for adult males or juveniles or females that don't have pups 'cause they can just go wherever the food is.

But a female that has a pup is tied to the rookery island until she weans her pup almost a year later. So a little bit of their life history basically from the time she has her pup, she will go out for maybe two to five days, depending on the time of year, and she'll go out on a foraging trip. And while she's gone, the pup is on shore and it's fasting. And she's out and she's collecting food and producing milk. And then she comes back and she nurses the pup for a day and a half or so. And then she goes back out and she does this again.

What's happening now in this year is that those prey sources that females use in the wintertime are not where they normally would be or they're too deep in the water column for females to access them. So sometimes the prey will go deeper when the surface waters get warm. And so basically their primary prey, which are sardine and anchovy and rock fish and pacific hake and market squid, those are kinda their five top prey, those things are all basically not available to females this year. And that's largely because of this warm-water phenomenon that's going on in the environment.

Rich Press: So the females with pups are having to travel farther, dive deeper to find food. Are you assuming that that's what they're doing because we know that's where the prey has gone? Or have you been able to observe that behavior directly?

Sharon Melin: So we have – in last December of 2014, we satellite tagged twelve adult female pup pairs. And then we sort of let them go and we've been tracking them ever since, tracking the females. So many of them stayed around the island through much of December. But by January, we started seeing females sort of taking off and not returning, which is indicative of their pup probably dying.

And so we had only six of the twelve were still coming back to San Miguel Island in March, and they are consistently diving to 400, 500, 600 meters. To have half of our sample diving into those kind of depths is unusual. These females that were doing this deep diving they were going very deep and they were going out into very deep water. They were also the four females whose pups are still alive, and we were able to capture their pups. And although their pups were giant, healthy pups, they were alive.

So those females seemed to have figured something out that is actually at least sustaining their pup at a level that the other females simply weren't.

Rich Press: So some pups will make it through these lean times. Others won't. Are stressful years like this one something that we should expect to see more of in the future?

Sharon Melin: Yes, I think so. The predictions I've seen for the California current, it looks as if this type of variability and this type of warming is probably gonna be sort of the new normal. And the animals are going to have to adjust to that. And they have lots of options. They can – as we often say, they move, adapt or die. Those are kind of their three choices. I think what we will see and what we are seeing is that those animals that are figuring it out, the females that are able to keep their pups, they're the ones that are adapting their behavior. And it's their pups and their genetic sort of pool that is gonna become the new generations of sea lions.

So those abilities to dive deeper or to travel farther and still be able to support a pup are the traits that are going to be favored down the road if these kind of environmental conditions continue. And so that'll make it a stronger population and a healthier population with those animals in it. But in the meantime, we're going to probably see a little bit more of this dying off of animals that cannot make that adjustment or aren't capable of it either because they're physically not capable or because they just don't have the ability to learn a new behavior or do something differently.

Rich Press: Yeah, well, it's interesting because obviously these are mammals. So maybe they have a greater ability to learn new behaviors than some other animals in the ocean would. But the ones that are successful, in addition to being great athletes, they must also have other traits. They must be particularly adventurous or fearless to be able to accomplish some of the feats that you're talking about.

Sharon Melin: And what we don't know, which would be really interesting to know, is whether these females that are doing this behavior are older than the others. And that's something we just don't know 'cause when we catch them, we don't have any way of knowing their age. We do know that animals that live through El Ninos often have higher success in reproducing after an El Nino. And we've thought that that's probably because they've experienced one and they kind of know what to do when that environment shifts like that. And so they're more successful the next time around.

And so that's one kind of unknown we have in this study. It would have been really nice to have been able to age them and know how old they were to know whether we're seeing an experience component to this behavior.

Rich Press: How's the population doing overall, though? Is this a threat to their continued existence?

Sharon Melin: No. It's a very healthy – right now it's a very healthy population. The current estimate is at just over 300,000. And they're doing very well. We consider them a success story under the Marine Mammal Protection Act. This is certainly going to reduce the population, but we don't, at this point, think it's gonna be anything that would cause us worry.

Rich Press: So in terms of the oceans getting warmer all over the coasts, marine species are…

That was Sharon Melin, a wildlife biologist with the NOAA Fisheries National Marine Mammal Laboratory. The research Melin described isn't just in response to the sea lion strandings. NOAA Fisheries scientists have been marking and weighing pups and collecting other data at San Miguel Island every year since 1975. That type of long-term data collection is critical to understanding unusual events like the ones that we’re seeing today.

If you see a sick or stranded California sea lion on the beach, please do not touch the animal. Stay at a safe distance, keep your pets away, and call the rescue center that works in your county. We've put a list of the rescue centers and their phone numbers on our podcast page. That's www.fisheries.noaa.gov/podcasts. There you'll also find more information about the sea lion stranding event and what NOAA Fisheries and the California Marine Mammal Stranding Network are doing about it.

Thanks for listening. I'm Rich Press, and this is On the Line.


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You have been listening to the NOAA Fisheries’ Podcast, "On the Line". Join us next time for a firsthand look at the people and the science behind managing our nation’s fisheries. For more information, visit NOAA Fisheries at www.fisheries.noaa.gov.

"On the Line" is a production of the NOAA Fisheries Office of Communications.
 

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