Andrew S. Vowles

Passage of European eel and river lamprey at a model weir provisioned with studded tiles

ABSTRACT Using 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.