Sea Trout, Essential Facts, and Significance!
The brown trout, Salmo trutta, is a prominent salmonid species with a wide distribution across Northern and Western Europe, spanning from the White Sea to the Mediterranean and encompassing the entire Baltic Sea region. The anadromous form of brown trout, known as the sea trout, has a latitude from northern Scandinavia to northern Africa. Sea trout migrates from its native river or streams to the sea, where it forages until reaching sexual maturity, and then returns to its home river for spawning.
Sea trout differ from their close relatives, the salmon, in that sea trout are found in smaller streams and tributaries to larger rivers along the entire coast, and exhibit a more complex life history. It does not migrate as much as salmon and spends most of its life cycle in the sea and coastal waters. However, it’s worth noting that certain populations of sea trout, especially those in the southern Baltic, undertake longer migrations to reach open waters.
The migration patterns of sea trout populations exhibit diversity. Some adult fish remain within their river environment throughout their life cycle, while adults in other populations make feeding migrations to coastal sea areas, where they feed on invertebrates and small fish.
Sea trout, as predatory fish, play a structural role in ecosystem dynamics, particularly through top-down control at the lower trophic levels. They hold significant ecological, social, and economic importance for local communities across Northern Europe. Sea trout support important fisheries and encourage river conservation efforts. Sea trout play an important role in maintaining equilibrium within riverine food webs. They achieve this by both harvesting invertebrate populations and serving as a crucial food source for other predatory species. Additionally, sea trout contribute to both aquatic and terrestrial ecosystems by facilitating the transport of nutrients and energy from the sea to the lotic ecosystem.
In the life cycle of sea trout, individuals live as parr in streams for the initial 1 to 5 years of their lives. Following this period, parr undergoes smoltification, adopting a silver appearance and acquiring the physiological adaptations required for marine life. Subsequently, they embark on migrations to the sea, where they spend up to 5 years feeding, primarily on forage fish, before returning to their native streams for spawning. They exhibit a preference for smaller rivers and streams with swift currents, often selecting upper reaches and tributaries that provide suitable nursery areas. Spawning occurs during the autumn and winter months, with each female typically laying around 10,000 eggs in well-suited gravel beds. These eggs hatch in the spring, contingent on suitable water temperatures.
Sea trout is one of the two most important salmonids in the Baltic Sea. Despite the historical significance of sea trout in this region, it faces challenges. Currently classified as vulnerable in the Baltic Sea, there are only 500 remaining natural populations. Urgent measures are required to restore sea trout stocks and river conditions, given the impact of past management practices. To achieve this, it is crucial to gather data on river status and sea trout population. This information aids in comprehending the present state, understanding past trends, and formulating plans for future actions. Sea trout have historically ranked second only to Atlantic salmon in national fisheries assessment programs and management priorities. As sea trout and other dispersed fish species fall under EU policy areas, such as the Common Fisheries Policy (CFP) and the Marine Strategy Framework Directive (MSFD), it becomes imperative to enhance methods for assessing and monitoring stock status. This holistic approach ensures the conservation and sustainable management of this valuable species in the Baltic Sea and beyond.
Written by Ali Khari, Master’s student with the SEG.
Ali is currently a second-year master’s student in biology at the Department of Biological and Environmental Sciences at the University of Gothenburg. Currently, under the supervision of Johan Höjesjö and in the cooperation of ICES WGTRUTTA, he is undertaking his master’s thesis, which focuses on exploring the impact of various human factors on sea trout populations in different European countries. His aim in this thesis is to assess the impact of various anthropogenic pressures such as Fisheries, Habitat Degradation, Barriers, Climate Change, etc. on the Sea Trout recruitment index in different regions.