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Estimating Fishery Production
The HRS Guidance Manual Section 8.13, pages 305 through 316, provides many helpful tips regarding sources of information and methods of documenting the production of fisheries. The following are some basic principles.
- Fairly good catch information is more likely
available in the more heavily fished areas. In other areas, catch may be
light and production values low.
- Convert all data into an estimate of the poundage
of edible tissue. This is particularly important with data on the total tonnage
of shellfish.
- You are estimating the poundage associated with a
specific reach of a water body. If you have data from a larger area you will
have to apportion the poundage, usually on the basis of surface area.
- Beware of landing data for a port. It doesn't
usually document where the fish were caught.
- Make your best estimate of production and check it against HRS Table 4-18. It may not make sense to try to refine the estimate, because you'll still be in the same production category or, because the resulting number will be trivial after dilution weighting is taken into account.
Look particularly for productive or well-stocked fisheries that are subject to actual contamination.
For potential contamination, look for productive fisheries in low-flow regimes where dilution-weighting won't lower the population value to insignificance. Lakes with small inflows and oxbow lakes are examples. Note the usual dilemma: large water bodies that have large production are usually heavily dilution-weighted. Small water bodies with a dilution weight of 1 frequently have minimal production.
Scenario A: Production is 40 pounds per acre per year, a nice value for a stocked fishery. The river is about 40 feet wide and has a stream flow of 200 cfs. The fishery is 15 miles long and is exposed to potential contamination. What is the value for potential population? (Note that 40 feet x 15 miles x 5280 feet/mile / 43,560 ft2 per acre = about 73 acres.) ANSWER
Scenario B: What is the potential population value if the fishery is a minimal perennial stream with a production that is either unknown or less than 100 pounds? ANSWER
The HRS Guidance Manual suggests that you use "back-of-the-envelope" production values and check the impact on score to see whether the effort of getting good-quality data is worthwhile.
If data are lacking, or if the gathering of data is found to be "not efficient" (the HRS Guidance Manual term), you can resort to the default documentation of "production unknown but shown to be greater than 0 by the presence of a fishery" and assign a population value of 0.03 from HRS Table 4-18, page 51621.
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