Marine migrations in anadromous brown trout (Salmo trutta). Fjord residency as a possible alternative in the continuum of migration to the open sea

Abstract

Technical University of Denmark, National Institute of Aquatic Sciences, Vejlsøvej 39; 8600; Silkeborg, Denmark.ABSTRACT. Partial migration is a common phenomenon in many fish species. Trout (Salmo trutta) is a partially migratory species where some part of the population migrate to the marine environment, while another remains in freshwater.In the years 2008 and 2009, a total of 159 wild sea trout smolts were tagged with acoustic and PIT tags in the river Villestrup (Denmark) to study the initial post-smolt marine behaviour within a fjord system. We found that the strategies of the sea migrants vary: some stay in the fjord while others migrate to the sea suggesting that partial migration occurs even in the marine environments.Overall, a total of 53 %of the tagged smolts migrated from the fjord to the sea, and 47 % stayed (or potentially died) in the fjord. The ratios of fjord-resident vs. sea-migrating post-smolts were consistent at the study times and no differences between the early and late migration periods of the smolts were observed. The individual's size or body condition at the time of tagging did not affect survival or the migratory decisions in the fjord. High overall initial survival (74%) was found 30 days after the fjord entry. We suggest that within a continuum of migration to sea, there is a migratory decision point when sea trout post-smolts encounter a fjord system. At this point, post-smolts will assess the possibility of migration versus the alternative of fjord residency. AbstractPartial migration is a common phenomenon in many fish species. Trout (Salmo trutta) is a partially migratory species where some part of the population migrate to the marine environment, while another remains in freshwater. 2/28In the years 2008 and 2009, a total of 159 wild sea trout smolts were tagged with acoustic and PIT tags in the river Villestrup (Denmark) to study the initial post-smolt marine behaviour within a fjord system. We found that the strategies of the sea migrants vary: some stay in the fjord while others migrate to the sea suggesting that partial migration occurs even in the marine environments.Overall, a total of 53 %of the tagged smolts migrated from the fjord to the sea, and 47 % stayed (or potentially died) in the fjord. The ratios of fjord-resident vs. sea-migrating post-smolts were consistent at the study times and no differences between the early and late migration periods of the smolts were observed. The individual's size or body condition at the time of tagging did not affect survival or the migratory decisions in the fjord. High overall initial survival (74%) was found 30 days after the fjord entry. We suggest that within a continuum of migration to sea, there is a migratory decision point when sea trout post-smolts encounter a fjord system. At this point, post-smolts will assess the possibility of migration versus the alternative of fjord residency.

Potential of a no‐take marine reserve to protect home ranges of anadromous brown trout (Salmo trutta)

“…In contrast to our findings, an earlier study found that low body condition correlated with increased migration distance in sea trout, potentially for the purpose of maximizing feeding opportunities (Eldøy et al, 2015). Furthermore, home range size has been shown not to correlate with size for trout (Závorka, Aldvén, Näslund, Höjesjö, & Johnsson, 2015), and it has also been shown that migratory decisions in the fjord are not affected by size (del Villar-Guerra et al, 2014). Furthermore, home range size has been shown not to correlate with size for trout (Závorka, Aldvén, Näslund, Höjesjö, & Johnsson, 2015), and it has also been shown that migratory decisions in the fjord are not affected by size (del Villar-Guerra et al, 2014).…”

“…In addition, there is great variation in habitat use in marine regions, with some sea trout spending most of their time in fjords and some venturing out to the open seas (Bordeleau et al, 2018;del Villar-Guerra, Aarestrup, Skov, & Koed, 2014). Decisions made regarding staying in fjord habitats or moving to the open sea are made shortly after entering the fjord (del Villar-Guerra et al, 2014). Decisions made regarding staying in fjord habitats or moving to the open sea are made shortly after entering the fjord (del Villar-Guerra et al, 2014).…”

Comparison of vegetable shortening and cocoa butter as vehicles for cortisol manipulation in Salmo trutta

“…The stream runs for several km across agricultural land, where a number of tributaries join in before reaching the Mariager Fjord (56 ∘ 40 ′ N; 10 ∘ 00 ′ W). The stream is home to a large population of semi-anadromous S. trutta (del Villar-Guerra et al, 2014). Three different sites (1-2 km apart) within the same stream were used.…”

Extending the 2% rule: the effects of heavy internal tags on stress physiology, swimming performance, and growth in brook trout

“…Historically, acoustic tags have been fairly large, which has limited the use of this technology to larger species or adult life stages; however, advances in miniaturization and battery technology have permitted tag manufacturers to create functional tags as small 5 mm diameter and 12 mm in length, weighing 0.65 g (for example, V5, VEMCO, Bedford, Nova Scotia, Canada). These advances have permitted researchers to use acoustic telemetry on earlier life stages such as sub-yearling salmonids [15,16] and smolts [16][17][18].…”