I hope this happens soon

[zimmy]

The part you are missing is that you have to kill either one small fish or one large fish, you also have to add in the recruitment from the fish that come from the eggs. You also have to look at the mortality rates. You w0uld have to establish the population denisty in each age/size group and then evaluate the mortality in each scenario, then calculate the reproductive potential. It is an algebriac problem, not arithmetic. By the way, if you want to use your math to get an idea, kill one small fish and do your calculations for three time periods. Then kill the 40" and do the calculations for three years. That will give you some idea. Then multiply by millions and look at the difference. It isn't really valid, but it at least gives you an idea what happens when you kill a fish.

I'll do a quick estimate of the two scenarios using the math the way you did it, but with one fish killed. By year 10the numbers are even less valid as 35-40% of breeding females are harvested each year.

Kill one small:
Year 1
2x28"= 1,403,000
1 x 40 =1,985,454
(big fish +500,000 increasing each year for 5 years)


year 5
2x28= 2,805,000
1x 50 = 3,818,181.82
(1 million per year positive, diminishing over next 5 years)
roughly 6.6 million eggs annually combined

year 10
2x37= 5427675
(I will let the big fish be dead. The eggs it produced for years 2-4 and 6-9 more than make up for the difference.)

Scenario 2: Kill the big fish, protect the little fish
year one
3x 28 = 2,125,000
big fish dead

year 5
3 x 37 = 4,250,000
(would probably be 2 x 37 accounting for mortality, so 2,805,000 is more realistic)

It takes 5 years from the time they are 28" for those 3 fish to get to the point where the total release by three 37" equals the release of one 50lber.

Scenario one results in millions of more eggs annually and a tremendously greater recruitment. In scenario two, without the 40" fish in the mix, millions of fewer eggs annually leads to an exponentially smaller population in the future. Now you can imagine a scenario where either a 40" or 28" is killed, but there are 3 small fish and 2 40" fish. One has to die. Those two 40" fish will produce tens of millions more eggs in the scenario where a 28" is harvested then if a 40" is harvested.

There is no comparison between the ability for big fish to aid in recruitment compared to small fish.

eggs per year combined
years scenario 1 (kill a 28") vs. scenario 2 (kill a 40")
1-4 : ~3.5 million vs. ~2,125,000
5-9 : ~ 6.6 million vs. ~4,250,0000

Over the 10 year period, the kill a 28" group produce roughly 50 million eggs, the kill a 40" ~32 million.
once the breeding potential of recruitment classes are included it is an astronomical difference

[JLH]

Originally Posted by zimmy

The part you are missing is that you have to kill either one small fish or one large fish, you also have to add in the recruitment from the fish that come from the eggs. You also have to look at the mortality rates. You w0uld have to establish the population denisty in each age/size group and then evaluate the mortality in each scenario, then calculate the reproductive potential. It is an algebriac problem, not arithmetic. By the way, if you want to use your math to get an idea, kill one small fish and do your calculations for three time periods. Then kill the 40" and do the calculations for three years. That will give you some idea. Then multiply by millions and look at the difference. It isn't really valid, but it at least gives you an idea what happens when you kill a fish.

I'll do a quick estimate of the two scenarios using the math the way you did it, but with one fish killed. By year 10the numbers are even less valid as 35-40% of breeding females are harvested each year.

Kill one small:
Year 1
2x28"= 1,403,000
1 x 40 =1,985,454
(big fish +500,000 increasing each year for 5 years)


year 5
2x28= 2,805,000
1x 50 = 3,818,181.82
(1 million per year positive, diminishing over next 5 years)
roughly 6.6 million eggs annually combined

year 10
2x37= 5427675
(I will let the big fish be dead. The eggs it produced for years 2-4 and 6-9 more than make up for the difference.)

Scenario 2: Kill the big fish, protect the little fish
year one
3x 28 = 2,125,000
big fish dead

year 5
3 x 37 = 4,250,000
(would probably be 2 x 37 accounting for mortality, so 2,805,000 is more realistic)

It takes 5 years from the time they are 28" for those 3 fish to get to the point where the total release by three 37" equals the release of one 50lber.

Scenario one results in millions of more eggs annually and a tremendously greater recruitment. In scenario two, without the 40" fish in the mix, millions of fewer eggs annually leads to an exponentially smaller population in the future. Now you can imagine a scenario where either a 40" or 28" is killed, but there are 3 small fish and 2 40" fish. One has to die. Those two 40" fish will produce tens of millions more eggs in the scenario where a 28" is harvested then if a 40" is harvested.

There is no comparison between the ability for big fish to aid in recruitment compared to small fish.

eggs per year combined
years scenario 1 (kill a 28") vs. scenario 2 (kill a 40")
1-4 : ~3.5 million vs. ~2,125,000
5-9 : ~ 6.6 million vs. ~4,250,0000

Over the 10 year period, the kill a 28" group produce roughly 50 million eggs, the kill a 40" ~32 million.
once the breeding potential of recruitment classes are included it is an astronomical difference

Why are you changing things around and killing off fish? Your statement was that one dead 40" fish was like killing three 28" fish. The numbers don't support your statement so you start manipulating the inputs?

This was never a discussion about killing one 28" fish or one 40" fish. As I continue to point out your statement was that one dead 40" fish was like killing three 28" fish. Even in year 1 the three smaller fish produce more eggs than the 40" fish.

If you want to include Mortality rates they should be factored in as a percentage. If you assume a flat rate it doesn't really change anything as both groups are impacted equally. In reality i think its fair to say that mortality rates would increase with age (once the fish reached breeding size) so the larger fish would have a higher mortality rate and take a bigger hit.
Posted from my iPhone/Mobile device

[zimmy]

Originally Posted by JLH

Why are you changing things around and killing off fish? Your statement was that one dead 40" fish was like killing three 28" fish. The numbers don't support your statement so you start manipulating the inputs?
Posted from my iPhone/Mobile device

I didn't manipulate the inputs because the numbers don't support my statement, but I will say it was a mess. I was trying to make a comparison so people can see the impact of removing the big fish. It wasn't valid, but I was starting with numbers that you provided for three fish, which assumed all 28" fish will be female .

Even comparing females to females, my statement is pretty accurate.

Year 1:
3x 28” (10# each) fish produce roughly 2,125,000 eggs
1x 40” (26#) fish produces roughly 1,985,454 eggs

Three 28" females produce on average 7% more eggs than an average 40". But start harvesting and you won't get all females. And the numbers are estimates so that 7% is probably +/- 3%.



This is it for me... I agree my explanation wasn't great and I probably should have said 5 or 6 28" to one 40". Here it is in the most basic form, but including males and females:

A group of six 28" fish (3 males, 3 females) produces about 2 million eggs. A 40" fish, almost certainly female, produces about 2 million eggs.

An average harvest of six 28" fish will remove almost the same number of eggs (~7% more, to be as exact as possible) as removing one 40" fish.

It is even more dramatic if you compare a 24" to a 44".