Promised Oversize Information

[STGRule]

Here is the information I promised on oversized sturgeon below Bonneville Dam These data were published in Transactions of the American Fisheries Society in 1995. I was told not much has changed from these estimates. I am using these data, as some are reluctant to believe things that are not confirmed by outside interests. The journal article is reviewed by other scientists for accuracy of statistical analysis and adherence to standard scientific practices. This article is not published online but if you would like a copy, e-mail me and I will send it to you.
Here is the basic information asked for.
The estimates for oversized sturgeon below Bonneville Dam was between 6,900 and 10,900. The estimated sex ratio was 46.5% female and 53.5% male. The fecundity (number of eggs) of individual fish was 98,200 to 699,000. The bigger the fish, the more eggs. Ripe females were found between February and June with the peak in May and June. Hope this helps.

[Bait O' Eggs]

STG - thanks for the info.

If I take a low side estimate and assume there are 7000 adults of which about 1/2 are females. Of the 3500 females, only 1/3 will lay eggs in any year ( I believe I read this once every 3 years on the thin skinned thread ) With about 1200 females laying on the low side estimate 100,000 eggs would put 120 million eggs in the river bed.

If I use middle of the road estimates of 8900 fish, with 46.5% female laying 400,000 eggs each assuming a fish reproduces every 3 years I get 550 million eggs in the river bed every year.

thats a lot of eggs :shocked: :shocked: :shocked:

Questions
1. Is the estimate of a female laying eggs every 3 years a good estimate?
2. Are there any estimates of how many eggs will actually hatch, and of them how many make it to be a 10 or 12 inch fish (when I assume they dont look like lunch to a larger fish anymore )
3. Are there any estimates of how many fish each year make it thru the size slot for a keeper sturgeon and get big enough that they have to be released?

[TheRogue]

thanx for the data, STG!!!

kyle

[BottomFeeder]

Thanks for providing the info STGRule!

Long Live the Sturgeon!

TPM

[STGRule]

The estimate of 3 years is a little optimistic. In reality it probably averages 4-5 years. Three years is for fit, healthy females and is the soonest they could reproduce. It’s kinda like a human female is capable of reproducing about every year for about 30 years resulting in a potential 30 children. :shocked: In reality it’s ranges from 0 – ~15 with an average of 2.3 for human females.

We have no real good estimate of how many eggs will hatch. It depends on deposition of the eggs onto good substrate, water temperature, egg predator numbers, and basic water quality. We have an estimate of age-1 fish (about 8-12 inches). This is obtained by back-calculating from the estimated number of age-10 fish using an annual mortality rate of about 10%. From the report that I got the other information from this was estimated to be 399,500. The population estimates for very small and very large fish is not as accurate as estimates for legal size fish as they are not as vulnerable to the gear that we use to capture them. This means that we are not as confident in those estimates as we are for the sizes of fish that are fully recruited to the gear.

The estimates for the number of fish making it through the slot limit is another place that we have trouble. We need to be able to estimate the natural and fishing mortality to be very precise. Generally we would use a catch-curve for the estimates but with the changing regulations we haven’t had enough consistency for long enough to get them through the slot. Remember they are in that slot for 5-10 years. What we do have is estimate of the number of age-10 fish (about the age they are fully into the slot size) and the number of age-25 (about the time they are fully out of the slot limit). With the examples of the population range of 6,900-10,900 for oversized, age-10 fish was estimated at 124,800-189,000, and age-25 fish was estimated at 600-1000. These numbers are just a snap-shot of a population at a given time. The optimal goal of the slot limit is to maximize fishing potential while protecting recruitment to the breeding population. We use models to manipulate potentials and calculate an outcome. The basic problem with models is the fact that a lot of the numbers used are estimates. Some are more accurate than others. We can get a result but it has to be tested in the real world. In order to minimize damage from inaccuracies we tend to be conservative until we see the results.

I would like to add that potential damage caused by handling ripe females by fishermen is probably reduced by the fact that ripe females are not as likely to be caught by hooks. We found this out by comparing catch rates of fish that are caught in the year that they will spawn and the catch rates of females that will spawn in the year following capture. Above Bonneville Dam we found that about 25% of the females would spawn next year and only about 7% of the females would/did spawn in the year they were caught. It appears that ripe fish don’t actively feed. Some are caught but the majority are not.

Sorry for the length, it is hard to explain in a couple paragraghs. :smile:

[Paddlefish]

STGRule,

Don't apologize for the length. It's all good data, and more than we're used to seeing.

There is a heap of salmonid-related data readily available to the common guy, compared to what we know of sturgeon.

Thanks for helping to fill in some of our blanks.