![]() ![]() Armstrong et al., 2018 Millane et al., 2019 Nielsen et al., 2020). A secondary spread has resulted in regular spawning of pink salmon in rivers close to the Russian border in northern Norway in recent years (Berntsen et al., 2020 Niemelä, 2016 Sandlund et al., 2019).įrom 2017, the abundance and distribution of invasive pink salmon in Norway increased dramatically (Sandlund et al., 2019 Berntsen et al., 2020, NINA, unpublished data), while also spreading to numerous rivers in other countries draining into the North Atlantic Ocean, including Sweden, Denmark, the United Kingdom, Ireland, Iceland, Germany, France, the Faroe Islands and Greenland ( e.g. ![]() With an aim to establish a fishery resource, it was purposely introduced to rivers in the White Sea area in north-west Russia, which has resulted in the establishment of self-sustaining populations (Sandlund et al., 2019). Pink salmon ( Oncorhynchus gorbuscha) is an anadromous salmonid originating in the North Pacific. Their impact on native biodiversity is associated with predation, competition, hybridization, energy transfer and transfer of parasites and diseases. Invasive alien species are among the most prominent threats to native biodiversity and ecosystems (Pejchar & Mooney, 2009 Rahel, 2002). Hence, late summer and early autumn was likely an important period for marine growth and survival in the invasive pink salmon. Scale growth during late summer and early autumn explained more of the variation in fish length at spawning (27%). If mortality is selective, removing fish with poor growth may reduce a correlation between early growth and body size at spawning. The reason for this may be large individual variation in growth combined with large mortality during the first weeks at sea. When dividing scale growth into three periods, better growth during the first period at sea was related to increased fish body length at spawning, but this early growth explained only a minor part (6%) of the variation in final body length. Fish body size at spawning was positively correlated with the distance from scale focus to the last winter circulus, as well as with the number of circuli. Growth declined to a minimum during winter. This was followed by a period of growth increase and stability during late summer and autumn, which may reflect a transition to better food sources, as the fish migrate from coastal waters to the open ocean, and as they grow larger and can eat larger and more energy efficient food items. Analysis of pink salmon scales from two rivers draining to the western Barents Sea showed declining growth during the first weeks after entering the sea, and some individuals even showed a pronounced growth arrest, based on detailed scale circulus analyses. 1960, but beginning in 2017 their numbers have exploded in rivers in northern Norway, with considerable numbers also recorded in rivers in southern Norway and other countries bordering the North Atlantic. Invasive pink salmon ( Oncorhynchus gorbuscha) has been present in variable, but low, numbers in Norwegian waters since c. ![]()
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