Investigating patterns of straying and mixed stock exploitation of sea trout, Salmo trutta, in rivers sharing an estuary in south‐west England

Abstract

Fisheries Management and EcologyFor effective management, information on the stock composition of a fishery is essential. 5Here, we highlight the utility of a resident trout microsatellite baseline to determine the 6 origins of sea trout entering the Rivers Tamar, Tavy and Lynher in southwest England -all 7 share a common estuary and have major runs of sea trout. There is a high degree of 8 geographical structuring of the genetic variation in the baseline rivers. Testing with simulated 9 and real datasets showed fish can be assigned to reporting group with a high degree of 10 accuracy. Mixed stock analysis of over 1000 sea trout showed that fish entering the Tamar 11 and Tavy constituted mixed stocks. Significantly, in the Tamar, non-natal origin sea trout are 12 restricted to the lower catchment. As well as providing insight into sea trout behaviour, this 13 study also has important implications for the management of recreational rod-and-line 14 The perceived wisdom is that anadromous species such as salmon and trout, after spending 22 time feeding at sea, return to their natal river to spawn. This homing fidelity can lead to 23 reduced gene flow between rivers and gives rise to the strong genetic structure found in many 24 salmonid species (Dionne et al. 2008; Lohmann et al. 2008). 25 26 However, straying is known to occur and is thought to be an important evolutionary feature of 27 salmonids, playing an adaptive role over both short and long time scales. Straying is 28 especially important in colonization, re-colonization and range expansion (Quinn 1984; 29 Tallman 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Rivers' and as such is subject to intensive monitoring programmes in order to develop an 74 understanding of salmonid stock and fishery processes, and to improve the wider management 75 of sea trout and salmon. The Tamar monitoring programme includes extensive juvenile 76 electrofishing surveys, the trapping and tagging of smolts during their spring migration and 77 the trapping of returning adults in a trap immediately below a fish pass adjacent to a weir at 78 the tidal limit of the river (Gunnislake). Harris (2006) has provided a detailed description of 79 the rod-caught sea trout stock within the River Tamar. Tamar sea trout typically smolt after 80 two years in the river. The majority of the rod catch represents fish that returned to the river in 81 the same year that they smolted (known variously as school peal, finnock or whitling). Of the 82 repeat spawning fish, some were found to have spawned up to four times, however, the 83 majority had only a single spawning mark (Harris 2006). There is also temporal variation in 84 the composition of the sea trout run -multiple spawning fish enter the river early in the year, 85 while finnock start to return in July. 86 87 to increase sample size, fry were collected from some ...

Water level influences migratory patterns of anadromous brown trout in small streams

“…Instead, they appeared to stay the winter at sea, in estuaries or in some cases in another river according to recaptures of tagged fish, as also reported from some other studies (King et al, 2016;Knutsen et al, 2004;Olsen et al, 2006). Instead, they appeared to stay the winter at sea, in estuaries or in some cases in another river according to recaptures of tagged fish, as also reported from some other studies (King et al, 2016;Knutsen et al, 2004;Olsen et al, 2006).…”

“…However, runs of that size appear adequate to maintain viable populations of anadromous brown trout, as reported by Thomson and Lyndon (2018) from the Orkney, UK. Anadromous trout sometimes visit lower parts of rivers other than their home stream (Euzenat, 1999;Jensen et al, 2015;King et al, 2016;Masson et al, 2018;Solomon, 2006). The effective straying rate, however, may be low as immature first-time migrants tend to enter other streams more often than the mature veteran migrants do.…”

“…Degerman et al (2012) reported straying rates between 3% and 43% among Swedish populations of anadromous brown trout, with 16% as the average figure, but few of the strays may actually leave offspring (Masson, Lepais, Manicki, Prévost, & Chat, 2018). In addition, a part of the reported strays may just spend time in foreign watercourses, to feed or avoid adverse environmental conditions (King, Hillman, Elsmere, Stockley, & Stevens, 2016). In addition, a part of the reported strays may just spend time in foreign watercourses, to feed or avoid adverse environmental conditions (King, Hillman, Elsmere, Stockley, & Stevens, 2016).…”

Modeling fitness changes in wild Atlantic salmon populations faced by spawning intrusion of domesticated escapees

“…Within regions displaying a mosaic of small and large populations, straying and the degree of genetic connectivity may be skewed, whereby large populations can act as net‐exporters of strayers to smaller neighboring wild populations (Hansen, Skaala, Jensen, Bekkevold, & Mensberg, ). Straying of wild fish between rivers (Stabell, ) also varies in time and space for Atlantic salmon (Jonsson & Jonsson, ; Jonsson et al., ; Pedersen et al., ; Skilbrei & Holm, ) and other salmonids (Bett, Hinch, Burnett, Donaldson, & Naman, ; Ford, Murdoch, & Hughes, ; King, Hillman, Elsmere, Stockley, & Stevens, ). Recent experimental work has also indicated that introgression of domesticated salmon may increase straying rates in impacted wild Atlantic salmon populations (Jonsson & Jonsson, ).…”

Telemetry and genetics reveal asymmetric dispersal of a lake‐feeding salmonid between inflow and outflow spawning streams at a microgeographic scale

“…However, interrupted or imperfect imprinting during rearing or juvenile migration can increase straying rates (Keefer & Caudill, ). There also appear to be genetically based differences across populations in straying rates and distances (Jonsson & Jonsson, , ; Keefer & Caudill, ; King, Hillman, Elsmere, Stockley, & Stevens, ), with selection thought to favor higher straying when habitat quality or quantity fluctuates unpredictably through time (Hendry et al, ; Quinn & Tallman, ).…”