Sea Lions v. The Blob

The waters off the coast of Alaska are supposed to be cold, especially in winter. Yet, in the autumn of 2013, they cooled far less than they normally would. A great mass of warm water, 2,000 km (1,250 miles) across and around 100 metres (330 feet) deep, remained trapped in the North Pacific. Nicknamed 'The Blob', this was caused by the weather patterns over the region remaining stuck in a high-pressure mode, preventing the warm water from dissipating with the winds as it should do. With temperatures stuck at up to 4°C (7°F) warmer than normal, the high pressure did not dissipate for eight months.

When it did, tropical winds pushed the warm water up against the American coast, from southern Alaska to southern Mexico, where it basically sat until El Niño kicked off in 2015... and that kept things unusually warm for another year. Inland, this disrupted weather systems leading, among other things, to frequent thunderstorms that sparked what was (at the time) the worst wildfire season in California's history.

Pinnipeds: The Difference Between Seals and Sea Lions

Otariid (above) and Phocid (below)

Mammals, being air-breathing animals, mostly live on land. Even when they hunt or graze for food in the water, they generally return to dry ground to do things like sleeping. Nonetheless, an aquatic lifestyle has evolved several times amongst mammals, and four of those lineages survive today. Perhaps the best adapted, because their young are born able to swim, are the cetaceans (whales, dolphins, etc.) and the sirenians (such as manatees). The other two are sea otters and pinnipeds.

There are three recognised families of pinniped alive today: seals, sea lions, and another that includes only the walrus. All are distinguished by having flippers instead of feet, and a lifestyle that requires them to climb out of the water in order to breed and raise their young.

Leaving the walrus aside, the names I've just given to the other two families (and thus the title of the post) are really a bit misleading. This is because a group of animals called "fur seals" actually belong to what I'm calling the "sea lion family" (technically the Otariidae), and in casual usage, the term "seal" is often extended to pinnipeds in general. As a result, if we really want to be accurate, we need some term to distinguish members of the other family from seals more generally. The technical term for these animals is "phocids", but other commonly used terms include "true seals" and "earless seals".

Sea Lion Bachelor Pads

Spot the male

As I mentioned just a few weeks ago, male mammals are generally larger than female ones, although there are some notable exceptions. This is particularly the case where males have to compete for access to females, and there are few cases where this is more obvious than among seals and sea lions.

Sea lions and "true" (or "earless") seals belong to different, if closely related, families, but their reproductive strategy is much the same. In both cases, they spend most of their lives at seal, but they can't give birth there without their pups drowning. The majority of species breed once every year, with the females coming ashore, first to give birth, and then, almost immediately after, to get pregnant again before returning to the sea.

The precise details vary from species to species, but the South American sea lion (Otaria flavescens *) is a typical example. In December each year (that is to say, in early summer, this being the Southern Hemisphere), males haul themselves out onto beaches and fight one another for the best spots. Naturally, the largest and most aggressive males win, with the smaller and younger individuals forced out, to either wait another year, or to make daring raids when the larger ones aren't looking.

Seals, Sea Lions, and Finding Your Children

As I discussed just a few weeks ago, there are advantages to being able to identify your own children. It really does save the mother a lot of effort, especially when she can only look after a limited number of children at a time. As I pointed out then, mistakes do happen, and there are sometimes good reasons to look after other mothers' children, especially if the other mother happens to be your sister or something. But, generally speaking, getting the right child is a good idea.

Mother mammals can use three different methods to identify which child is their own, and likely often use a combination of them. Perhaps the most common method is smell, since most mammal species have a quite remarkable sense in this regard. If each child has a unique smell, or even if it just smells of you, that's a good way of identifying it. The other possibilities are identifying them by the sound of their voice, and, finally, by what they look like. For we primates, the latter may seem the most obvious, but facial recognition is something we're particularly good at.

Going for a Song

Aquatic mammals can be among the most difficult to study. Animals such as seals, dolphins, and whales spend a lot of their time below the water, or far from the shore, making long-term observation of them relatively difficult even compared with free-ranging animals on land. Learning more about their behaviour in the wild can therefore be a slow process. Seals and sea lions at least haul themselves onto land to breed and raise their young, which is handy for (among others) wildlife documentary makers, but, even then, that's hardly the whole of their life. Whales and dolphins, of course, don't even do that much.

So how can we study what they're up to? For land animals, there are a number of options. You could, of course, just watch them, and, for many purposes, that's enough. But if you want to know where they go on a 24-hour basis, that's not really going to work. For one thing, it's impractical, and, for another, you'll likely annoy the animal, so that (even leaving ethics aside) it isn't going to act normally. So, if you want to study an animal's movements over a long period of time, your best bet is to catch the animal, and fit it with a GPS tracking device. Then, having released it, you wait a while for it to calm down and get used to this collar thing around it's neck, and then see what it does.

What Fur Seals do at Sea

I seem to have done quite a few posts on cetaceans over the last few months, and have discussed, among other things, the difficulty of finding out what they're up to, compared with land animals. But, of course, whales and dolphins are not the only fully marine mammals. There are, in fact, four groups of such mammals, with the second largest, after the cetaceans, being the pinnipeds - seals and their relatives.

Seals differ from whales and dolphins in that, while they spend almost their entire lives at sea, they still have to come onshore to breed and give birth. Mammals have an advantage over birds, and most reptiles, in that they don't lay eggs, which would drown if you tried to lay them underwater, but it's still quite difficult for newborn, air-breathing, young to immediately take to swimming. Whales and dolphins have mastered this evolutionary trick (as have sea snakes, for that matter), but seals have yet to do so. Give them a few more million years, perhaps.

Seals, Sex, and Sickness

Fur seals are members of the sea lion family, and not, as their name might suggest, the seal family. One of the easiest ways to tell the difference is to check the hind flippers. In sea lions and fur seals, the flippers stick out to the sides (at least when on land), enabling the animal to waddle about on all fours, or even rear up on its hind limbs. True seals, however, are more thoroughly adapted to life in the water, and their hind flippers, while great for swimming, stick out to the rear, making them pretty much useless on land - the animal has to drag itself about using only its front flippers, and cannot walk.

Of course, the two families are related, and share a number of features in common. Some of these are related to the difficulty of breeding in an air-breathing animal that spends almost all of its time in the water. They come ashore just once a year, during which time the females give birth to their pups, and then almost immediately mate again before retreating back to the sea. As a result, gestation almost always lasts just under twelve months, regardless of species, and the animals show a great ability to synchronise their births to the same time of year.

In both groups, the males tend to be much larger than the females, aggressively defending patches of shoreline and dominating a harem of females, once the latter have finished raising their pups and are ready to mate. Their larger size, visible differences from the female (such as a sea lion's mane), and aggressive attitude all require a lot of energy, and are controlled, as in other mammals, by the hormone testosterone.

One might think, therefore, that having more testosterone is an undoubtedly good thing, if you happen to be a male fur seal - you're bigger, sexier, and more likely to be a hit with the females, and overall, end up with more children. But there could be a downside as well - you're more likely to get sick.

A couple of recent studies, published in PLoS ONE and the Australian Journal of Zoology, looked at the breeding tactics of New Zealand fur seals (Arctocephalus forsteri) at a breeding colony near Kaikoura. These are one of eight species of fur seal found in the southern hemisphere, and are actually more closely related to the sea lions than to the single northern hemisphere species.

Southern   Sea Lions    Northern     Walrus    True Seals
Fur Seals               Fur Seal
   ^           ^           |            |          ^
   |           |           |            |          |
   |           |           |            |          |
   -------------           |            |          |
          |                |            |          |
          |                |            |          |
          ------------------            |          |
                  |                     |          |
                  |                     |          |
                  -----------------------          |
                             |                     |
                             |                     |
                             -----------------------
                                        |
                                        |

The breeding males fell into two main groups. Around half of them followed what is, perhaps, the more obvious breeding tactic. They established patches of ground, vigorously defending them from other males, and gathering harems of up to fifteen females each. New Zealand fur seals are, compared with some of their relatives, not especially aggressive - they are more likely to posture, shout, and threaten than to physically attack their rivals, but even so they spent a lot of time showing off their masculinity. These were, as might be expected, the bigger, more muscular males - presumably the sort that the females tend to fancy. And, as a result, they got to have a lot of sex.

However, nearly as many adopted a quite different tactic. They tended to spend only a couple of days at the breeding site, wandering about and looking for a good opportunity to have a quickie while the territorial males weren't looking. They were generally smaller than their counterparts, with less pronounced masculine features, and they spent a lot of time running away. A third, much smaller group, were somewhere in between, sticking to a specific area of the shoreline for a few days at a time, but not establishing long-term territories. Nonetheless, the differences in behaviour between the two main groups were quite clearly defined, rather than just being points at either end of a spectrum.

Interestingly, when it came to doing paternity tests on the pups born the following year, it turned out that about as many of them were fathered by the wandering transients as by the big, masculine males. Certainly (so far as could be determined), the transients had had sex far less often than the territorial males, but it didn't seem to make much difference to their eventual chances of fathering offspring. Which, from an evolutionary perspective, is all that matters.

New Zealand fur seals, it seems, depend on a balance between two different tactics to father offspring, with each tactic having its own strengths and weaknesses.

The researchers also studied the urine and dung of the various males. This has to be collected fresh, which isn't terribly easy when you have large and aggressive males stomping about (they weigh up to 185 kg / 410 lbs). It doesn't help that, since they are spending so much time posturing and so little time hunting at this time of year, they really aren't eating much, and consequently, don't poo very often, either. But, with due Antipodean diligence, the researchers managed to collect enough of the stuff to analyse.

Perhaps unsurprisingly, the big territorial males had much higher levels of testosterone than their wimpier cousins. But all this male hormone sloshing about and making them macho had apparently come at a price - because their dung also contained many more parasites than that of the transients. Roundworms, tapeworms, and flukes were all present, often in relatively high numbers. The price of so much masculinity, it seemed, was that they were also more likely to get sick.

Why would this be? One possibility is that, in order to bulk up their muscle, they had eaten more food before arriving at the beaches than the transients had. Since most of these parasites are passed on in food, that would mean they were more likely to get infected. But another possibility is that it's the testosterone itself that's the problem. Even assuming the parasites don't literally thrive on the hormone, its possible that because the seal's body is diverting energy reserves to building up mass, a thick and manly mane, and so on - not to mention all that exhausting posturing and fighting - they have relatively little left over to run their immune system properly.

The smaller males may not get to have sex as often, but they are healthier for it, and they seem to have just as many kids in the end, anyway. Their tactics only work because the other males are busy defending their harems, so both approaches are needed... but the big males don't get everything their own way, as casual inspection might lead one to think.

[Picture from Wikimedia Commons]