Dolphin species living together do not necessarily compete for food. A new molecular method has revealed how different species of toothed Whales compete for prey, and which food they prefer to eat in one another's company. NIOZ marine scientists published their research in Environmental Research, a scientific journal.We know very little about the behaviour of toothed whales in terms of food and search behavior. The only thing we know about toothed whales' food habits is what we have seen in their stomach contents. It is difficult to study them in their natural environment. You can only wait for the animals to come ashore. It is therefore difficult to conduct ecological research that reveals how different species of sea mammals interact in choosing their food.There is no overlap between top predators and food sources.Researchers from the Royal NIOZ (the Netherlands Institute for Sear Research) found a solution to this problem. Stable nitrogen isotopes were used to extract amino acids from small amounts of skin tissue taken from living sperm whales.Marcel van der Meer, researcher, says that it was well known that different food preferences existed for fish and squid. "But, previous research had shown that the top predator in the area was the rough-toothed Dolphin Steno Bredanensis, which is highly unlikely. We discovered that the trophic level of Steno bredanensis is significantly lower than we had previously thought.The previous method suggested that there was a lot of overlap between the food of three species of dolphins. Van der Meer: "We now know there's no overlap at all. The common Delphinus delphis short-beaked dolphin hunts at a different depth in shallow waters, while Stenella frontalis, the Atlantic spotted dolphin, and Tursiops trincatus, the common bottlenose dolphin, hunt in water as deep as 500 meters. These two species have different prey, even though they feed at the same level. The dolphin species seem to have discovered a way for them to co-exist without fighting over food.Correcting the noiseGenyffer Troina, the first author of this research project (Federal University of Rio Grande in Brazil), visited NIOZ on Texel with Philip Riekenberg and Marcel van der Meer to work on her samples. This is an improvement on the more common isotope analysis (see frame), but uses nitrogen in free amino acid instead of in whole tissue. They use the nitrogen isotopes from the amino acid Phenylalanine. This is a building block for every living cell and is almost unchanged after it is taken up by plant-eaters.Scientists can determine the environment's base nitrogen value by using the nitrogen isotope of this amino acid. This allows them to correct the noise caused by unknown living environments in which researchers are unable to measure the nitrogen value. They can compare the base value to the sea mammal value they are studying and determine the species' trophic level, which is its ability to absorb the amino acids. A top predator might be at level 5, while a plant would be at level 1.It is roughly as follows that research with stable isotopes proceeds. One small portion of the atoms, such as nitrogen (N), that are found in every living cell is slightly heavier than the rest. The heavy atoms are more commonly found in animal tissues than the lighter ones. This is because the nitrogen that an animal consumes with its food causes digestion (metabolism), to separate them slightly slower. This uptake pattern is a result of the fact that the animal's food web contains more heavy N-atoms.To be sure that the method is accurate, however, it is important to know the level of the original food. This value, which is most commonly found in marine environments and can vary greatly depending on the species, is hard to determine. This problem is solved by the amino acid isotope technique.#
