Reproductive ecology of muskellunge (Esox masquinongy), an introduced predator, in the lower Wolastoq/Saint John River, New Brunswick, Canada

Abstract

Introduced predators can have harmful top-down effects on their newly colonized system through competition with and direct predation on native species. Following an initial introduction of muskellunge in Lac Frontière, Québec in the 1970s at the headwaters of the Wolastoq/Saint John River, the species rapidly migrated downstream, expanding its range by $500 km over $20 years. Despite this expansive colonization and concern over possible threats to native species, little is known about the basic ecology of muskellunge in this system. The last downstream barrier is the hydroelectric facility, Mactaquac Generating Station (MGS), 150 km upstream of the sea. While there are no downstream fish passage facilities at MGS, adult muskellunge have been recorded downstream. In this study, muskellunge (n = 23) were surgically tagged with very-high-frequency (VHF) radio or combined acoustic radio telemetry (CART) tags and tracked over two spawning seasons. We sought to determine if there was a reproducing population downstream of MGS and tracked Tagged muskellunge over two spawning seasons. We tracked fish to locate and confirm spawning sites, and followed up with egg and/or juvenile sampling surveys. Tagged muskellunge (90%) moved upstream towards the MGS during the spawning period in each year (2016 and 2017), where they remained throughout the entire spawning period.No spawning or nursery sites were confirmed near MGS, but in 2016 three distinct spawning locations and six distinct nursery sites were confirmed 10-12 km downstream amongst a chain of flooded islands. In 2016, eggs, sac-fry and juveniles were collected and confirmed as muskellunge by genetic sequencing, providing the first empirical observation of successful spawning downstream of MGS.

Global introductions and environmental impacts of freshwater megafish

“…For example, grass carp have travelled over 100 river km in 3 months in their ongoing invasion of North American freshwater ecosystems (Chapman et al., 2013; Embke et al., 2016; Hessler et al., 2023). Muskellunge ( Esox masquinongy ) spread 500 km within 20 years after their introduction to Lac Frontière (Canada) in the 1970s (Zelman et al., 2023). However, it is worth noting that the life‐history traits of some megafish species may not always improve their chances of establishment when introduced to new environments.…”

“…Muskellunge (Esox masquinongy) spread 500 km within 20 years after their introduction to Lac Frontière (Canada) in the 1970s (Zelman et al, 2023). However, it is worth noting that the life-history traits of some megafish species may not always improve their chances of establishment when introduced to new environments.…”