 Temperature plays a big role in the life of an Atlantic salmon. Just like this thermometer can tell us the temperature inside the aquarium tank, the life of a salmon can tell us a lot about the environment where it lives. Atlantic salmon are considered to be an indicator species. This means that the health of these fish can tell us a lot about the changes in their environment. Starting out as tiny eggs on the bottom of a river or stream, the water temperature has a direct impact on how the eggs will develop. If the water is too warm, the eggs won't survive. But even slight changes in the water temperature can affect the timing of when eggs will hatch. Emerging from the gravel just a few days earlier or later could directly affect the ability of these young fish to find available food resources. Even in the best of years, out of the thousands of eggs that a single female salmon will lay, only a few of these will survive to become adult fish. Many other animal species in the environment depend on salmon for their survival. The millions of eggs that salmon deposit along the bottom of our rivers and streams often become food for other fish. Once they become par, salmon are voracious consumers of aquatic insects. The bigger they can grow, the better chance they have to survive. So eating is very important. Salmon at this stage are also eaten by larger fish such as trout and fish eating birds like herons and mergansers. If a salmon is able to survive and become a smoke, it will enter the marine environment and face a whole new set of challenges. Larger predatory saltwater fish such as striped bass, tuna, swordfish and sharks prey on salmon, as do marine mammals like seals and porpoises. When they're in the ocean, young salmon will eat smaller fish, crustaceans and worms. As they continue to grow into full-size adults, Atlantic salmon will feed on squid, shrimp and other fish such as herring and capelin. Even out in the ocean, a salmon's survival is dependent on the temperature of its environment. Salmon will migrate to water temperatures that are suitable for growth, following the cycles of their prey as the ocean temperature changes during the seasons. The distribution and abundance of these prey species that Atlantic salmon depend on are all dependent on the temperature of the ocean where they live. Some scientists have suggested that the major changes that have been seen in the distribution of sea surface temperature in the North Atlantic may be contributing to greater mortality among young adult salmon. As our climate continues to change, this will have direct impacts on many animal and plant species. By studying key indicator species such as the Atlantic salmon, we can better understand how these changes are impacting our ecosystems. If your classroom is raising salmon as part of the Fish Friends program this year, there will come a time that your fish will have to leave the controlled environment of the aquarium for the natural environment. Hopefully, you'll have the opportunity to release these fish into a local stream or river this spring. As you release the salmon, take a moment to reflect on the many factors in a salmon's environment that contribute to the successful survival of this species. Who knows, maybe one of the fish you release will be the one in a thousand that survives to adulthood and returns to that very stream to lay her eggs.