Marine depth use of sea trout Salmo trutta in fjord areas of central Norway

Abstract

The vertical behaviour of 44 veteran sea trout Salmo trutta (275-580 mm) in different marine fjord habitats (estuary, pelagic, near shore with and without steep cliffs) was documented during May-February by acoustic telemetry. The swimming depth of S. trutta was influenced by habitat, time of day (day v. night), season, seawater temperature and the body length at the time of tagging. Mean swimming depth during May-September was 1·7 m (individual means ranged from 0·4 to 6·4 m). Hence, S. trutta were generally surface oriented, but performed dives down to 24 m. Mean swimming depth in May-September was deeper in the near-shore habitats with or without steep cliffs (2·0 m and 2·5 m, respectively) than in the pelagic areas (1·2 m). May-September mean swimming depth in all habitats was slightly deeper during day (1·9 m) than at night (1·2 m), confirming that S. trutta conducted small-scale diel vertical movements. During summer, S. trutta residing in near-shore habitat progressively moved deeper over the period May (mean 1·1 m) to August (mean 4·0 m) and then reoccupied shallower areas (mean 2·3 m) during September. In winter (November and February), individuals residing in the innermost part of the fjords were found at similar average depths as they occupied during the summer (mean 1·3 m). The swimming depths of S. trutta coincide with the previously known surface orientation of salmon lice Lepeophtheirus salmonis. Combined with previous studies on horizontal use of S. trutta, this study illustrates how S. trutta utilize marine water bodies commonly influenced by anthropogenic factors such as aquaculture, harbours and marine constructions, marine renewable energy production or other human activity. This suggests that the marine behaviour of S. trutta and its susceptibility to coastal anthropogenic factors should be considered in marine planning processes.

Environmental influences on life history strategies in partially anadromous brown trout (Salmo trutta, Salmonidae)

“…Trout from streams with low water level during winter may migrate to a neighbouring watercourse for overwintering (Aldvén & Davidsen, 2017) or stay in marine waters (Eldøy et al, 2017;Olsen et al, 2006). Trout from streams with low water level during winter may migrate to a neighbouring watercourse for overwintering (Aldvén & Davidsen, 2017) or stay in marine waters (Eldøy et al, 2017;Olsen et al, 2006).…”

“…In northern Europe, immature trout can also return to freshwater in summer after a short stay at sea. Ionoregulation in sea water at low temperature is arduous, but anadromous trout have been observed at sea during winter and tolerate full salinity seawater at temperatures as low as 1-2°C (Eldøy et al, 2017;Knudsen et al, 2009;Olsen, Knutsen, Simonsen, Jonsson, & Knutsen, 2006). In the brackish Baltic Sea, parr can migrate from freshwater to the Baltic coastal zone without undergoing smolting.…”

“…This pattern resembles the strategy followed by some Pacific salmonids, such as pink salmon (Oncorhynchus gorbuscha, Salmonidae) and chum salmon (Oncorhynchus keta, Salmonidae), which both start their seaward migration early in life. Trout from streams with low water level during winter may migrate to a neighbouring watercourse for overwintering (Aldvén & Davidsen, 2017) or stay in marine waters (Eldøy et al, 2017;Olsen et al, 2006).…”

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

“…Previously, low biodiversity has been observed at sampling stations in Zone 2, close to the border between Zone 1 and 2, indicating a reduced selection of prey for sea trout in this habitat (Kroglund, Dahl, & Oug, 1998). Salmonids have shown great differences in movement rates contrasting day and night (Alanärä, Burns, & Metcalfe, 2001;Candy & Quinn, 1999;Eldøy et al, 2017;Goetz, Baker, Buehrens, & Quinn, 2013), and it has been shown for steelhead trout (Oncorhynchus mykiss) that horizontal movement rates increase twofold during daylight compared to night in the marine habitat (Ruggerone, Quinn, Mcgregor, & Wilkinson, 1990). There were significantly more excursions from the reserve during day than night, implying greater horizontal movement during day.…”

The influence of aquaculture unit proximity on the pattern of Lepeophtheirus salmonis infection of anadromous Salmo trutta populations on the isle of Skye, Scotland

“…As a result of its cultural and economic importance, considerable previous research has focused on the challenges facing S. salar populations (Limburg & Waldman, 2009). In contrast, considerably less attention has been given to the causes of decline of S. trutta (Drenner et al, 2012;Eldøy et al, 2017;Glover et al, 2017).…”