Fig 1.
Schematic of the laboratory raceway setup for the behavioral assay.
Water flow is left to right in the image. Four groups of ten female lampreys were held upstream of the polymer emitter in holding cages (HC). At the start of the trial a group is moved into the experimental arena and released. During each trial a single emitter was used, alternating from right to left sides of the channel across trials. A video camera above the experimental arena recorded movements.
Fig 2.
A schematic of the Ocqueoc River field site.
(a) Lampreys were held in cages at the release point (RP) until the start of the trial. The upstream test area (TA) was equipped with four PIT antennas; two to detect upstream movement into the area (#1 and #2), and one each surrounding the point of emission of 3kPZS, either by polymer emitter or pump tube, to detect attraction (#3 and #4). (b) Detail of the 3kPZS emission apparatus. The PIT antenna surrounded a simulated lamprey nest. At the center of the nest either a PEG6000 emitter was placed (both tests), or the end of a buried tube emerged from the sediment (Test #2 only). When used, the 3kPZS-methanol mixture was pumped from a carboy placed on the platform. In both diagrams the white arrows indicate the direction of water flow.
Fig 3.
Emitter housing and test tank used during Objective 4.
(a) Design of the emitter housing. The emitter was attached to the dowel with a single rubber band. The housing was mounted in the flow tank as shown, with the bottom open to the water. (b) Schematic of the recirculating flume tank. Flow was maintained with two trolling motors mounted upstream of a PVC collimator. During each trial five emitters were mounted at mid-depth and equidistant across the channel.
Fig 4.
Migratory sea lamprey do not respond to the odor of PEG6000.
Dissolution of PEG6000 (stimulus) into one side of the laboratory raceway did not alter the lateral distribution of sea lamprey vs. the pre-stimulus period (paired t-test, n = 8, P = 0.69).
Fig 5.
Results from the field behavioral experiments for Objective 2.
(a) Preference Test #1. Ovulated female sea lampreys were significantly more likely to approach a PEG6000 emitter releasing the pheromone 3kPZS vs. a blank PEG6000 emitter or neither (χ22,51 = 38.235, P<0.001). (b) Preference Test #2. Ovulated female sea lampreys did not prefer 3kPZS emitted from a PEG6000 emitter or pumped as a liquid in methanol and water (χ2(2,48) = 1.50, P = 0.447).
Fig 6.
Performance of the emitter-baited traps (vs. a paired unbaited trap) during sea lamprey control operations.
(a) Box and whisker plots of historical trap efficiency (proportion of the run captured) for each stream as estimated by mark-recapture (data obtained from P. Hrodey, USFWS, outliers omitted). The black triangle indicates the observed trap efficiency during 2012 when 3kPZS-PEG6000 emitters were applied, “n” indicates the number of years historical trap efficiency was estimated. (b) The proportion of the total catch that was captured in the 3kPZS emitter-baited trap with 95% binomial confidence intervals, “n” refers to the total number of sea lamprey captured in baited and unbaited traps during 2012. The dashed line indicates the null expectation of equal catch rate between the paired traps if the 3kPZS-PEG6000 emitter did not influence capture rate (which trap received the bait was alternated on subsequent nights).
Fig 7.
Housing the PEG6000 emitter better controlled the rate of dissolution at high water velocity.
In a recirculating flume, increasing water velocity accelerated the rate of PEG6000 dissolution. However, housing the emitter (filled circles, r2 = 0.69) reduced the effect of velocity on the dissolution rate at velocities >0.25 m s-1 relative to emitters fully exposed to the flow (white circles, r2 = 0.87). Linear regression fits with 95% CI (dashed lines) are included to illustrate the patterns, see text for GLM results.