Diverse and changing use of the Salish Sea by Pacific salmon, trout, and char

Each year, juveniles of eight salmonid species enter the Salish Sea - the inland marine waters between northwestern Washington, USA and British Columbia, Canada. These species vary in the proportions remaining there and migrating to feed in the Pacific Ocean. Such differential migration affects their growth rates, and exposure to habitat alteration, predators, fisheries, and contaminants. We review these diverse migration patterns and present data from Puget Sound illustrating the variation in downstream migration timing, residency in the Salish Sea, and upriver return timing. Recreational catch records indicate that proportionally fewer remain in the Salish Sea than in past decades for several species, and the declines began after peaks in the late 1970s – early 1980s. These declines resist easy explanation because the factors controlling residency are poorly understood, and the Salish Sea has changed over the past decades. Regardless of the cause, the diversity of migration patterns is important to the ecology of the salmon and trout species, and to the humans and other members of the Salish Sea community with which they interact.

Eel (Anguilla spp.) fishing activity in Poso Area Central Sulawesi, Indonesia

Poso in Sulawesi, primarily the Lake Poso and Poso River, is known as eel (Anguilla spp.) fishing areas. Therefore, research of eel fishing is required as base information for evaluating and determining policies for its activities. The eel fishing research in the Poso area was conducted through primary data observations, secondary data traces, and interviews from April to June 2021. The fishing activities take place in the Lake Poso and Poso River shore and the rivers of the lake inlets. The fishing gear that contributed greatly to the catch was fence traps and spears. The local community’s fence trap called waya is a unique gear only found in this area, and it is installed in Poso River around the lake outlets. The gears block the rivers to catch downstream migration eels. The spear is fishing gear (including for eels) operated at night in shallow waters, especially in the outlets of Lake Poso. The eel production recorded from the Poso areas for the last four years has been 6.7–15.5 tons per year, and the highest production was in Pamona Puselemba.

Characterization of feeding and downstream migration of juvenile chum salmon in the Kichiga river (north-eastern kamchatka)

Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.

Joint temporal trends in river thermal and hydrological conditions can threaten the downstream migration of the critically endangered European eel

Climate change is modifying the hydrological and thermal regimes of rivers worldwide, threatening the triggering of organisms’ key life-cycle processes. European eel (Anguilla anguilla) is a critically endangered fish species that migrates over several thousand kilometres between its rearing habitats in continental waters of Europe and North Africa and its spawning area in the Sargasso Sea. Downstream migration of adult eels occurs during periods of decreasing river water temperature associated with high discharge but changes in these environmental cues may affected eel migratory conditions. An innovative multivariate method was developed to analyse long-term datasets of daily water temperature, discharge and eel passage in two European rivers. Over the past 50 years, water temperature and discharge increased in both rivers during the downstream migration period from August to November. Silver eels preferentially migrated at temperatures between 10 and 20 °C combined with high discharge. Environmental changes have resulted in the migration of silver eels under warmer water temperatures. This example illustrates how the changes in environmental cues have led to a growing mismatch between the migratory conditions preferentially selected and those actually used, which may threaten the completion of the eel’s life cycle and ultimately the persistence of this already critically endangered species.

Validation of a Swimming Direction Model for the Downstream Migration of Atlantic Salmon Smolts

Fish swimming performance is strongly influenced by flow hydrodynamics, but little is known about the relation between fine-scale fish movements and hydrodynamics based on in-situ investigations. In the presented study, we validated the etho-hydraulic fish swimming direction model presented in the River Mandal from Southern Norway, using similar behavioral and hydraulic data on salmon smolts from the River Orkla in Central Norway. The re-parametrized model explained the variation of the swimming direction of fish in the Orkla system in same degree as the original model performed in the Mandal system (R2: 84% in both cases). The transferability of the model when using it from one river to predict swimming direction in the other river was lower (R2: 21% and 26%), but nevertheless relatively high given that the two localities differed in hydraulic conditions. The analyses thus provide support for the fact that the identified hydraulic parameters and their interaction affected smolt behavior in a similar way at the two sites, but that local parametrization of the base model is required. The developed etho-hydraulic models can provide important insights into fish behavior and fish migration trajectories and can be developed into prediction models important for the future development of behavioral downstream migration solutions.

Fishways as Downstream Routes in Small Hydropower Plants: Experiences with a Potamodromous Cyprinid

Fish need to move upstream and downstream through rivers to complete their life cycles. Despite the fact that fishways are the most commonly applied solution to recover longitudinal connectivity, they are not considered viable for downstream migration. Therefore, alternative facilities are recommended to facilitate downstream migration. However, a few recent studies have disagreed with this general assumption, showing the potential for bidirectional movements. This study advances our understanding of the potential of fishways for downstream migration by studying their efficiency in a run-of-the-river hydropower plant in the Duero River (Spain). To achieve this, downstream movements of the Iberian barbel (n = 299) were monitored in a stepped fishway for two years with passive integrated transponder (PIT)-tag technology, considering the effect of fish origin and release zone. The results showed that 24.9% of barbels descended through the fishway, with the origin and release zone affecting the fishway location. In addition, downstream movements were observed throughout the whole year, except in winter. The study concludes that, under specific scenarios, fishways could act as safe alternative routes for downstream migration.