Jonsson B, Jonsson N, Albretsen J
Norwegian Institute for Nature Research, Landscape Ecology Department, Gaustadalléen 21, 0349 Oslo, Norway.
Institute of Marine Research, Flødevigen Research Station, Nye Flødevigveien 20, 4817 His, Norway.
J Fish Biol. 2016 Feb;88(2):618-37. doi: 10.1111/jfb.12854. Epub 2016 Jan 3.
Annual mean total length (LT) of wild one-sea-winter (1SW) Atlantic salmon Salmo salar of the Norwegian River Imsa decreased from 63 to 54 cm with a corresponding decrease in condition factor (K) for cohorts migrating to sea from 1976 to 2010. The reduction in LT is associated with a 40% decline in mean individual mass, from 2 to 1·2 kg. Hatchery fish reared from parental fish of the same population exhibited similar changes from 1981 onwards. The decrease in LT correlated negatively with near-surface temperatures in the eastern Norwegian Sea, thought to be the main feeding area of the present stock. Furthermore, S. salar exhibited significant variations in the proportion of cohorts attaining maturity after only one winter in the ocean. The proportion of S. salar spawning as 1SW fish was lower both in the 1970s and after 2000 than in the 1980s and 1990s associated with a gradual decline in post-smolt growth and smaller amounts of reserve energy in the fish. In wild S. salar, there was a positive association between post-smolt growth and the sea survival back to the River Imsa for spawning. In addition, among smolt year-classes, there were significant positive correlations between wild and hatchery S. salar in LT, K and age at maturity. The present changes may be caused by ecosystem changes following the collapse and rebuilding of the pelagic fish abundance in the North Atlantic Ocean, a gradual decrease in zooplankton abundance and climate change with increasing surface temperature in the Norwegian Sea. Thus, the observed variation in the life-history traits of S. salar appears primarily associated with major changes in the pelagic food web in the ocean.
挪威伊姆萨河野生一龄海生（1SW）大西洋鲑（Salmo salar）的年平均全长（LT）从63厘米降至54厘米，1976年至2010年洄游入海的鱼群的条件系数（K）也相应下降。全长的减少与平均个体体重下降40%有关，从2千克降至1.2千克。1981年起，用同一群体亲鱼培育的孵化场养殖的鱼也出现了类似变化。全长的减少与挪威东部海域近表层温度呈负相关，该海域被认为是当前种群的主要摄食区。此外，大西洋鲑在海洋中仅度过一个冬季后达到成熟的鱼群比例存在显著差异。20世纪70年代和2000年之后，作为一龄海生鱼产卵的大西洋鲑比例低于20世纪80年代和90年代，这与洄游后幼鱼生长逐渐下降以及鱼体内储备能量减少有关。在野生大西洋鲑中，洄游后幼鱼生长与返回伊姆萨河产卵的海洋存活率之间存在正相关。此外，在幼鱼年份组中，野生和孵化场养殖的大西洋鲑在全长、条件系数和成熟年龄方面存在显著正相关。目前的变化可能是由北大西洋中上层鱼类数量崩溃和重建后的生态系统变化、浮游动物数量逐渐减少以及挪威海表层温度上升的气候变化引起的。因此，观察到的大西洋鲑生活史特征的变化似乎主要与海洋中上层食物网的重大变化有关。
