An existing conceptual model that assessed the timing of and size at release of juvenile Japanese chum salmon in Japanese waters is modified using data obtained from young salmon collected in coastal waters off Kombumori, eastern Hokkaido, Japan. The early life histories of Tokachi River late-migrating chum salmon are estimated based on microstructural analysis of thermally marked otoliths from recaptured fish. A revised model is presented that reveals the optimal timing of and size at release of chum salmon juveniles to be dependent upon their size at sea entry and sea surface temperature (SST) near Tokachi River mouth. Juvenile salmon are assumed to grow at a fixed rate after sea entry and to reach a target fork length upon arrival in Kombumori waters when SST conditions are within a specific optimal range. However, because of annual variation in SST, the size at and timing of juvenile chum salmon sea entry following their release from hatcheries represents a moving target, which flexible hatchery release practices are required to meet. Return rates of adult chum salmon to Tokachi River correlate positively with the number of days elapsed between the period when SST is suitable near the river mouth where they enter the sea, and SST conditions in Kombumori waters, which suggests that in years when SST increases rapidly the survival of salmon tends to decline. Windows of optimal times of and sizes at release are proposed for juvenile chum salmon to improve their survival and hatchery success.

中文翻译：

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释放鲑鱼的最佳时机和大小：通过修改孵化场实践来提高生存率

使用从日本北海道东部 Kombumori 沿海水域收集的幼鲑鱼获得的数据，对评估日本水域中日本鲑鱼幼鱼释放时间和大小的现有概念模型进行了修改。十胜川晚期洄游鲑鱼的早期生活史是根据重新捕获的鱼的热标记耳石的微观结构分析估计的。提出了一个修改后的模型，该模型揭示了鲑鱼幼鱼释放的最佳时间和大小取决于它们在入海时的大小和十胜河口附近的海面温度 (SST)。假设幼鲑鱼在入海后以固定速率生长，并在 SST 条件处于特定最佳范围内时，在到达 Kombumori 水域时达到目标叉长。然而，由于 SST 的年度变化，幼鱼从孵化场放归后进入海洋的大小和时间代表了一个移动目标，需要灵活的孵化场放归实践来满足这一目标。成年鲑鱼返回十胜川的率与它们入海的河口附近适合海温的时期与小森水域海温条件之间经过的天数呈正相关，这表明在海温迅速增加的年份三文鱼的存活率趋于下降。建议为幼鱼鲑鱼提供最佳放归时间和大小的窗口，以提高它们的存活率和孵化成功率。需要满足哪些灵活的孵化场放归规范。成年鲑鱼返回十胜川的率与它们入海的河口附近适合海温的时期与小森水域海温条件之间经过的天数呈正相关，这表明在海温迅速增加的年份三文鱼的存活率趋于下降。建议为幼鱼鲑鱼提供最佳放归时间和大小的窗口，以提高它们的存活率和孵化成功率。需要满足哪些灵活的孵化场放归规范。成年鲑鱼返回十胜川的率与它们入海的河口附近适合海温的时期与小森水域海温条件之间经过的天数呈正相关，这表明在海温迅速增加的年份三文鱼的存活率趋于下降。建议为幼鱼鲑鱼提供最佳放归时间和大小的窗口，以提高它们的存活率和孵化成功率。这表明在 SST 迅速增加的年份，鲑鱼的存活率往往会下降。建议为幼鱼鲑鱼提供最佳放归时间和大小的窗口，以提高它们的存活率和孵化成功率。这表明在 SST 迅速增加的年份，鲑鱼的存活率往往会下降。建议为幼鱼鲑鱼提供最佳放归时间和大小的窗口，以提高它们的存活率和孵化成功率。