Everyone’s favorite sea mammal: Otters today! Reader Bruce Lyon contributed a bunch of nice photos and a nice summary of sea otter ecology. THIS COUNTS AS A SCIENCE POST, so read it!
Sea otters
Otters [Enhydra lutris] are quite common around Santa Cruz [California] and they are pretty easy to see right from town floating in the kelp beds just offshore. They are even more abundant a few miles to the south, particularly in Elkhorn Slough, an estuary that empties into the ocean at Moss Landing.
Below: a large group of otters hanging out in Moss Landing Harbor. At times there can be up to 50 animals in this group.
Otters are famous for being cute and photogenic, but they are also really interesting from a behavioral and ecological perspective. My colleague Jim Estes showed that otters are ‘keystone’ predators—i.e., they have a disproportionate effect on the structure of the ecosystem in relation to their abundance. The presence or absence of otters fundamentally changes the structure of the near-shore habitat, due to cascading effects down the food chain. When sea otters were virtually extirpated from the coast of California, sea urchins increased and ate all of the kelp, creating what are known as urchin barrens. With the recovery of the otters, urchins declined (because the otters ate them) and the kelp returned.Otters are also really interesting with respect to diet breadth and specialization. It’s fairly easy to see what see otters eat because they bring prey items back to the surface to eat.Below: this sea otter seemed to specialize on capturing crabs, at least over the hour that I watched it.
My colleagues Jim Estes and Tim Tinker discovered that sea otters show individual foraging and diet specializations. As a species, otters eat a great diversity of invertebrates, but individual otters specialize on a small subset of the total prey items consumed by the species. Different otters specialize on different suites of prey species. Prey specialization is favored because different prey items require different skills to process the prey items quickly and it takes a long time to learn to be an efficient forager.
Otters have high relative metabolic rates and have to eat a lot of food so foraging efficiency is important. The otters are not perfectly specialized, which allowed the biologists to compare foraging intake rates when handling favored items versus prey species that are normally not taken. Feeding efficiency was higher for the prey species that an individual normally specializes on. There is also some evidence that these specializations may be culturally transmitted between mothers and their pups.
An obvious question is this: why don’t all otters specialize on the same prey items—surely not all prey items are equally valuable? It turns out that the relative numbers of otters eating the different prey items matters. If everybody eats the same high quality food items, then the availability of that food decreases, which makes lower quality but now more abundant prey items profitable for a specialist that eats those prey items. Evidence for this effect of numbers (“density-dependence” in ecological jargon) comes from a transplant experiment in which a small number of otters were reintroduced to San Nicolas Island in the Southern California Bight (west of Los Angeles) a location that has been devoid of otters for a long time. This was a conservation effort but it revealed something interesting about the diet specialization. Most of the introduced otters—few in number relative to the bounty of available prey—had similar diets and ate mostly urchins and kelp crabs, both high-quality prey items. It will be interesting to see if some animals switch to different prey items as the population increases.
Below: I often see gulls hanging out next to otters and it seems that they may be trying to steal bits of the prey. Perhaps though they are just waiting for scraps the otters do not want. The fact that the otters often try to flee from the gulls suggests that the gulls steal food.
Below: Otters are very active and seem to be constantly in motion. They often roll their bodies in the water like a corkscrew—even while eating. They also often thrash their prey about, pounding them against their chest (as shown below) and some animals carry rocks with them that they use as tools to bash their prey open.
Below: This pair of otters seemed to be playing—they chased each other and rolled around in the water for several minutes. I asked my colleagues what might be going and their best guess was that these were young males having a good time.
Great pictures of a beautiful and charismatic animal.
Feeding specialisation is known in birds too with the Eurasian Oystercatcher, Haematopus ostralegus, being a well known example. In this species some individuals are mud probers specialising in digging out worms whilst others specialise in shellfish especially mussels (Mytilus) or cockles (Cerastoderma). These birds further specialize in the technique of opening shells with some hammerers that smash the shell and others that probe the gape between valves of the prey to cut the adductor muscle. These different feeding techniques seem to be learned from the parents and are persistent from year to year. The different feeding techniques result in noticeably different bill shapes as a result of differential wear due to abrasion.
That’s most interesting!
I wonder if otters pick up dietary preferences culturally… learning from mom how to hunt, and thus, what to hunt.
Otters are just so damn cool. Great pictures, thanks for sharing.
The mammals who went back to the ocean are the cleverest of all mammals. Their superiority over the majority of the marine world must give them the most amount of disposable free time of any other mammals on the planet.
Well.. that depends on how much time to they spend looking at funny cat pictures online.
I doubt that’s the case for sea otters. As mentioned above, they have to eat a lot to preserve body heat. I suspect they do a heck of a lot more foraging than your average mammalian predator.
Incidentally, one of the greatest threats to sea otters in the open ocean is predation by a “dumb” marine animal, the Great White.
Wouldn’t the specialization also preserve the species if something happened to one of the prey animals? If competitors or disease wiped out the crabs, the urchin-eaters would continue the species.
As a picky eater, I’m going to have to remember this story to explain how not eating mushrooms, melons or seafood is an evolutionary adaptation and that I’m doing the people who do eat those things a favor. (As long as they keep their mitts off my strawberries, parmesan chicken, and broccoli!)
Not too keen on broccoli, but my late wife always insisted that it’s good for me. Can’t quite remember why… 😉 Anyway, so long, and thanks for all the seafood.
Pretty much everything in the cabbage family (a very large and diverse family) makes for an healthy source of vegetable matter.
One version that I think most people would go for…lightly steamed Romanesco florets with a light drizzle of balsamic vinegar and olive oil, a sprinkling of salt and fresh-ground pepper, and a small shaving of fresh Reggiano cheese.
Make a meal out of it with some clam chowder and crab cakes, and invite the otters to join the feast….
b&
I love the cabbage family. My go-to veggies unless there’s fresh asparagus available.
Asparagus is on the menu for tonight…but I think the artichoke would have to be my favorite vegetable. But I also eat lots of carrots and celery and radishes and….
b&
None of you has to worry about me competing with you for these food sources.
3 As: asparagus, avocado, and artichokes for me.
Sea urchin ‘eggs’ (actually, gonads) are good eating.
http://www.sushiencyclopedia.com/sushi_menu/sea_urchin_sushi.html
Otterly fascinating! Thanks Jerry and Bruce!
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Always loved otters and their frolicsome nature, but never knew much about them. Thanks for the many pics and informative notes. Now I can appreciate the otters even more. 😊
Agree. I didn’t know nearly as much about otters as I thought I did. That’s great photography and writing too. Thanks!!
What gregarious looking otters, seemingly smiling at the camera at times!
I didn’t know about that specific ecological niche!
Great otter pictures. I love the one of the two males playing – they look so happy! That’s a fine looking juvenile Western Gull (Larus occidentalis) too. 😉
Great photos and article, thanks!
Any notes on the photo equipment used?
Cheers!
Hi
I used a Canon D6 body and a 100-400 zoom Canon lens (relatively inexpensive). The otters are very tame. In fact one animal is a bit too tame and kept trying to climb up on the back of my kayak so I had to be vigilant and paddle away quickly whenever it approached.
Gorgeous! I love how Otto saves the big crab claw for last, just like me. 😀
Love otters (who doesn’t?)! Great pictures and interesting article.
I’m surprised that sea otters haven’t been taken off the endangered species list since hunting them has been banned. They don’t have a lot of predators, although certain species (Great Whites, Killer Whales) will bite them (often resulting in death) they are rarely eaten. They don’t taste good.
I was reading somewhere that sea otters are now a host of the H1N1 virus, but I don’t know if it kills them (do otters get the flu?). I wonder how they contracted this virus?
So having poor taste is an adaptation? I’ll have to tell people that when they question my choice of music.
LOL!
The reason they haven’t been taken off the endangered species list may be that their numbers really haven’t recovered. Their population growth has stalled, which has biologists concerned.
Yes, I did a little internet research and found out that the numbers of otters has actually been declining recently. Too many man-made problems exist for the colonies to prosper. These include: environmental contaminates that affect habitat, oil spills and entrapment in fishing gear. Add to this disease and food limitations and you get a species that is still endangered.
Sea Otters are wonderfully cute, but they also have a rather “dark side”–some have been seen raping and killing seal pups (http://news.discovery.com/animals/the-other-side-of-otters.htm). My brother’s fiancee worked at a zoological center near Santa Cruz and actually interacted with one of the “evil” otters. Apparently he was quite nice in captivity!
Unfortunately, seals vs penguins too. Because of environmental pressures, there are not enough female seals to go around. 🙁
sure, that’s their excuse. They just need to work on their manners, like every other unsuccessful male!
Should one interpret the science to mean these animals are otterly effective when it comes to nomming? If so it is another thing that is awesome with them!
Wow, terrific otters and article. Thanks for the new knowledge about these beautiful mammals.
Also, it was a welcome relief from the pain post. OUCH!
Here’s an otter story from my youth. I was once a SCUBA instructor and would take my students for their check out dives to Fort Wetherill State Park in Jamestown RI, just across the bay from Newport. Dockage was so expensive in Newport that sometimes yachts would moor in the small, deep coves of the park. One morning while getting ready (we’d camped at the park) we watched two couples get off their very large sailing yacht moored in one of the coves. They rowed ashore in a dingy to be picked up by a waiting car.
We weren’t the only ones watching them depart, however. A group of otters sunning themselves on an nearby emergent rock watched them carefully too. As soon as the people got ashore SHOOP! all of the otters slipped into the water. There were perhaps seven or eight. They darted up into the boat and disappeared into the pit.
Next thing we know all the curtains in the windows of the cabin came tearing down, begining aft like someone unzipping them from the windows. We could hear loud crashing and banging from inside the boat. Every now and then an otter would peer over the pit or through a window. They were tearing that boat apart.
One of the otters must have gotten hold of a large tin of flour because a huge puff of white powder came billowing up from the pit. Two or three otters covered in white appeared on deck rolling the large tin which continued to spray white dust all over the boat.
The noise got loud and someone must have gotten word to the boat owners because soon the car that had picked them up came tearing down the road. As soon as the people got into their dingy one of the otters must have called the alarm because the otters slipped off the boat one by one before the sailors could return. They made their way back to their rock and when they got there I swear they were laughing.
They were definitely looking for stuff to eat, but they were also having one hell of a good time doing it.
Maybe that wasn’t flour.
Wonderful story, thanks for the great imagery!
Now that is FUNNY! And mordacious1 one added to the hilarity. Thanks for the story.
Great story!
We are otter fans in my family – my daughters recently bought me a “Godfotter” t-shirt, which is a synthesis of my favorite movie and mammal – so I was thrilled to learn a new fact, which is the individual prey specialization. Next trip to the bay, we will be watching closely to see who in the romp (our preferred name for an otter group) is eating what!
Here’s my otter story.
Some years ago I owned a beach house on Bainbridge Island, WA. A small stream ran through a pipe under my carport on its way down to the beach.
One day I was charging the battery of my car when I heard a noise in the brush. An otter came ambling up out of the stream bed and crossed the concrete slab of the carport between me and the bumper of the car while I stood there with the hood open and jumper cables in hand. Then he plunged back into the stream bed on the other side and continued on his way without showing any awareness of my presence. So I hooked up the cables, plugged in the charger, and went about my business.
Now that is just strange…I wonder what compelled the otter to leave the Puget Sound and travel up a small stream. Salmon hunting?
Maybe looking for nesting sites? I said “he” but for all I know it could have been a she.
Perhaps there is confusion over river otter versus sea otter? They are different species with completely different habits.
This was a sea otter. They’re common in that part of Puget Sound, and we often saw them feeding offshore. This was the first time I’d seen one that far inland.
To my knowledge there are no river otters on the island, nor any rivers large enough for them. (I have seen river otters on campus at UC Davis in California.)
That’s wild! 😀
That second otter-with-crab pic. I feel exactly the same way when tucking into a batch of steamed blue crabs.
sub- late to the wonderful sea otter party
Wonderful pictures!
Hope this is not too far off base – perhaps you’ll find “How Wolves Change Rivers” from Sustainable Human interesting:
They call it trophic cascade; it sounds like keystone predators to me.
Reblogged this on merritt727wordpress.
Great pictures and read! Thank you, Bruce!