We monitored fish movements in the creek from the mouth of the headwater culvert (0 m) to a pool 521 meters downstream, below a perched (30 cm) road culvert that is a potential passage barrier.
The headwater culvert daylighted to a 12 m long cement trapezoidal channel, with water depth of approximately 30 cm within the pool and 3-5 m upstream into the culvert exit. Upstream of the backwatered area, water depth in the culvert is extremely shallow (2-4 cm) at baseflow. Downstream of the trapezoidal channel, the stream channel is composed of natural substrates, with typical wetted width 1-3 m and average depths < 0.1 m, and most pools between 0.2 and 0.5 m in depth (Figure 1). The creek downstream of the trapezoidal channel is spatially and seasonally intermittent, and during the period of study (March to November 2019), non-pool habitats typically were frequently dry throughout much of the reach except during periods of rainfall. Data on the flow of Cooper Creek was provided by Hamilton County Soil and Water Conservation District from a flow gage at the headwater culvert. Flow data was available from 22 March 2019 to 28 October 2019. Non-weather related flows (up to 0.1 m3/s, due to periodic draining of a spill containment facility in the industrial complex) occurred for 0.5 – 2.5 hr (mean 1.25 hr) periods on multiple dates throughout the study period and entered the stream channel through the perched sewer downstream of the dry gap. Such flows were only directly observed by surveyors on two occasions, but records obtained from the Hamilton County Public Health agency in 2023 indicated that more than 20 releases occurred during the study period. These non-weather related flows appeared sufficient to provide connectivity within the lower section of the study reach.
The fish community of Cooper Creek is dominated by minnows (Leuciscidae) in the study reach. Creek Chub (Semotilus atromaculatus), Central Stonerollers (Campostoma anomalum), and Western Blacknose Dace (Rhinichthys atratulus) composed over 90% of fishes sampled; Bluntnose Minnow (Pimephales notatus), White Sucker (Catostomus commersoni), Orangethroat Darter (Etheostoma spectabile), and Green Sunfish (Lepomis cyanellus) are present lower in the watershed, but numerous barriers currently appear to prevent upstream movement of these species.
Fish movement
We tagged fishes on six dates between October and December 2018. Fishes were primarily captured (n = 82) using a seine in the headwater culvert (Figure 1). Three to four baited minnow traps were deployed overnight to capture fish (n = 19) throughout the first 150 meters of the stream channel. We tagged all fishes larger than 60 mm standard length (SL), however, stonerollers and dace (>60 mm SL/75 mm TL) were rare in the study reach. Fishes were anesthetized using Tricane-S (MS-222, tricaine methanesulfonate). Fishes were tagged with a passive integrated transponder (PIT) tag inserted into the body cavity through a small incision in the ventral musculature near the pectoral fins using a customized syringe. The PIT tags used were 12 mm long and 2.12 mm diameter 134.2 khz duplex tags (OregonRFID, Portland, OR), 0.1 g weight in air (< 2% of body weight). Injectors and scalpels were sterilized in 95% ethyl alcohol. The incision was coated with an antiseptic liquid bandage (New Skin). The fish were weighed to the nearest 0.1 g and measured to the nearest mm for both standard (SL) and total (TL) length. Tagged fish were held in an aerated bucket for 20-30 minutes post-tagging to ensure a return to normal activity, then released at their capture location. Tagging efficacy was not measured in this study but appears to be high for small-bodied fish (Skov et al. 2005), with negligible effects on movement or survival, and high retention rates for minnows (up to 100%; Musselman et al. 2017). During the initial tagging period, some tagged individuals were physically recaptured and we did not observe any individuals with a tagging scar, but no tag.
We deployed fixed location flags (metal tree tags) every 3-4 m along the streambank and used these to assign a longitudinal location relative to the headwater storm sewer outlet (assigned as 0 m). From March to November 2019, the creek was scanned for PIT tags at approximately 1-3 week intervals. A custom fabricated submersible PIT tag antenna connected to a PIT tag reader (Dual Mode FDX/HDX ISO Reader, OregonRFID, Portland, OR) was used to scan the creek bed, including both currently wetted habitat and dry streambed. This antenna detected tags underwater and under rocks, and read range was approximately 0.3-0.5 m. Tag ID and detection time was continuously recorded by the PIT reader, and we manually recorded the detection time, longitudinal distance along the center line of the stream channel relative to the headwater storm sewer opening (using fixed location flags), and notes about likely tag status (live/dead/dropped) to assign each detection to a location and determine whether the tag was still in a live fish. Tags which were found in currently dry habitat areas were marked as “dropped” in field notes, indicating that either the fish had died or the tag had been ejected from the fish. Further evaluation of tag status (live, dead, or dropped) was performed during data processing, described below in the Data Analysis section.
For all surveys, we began at the downstream end of the reach and surveyed in an upstream direction. Surveys were typically completed within 4 hours. During nearly all surveys, flow in the stream was low and fish were only found in isolated pool habitats. In most cases, pools were small enough that fish were unable to leave the habitat unit being surveyed. Only the culvert outlet at the headwater was a pool large enough that fish could move outside the antenna range during the survey. However, in the headwater pool, disturbed fish typically hid under rocks or entered the culvert, where they could be detected again. Unlike other habitats in the stream, fish detected inside the headwater culvert pipe could swim upstream (>50 m) within the culvert pipe during a survey, so all fish detected in the culvert were assigned a single location of -1 m. However, as only last first 3-5 m of the culvert were >4 cm deep, fish did not appear to use the upstream areas except when attempting to escape from the surveyors. Tags located in the industrial outflow channel were identified and the location was recorded as the distance relative to the confluence of the main channel.
As part of our tagging project, we seined the headwater outlet pool on 14 May 2019, however, no fish (tagged or untagged) were captured and no fish were visually observed in the culvert pool. Additionally, as part of our long-term monitoring program in Cooper Creek, we performed full community electrofishing surveys in two 150 m reaches (upstream and downstream of the dry gap) on 3 September 2019 and no tagged fish were encountered. Telemetry surveys were discontinued in November 2019.
Flow events in Cooper Creek were typically short-duration (hours) and strongly influenced by local rainfall. To categorize flow event magnitude, we calculated the daily maximum discharge for each date and split flows into 75%, 90%, and 95% quantiles and categorized events as major (> 0.863 m3/s), moderate (0.132 – 0.863 m3/s), minor (0.015 – 0.132 m3/s), or baseflow (0 – 0.015 m3/s). The division between baseflow and minor storms coincides with the estimated discharge required to connect the intermittent reach (“dry gap”, Figure 1). We then assigned a flow category to each sampling interval based on the largest flow event that occurred between survey events. For analyses relating flow events to fish movement among habitats or movement distance, we only included the subset of fish with known locations immediately prior to and subsequent to the flow event. Since the source, timing, and duration of dry weather releases was not known during the survey period, individual surveys did not intentionally target movements around these unpredictable flows.
