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\nhabitat discontinuity within rivers and a subsequent reduction in freshwater biodiversity,\nparticularly of anadromous fishes. Fishway installation is one mitigation technique, but\nthe effectiveness of these structure is often untested. In this thesis, I present a holistic\napproach to understanding issues related to fish passage, particularly of rainbow smelt\n(Osmerus mordax), on Prince Edward Island (PEI). Using passive integrated transponder\ntags and associated stationary antenna arrays, passage assessments at five fishways,\nincluding both nature-like and technical (i.e., pool-and-weir) designs, revealed highly\nvariable passage among species. Brook trout (Salvelinus fontinalis) passage exceeded\n90%, while rainbow smelt passage varied from 0% at a pool-and-weir fishway to slightly\nmore than 40% at a nature-like fishway. Of note were observations of active spawning\nrainbow smelt at nature-like fishways. This observation suggests that nature-like\nfishways double both as fish passage structures, but also as viable spawning habitat. Low\nattraction at a nature-like bypass channel – and lack of success modifying the river\nchannel to increase attraction – illustrated the importance of correctly locating fishway\nentrances. Given questions about the effect of behaviour on passage success, assessments\nof behavioural type were conducted on rainbow smelt with the goal of linking passage\nsuccess to individual behaviour. However, despite detecting distinct behavioural\nsyndromes in rainbow smelt, passage success was unrelated to behavioural type at a full\nwidth, nature-like rock-ramp fishway. This novel approach to studying fish passage\nshould be applied to other species and fishway designs. Finally, facilitating passage to\nfreshwater habitats has important implications for the movement of seasonal pulses of resources by anadromous fishes. Marine-derived nutrients (MDNs) transported by\nmigratory rainbow smelt, principally in the form of eggs, were traced into multiple\ntrophic levels of a PEI river. Strong evidence of MDN incorporation was specifically\nfound in macroinvertebrates and stream-resident brook trout. Furthermore, this seasonal\npulse of nutrients provided brook trout with access to essential fatty acids that contribute\nto whole organism function and health (e.g., robustness of the immune system, cell\nmembrane fluidity, nervous system development). Additionally, remote camera traps and\nfield-based observations revealed linkages between anadromous rainbow smelt and\nterrestrial environments. Together, these studies illustrate the complex issues associated\nwith providing habitat connectivity in rivers, including challenges associated with\nproperly locating fishways, accommodating passage of multiple species, and accounting\nfor the effect of individual behaviour on passage. The end two chapters of this thesis\nfurther demonstrate the interconnectedness between marine and freshwater ecosystems,\nhighlighting the importance of maintaining passage not only to improve an individual\nspecies’ reproductive success but also to provide ecosystem services.

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