Proposed Abstract Title

Finding openings to balance flood protection and fish in the Lower Fraser

Type of Presentation

Oral

Session Title

Flood Management, Climate Adaptation and the Environment in the Salish Sea

Location

2016SSEC

Description

Tidal creeks in large coastal deltas, such as the Lower Fraser River, can be important habitat for fish, but are often highly modified by human activities. Connectivity between tributary creeks and mainstream channels is often constrained by structures such as dikes and floodgates, designed to protect urban and agricultural areas from flooding. While playing important roles in flood mitigation, floodgates have been shown to diminish habitat quality and block fish from accessing tidal creeks. It is likely that floodgates differ in their operations and may consequently open for different amounts of time, however, these data are currently lacking. We ask the question – how does the mechanical functioning of these floodgates affect fish communities in tidal creeks? We studied 22 tidal creeks in the Lower Fraser region. At each site, we quantified floodgate operation, using time-lapse cameras to determine timing and duration of gate openings. We found substantial variation in the opening patterns of floodgates throughout the region, with some floodgates remaining closed for weeks and others opening daily. While a majority of floodgates opened infrequently, there were several sites with floodgates opening for more than half of the day on average. In addition, we sampled fish up and downstream of floodgates to assess how floodgate openness relates to fish community differences. We found that floodgates that seldom opened were associated with greater differences in fish communities and with reduced upstream native species richness by about one species on average. Where floodgates typically opened for longer periods of time, however, native species richness and fish communities were more similar in upstream and downstream reaches. Thus, improvements in floodgate operation will likely translate into benefits for fish communities. These data can help prioritize restoration activities and inform management to balance fish and flood protection in the Lower Fraser River.

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Finding openings to balance flood protection and fish in the Lower Fraser

2016SSEC

Tidal creeks in large coastal deltas, such as the Lower Fraser River, can be important habitat for fish, but are often highly modified by human activities. Connectivity between tributary creeks and mainstream channels is often constrained by structures such as dikes and floodgates, designed to protect urban and agricultural areas from flooding. While playing important roles in flood mitigation, floodgates have been shown to diminish habitat quality and block fish from accessing tidal creeks. It is likely that floodgates differ in their operations and may consequently open for different amounts of time, however, these data are currently lacking. We ask the question – how does the mechanical functioning of these floodgates affect fish communities in tidal creeks? We studied 22 tidal creeks in the Lower Fraser region. At each site, we quantified floodgate operation, using time-lapse cameras to determine timing and duration of gate openings. We found substantial variation in the opening patterns of floodgates throughout the region, with some floodgates remaining closed for weeks and others opening daily. While a majority of floodgates opened infrequently, there were several sites with floodgates opening for more than half of the day on average. In addition, we sampled fish up and downstream of floodgates to assess how floodgate openness relates to fish community differences. We found that floodgates that seldom opened were associated with greater differences in fish communities and with reduced upstream native species richness by about one species on average. Where floodgates typically opened for longer periods of time, however, native species richness and fish communities were more similar in upstream and downstream reaches. Thus, improvements in floodgate operation will likely translate into benefits for fish communities. These data can help prioritize restoration activities and inform management to balance fish and flood protection in the Lower Fraser River.