Salmon Spawning Science

A Intern's Trip to the River Documented

Wednesday, November 30, 2011 the American River was busy with fish.  It was spawning season and the salmon were returning to their birthplace to lay their eggs.

The American River in SacramentoI was on a trip to the river with my supervisor Sarah Swenty, and Rick Williams, Mark Gard, Ed Ballard, and Craig Anderson.  Once we arrived we put on all our gear, such as waders and life jackets, and got on a small boat which took us down the river. The scientists we joined were collecting data to figure out the amount of spawning in the river and how the water levels would affect the salmon’s success.

The American River runs through Sacramento and this was my first time on the river with its rocky banks and colorful trees.  The wind was picking up speed, the sky was blue and the clouds were moving fast.  Overall it was beautiful day, despite the smell of decaying salmon.

Salmon die after spawning in the same river they were born inSalmon are born in fresh water and migrate to the ocean to live in salt water, where they live for about 2 – 4 years.  Then after many miles of migrating, they return to their birthplace to spawn.  There the female salmon makes a spawning bed called a redd.  The closest thing I can compare it to is a nest, but it doesn’t look like a nest. It looks like a mound of rocks. The female prepares a spawning bed by turning on her side to dig it while the male protects the area.  Then the female lays her eggs in the water and the male fertilizes them.

A redd is about two to 10 feet long and one to six feet wide and it’s amazing how well the eggs are hidden. You wouldn’t even know they were there if you didn’t know what a redd was and how to look for one.  After spawning, the salmon die in the same river they were born.

The boat took us to where the salmon were spawning and we got in the water.  Then the biologists used their GPS to mark where the redds were located once they found them. They also used a water meter to measure the speed of the water flowing over the redds. The flow of the water is important because if the flow is too low, the baby salmon could become stranded and die. If there is an overflow the eggs can be washed away.

Scientist's Ed Ballard and Mark Gard test the water depth and speed over salmon reddsThis was my first time in waders, and the current was strong in some areas; I had to hold on to Sarah so I wouldn’t fall. As we struggled to stay upright in the shallows we watched the guys measured the deeper water for speed and depth. It was impressive that they didn’t get pulled away by the strong current.  All around us there were salmon swimming in the water and every once in a while we heard a splash from the salmon jumping out of the water.

To locate the redd, we looked for an area where the rocks were free of algae. I found it very interesting how a female salmon can move heavy rocks to create a redd.  Once the scientists found one, they used their water meter to determine the speed and depth of the water.  There were about 50 redds in the short portion of the river we walked. When they got back to the office they analyzed these results to make recommendations for water managers in the valley.

With the redds located and measured, we headed back to the office.  The salmon eggs have been laid. Up to 2500 to 7000 eggs per pair. The eggs will hatch 50 – 150 days after being laid. Once the young fish are old and big enough to leave the river, they will migrate to the ocean and their bodies will change so they can adapt to the salt water. Finally, the salmon will go through the same incredible journey, returning to what we hope will be a healthy river in the years ahead. 

Overall I enjoyed my time at the river. I learned things about salmon that I never knew before. The things scientists at our office do to help the species were interesting to learn about too.  It was a great experience, and I wouldn’t mind going back.   

Sabrina D'Souza on the American RiverPhotographs by Sarah Swenty/USFWS