As the California sea lion population got bigger, so did male sea lions
news.ucsc.edu
news.ucsc.edu
Many fish used to be much bigger than today because they survived for much longer since they had no predators. Within years, the average fish size of those caught at any popular vacation destination fall precipitously as can be observed by vacation photos [2]. If a mammal were to acquire this adaptation, it makes sense that it would be a marine one - I think whales and dolphins exhibit it too
[1] https://en.m.wikipedia.org/wiki/Indeterminate_growth
[2] https://psmag.com/environment/fish-stories-the-ones-that-got...
Must be taken in mind that the photos don't support that claim.
My reading of the article is that the pictures don't show a particular species getting smaller over time, but that the species of fish that grow large aren't caught anymore. Yes the fish in the pictures got smaller over time, but they also changed species.
From the article:
> Yes. This really isn’t a story about shifts in size within a particular species. I didn’t find that. What I did find is that the big species just aren’t there anymore.
1) Photos show a mix of pelagic and coastal species. There was an incredibly stupid extinction of 10-20 years old local groupers the first year. Those were probably the fishes saved by World War II. Men killing themselves was a blessing for fishes. After removing all the big coastal species, if you have pelagic species your average size increases, otherwise is the last photo (with fishes that aren't small in fact, More or less on the average for the species shown).
2) The big pelagic species are seasonal migrators, and the migrations don't overlap exactly with the holiday season. This Carangidae could decide to travel one week before of after holidays, or pass at 50 Km more far of the coast and neither this giant fishes nor its even bigger predators will appear in the photo. This does not mean that they were extinct. Warming sea temperatures changed the migration patterns also.
Are fishes reducing its size when the predatory pressure increases? yes. Some Mediterranean fishes are also maturing much faster than before. But the proofs are in the scientific journals, not here. When the predator pressure skyrocket we have this escape response when the animals became giants or dwarfs. We can see the same effect on elephant tusk being shorter when they are hunted too much.
Having this in mind, we can understand better why we have a problem here with the sealions.
It means that Killer whales and white sharks are silently [1] vanishing. Either they are being hunted by us (or killed by our machines), and/or their preys disappeared by a climatic event, and/or we can suspect a major disease.
If this disease extends to the functional category "predator" instead to the taxonomic category "Dolphinidae" the problem lies most probably in the trophic chain, and we can suspect bioaccumulation also.
If the big predators that eat fish are going locally extinct, we have a problem, because we are big predators that eat fish.
If predators are not anymore to do their jobs, we can safely predict that next-in-list group of preys will start suffering from major epidemics... that lead us directly to summer 2022:
"More than 150 sea lions have been found sick or dead along Oregon’s coast due to a bacterial outbreak of Leptospirosis this summer" [2].
"Hundreds of dead or dying sea lions have washed up on the beaches of Peru since January 2023 affected by bird flu" [3]
So it seems that what we have here is an ecosystem eroding and collapsing over the next lower level like a house of cards. Probably because there is a serious problem with the trophic chain that lead animals unable to trigger a good immune response. The wave will travel slowly toward the basis until eventually losing momentum and stopping. If the most affected seals were the older ones and the sample was focused in stranded animals, we would have a direct alternative explanation for the bigger skulls: Bad sampling.
[1] As they are pelagic and just sink on open sea most of the effect was silent and missed.
[2] https://www.opb.org/article/2022/11/04/disease-outbreak-leav...
[3] https://english.elpais.com/science-tech/2023-02-15/mass-deat...
"As the California sea lion population got bigger, so did the collected skulls", is what I read. I cannot find the method of collecting the skulls from the paper or the one paper I was able to read that this paper sourced.
If humans were hunting, poaching, or collecting dead animal skulls, there could very well be some influence on the size of the skulls from their desire to hunt/poach bigger game and or collect a bigger specimen than they previously collected/hunted/poached. If I was out collecting for grins and giggles, and I had a sack full of skulls, I would likely throw out the small ones to fit a bigger one than is in my sack or larger than what I have at home.
Another possibility is that they collected larger skulls because there is more pressure on the larger animals as time progressed in the study period, creating a larger supply of the larger skulls. On average, the animals may in fact be smaller.
They do indeed eat salmon and will go out of their way for the tasty treat.
I cannot understate their size. The males are terrifyingly large.
I'm not surprised by these findings though, sexual dimorphism is pretty extreme in California Sea Lions, especially compared to the comparitively non-dimorphic earless (true) seals
I'd be curious if this would replicate in Elephant Seals but I'm not sure how you could control the positive environment to grow their numbers in the same way
The biggest danger to swimmers has been, is, and will likely always be boats, especially ones with propellers.
By expanding the breadth of their diets, the sea lions have been able to get bigger even as their numbers increased. In theory, larger sea lions should be able to travel further, dive deeper, and handle larger prey. In addition, as their breeding sites became more crowded, increased competition between males during the breeding season may have favored larger males over time.
“Body size is very important in competition with other males to control territory at breeding sites. Being bigger also means they can fast longer and stay on the beach to defend their territory,” Valenzuela-Toro said.
[1] https://www.niehs.nih.gov/research/programs/geh/geh_newslett...