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Tidal creeks in large coastal deltas can be important habitat for fish but are often highly modified by human activities. Connectivity between tributary creeks and mainstem channels is often constrained by structures such as dikes and floodgates, designed to protect urban and agricultural areas from flooding. While they play important roles in flood mitigation, floodgates can 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, floodgate operations and their effects are not well quantified. We asked the question: how does the mechanical functioning of these floodgates affect fish communities in tidal creeks? We used time-lapse cameras and quantified 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. Floodgate operations varied substantially, with some floodgates opening daily while others opened less than 20% of the day, on average. Sites with 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 opened infrequently, we also found lower upstream dissolved oxygen concentrations than at sites where floodgates opened for longer periods of time. Thus, floodgate operations can influence fish communities as well as water quality. These data indicate a large scope for improving floodgate operations for connectivity.

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Globally, competition and disease from introduced Red-eared Slider (Trachemys scripta elegans) is a threat to co-existing native turtles. Red-eared Slider has been introduced throughout south coastal British Columbia (BC), mainly as pet turtle releases. Urban centres receive the most individuals, particularly in the Lower Mainland area outlying Vancouver, on southern Vancouver Island, and on the Sunshine Coast. The range of Red-eared Sliders in BC overlaps that of the Threatened Pacific Coast population of Western Painted Turtle (Chrysemys picta bellii). Herein we report on a survey for both species, noting presence, assessed population sizes, and nesting activity. Across 19 sites in the south coast occupied by both turtle species, we found the median abundance of Red-eared Sliders to be 2.5 times larger than that of Western Painted Turtles (Mann–Whitney U = 104, n1 = n2 = 19, Z-Score = −2.2188, P = 0.02642, two-tailed). There had been no evidence of Red-eared Sliders successfully hatching in the wild in BC until our study. We observed complete development, with 19 neonates from three different nesting sites between 2015 and 2017. Thus, Red-eared Slider is indeed established and able to breed in BC and thus competition and disease introduction from the species likely contributes to the decline of the Pacific Coast population of Western Painted Turtle, particularly at sites with low painted turtle numbers. The scale and mechanisms of impact requires further investigation.

Urbanization has altered fish communities in many ways. However, as cities expand and redevelop, it is challenging to assess the impacts of new projects given existing alteration. We investigated how new and old infrastructure alters fish communities over a 4-year period in Metro Vancouver, British Columbia (Canada). We compared fish communities from a stream altered by a new rapid transit rail line and seven reference sites over 4 years, from before to after construction. We provide evidence that new and old projects depress the density, species richness, and diversity of fish communities. During and after construction, sections of the altered stream had one fewer species and lower density compared with preconstruction and reference streams. Streams without existing culverts had more species and greater diversity than those with culverts, but only in some years. Diversity was lower in 1 year of the study across all streams. We argue that most monitoring in Canada is insufficient to detect the incremental changes that new projects may cause and suggest improvements in monitoring and protecting reference streams.