A scale might be removed, their fins might be marked so they can be identified later, or their stomach contents might be washed out for later sorting and counting, to see what they have been eating. Whenever organic specimens are collected to be taken back to the lab, including stomach contents, they must be preserved immediately. Formalin is often used for this, although alcohol is becoming more popular, as it is not so dangerous to people and the environment. This is a good way to get aquatic invertebrates, like insect larvae, worms, snails, and clams. Often he will want to sample drift , the matter that is floating along down the stream.
Drift is important because it is the main source of food for many fish, including trout and salmon.
It may include mayflies that are travelling, dead or dying insects and other small creatures, terrestrial insects that fall from the trees, leaves, and other matter. Microscopes are used to assist in identification of tiny bugs, and counts are taken. To learn more about stream monitoring and research, check out the reading list , where you will find some of the very best references listed. Find out about fisheries biology, and where you can go to learn more, at the University of Washington's School of Fisheries . By adding the width to the length and then dividing by 2, the biologist obtains the average size of the rock.