Norwegian Institute for Nature Research, Tungasletta 2, NO-7485 Trondheim, Norway.
J Fish Biol. 2009 May;74(7):1532-48. doi: 10.1111/j.1095-8649.2009.02219.x.
The abundance of returning adult Atlantic salmon Salmo salar, in the River Orkla in mid-norway (1 sea-winter, SW, fish) and River Hals in north Norway (1-3 SW fish), was tested against the early marine feeding and the seawater temperature experienced by their corresponding year classes of post-smolts immediately after entry into the Trondheimsfjord (Orkla smolts, 22 years of data) and Altafjord (Hals smolts, 17 years of data). In both river-fjord systems, there was a significant positive correlation between the abundance of returning S. salar and the mean seawater temperature at the time of smolts descending to the sea. The number of 1SW fish reported caught in River Orkla was positively correlated to the proportion of fish larvae in the post-smolt stomachs in Trondheimsfjord. The abundance of returning S.salar was, however, neither correlated to forage ratio (R(F)) nor other prey groups in post-smolt stomachs in the two fjord systems. In the Altafjord, the post-smolts fed mainly on pelagic fish larva (70-98%) and had a stable R(F) (0.009-0.023) over the 6 years analysed. In the Trondheimsfjord, however, there was a higher variation in R(F) (0.003-0.036), and pelagic fish larvae were dominant prey in only two (50 and 91%) of the 8 years analysed. These 2 years also showed the highest return rates of S. salar in River Orkla. These results demonstrate that the thermal conditions experienced by post-smolts during their early sea migration may be crucial for the subsequent return rate of adults after 1-3 years at sea. Pelagic marine fish larvae seem to be the preferred initial prey for S. salar post-smolts. As the annual variation in abundance of fish larvae is related to seawater temperature, it is proposed that seawater temperature at sea entry and the subsequent abundance of returning adult S. salar may be indirectly linked through variation in annual availability of pelagic fish larvae or other suitable food items in the early post-smolt phase.
挪威中部奥尔克拉河（1 龄海化，SW 鱼）和北挪威哈尔斯河（1-3 龄海化，SW 鱼）洄游成年大西洋三文鱼（Salmo salar）的丰度与当年幼鱼进入特隆赫姆峡湾（奥尔克拉幼鱼，22 年数据）和阿尔塔峡湾（哈尔斯幼鱼，17 年数据）后立即经历的早期海洋摄食和海水温度进行了对比。在这两个河-峡湾系统中，洄游三文鱼的丰度与幼鱼下海时的海水平均温度呈显著正相关。报告在奥尔克拉河捕获的 1 龄 SW 鱼数量与幼鱼在特隆赫姆峡湾胃中鱼类幼体的比例呈正相关。然而，在这两个峡湾系统中，洄游三文鱼的丰度与幼鱼胃中的饵料比（R(F)）或其他猎物群均无相关性。在阿尔塔峡湾，幼鱼主要以浮游鱼类幼体（70-98%）为食，在 6 年的分析中，R(F)保持稳定（0.009-0.023）。然而，在特隆赫姆峡湾，R(F)的变化较大（0.003-0.036），浮游鱼类幼体仅在 8 年分析中的 2 年（50%和 91%）中占主导地位。这两年也是奥尔克拉河三文鱼洄游率最高的两年。这些结果表明，幼鱼在早期海洋洄游期间经历的热条件可能对 1-3 年海上生活后成年鱼的返回率至关重要。浮游海洋鱼类幼体似乎是三文鱼幼鱼的首选初始猎物。由于鱼类幼体的丰度年际变化与海水温度有关，因此有人提出，进入海洋时的海水温度以及随后返回的成年三文鱼的丰度可能通过浮游鱼类幼体或早期幼鱼阶段其他适宜食物的年度可获得性的变化而间接相关。
