Floodgate operations and implications for tidal creek fish communities

Tidal creeks represent important fish habitats that are often highly modified by human activities. Floodgates can protect developed areas but also restrict connectivity of tidal creek habitats; however, floodgate operations and their effects are not well quantified. I used time-lapse cameras to quantify the timing of gate openings for 22 tributaries of the Lower Fraser River in British Columbia, Canada, and related these operational data to differences in fish communities above and below floodgates. I found that floodgate operations varied substantially, with some floodgates opening daily while others opened less than 20% of the day. Where floodgates opened infrequently, I found lower upstream dissolved oxygen concentrations, greater differences in fish communities, and lower native species richness relative to sites where floodgates opened more. Thus, improvements in floodgate operation will likely benefit fish communities. These data can inform management activities to balance fish and flood protection in the region.