Weir design and sampling methods
This page provides a brief description of the design and sampling methodology for the weir used in my tidal marsh creek studies. Basically a portable weir was used to block off the mouth of large tidal marsh creeks. The weir was set at high tide, captured fishes and invertebrates moving out the creek with the ebb tide, and was "hauled" out at low tide to sample the fish. A large seine was also used to sample fishes and invertebrates trapped above the weir at low tide.
Figure 1. Schematic illustration of the weir and associated seine design and sampling methods.
Figure 2. Photograph of the weir loaded aboard a small outboard motorboat and about to be transported to a study site.
Figure 3. Photograph of weir being transported by small motor boat.
Figure 4. Photograph of the weir being put in place in a marsh creek. The steel poles were the only permanent structure left in the creeks. They were used to anchor the weir and its wings.
Figure 5. Once the weir was in place, the wings were stretched out along a "clothesline" to block off the creek completely and lead nekton into the weir. Note that the wings pictured here, and in subsequent photographs are an early version, in later sampling the wings were reinforced with 10'lengths of 1" PVC pipe at 10' intervals (see illustration).
Figure 6. Photograph of the weir and wings fully set-up. The gear was then left in place throughout the ebb tide.
Figure 7. Aerial photograph of the fully set weir at low tide.
Figure 8. At low tide, the mouth of the weir was blocked off with a sliding mesh door prior to any other activity. Once the opening was secured, then environmental data was collected and a seine haul was made.
Figure 9. Once the weir opening was secured, a large seine was used to capture fishes traped above the weir. The area within the wings was "pursed" in by first stretching the net across the creek at the head of the wings,
Figure 10. then one end of the seine would be held in position, while the other end was swept through the wing area to "purse" in the fish.
Figure 11. Once the seine haul was completed, the weir itself was hauled. First a floating live-car was attached to the cod-end of the weir. Then the entire weir was lifted above the water line.
Figure 12. Fish were then shaken down into the live-car through the cod-end.
Figure 13. Unusually large catch August 1989.
Once sampling was complete, the weir, wings and "clothesline" were removed from the creek, leaving only the supporting steel poles.
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