What marine mammals’ scats analysis can tell us about them

Adélaïde Fouache

Humans have been collecting information about animals, whether the animals are on land, underwater, or in the air, for thousands of years. Yet, a recent study by Boris Worm and his team from Canada’s Dalhousie University, has shown that there is still 86% of all species (not only animals but also plants, fungi, chromista and protozoa, which are one-cell organisms) left to discover on Earth, and 91% in the ocean, which could account for nearly 8.7 million species. This number is not precise but rather an average, and the actual number could be much lower, or much higher. Around 2000 underwater species are registered each year and 242,500 have been discovered so far. However, registration does not mean that we know everything about the species discovered, as it takes an average of 21 years for a proper description to be made.

There are multiple ways to learn about and make sense of animals’ diet and behavior. The most common and least invasive one, if done properly, is observing them in the wild. One method that does not usually come to mind, is the analysis of animal’ scat, which although not the most glamorous, is helpful in learning about a species’ diet and health among other things. This article will focus on the marine animals’ scats and what they teach us about their life on the water or underwater. For example, the  analyses of grey seals’ scat in the Baltic Sea shows us that depending on where the seal lived, its feed differed from others, and that the age also had an impact on what a grey seal eats. It is not only interesting to see the diet of animals, but it can sometimes be surprising also. For example, rocks have been found in sea otters’ scat, supposedly a result of a sea otter pup making mistakes when foraging.

Analyses of scats can also tell us about an animal’s health. As an example, all samples collected from the endangered Southern Resident Killer Whales in the Salish Sea (between Washington State and British Columbia) were examined for DNA stress, reproductive and nutrition hormones, as well as toxicants, to try and understand the reasons for the decline of this population. The results showed that their level of cortisol, which indicated psychological and nutritional stress, peaked when the presence of prey (chinook salmon) was at its lowest. It also found that the presence of commercial and private vessels do not have much effect on them as long as they have food. The level of thyroid hormones also shows how nutritionally stressed the killer whale is. The higher the level, the fatter the prey they ate, but if the level is low, the metabolism will slow down so the remaining resources will last longer. 

As useful and important as it is, the analysis of scats’ samples does not give certitude on the amount of food ingested and there is information that can not be assessed through animals’ feces. To enhance the knowledge of a species’ diet and health, other methods also need to be included for more comprehensive data.

The ways of collecting scats are also diverse and creative. Some collect the scats of marine animals such as sea otters on low tides, others by using trained dogs on boats to scent the presence of scats when following the whales a few hundred meters behind. The dogs will change their behavior when scenting scats and the sample can then be captured in a net and analyzed in the lab later. 

More than learning about a species’ diet and health through their feces, scats can also help fertilize the pelagic food web, starting with the single-cell algae phytoplankton. These phytoplankton are algae which multiply and feed species and then in turn feed more species themselves. This continues up the food chain. This is the result of big marine mammals such as whales doing the “whale pump”, meaning foraging in the deeper waters but defecating at the surfacing.

Another role that  feces can play is as a toxic substance. The presence of a parasite in cats’ scats, called Toxoplasmosis gondii, affects all types of marine mammals, from sea otters to dolphins, whales and even land mammals such as polar bears. How would marine animals even get access to cat’s feces? By eating said scats, birds, dogs, pigs, sheep and many more carry the parasite and then it finds its way into the water system. It can also be simply from flushing your cat’s poop down the toilet, as it will eventually enter the sea and contaminate species such as anchovies, oysters or crabs that are then eaten by marine mammals. Once the aquatic animal is contaminated, it gets encephalitis, an infection in its brain that will end up killing it, or it may be killed beforehand by one of its predators if it is weak. 

As a lighter end to this article, a diet of poop in the turquoise killfish can help slow the ageing process in the older fish, and scat also helps eelgrass to reproduce by scattering its seed. We don’t really know how much a marine animal poops in one day, however it is thought that a fin whale produces over 950 liters of urine per day!

Sources: The Conversation, Live Science, National Geographic, Ocean Health Index, Pets on Broadway, Washington University Conservation Biology, World Register of Marine Species