1. How many calories are in a sockeye salmon?
A sockeye salmon fresh from the ocean has about 4,500 calories while a spawned out salmon in September may only have half that many. Salmon do not eat once they reenter fresh water. They are slowly starving, only surviving on stored body fat. That, combined with the tremendous energetic demands of spawning, lowers the total energy (calories) in each salmon over time.
2. Where do sockeye salmon spawn?
Sockeye salmon spawning areas are almost always adjacent to lakes (sockeye salmon fry typically rear in lakes). In the Bristol Bay watershed, which includes most of Katmai, rivers between lakes are utilized heavily for spawning. Rivers between lakes provide more stable flow than headwater drainage streams unbuffered by lake reservoirs. Small spring fed creeks and spring pond areas also tend to be heavily used for spawning, again apparently because of stable flow and temperature conditions. In the Brooks River area, sockeye salmon will spawn in Naknek Lake, Lake Brooks, and throughout the length of Brooks River from mid August to early November.
3. Do all salmon return to the exact same river in which they were born?
No. A small percentage of salmon spawn in a different location than their parents. This behavior is called straying. It allows salmon to colonize water bodies that do not have established spawning populations or to recolonize water where salmon have been extirpated by environmental conditions. For example, on the Alaska Peninsula large volcanic eruptions can fill river systems with ash & debris that destroy salmon spawning habitat. If these conditions last longer than a full generation, the population will be completely extirpated and the habitat will need to be recolonized by straying salmon when it becomes suitable again.
4. How old are sockeye salmon when they return to spawn?
Sockeye salmon are usually 3-5 years old when they return to spawn. A typical sockeye will spend 1-2 years in fresh water before migrating to sea and 2-3 years in the ocean before reversing the journey.
5. Why do salmon go to the ocean instead of staying in freshwater year-round?
There is more food in the ocean, so they grow much faster at sea than they do in freshwater. For most Pacific salmon, being anadromous (spawning in freshwater but spending most of their life in the ocean) seems to be the most successful survival and reproductive strategy. Anadromy allows these fish to grow faster and lay more eggs. Some populations of sockeye salmon, called kokanee, do not run to sea. These sockeyes are typically smaller at maturity and kokanee females lay fewer eggs than anadromous sockeyes.
6. How do salmon navigate to find their natal stream?
Salmon possess amazing abilities to navigate long distances. In the ocean, they navigate by using magnetic cues, the position of the sun, and day length to find their way back. Remarkably, out in the ocean with no visible landmarks millions of salmon know where they are, where they are to go, and when they need to leave to get there on time.
Their freshwater migration is no less demanding and just as amazing. An adult salmon’s ability to navigate a maze of lakes, rivers and streams begins when they are fry and smolt. Juvenile salmon imprint on the unique chemical signatures of the waters that they reared in and migrated through to the ocean. Essentially, they smell the water on the way to the ocean. On the return migration, they use those same chemical cues to smell their way back to their natal stream.
7. Why would all the salmon return and spawn in the same short time period?
Two factors—water temperature and predation—may drive salmon to return en masse and spawn within a short period of time.
Salmon only spawn during open-water seasons and the development rate of eggs and alevins (larval salmon) is directly related to water temperature. Higher water temperatures shorten incubation time. Colder water temperatures lengthen it. Sockeye salmon in Katmai spawn in late summer and autumn when water temperatures are dropping, which helps to ensure that their eggs incubate over the optimal period of time.
Predation may also influence the mass migration of salmon. Tens of thousands of fish can enter the Brooks River over a matter of hours or days overwhelming the predators trying to eat them. Like a school of sardines chased by whales, there are simply too many salmon for all the bears to eat them. Running upstream in large numbers lowers the chance that any one salmon will get eaten before it spawns. These fish are playing the odds to their advantage.
