My bet is that this is probably the first evidence of indeterminate growth [1] in the species. Increasing skeletal size is a pretty tell tale sign. With all the conservation programs working, they’ve started to get old enough that we can see enough of a difference to overcome individual variance in their growth cycle.
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
These photos might not support the claim, but it is well known in fishing communities that many species of fish have gotten smaller. For instance, the size of lake trout in the great lakes has decline greatly. People used to catch 100+ lb lake trout. That's unfathomable to me.
> 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
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.
My comment said exactly the same. This photos don't support the claim that fishes are reducing its size.
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.
Size change in male sealions suggest that the predatory pressure over seals was alleviated. This is bad news.
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.
There is also selectivity for smaller fish for those that are caught using gillnets since they target a specific size. Smaller fish can swim right through and thus are advantaged at avoiding being fished.
> Valenzuela-Toro looked at the size and morphology of sea lion skulls collected between 1962 and 2008 in central California and now held at the California Academy of Sciences
"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.
Its a scientific collection. Not just some random poacher's loot. Building such collections of specimens to support is crucial to life sciences in particular.[0]
This skull collection is the life work of Ray Bandar.[1]
I swam with a 32 year old male California Sea Lion
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
Members of the Dolphin Club & South End Rowing Club swim and co-exist happily with the seals and sea lions in the waters of the San Francisco Bay. Give them the space they deserve and they rarely are cause for much concern. Fairly frightening when you see one pop his head up close to where you're swimming, but it's not dangerous.
The biggest danger to swimmers has been, is, and will likely always be boats, especially ones with propellers.
Maybe the males are fighting for breading rights, and the bigger you are, the more likely you are to win. I think this is an example of sexual dimorphism.
Another thing could be that as populations get bigger, so does genetic diversity, creating more sea lions that are bigger than usual. And since bigger male sea lions have an advantage in mating, those traits get passed on to more lions and over generations, become common.
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.
Right, it talks about increased competition and size advantage. I was thinking more about the size itself. Increase in numbers means more genetic diversity, and more individuals with bigger size in a generation. Therefore, speeding up the generational size growth.
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...