I am frequently asked by my guiding guests and angling friends how I decide to change locations or move on when fishing. While I like to think that I have a magic formula for this, in truth, most of it is instinct muddled with a strong shot of the "explore or exploit" algorithm.
An interesting book that I read over the winter is called Algorithms to Live By Brian Christian and Tom Griffiths. A book about using computer science algorithms in our daily life to make decisions. For someone like me, who likes to analyse the mundane such as counting every single thread wrap while I tie flies or how many casts I should make in each spot; Algorithms to Live By further confounds the mind into thinking that an underlying logic exists in an otherwise random order of things.
The "explore" or "exploit" algorithm in chapter two is simply how much time should someone spend exploring a topic or experience versus how much time they should spend exploiting it. In our instance, it is how much effort to give while fishing a given body of water. For someone unfamiliar with a particular body of water, such as a pool, riffle or run, the algorithm leans heavily towards exploration. When someone is in exploration mode, they should take more time observing each hydrological feature that fish may use to find cover from above, reliable supply of food being channelled into a small area, and respite from the current. If on the other hand, you have already explored a given piece of water and have had success, you will have the location logged in your mental catalog and are thus free to spend more time exploiting it. As your mental catalog fills with more and more successful locations, your algorithm starts to lean towards spending more time exploiting instead of exploring.
On a daily basis when I decide where I would like to go fishing, I think about how much effort I may have applied using the explore/exploit algorithm. When I moved to the banks of the Roaring Fork River in 2014, I spent 70% of my time over the better part of two seasons exploring the river outside my front door and 30% of my time exploiting its bounty. Now that I have a full portfolio of locations that I like to fish, I can easily choose where to go fishing. For example today, I am planning on going to an area where I have had a lot of success when the conditions are very similar to today. In short, I know where the Baetis will be hatching and where the fish will gather to exploit the resource based on the ambient temperature and cloud cover.
Once you have chosen a location based on your personal inventory of successes, you can reduce the granularity of our algorithm and apply it to smaller features. When I approach a pool that I have fished many times and know where the fish are, I have to make another decision on how much effort to apply while fishing it. In historically productive locations, I will make more casts or change flies more frequently in an effort to exploit it to its fullest known potential. In water that occasionally produces a fish, I will apply less effort and move through it more quickly on my way to find better spots. In essence, I am applying the 70% exploit and 30% explore on a smaller scale while fishing each pool.
When I am guiding, I only take my guests to water that I have a high degree of personal success fishing. I will not spend a lot time exploring the big river as I have already done that over the course of four seasons, instead, I will spend all of our effort exploiting. I know through experience how many fish I should be able to catch in each pool. If the guests are not catching to my expectations and they are fishing the location well, I will have them move through the water at a faster pace so that we can find the fish. We may spend more time working a pool if I know the fish are there and they are not fishing it to its potential.
In closing, when you are unfamiliar with a body of water, you should spend a majority of your time exploring the possibilities searching new locations on the map and fishing every possible spot. As you grow in familiarity, you can shift your time towards exploiting the water and fish the productive runs at a speed that fits that particular spot. If the fish aren't biting...move along.