Survival and migration patterns of naturally and hatchery‐reared Atlantic salmon (Salmo salar) smolts in a Lake Ontario tributary using acoustic telemetry

Abstract

Atlantic salmon (Salmo salar) smolts are often stocked into rivers to supplement natural reproduction, yet hatchery‐reared fish have lower survival compared to wild conspecifics. However, few studies have assessed riverine migratory performance and survival differences in hatchery and wild smolts, or more specifically naturally reared smolts (hatchery fish released earlier as parr), particularly in rivers with weirs which may further reduce survival. Using acoustic telemetry, including a subset of fish with novel transmitters that identify predation events, we assessed survival and migration patterns of hatchery‐ (2017: n = 32; 2018: n = 30) and naturally reared Atlantic salmon smolts (2017: n = 8; 2018: n = 30) in a Lake Ontario tributary with two weirs to better understand their ecology and assess the influence of environmental parameters on migration. Naturally reared smolts were 13.9 times more likely to survive than hatchery‐reared smolts and mark–recapture models indicated that weirs did not reduce survival for either group. Survival per km was lowest at the release site, indicating pre‐migration mortality, and specifically high stocking‐related mortality of hatchery‐reared smolts. Speed and times of day fish migrated (i.e. migratory performance) did not vary by rearing group, suggesting that the high mortality of hatchery‐reared smolts may be due to other factors related to hatchery and stocking operations. Overall mean (± SD) migration speed for smolts was 0.70 ± 0.39 km/hr and movements occurred significantly more frequently at night (18:00–06:00). Smolts were detected in Lake Ontario after they left the river; however, the array in Lake Ontario was not conducive to providing much detail regarding movement patterns. There was no predation of the two predation tags detected in Lake Ontario, indicating that movements were made by smolts and not predators. With ongoing restoration efforts of Atlantic salmon in Lake Ontario, it was important to understand the smolt migration patterns and success of the stocked fish. Our findings of similar migratory performance yet different relative survival of hatchery‐ and naturally reared smolts help inform management with regards to stocking strategies that could improve Atlantic salmon reintroduction success.

Investigating the behaviour of Atlantic salmon (Salmo salar L.) post‐smolts during their early marine migration through the Clyde Marine Region

“…Goodness of fit of the global model () was tested prior to model selection using the bootstrapping method ( n = 1000 simulations) to calculate the overdispersion parameter of the global model as discussed in Laroque et al . (2020). For the River Endrick combined model, the estimated quasi‐likelihood overdispersion parameter was greater than one (1.13); therefore, overdispersion parameters were adjusted and the quasi‐likelihood AIC was calculated for each candidate model (Halfyard et al ., 2013).…”

“…Cormack Jolly Seber mark-recapture models (CJS) for live recaptures (Cormack, 1964;Jolly, 1965;Larocque et al, 2020;Seber, 1965) have been used in acoustic telemetry to estimate both migration success (S) of the target species and the detection efficiency of acoustic receivers (p) (Halfyard et al, 2013;Kocik et al, 2009;Larocque et al, 2020).…”

“…CJS models were fitted separately for River Endrick combined and Gryffe post-smolts as River Gryffe post-smolts had a farther distance to travel to reach the first monitoring line (Figure 1, D) in comparison to River Endrick combined post-smolts.The additional covariates included in the model assessing the probability of migration success included release site (for River Endrick combined only), monitoring line (C,D,E), FL and to test for potential tagging effects on survival tag burden was included(Halfyard et al, 2013). Monitoring line (C,D,E) was the only covariate tested against detection efficiency (p)(Larocque et al, 2020).Goodness of fit of the global model (b c) was tested prior to model selection using the bootstrapping method (n = 1000 simulations) to calculate the overdispersion parameter of the global model as discussed in Laroque et al…”

American mink (Neovison vison) preying on hatchery and wild brown trout (Salmo trutta) juveniles in semi‐natural streams

“…Hatchery fish are typically raised to large sizes as larger fish have higher survival rates in the wild (the bigger is better hypothesis; Sogard, 1997). However, hatchery reared salmonids have lower survival rates in the wild compared to their wild counterparts or to fish raised in enriched environments (Einum & Fleming, 2001; Hyvärinen & Rodewald, 2013; Larocque et al., 2020). One major reason for lower survival in the wild is that stocked individuals have not been raised in environments that stimulate predator avoidance behaviours (Mes et al., 2019; Olla et al., 1998), and they are thus heavily preyed upon (Alioravainen et al., 2018; Berejikian, 1995; Einum & Fleming, 2001).…”

Global trends in aquatic animal tracking with acoustic telemetry

“…In particular, the proliferation of salmon (Salmonidae) fisheries and eel (Anguillidae) conservation along the west coast of North America and in freshwater European systems, respectively (Figure 3B), has necessitated a more comprehensive understanding of migration across different life stages. Not only has AT research identified key movement corridors [21] it has also been instrumental in estimating survival rates along different segments of migration routes, contributing to more adaptive resource planning [8,38].…”