Hello and welcome to Conservation Skills
in 10 Minutes or Less.
This series of short, skill based videos
is brought to you by the US Fish and Wildlife Services National
Conservation Training Center in Shepherdstown, West Virginia.
If you have a couple of minutes, pull up
a chair AND pick up a new conservation skill,
or maybe refresh an old one, on topics ranging from fish
culture the bird identification to stream restoration.
Enjoy.
Hello, my name is Matthew Patterson,
and I'm a course leader at the National Conservation Training
Center.
And I'm going to lead you improve the skill practice
today.
So what's the lesson for today?
Today, we're talking about determining fish length.
Now in previous videos, we've talked about calculating
density index and flow index.
And both of these use average length
of the fish in the calculations.
So the question is, how do I determine the average length
of my fish without getting out in the raceway
and measuring all the fish?
Well, this is a 2-step process.
Step one-- you want to complete a sample count,
and calculate the number of fish per pound in the raceway.
Second, you'll use something called condition factor
to convert that fish per pound calculation to fish length.
And we're going to walk you through this entire process.
So as we've done with the previous videos,
there will be a skilled demonstration, where I show you
how to do the calculation.
And then there'll be a skill practice,
which will allow you an opportunity to practice
the calculations yourself.
So the first thing you want to do when running a sample count
is to crowd up the fish.
It's important to get the fish crowded
together so that they aren't sorting
in the raceway based on size.
And there's an equal chance of getting any sized fish
in your sample.
And you see here in the video, you
want to get some water in a bucket.
And then tare that bucket, so that you get a zero weight.
And then you want to dip your net into the crowded fish, all
the way to the bottom.
Fish consort vertically as well.
So you want to make sure every fish has the same chance
of getting collected.
Then you drain off all the water,
because you're getting a weight.
And you want to make sure you're weighing fish and not
weighing water.
So all the fish in the net get dumped into the bucket.
And then you record the weight.
Finally, one at a time, you put the fish back into the raceway,
and count every fish that went into the bucket.
Now, when these guys were taking a sample,
this was a Happy Hatchery, and they
were raising rainbow trout.
They collected the following five sample counts
from raceway B. They collected five,
because the more samples you collect,
the better your data is going to be.
They had-- the first collection was
149 fish that weighed 0.25 pounds, 118 fish that weighed
0.2 pounds, 152 fish weight 0.25 pounds,
119 fish weight 0.2 pounds, and 140 fish that
weighed 0.24 pounds.
The next step is to plug this into our equation.
The equation is the average fish per pound
equals the total of all fish sampled,
divided by the total pounds sample.
So we plugged our numbers in here.
For each sample, we add all the total fish
across the top and the total pound sample on the bottom.
If you plug this into your calculator,
you'll get 678 total fish sampled,
divided by a total weight of 1.14 pounds.
When you run this through the calculator,
you get 595 fish per pound.
The next thing that we have to do once we have fish per pound
is to convert that--
the length.
And to do that, we need to use the length
wait tables in the fish Hatchery Management,
in the first edition, which you see over here to the right.
And you'll notice that rainbow trout, if you look down
the list of species there on the right,
has a condition factor of 4,000 times 10 to the minus 7.
That's the condition factor that we're
going to use moving forward.
Now condition factor is different for every species.
It also can be different within a species
at different hatcheries.
We're not going to go into great detail on this.
But if you want to calculate your own condition
factor for a given species at your hatchery,
you would take a sample of 100 to 150 fish
and weigh those fish.
And then divide the fish weight by the average length
cubed in inches to get your condition factor.
So here is the table that we're going to use in Fish
Hatchery Management.
If you go to the back, you'll notice
the condition factors are listed at the top of the page.
You want to make sure you have the one that
says c equal to 4,000 times 10 to the minus 7.
In our case, we had 595 fish per pound.
So in the table, on that third column over,
where it says fish per pound, you'll
follow that down until you find something close
to 595 fish per pound.
And then you'll come across the table
to the left to find the length in inches.
In this case, the length is 1.61 inches.
As always, after you see the skill demonstration,
you have a chance to practice.
So now it's your turn.
I would recommend pausing this video
after I read through the problem.
Work the problem on your own, and then
come back for the answers.
So here is the skill practice.
At the Good Times Hatchery, you collected the following sample
counts of rainbow trout in raceway number 11.
You had 103 fish that weighed 1.32 pounds, 129 fish that
weighed 1.67 pounds, 180 fish that weighed 2.24 pounds,
111 fish that weighed 1.47 pounds,
and 137 fish that weighed 1.71 pounds.
Calculate the average fish length.
So I would go ahead and it here.
And when you come back, we'll walk you through the answers.
OK, welcome back.
The first thing you should have done
was calculate average fish per pound.
This is done by dividing the total number of fish
sampled by the total number of pounds sampled.
We plug our numbers in.
Total fish sample added up on the top.
Total pounds sampled added up on bottom.
We had 660 total fish sampled and 8.41 pounds.
The average fish per pound is 78.5 fish per pound.
The next step is then to use the tables to convert
78.5 fish per pound to inches.
So we see that table over here to the right.
Again, you go to the far right column under fish per pound.
You work your way down until you find something close to 78.5,
and then work your way over two inches.
You can see, these are 3.17 inches in length.
I also wanted to draw your attention to the fact
that there are calculators on the AFS fish culture section
if you don't have access to fish hatchery management tables.
Here, we're on the fish culture section.
If you go down to Resources and Fish Hatchery Management
Calculators, you can say the calculators.
It says do the math.
And then there's a length weight calculator and length weight
tables.
And if you pull up the calculator, it looks like this.
You can see there are several species listed.
There are several condition factors.
Then if you scroll down, under compute weight when
length is known, you can type a length in here--
say six Inches.
Hit Enter.
And it'll give you fish per pound.
You can also compute length on the weight this known
and do your calculations that way.
So you'd like to learn more?
I would recommend signing up for the coldwater fish culture
course at the National Conservation Training Center.
And if you hold on after this video,
I'll walk you through how to find
that course on our website.
Thanks for joining us.
If you have questions about this particular skill
or any other skill related to fish culture,
or if you have a question about any class at the National
Conservation Training Center, you
can contact me at the email or the phone listed below.
Thank you.
OK, as promised, I was going to show you
how to find coldwater fish culture on our website.
Best thing to do is just go to Google and type in National
Conservation Training Center.
Hit Enter.
Typically, the first search that comes up--
open our website, and then go to the Search bar here.
Type in coldwater fish culture.
Hit Search.
The first PDF that comes up will take you to this PDF
with more information about the course,
including course description, course objectives, target
audience.
And then down at the bottom, you see
what course is coming up next.
Thanks again for joining us for Conservation
Skills in 10 Minutes or Less.
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Have a great day, and always remember--
the beautiful thing about learning
is that no one can take it away from you.