How Does a Dolphin Excrete?

Solid waste excretion

The issue of dolphin excretion has three parts: solid waste excretion, salt excretion and urine excretion. Solid waste excretion begins with the stomach. Dolphins possess a three-chambered stomach in which food is broken down, not unlike a cow or deer, which is indicative of the likelihood of a terrestrial ancestor. Food is initially stored in the forestomach, which serves as the primary chamber. Here the food is partially digested and broken down. Mastication exclusively occurs here, as dolphins do not chew the food they intake. However, the majority of digestion occurs in the main stomach, also known as the second chamber. Food is stripped of the nutrients the body can use and absorbed in the pyloric stomach, while additional absorption is performed by the small intestines. The pyloric stomach is where the last bit of digestion takes place. The large intestine plays an important role as well, acting as a thoroughfare for waste that could not be used by the dolphin. This waste is passed through the large intestine and out through the anus/rectum.

Kidneys

The kidneys of a dolphin are unique and differ drastically from humans. While both humans and dolphins possess two kidneys, the evolution of the dolphin from a terrestrial to a water dwelling life form demanded that their inner processes could change so as to allow for adaptation to an environment with higher salinity. Both of the dolphin's kidneys thus have multiple renules that act as individual kidneys that can filter out the additional salt content. Salt excretion is pivotal to the dolphin's processes.

Small bladder

Dolphins possess an unusually small bladder which makes liquid waste difficult to store. As a result, dolphins must urinate extremely frequently and can even urinate on command for medical test purposes when prompted by humans.

Large amount of excreted material

In general, dolphins are also unusual in the sheer amount of total waste they excrete. Adult dolphins excrete four to five times as much as humans do. This is due to two factors that combine to achieve these results. Dolphins eat four to five percent of their total body weight each day, and pregnant or nursing dolphins can consume as high as seven or eight percent of their total body weight. For this reason and to remove the abundance of waste, the dolphin's stomach is suitably compartmentalized into the three above mentioned segments so as to promote fast digestion and swift removal of waste.