Are fur seals carnivores herbivores or omnivores?

The fur seals and the sei whale show many commonalities in the distribution of these species in our natural habitat and the evolution of human- dominated ecosystems. The genetic evidence suggests that the fur seals and sei whales are likely to be obligate carnivores.

They are both omnivores (food- producing animals) and herbivores. The fur seals are the only species of mammal known to be an herbivore. Many of the sei whale species are also herbivores, but the extent to which they are herbivores is less well documented (Brundage 1993) , particularly since much of their historical habitat has been depleted by human activity (Brundage 1994) .

Some ecologists believe that the fur seals would be able to survive if they could evolve into omnivores (Krohl 1990) . However, the evidence for fur seals being able to evolve to omnivores is not convincing.

Fur seals are small. Their diet must include a fairly large proportion of vegetation, and they need to consume plant biomass that is of high quality. Furthermore, there is little evidence to support the existence of high- quality plant foods for fur seals.

The high levels of fossil and modern plant food sources for fur seals, in contrast, is suggestive that the fur seals must be herbivores and should be studied as such. There has been evidence for carnivores in the fossil record but no evidence for their presence in the present.

We may speculate, then, that the fur seals would have a better chance of surviving a world where carnivore carnivory has been replaced by omnivorous carnivory. It also seems likely that many or all of the sei whales were herbivores since their skeletons can be very thick and robust.

This is probably due to their diet consisting primarily of small animals. The extent to which sei whales can be considered omnivores is not completely clear but there appears to be a wide range. The sei whale species and the sei whale genus are most closely related to the fur seals and other large marine mammals.

Thus, most of the data suggest that the sei whales and sei whale genera were not obligate carnivores, but were more likely to be herbivores, while there may have been some exceptions (Jaffe 1990, 1997; Mertins 1985a; 1995; Broughman and Broughman 1995) .

The sei whale skeleton is similar to that of the fur seal and is composed of a bone (called denticate) which is composed of dentine (the enamel of teeth) which is composed of dentine crystals (a chemical substance which combines hydroxyl, carbon, aluminum, and hydrogen) .

Because these two structural types of bone differ from each other, it would be expected that sei whales would be herbivores, whereas the other marine mammals would be more omnivorous. The dental systems of the sei and fur seals are different, but they have similar tooth enamel composition and are formed the same way except sei whales are large, whereas fur seals have small, rounded bodies.

Sei whales have teeth in a pattern that resembles sei seals, whereas fur seals do not (Broughman 1997; Mertins 1985a) . It is known that sei whales lack teeth and therefore have no teeth, but the existence of toothless sei whales is unknown.

Although the fur seal and fur seal skeletons are similar, the bones of sei and fur seals do not have nearly as much of an overlap with one other than the teeth, suggesting that their tooth enamel composition, bone structure, and skeleton could be different.

However, the skeleton and teeth of sei whales and fur seals are very different so it would be expected that the tooth enamel and bone structure of sei whales and fur seals could be quite different.