Abundance indices from scientific surveys are key stock assessment inputs, but when the availability of fish varies in space and time, the estimated indices and associated uncertainties do not accurately reflect changes in population abundance. For example, indices for many semi-pelagic species rely on acoustic and bottom trawl gear that differ in water column coverage, and so spatiotemporal trends in fish vertical distribution affect the availability of fish to each gear type. The gears together cover the whole water column, and so in principle allow estimation of more accurate, combined indices of the whole population. Here, we extend previous methods and develop a vertically integrated index, which accounts for spatiotemporal correlation and works with data unbalanced spatially or unpaired from distinct surveys. Using eastern Bering Sea walleye pollock (Gadus chalcogrammus) as an example, we identified clear spatial and temporal patterns in vertical distribution and gear availability from 2007 to 2018. Estimated acoustic annual vertical availability ranged from 0.339 to 0.888 among years, and from 0.588 to 0.911 for the bottom trawl survey. Our results highlight the importance of accounting for the spatiotemporal and vertical distribution of semi-pelagic fish to estimate more accurate indices, and provide important context for gear availability.

中文翻译：

---

在指数标准化中纳入垂直分布可解释半远洋物种声学和底拖网设备的时空可用性

来自科学调查的丰度指数是重要的种群评估输入，但当鱼类的可用性在空间和时间上发生变化时，估计的指数和相关的不确定性不能准确反映种群丰度的变化。例如，许多半远洋物种的指数依赖于水体覆盖范围不同的声学和底拖网渔具，因此鱼类垂直分布的时空趋势会影响每种渔具类型的鱼类可用性。这些齿轮一起覆盖了整个水柱，因此原则上可以对整个人口的综合指数进行更准确的估计。在这里，我们扩展了以前的方法并开发了一个垂直整合的指数，该指数考虑了时空相关性，并适用于空间不平衡或来自不同调查的不配对数据。以白令海东部鳕鱼 (Gadus chalcogrammus) 为例，我们确定了 2007 年至 2018 年垂直分布和渔具可用性的清晰时空模式。估计的年度声学垂直可用性在 0.339 到 0.888 之间，从 0.588 到 0.911用于底拖网调查。我们的结果强调了考虑半远洋鱼类的时空和垂直分布以估计更准确的指数并为渔具可用性提供重要背景的重要性。