Movement, behaviour, and marine-derived nutrients: A comprehensive assessment of issues related to fish passage in Atlantic Canada

Demand for water resources and the subsequent proliferation of dams has led to habitat discontinuity within rivers and a subsequent reduction in freshwater biodiversity, particularly of anadromous fishes. Fishway installation is one mitigation technique, but the effectiveness of these structure is often untested. In this thesis, I present a holistic approach to understanding issues related to fish passage, particularly of rainbow smelt (Osmerus mordax), on Prince Edward Island (PEI). Using passive integrated transponder tags and associated stationary antenna arrays, passage assessments at five fishways, including both nature-like and technical (i.e., pool-and-weir) designs, revealed highly variable passage among species. Brook trout (Salvelinus fontinalis) passage exceeded 90%, while rainbow smelt passage varied from 0% at a pool-and-weir fishway to slightly more than 40% at a nature-like fishway. Of note were observations of active spawning rainbow smelt at nature-like fishways. This observation suggests that nature-like fishways double both as fish passage structures, but also as viable spawning habitat. Low attraction at a nature-like bypass channel – and lack of success modifying the river channel to increase attraction – illustrated the importance of correctly locating fishway entrances. Given questions about the effect of behaviour on passage success, assessments of behavioural type were conducted on rainbow smelt with the goal of linking passage success to individual behaviour. However, despite detecting distinct behavioural syndromes in rainbow smelt, passage success was unrelated to behavioural type at a full width, nature-like rock-ramp fishway. This novel approach to studying fish passage should be applied to other species and fishway designs. Finally, facilitating passage to freshwater habitats has important implications for the movement of seasonal pulses of resources by anadromous fishes. Marine-derived nutrients (MDNs) transported by migratory rainbow smelt, principally in the form of eggs, were traced into multiple trophic levels of a PEI river. Strong evidence of MDN incorporation was specifically found in macroinvertebrates and stream-resident brook trout. Furthermore, this seasonal pulse of nutrients provided brook trout with access to essential fatty acids that contribute to whole organism function and health (e.g., robustness of the immune system, cell membrane fluidity, nervous system development). Additionally, remote camera traps and field-based observations revealed linkages between anadromous rainbow smelt and terrestrial environments. Together, these studies illustrate the complex issues associated with providing habitat connectivity in rivers, including challenges associated with properly locating fishways, accommodating passage of multiple species, and accounting for the effect of individual behaviour on passage. The end two chapters of this thesis further demonstrate the interconnectedness between marine and freshwater ecosystems, highlighting the importance of maintaining passage not only to improve an individual species’ reproductive success but also to provide ecosystem services