First You Hatch, Then You're Fry

By Bill Hauser

Salmon fry. What do you know about salmon fry? There is a lot more to this than you may think.

Let’s begin with a brief overview of a generalized salmon life cycle.

In fact, let’s begin the story with the egg. The egg is deposited during summer and incubated through winter until the fish hatch and later become free swimming fry. After some development and growth, they become juveniles called parr or fry until they become smolts that migrate to the ocean. In the ocean, they grow and mature until they migrate back to freshwater to spawn. This sounds easy enough but it is really not so simple. Lots of stuff are going on here.

Okay. What is a fry? The free swimming fry stage begins after the alevin has absorbed all of the yolk in their yolk sac and the little fish swim up and out of the gravel of the redd. Most emergent fry are not more than 1 ¼ inches in length. They appear as miniature, skinny fish. This lifestage occurs in freshwater and lasts until the fish become smolts and it may last from a day or so to as much as several years.

Easy things first, so we begin with pink and chum salmon. Fry of these species migrate directly to the ocean after emerging so there is little or no rearing in freshwater. Some pink salmon populations actually spawn in the upper intertidal region so there is no feeding at all in freshwater. Some populations of chum spawn in upriver locations such as in Canada in the Yukon River so there must be some feeding while moving downriver to the ocean.

Sockeye salmon fry like to rear in lakes. Hmm. Here is a dilemma. Lakes often have an inlet and an outlet. Sockeye salmon spawn in both inlet and outlet streams. This means that some fry need to migrate upstream to get to the lake and some need to migrate downstream. Guess what. That is exactly what they do. Each population of spawners is a different population that is genetically programed to swim the correct orientation to get to the lake.

Sockeye fry, rearing in the lake, feed primarily on small zooplankton – small (about the size of a pin head), free swimming, animals – called daphnia and copepod. Most feeding occurs close to the surface during the night. During daytime, the fry migrate into deeper water. The fry live and rear in the lake at least one year, but up to three years, before they migrate to the ocean as smolts.

Coho and Chinook salmon typically rear in moving waters. These little guys are camouflaged by darkened vertical oval bars on their sides. These bars are called parr marks and the fry are often referred to as parr.

Chinook salmon typically prefer to rear in the margins of larger streams and rivers, especially in some form of cover such as tree branches that have fallen into the water. They hover where the water velocity is about six inches per second. When bits of food drift by on the faster conveyer belt we call a current, they dart out and grab what they want. These guys jostle for the best feeding location as if they knew their life depended on it.

As fry, their job is to grow and store enough fat to survive over winter and to be large enough to emigrate as a smolt the following spring. Fry from some populations – particularly in the southern part of their range – actually migrate to the sea during the first part of their life.

Now, they have another challenge. To find a place to overwinter. In larger rivers, this usually is in the deeper pools and or in ice free areas where the fry wriggle down into the spaces and cracks between the large rubble. In May or June, they are out and swimming and ready to become smolts at one year of age.

Guess what. Coho salmon behave differently from all the others. Coho salmon fry – or parr – usually start their life higher up in the drainage, in smaller streams. Most fry prefer to rear in slower moving waters. Beaver ponds and side channel sloughs are ideal because the fry have less current to work against and food is abundant. The water is usually warmer so their metabolism works better. They find cover and set up territories while they feed on drifting organisms.

When the water begins to cool in the fall, they usually move lower in the drainage to deeper water areas such as pools and side channels with woody pieces. The following spring, they spread out to other areas but usually stay in the lower parts of the drainage. Most coho salmon fry remain in freshwater two years – some, three or more years before becoming smolts.

As often with fish, these fry lifestyles represent only the most common or typical rearing strategy. Over their range, there are many geographic and hydrologic differences and individual populations evolve to take advantage of the various unique habitats. Some populations of sockeye and Chinook salmon, for example, rear in more brackish areas and some sockeye salmon rear in sloughs instead of lakes.

What is the take home message? Each species of salmon has a different rearing strategy and therefore have different habitat requirements. And rearing fry need different types of habitat during different seasons. Migratory pathways within the drainage, therefore, must be maintained for juveniles as well as adults. (This means man-made potential obstructions like culverts must be properly installed and maintained.)

Just remember . . . the next time you look down in the water in some Alaska stream and see a lot of small fish, call them parr; not minnows.