The productivity of Fraser River sockeye salmon has declined in recent years, with 2019 being the lowest return on record. The cause of the decline is still not fully understood; however, bottom‐up drivers and trophic interactions during the early marine migration are considered to be important contributing factors. McKinnell et al. (Fisheries Oceanography, 23, 2014 and 322) developed a “trophic gauntlet hypothesis,” proposing that low biological productivity leads to an energy deficit from poor foraging opportunities in migrating salmon. When combined with poor foraging conditions in typically productive waters elsewhere on the migration, low marine survival may result. Our study examined prey availability and stomach fullness of juvenile sockeye salmon along the 120 km stretch of the coastal migration through the Discovery Islands and Johnstone Strait to determine whether this section of the migration is indeed food limited. We observed low stomach fullness throughout tidally mixed waters, providing empirical support for the trophic gauntlet hypothesis. Zooplankton abundance was high in these regions so it appeared that unfavourably small prey size may have been the cause of low foraging success. We also observed foraging hotspots at both ends of the gauntlet, indicating that such areas may be key feeding grounds for migratory salmon.

中文翻译：

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运行营养措施：减少潮汐混合沿海水域幼鲑觅食成功的经验支持

近年来，弗雷泽河红鲑鲑的生产力下降，2019年是有记录以来的最低回报。下降的原因仍不完全清楚；然而，早期海洋迁移过程中自下而上的驱动因素和营养相互作用被认为是重要的促成因素。McKinnell等。（Fisheries Oceanography，2014年第23期，第322页）提出了“营养性手套挑战假说”，认为生物生产力低下会导致鲑鱼觅食机会不足，导致能量短缺。如果再加上迁徙其他地方通常在生产性水域中较差的觅食条件，则可能导致海洋生存率低下。我们的研究检查了通过发现岛和约翰斯通海峡进行的沿海迁徙的120 km沿线幼体红鲑鱼的猎物可用性和胃部饱腹感，以确定这部分迁徙是否确实在食物上受到限制。我们在潮汐混合水中观察到胃部饱满度低，为营养性手套的假说提供了经验支持。在这些地区浮游动物的丰度很高，因此看来猎物尺寸过小可能是导致觅食成功率低的原因。我们还观察到了铁手套两端的觅食热点，这表明这些地区可能是迁徙鲑鱼的主要觅食地。为营养性手套的假说提供经验支持。在这些地区，浮游动物的丰度很高，因此看来猎物尺寸过小可能是导致觅食成功率低的原因。我们还观察到了铁手套两端的觅食热点，这表明这些地区可能是迁徙鲑鱼的主要觅食地。为营养性手套的假说提供经验支持。在这些地区，浮游动物的丰度很高，因此看来猎物尺寸过小可能是导致觅食成功率低的原因。我们还观察到了在铁手套两端的觅食热点，这表明这些地区可能是迁徙鲑鱼的主要觅食地。