K. R. Bestgen, K. A. Zelasko, and G. C. White. Monitoring ...

that simulate Green River backwaters, which could be used to determine attraction distances at
even greater lengths than are possible with relatively short and restricted troughs.
A field test of attraction and capture efficiency of razorback sucker larvae would follow.
This second experiment would be relatively easy to accomplish if a hatchery could provide
relatively small quantities of larvae for marking, as has been done in prior experiments (Hedrick
et al. 2009), and would inform aspects of sampling effort and spatial coverage in a natural setting
to accurately monitor larvae presence with an appropriate level of effort. The assessment would
proceed in two parts. First, we recommend assessing capture efficiency of larvae released within
backwaters sampled with standard light trap gear. We propose a staged release of batches of
larvae over a three-day period. On the first day, a small number of tetracycline-marked larvae (n
= 10?) would be released in the morning, with subsequent light trap sampling in the evening and
overnight. Traps would be emptied the following day, and a larger number of similarly marked
larvae would be released (n = 100), followed by subsequent sampling. The final day would use a
larger batch of released larvae (n = 500) followed by similar sampling effort. Such an effort,
completed in 4-6 different backwaters, with similar-age fish but different backwater size, would
allow for estimation of sampling detection probabilities by trap (each trap as a sampling unit)
and by backwater night (traps combined) over a range of habitat types, and importantly, would
allow for estimation of density effects of larvae and backwater size on capture success.
The standard number of traps set in a backwater typically depends on backwater size,
with up to 5–10 traps set in each. Traps are set far enough apart such that the halo of light from
each does not overlap with others. In large backwaters, larvae and traps would be placed in
about the same proximity. A main complication would be availability of similarly aged fish over
a long enough period to complete the experiments, because the number of light traps available is
limited enough to not allow for simultaneous sampling in 4–6 backwaters. Sampling could occur
prior to known wild razorback sucker larvae occurrence, which may negate the need to use
marked fish, but use of unmarked fish is not a preferred technique. Sampling before presence of
wild fish would not then interfere with or dilute other sampling efforts, and is possible because
hatchery-produced larvae are typically available before wild larvae are present.
A third complementary experiment conducted simultaneously would be to release
relatively small batches of larvae that are differently marked (e.g., single and doubletetracycline-marked
larvae, [n = 25,000–50,000]) into the Green River at or near spawning areas
to further test dispersal times to backwaters. Some tests of this were conducted during the
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