Thursday, August 2, 2012

Splitting Salmon


It is common to hear hatchery folk saying things like, “it’s time to split the steelhead again” or “the fish are getting crowded, let’s split ‘em”. But what on earth does that mean? Rest assured we aren’t cutting the fish in half; rather we are moving fish from one pond into several. 
These steelhead are very crowded and need to be split.

There are a few reason we split our fish here at Dworshak. The main reason is that at some point the fish get too large for their current pond, or there are too many fish in the pond, and become crowded. If fish are crowded they become stressed and are more likely to get sick. Steelhead are more likely to become aggressive and nip at fins when they are crowded so this is another reason to split the fish. Fin loss and fin erosion can also lead to disease. Since our goal is to raise healthy, high quality fish we defiantly don’t want to keep the fish stressed or over crowded.

Crowding fish, the pipe on the left is the inlet to the fish pump.
The process of splitting fish is simple. One person uses an aluminum mesh screen to crowd the fish close together so they can be pumped from their current pond into a vacant pond. The fish make a pass through a computerized fish counter so we know exactly how many fish end up in the new pond. (The video below show how fish move through the fish counter.) Another person controls the speed of the pump and watches the fish counter to be sure there is always just the right amount of fish traveling through the fish counter. If too many fish are being pumped at once the counter can’t keep up and the final ponding number will be off. This can affect feed rates and growth estimates. 
video

This marking trailer will clip fins and tag our Chinook salmon.
We will begin splitting our 2011 Chinook next week. These fish are still pretty small, only about 3.25” or 120 fish to the pound. But because of the number of fish in each pond, they have out grown their current rearing space. The Chinook will not only be counted on the trip to their new raceway, but will go through a marking trailer. Their adipose fin will be clipped off to designate them as a hatchery fish- legal to keep if it ends up on the end of your line! A smaller portion of the fish will also receive a coded wire tag. This tiny tag is encoded with a number that is hatchery, species, and brood year specific and is used by biologists for management purposes.
A Chinook with a tiny coded wire tag in its snout

It will take about two weeks for the tagging team to split, mark, and tag our 1.8 million Chinook. But once those fish are moved they will remain in their new pond until March, at which point they will be released into the North Fork Clearwater River. If any of these fish end up on your fishing line when they return as adults, you may split them however you like!

By Angela Feldmann

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