As fish move, they incur an energetic cost of transport (COT) from the use of aerobic muscles. Water currents are an integral component of the physical world of fishes, and if water currents are present, fish may pay higher costs fighting the currents, or may use the currents to facilitate movement and reduce COT. Some fish use “selective tidal stream transport” (STST) to move efficiently through tidal regions, swimming into the water column when the current is favorable, and returning to the bottom during opposing tides. This behavior has been reported in marine fish migrating through tidal habitats, but it is also likely of value in daily movements of fish residing in those habitats. It is extremely difficult to directly measure COT in wild fish; however, it is possible to combine analysis of field telemetry data of individual swimming efforts and measurements of metabolic costs of swimming from respirometry in order to estimate the COT in the wild, and to calculate the costs or savings of swimming with or against currents. We describe this novel analytical approach and demonstrate it using data from two green sturgeon tracked in San Francisco Bay, California. In this analysis, when moving at the surface and employing STST, the fish benefited from the current, swimming within 85.5% of optimal efficiency. When conducting non-STST movements near the bottom, swimming was less efficient, with a COT similar to swimming directly into the current. These results suggest that green sturgeon may opportunistically utilize stream transport in daily movements, swimming at the surface and orienting with currents to achieve substantial energetic savings.

中文翻译：

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估计通过选择性潮汐传输移动绿鲟的能量节省

当鱼移动时，它们会因使用有氧肌肉而产生能量运输成本 (COT)。水流是鱼类物理世界的一个组成部分，如果存在水流，鱼可能会付出更高的成本来对抗水流，或者可能使用水流来促进运动并降低 COT。一些鱼使用“选择性潮汐流传输”（STST）来有效地穿过潮汐区域，在水流有利时游入水体，并在逆潮时返回底部。这种行为在通过潮汐栖息地洄游的海洋鱼类中已有报道，但它也可能对栖息在这些栖息地的鱼类的日常运动有价值。直接测量野生鱼类的 COT 极其困难；然而，可以将个人游泳努力的现场遥测数据分析与呼吸测量法对游泳代谢成本的测量结合起来，以估计野外的 COT，并计算顺流或逆流游泳的成本或节省。我们描述了这种新颖的分析方法，并使用在加利福尼亚州旧金山湾追踪的两条绿色鲟鱼的数据进行了演示。在该分析中，当在水面移动并使用 STST 时，鱼受益于水流，在最佳效率的 85.5% 内游动。在靠近底部进行非 STST 运动时，游泳效率较低，COT 类似于直接游泳到水流中。这些结果表明，绿鲟可能会在日常活动中机会性地利用河流运输，