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AbstractAnthropogenic infrastructure in rivers (e.g. culverts, dams and weirs) can block the movements of fish and negatively impact their communities. Recent research has shown that fish passage at such barriers can be improved through the use of cylindrical bristle cluster (CBC) arrays. The relationship between the hydrodynamic environment created by different CBC array geometries and passage efficiency, the number of fish that passed as a percentage of those that attempted to do so, and swimming behaviour of a native wide spread European cyprinid species, the roach (Rutilus rutilus), was investigated. Passage efficiency was a function of cluster diameter and spacing; efficiency was highest (>80%) when the ratio of lateral cluster spacing (centre to centre) (Sc) to diameter was less than 5. Fish exhibited a range of swimming behaviours while manoeuvring through the CBC array to ascend the weir, the most common of which was zigzagging between two lines of clusters. Additionally, fish utilised lower velocity areas when swimming through a CBC array, often combining different swimming behaviours to successfully navigate at burst speeds. Fish passage efficiency can be improved by increasing the size of the wake behind clusters and the overall hydraulic resistance created within the array while ensuring sufficient space is available for fish to manoeuvre.

ABSTARCTCulverts used to convey river water under roads and embankments are one of the most common small-scale barriers to longitudinal fish movements worldwide. Using an open channel flume, this study assessed the ability of upstream migrating adult river lamprey (Lampetra fluviatilis) to ascend a pipe culvert when unmodified (control [C]) and retrofitted with spoiler baffles (treatment [T]) under three flow regimes (low discharge [L], high discharge [H] and high discharge with a raised downstream water level [HD]). Few lamprey attempted to ascend the culvert under low (11%) and high (21%) discharge in both the control and the treatments. Despite a greater percentage attempting to pass (75%) under HD, they frequently failed. Contrary to our predictions, upstream progress was impeded by the spoiler baffles and may reflect low motivation or avoidance of the physical and/or hydraulic conditions encountered. This study emphasizes the need to better understand the factors influencing the behaviour and motivation of fish as they ascend fish passage structures, and of the importance of reporting negative results as fish passage solutions that are promising for some species may be ineffective for others.

ABSTRACTUsing an open channel flume, this study quantified upstream passage of European eel (Anguilla anguilla) and river lamprey (Lampetra fluviatilis) at a model Crump weir provisioned with vertically or horizontally oriented studded tiles, under high and low velocity. Tiles stopped short of the weir crest, as often required at gauging weirs. For eel, when velocity was high, passage efficiency improved from 47% during the control (tiles absent) to 67% and 93% under the vertical and horizontal treatment, respectively. Under the same velocity, passage efficiency was lower for lamprey (0%, 20% and 22% for the control, vertical and horizontal treatments, respectively). Number of passage attempts and delay were lowest for eel during the horizontal treatment, while for lamprey were lower compared to the control during both vertical and horizontal treatments. Although ≥50% of initial attempts made by eel to ascend the weir were through the tiles, the fish did not necessarily continue to use them to pass upstream. Weir passage having used tiles to ascend was higher for lamprey and often provided the only route they were capable of passing. Thirty-three and 80% of eel and lamprey that reached the top of the vertical treatment were washed downstream on exiting the tiles or turned around within the tiles and moved back below the weir. Extending tiles to the crest of a weir will help improve passage performance. Despite difficulty manoeuvring between the smaller stud spacing, indicating further design optimization is required, the tiles did improve upstream passage for both species.

The efficiencies of fish passes specifically designed and constructed to facilitate the movement of a limited number of species and life‐stages past structural barriers are likely to decline as site‐specific conditions shift with a changing climate. There is a need to develop realistic fish passage criteria based on understanding swimming capability and behaviour of multiple species in relation to temperature and flow. The influence of temperature and discharge on behaviour and ability of groups of migrating adult river lamprey (Lampetra fluviatilis), a threatened species, to pass a small overshot or undershot weir at night was investigated using a large experimental flume. Lamprey approached the weirs less, and more often maintained station by using the oral disk to attach to structure, under high flows. Oral disk attachment was more commonly observed during tests employing the undershot weir. Upstream movement tended to be in close proximity to the channel walls and floor where, compared to the mid‐channel, velocities were generally lower and velocity vectors more likely to be in a direction other than the bulk flow. Upstream movement was positively related to temperature, and was higher for the overshot weir. Weir passage rate was higher for undershot than overshot weirs, and negatively related to the maximum velocity at the weir. Passage rate was low when maximum velocities at the weir exceeded 1.5 m s−1, although some fish passed at c. 1.7 m s−1. Passage efficiency, the number of weir passes as a percentage of the number of approaches, was also higher for the undershot weir, but was not affected by discharge because lamprey approached less frequently at high flows. This study provides fish passage criteria under realistic conditions for an infrequently studied anguilliform species of conservation concern and provides a methodological perspective by which to improve fishway suitability for a wider range of species subject to changing climate. Copyright © 2010 John Wiley & Sons, Ltd.