A Method to Quantitatively Sample Nekton in Salt-Marsh Ditches and Small Tidal Creeks

We designed a novel gear to quantitatively sample nekton (free-swimming fish and crustaceans) from salt-marsh ditches and small tidal creeks. This gear, the ditch net, is portable and inexpensive to manufacture, and many replicate samples can be simultaneously collected. The ditch net can sample ditches and tidal creeks as narrow as 25 cm and up to 1 m wide (or wider if the design is modified). The net is suspended between four stakes and covers a 1-m length of ditch bottom. To sample nekton, the mesh doors on both ends of the ditch net are raised, thus enclosing a known area of water and trapping nekton within the net. Catch efficiency of the ditch net was comparable with the actual density of fish traversing the ditch as estimated from video data. Recovery efficiency of the gear was high (99%), indicating that fish rarely escape after the net is triggered. A power analysis indicated that a sample size of 20 provided good power (>0.80 at an alpha level of 0.05) to detect temporal or site differences in nekton community composition.