Blue Whales Research Paper

A question that stumped me every time I walked by the giant blue whale hanging up at the Natural History Museum in New York City was, “Why are whales so huge?!” Years and years later, I have found the answer. Using the research paper entitled “Energetic Tradeoffs Control the Size Distribution of Aquatic Mammals,” published last month by leading scientist, professor William Gearty, as well as news article based off of his discoveries, the solution to my childhood puzzlement has been revealed.

The biggest species to ever live on the planet is Balaenoptera musculus, colloquially known as the blue whale (Viegas). The species is extant, meaning these whales are still alive today. Blue whales grow up to thirty-three meters long and weigh an average of two hundred thousand kilograms (Viegas). Not only

blue whales are this heavy. Other large bodied aquatic mammals include walruses, narwhals, manatees, dolphins, sea lions, and seals. A majority of the heaviest species in the world live in underwater habitats.
Originally, scientists theorized that “marine mammals could be so large because the buoyancy of water frees them from the constraints of gravity” (Arnold). Terrestrial animals require sustainable arteries, veins, bones, and muscles to hold up their mass against the force of gravity in order to easily move around (Arnold). Other ideas that attempt to explain the weight gain include the selection of food, specifically the opportunity for high protein consumption or increased vegetation, as herbivores are usually larger than carnivores, or perhaps their larger environment (Gearty, McClain, Payne).
However, new information discovered by Gearty, a professor of Geological Studies at Stanford University, as well as scientists McClain and Payne, better proves why these sea creatures grow to such massive sizes. Aquatic mammals require large bodies in order to stay warm in the frigid marine environment. Since mammals are warm blooded, thermoregulation, the process of maintaining body temperature around a certain temperature, is what makes them huge (Hall-Geisler). With a bigger size comes more body heat, and these animals are better able to trap this heat because their volume grows more quickly than their surface area. The underwater mammals generate more warmth in their body but much less of it escapes from their skin (Yong).
For example, humans, a form of terrestrial mammal, can only stay in the water for short periods of time. We cannot stay in too long or else we will experience hypothermia, which is when the body’s internal temperature goes below ninety-four degrees Fahrenheit. It is impossible for us to indefinitely maintain the necessary body temperature for survival because our body heat is being sucked out by the cold temperature of the water. Payne clarifies, “when you're very small, you lose heat back into the water so fast, there's no way to eat enough food to keep up” (Why are whale’s big?). Thus, aquatic mammals were evolutionarily forced to get bigger, or else they would not stay alive.
In his research, Gearty and his team amassed 3,859 living and 2,999 fossil records of mammals, so about two thirds living and one third fossil, and created a computer model to figure out the evolutionary courses of the body masses of water mammals (Gearty, McClain, Payne).

The orders of terrestrial mammals they used were Caniformia (dog-like), Artiodactyla (even toed ungulates), Afrotheria (African), and Musteloidea (similar skull and teeth shapes), and the aquatic mammal orders studied were Sirenia (sea cow), Pinnipedia (seals), Odontoceti, (toothed whales) and Mysticeti (baleen whales) (Gearty, McClain, Payne). Gearty explains the reason they choose these two types of evidence, "the tree of ancestral relationships allows us to build models based on data from modern species to predict what the ancestors' body sizes would have been and see what evolutionary trajectories best fit with what we see in the modern day" (Why are whales so big?). The process from land to water is a gradual one, but according to the fossil record, mammals have gone back and forth six times (Viegas). Their data included seventy percent extant species and thirty percent extinct species

(Viegas).
Using their examples, they phylogenetically examined the species as well as their fossil records (Gearty, McClain, Payne). The researchers found that mammals gained a substantial amount of weight during their evolution to the water. On average, they increased their mass to about five hundred kilograms (Gearty). For comparison, the average weight of land mammals is about fifty kilograms (Bardinelli). There is much variation, contrast an otter and a blue whale, but the weight that the smallest size underwater mammals are able to be is a thousand times greater than of the land mammals’ weight, and the maximum size is twenty-five times larger than terrestrial animals (Arnold). Additionally, there is a smaller gap in weight between the smallest and biggest sea mammals compared to the gap between the respective land mammals (Viegas). The variation between terrestrial mammal’s sizes is enormous, compare a mouse to an elephant. The marine environment inflicts more powerful restrictions on body size than does the land environment, which limits sea mammals to larger sizes (Gearty, McClain, Payne). Stress from thermoregulatory needs accounts for the growth of the minimum body weight requirement (Gearty, McClain, Payne). Thusly, animals must gain weight and become larger in order to survive in this marine environment.
There is a cap on the weight these mammals can grow to because there are not enough metabolic resources in the ocean to allow for infinite enlargement. In addition to this, as size increases, so does metabolism, so their big bodies burn off more energy (Why are whales so big?). McClain explains, “basically, animals are machines that require energy to operate. This need for energy places hard limits on what animals can do and how big they can be” (Why are whales so big?). Blue whales can ingest food fairly quickly because of their filtering feeding technique of using their baleen instead of teeth (Hall-Geisler). Because of their lunge feeding, in which they suck in a great deal of water and filter out their food (Yong), they are able to eat thousands of pounds of krill and other types of tiny crustaceans a day (Gearty). Nevertheless, even with their large, constant meals, blue whales do in actuality hit a limit on their weight. They are, however, able to grow bigger than toothed species of whales, such as sperm whales or orca whales, because of the efficiency of their mouth filtering (Gearty).
The otter is the one marine mammal that does not fit the mathematical trend Geatry and his fellow scientists produced. Otters have just recently, relatively speaking, evolved to the marine realm, so that could be the reason for their small size. They also spend quite a bit of time on land and have a thick coat of fur, around a million hairs per six square centimeters, that keeps them warm (Yong).
According to the models, blue whales could potentially grow much bigger than they are currently are able. McClain believes that their growth is stunted by the fact “that humans have a tremendous impact on the body-size distributions on both land and in the oceans” (Viegas). Human caused stressors, for instance, overfishing of the constituents of the whale’s diet and pollution that diminishes the population of both the mammals and their prey, on the ecosystem are hampering the blue whale’s ability to develop into its full possible size. Furthermore, he suspects the whaling industry also reduces the size of the whales (Viegas).
The older explanations regarding aquatic mammal’s size do not fit the researcher’s data and results. Many of the previous claims for their large sizes, specifically lack of gravity, larger habitat ranges, and higher protein diets, envision a freeing from earthly hindrances, but as mentioned above, sea mammals actually have stricter sizing requirements than land mammals (Gearty, McClain, Payne). The increased vegetation in diet hypothesis is incorrect because the majority of aquatic mammals are carnivores, so for the average weight of all these mammals to increase, many would change their diets to vegetarian. This did not happen, and the only meatless mammals in this environment evolved from vegetarian ancestors (Gearty, McClain, Payne).
Scientists Gearty, McClain, and Payne discovered revolutionary new insight regarding the sizing requirements of both water and, to a smaller extent, land mammals. They disproved previous theories, and using mathematical models, demonstrated that aquatic environments actually impose more constraints than land environments. Mammals living underwater need to balance their body size between preserving optimal internal temperature as well as accounting for a constraining metabolism. As far as future research goes, Payne remarks, “the hope is there's simpler explanations that can apply to other species, including terrestrial animals. It opens up some possibility that body size can be explained by basic principles of physics and chemistry” (Why are whales so big?). After all these years, my childhood inquiry is finally put to rest.