Tidal Creeks and Connectivity: Toward Balancing Fish and Flood Protection

Tidal creeks in large coastal deltas can be important habitat for fish, but are often highly modified by human activities. Connectivity of tidal creeks is frequently compromised by structures such as floodgates, designed to protect agricultural and urban areas from flooding. Floodgates act as one-way valves preventing water in the mainstem channel from backing up and flooding land around tributaries, but by doing so block fish from accessing these tidal creeks. We ask the question – how does the mechanical operation of these floodgates affect fish communities in tidal creeks? We studied 23 tidal creeks in the Lower Fraser region of British Columbia, Canada, an area encompassing over half of B.C.’s human population but also supporting high fish diversity and abundances. We quantified floodgate connectivity, using time-lapse cameras to determine timing and duration of gate openings. Different floodgate types had substantially different operations, with some floodgates remaining closed for weeks at a time and others opening daily. In addition, we sampled fish communities and discovered lower species richness and abundances of some native fishes upstream of floodgates. By improving understanding of mechanical and biological connectivity in tidal creeks, these data can inform management to balance fish and flood protection.