Sunday, January 26, 2014

I'm Learning - pt. 2

This is a continuation on some information that I've been looking into about fisheries management. Part 1 can be found here

One of the many myths out there is that it takes a really long time to grow a trophy trout. But in most cases it's a fast growth rate that makes for large fish, not necessarily an older fish. For example, in some Southern Utah streams Brown Trout often grow from fingerlings to the 18-20 inch class in as little as 3-4 years. Brook Trout, also in Southern Utah, have reached the 5 pound mark after surviving only 2 winters (3 Summers). With these fast growth rates it means that even if 80-90% of the 16-18" trout are introduced to the dinner table they will still be replaced each year. The left over 10-20% will still be around to potentially grow even larger. 

Great! But what if we only harvest 50%? That'd mean that the other 50% of the population would be left to grow larger and there would be even more large trout to catch admire and release right? Unfortunately, it doesn't work this way. Remember that pounds per acre decides how much any system can sustain. More simply put, there's only so much room in our bucket. If there are a lot of 16-18" fish the growth rates would slow. Sometimes harvesting fish can actually promote fish growth. With fewer fish, we can fill our bucket with less fish of a greater size. This all applies to a point, since no one wants fisheries to be over-harvested either.

Limiting Factors

There are four main limiting factors when looking at fisheries: Water temperature, water habitat, sport fish harvest, and size of holding pools. These limiting factors can prevent fish from attaining potential growth. 

These seem simple, and they are, but the real trick is in identifying which factor is limiting your fishery. Improving an attribute that isn't the real source of your problem doesn't help the situation. Just like when the doc gives you the wrong prescription (pain meds instead of more cowbell). 

Two scenarios that have been played out around my home state are the "low pounds per acre" and the "high pounds per acre" stories. Automatically we assume that high pounds per acre is good right? But if that population is made up of small fish that aren't in good condition is that really a better fishery? Of course not. In this case habitat improvement wouldn't necessarily help out much. What's really needed is an effort to reduce the overall population density. There are a few options here including a rotenone treatment (after which a different species could be introduced to the fishery), the introduction of a new predator and/or sportfish harvest increases. All of these options are an attempt at taking some fish out of the bucket so the ones left can grow bigger and/or grow faster.

Low pounds per acre with a potential to improve conditions usually calls for habitat improvement projects. These projects basically increase the size of our bucket. Then we can manage the fishery how ever we'd like to fill that bucket.

These posts are meant give you some info, or at least something to think about. They don't seem to help much with the shack-nasties and seem to make me want to get out even more. Hopefully you can get out and enjoy the water, I know I need too!

- Kidder