Ross, meet Sam. Sam, meet Ross.
I haven't had time at all to type out some info for this, but here is a C&P of a post I did on FishBC awhile ago:
Some numbers for those who are interested. Between October 1999 and December 2004, the Lower Fraser White Sturgeon Monitoring and Assessment Program has produced these sample sizes:
20,015 PIT tags released (in the "head" location) by program volunteers.
4,696 of these tags recaptured.
27,932 individual sturgeon sampled (scanned for the presence of a PIT tag).
The number of white sturgeon captured by the Albion test fishery between 1980 and 2004 (courtesy of the Fraser River Sturgeon Conservation Society):
Using comparative studies between present and historical numbers of the white sturgeon population to determine the health of the current sturgeon population is almost impossible.
First one has to know what the historical numbers are. There are no historical numbers available, population study did not exist until the 1980s.
Researchers use historical commercial catch data to get a good idea on how the numbers have changed, except historical catch data were recorded as total weight, not number of fish. To further complicate the problem, these total weights were the sum of the weight of both green and white sturgeon. The total weight data also don't take poaching into the equation. Poaching back in the late 1800s was believed to harvest as much as 50% of the commercial catches.
The commercial white sturgeon catches reached as high as just over 500,000kg per year in the late 1800s.
The bottom line is, historical population numbers, which do not exist anyway, cannot be used to assess the current population status. Commercial catch data provide a good indication, but there are too many uncertainties involved (eg. CPUE or catch per unit effort changes overtime, the improvement of commercial fishing technology).
The health of a population cannot be exclusively determined by the number in that population. One needs to consider other factors that can be used to forecast where that population is going in the future. These factors include:
- Fecundity (number of eggs produced) of females.
- Gender ratio.
- Age class size.
As Ripple has brought up, the large fish of the population, although do exist, but are rare. Large females produce large number of eggs, they are the driving force of the population recruitment. However, the PIT tag program and the Albion test fishery catch data have indicated that recruitment is in fact on the rise over the last decade.
There is a strong surge of recruitment in the younger age classes (age 4 to 10), which can simply be the result of the ceasing of the gill net exploitation that took place in the 1970-90 period. If that's the case, we should expect to see the same trend in this recruitment in the future. The data from the next ten years will show that.
The PIT tag program produced some fantastic data, but the program was narrowed to a very small sampling area. Walters et al. recommended that in the next decade, the PIT tag program should be conducted further downstream on the Fraser River to produce a better picture on the overall population size.
In "An Asssessment of White Sturgeon Stock Status and Trends in the Lower Fraser River", Walters et al in the end concluded that "it is discouraging to see that these data sources do not imply a single, unambiguous interpretation or hypothesis about what is happening."
There are too many uncertainties and assumptions used in the population forecast models, but they are the best available so far.
They further provided an allowable harm assessment. They expect:
- a target of 10,000 reproducing adults could be achieved in 8 years (2013.
- a target of 50% of historic egg production could be achieved in 61 years (2066).
- a target of 25% of historic egg production could be achieved in 27 years (2032).
These are the more important numbers that we should be concerned, not the number of the total population. Large number of fish doesn't always mean good.
As mentioned in my second post, catch and release mortality rate cannot be determined simply by looking at how the fish swim away and basing on the catch and recapture data. As Floon brought up, the Fraser is a large water body that has poor clarity most time of the year. It is impossible to know the outcome of the fish that are released without acoustic tags on them. The P.O.S.T. program should hopefully kick in very soon after its success on tracking the salmon and steelhead migrations, it will be able to provide us a better look at the implications of this catch and release fishery.
To make the assumption that catching and releasing white sturgeon has little or no impacts on the fish is a recipe to failure. One needs to consider the behavioral, physiological effects on the fish that are caught and released. Will the capture develop stress in females and influence egg production (number and health of the eggs)? Would repetition of captures in popular angling grounds changes the feeding, mating, territorial, and other social behaviours of the fish?
On a related note, back in late July I posted the
Fraser River White Sturgeon Conservation Plan from the Fraser River Sturgeon Conservation Society. The plan was a draft that will eventually be used to make recommendations to the panel that decides whether the Fraser River white sturgeon is to be listed on SARA or not. The public was asked to review it and send in comments by September 15th, I hope those who are in the interest group have done so.
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Topic: Question For SDA / Chris re Sturgeon Fishing - SARA (Read 5665 times)