坝拆除改善了鲥鱼产卵场，可以提高生存率

Research from North Carolina State University finds that dam removal improves spawning grounds for American shad and seems likely to improve survival rates for adult fish, juveniles and eggs – but for different reasons.

The researchers focused on a small tributary in North Carolina called the Little River, where three dams were removed in the late 1990s and early 2000s. American shad (Alosa sapidissima) spend the bulk of their adult lives in saltwater, but return to freshwater rivers like this one to spawn. While in these freshwater environments, the adult shad do not feed. As a result, many of the adult fish die before they have a chance to return to the ocean.

Between 2008 and 2010, the research team tagged, weighed and released approximately 3,000 American shad at a weir – or fish gate – that was sited at one of the dam removal sites on the Little River. The shad were tagged on their way upstream to spawn. Researchers set up antennas along the length of the river to detect the fish tags, allowing the scientists to tell how far upstream the fish traveled.

“Shad were using all of the restored habitat,” says Dr. Joshua Raabe, lead author of a paper on the research and an assistant professor at University of Wisconsin-Stevens Point who worked on the project while a Ph.D. student at NC State.

“This is important because upstream sites are generally higher-quality spawning sites, which should improve survival of eggs and juvenile fishes,” says Dr. Joe Hightower, co-author of the paper and a U. S. Geological Survey scientist and professor of applied ecology at NC State. “For example, some key predator species, such as flathead catfish, become less common the further you go upstream.”

研究人员还在下游的路上捕获了幸存的曲线，让他们看看鲥鱼在产卵时失去了多少重量并估计死亡率。死亡率总体上很高。在产卵时，男性鲥鱼可能会失去30％的体重，而女性可能会失去高达50％。

研究人员发现,减肥是primarily linked to water temperatures and the amount of time the fish spent in the river, rather than how far upstream the fish went to spawn.

“这告诉我们，越来越长的鱼被拘留，他们失去的重量就越多，他们就越可能死亡，而且他们在产卵前达到优先栖息地的可能性就越不少，”Raabe说。“这是在考虑水坝或其他障碍物可以减缓鲥鱼进步的地方的重要信息。”

“Basically, the clock is ticking and these fish have a job to do,” Hightower says. “The study indicates that anything we can do to improve fish passage should improve survival rates.”

The paper, “American Shad Migratory Behavior, Weight Loss, Survival, and Abundance in a North Carolina River following Dam Removals，“在线发布于5月13日美国渔业协会的交易。Hightower也是美国地质调查的北卡罗来纳州合作鱼和野生动物研究单位的一部分。该研究得到了美国鱼类和野生动物服务的支持。

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Note to Editors:这项研究摘要跟随。

“美国鲥鱼行为，减肥，北卡罗来纳河河河后的减肥，生存和丰富的丰富”

作者：Joshua K. Raabe，威斯康星大学 - 史蒂文斯点;Joseph E. Hightower，北卡罗来纳州立大学和美国地质调查

发表: online May 13,美国渔业协会的交易

DOI：10.1080 / 000028487.2014.882410

Abstract:Despite extensive management and research, populations of American Shad Alosa sapidissima have experienced prolonged declines, and uncertainty about the underlying mechanisms causing these declines remains. In the springs of 2007 through 2010, we used a resistance board weir and PIT technology to capture, tag, and track American Shad in the Little River, North Carolina, a tributary to the Neuse River with complete and partial removals of low-head dams. Our objectives were to examine migratory behaviors and estimate weight loss, survival, and abundance during each spawning season. Males typically immigrated earlier than females and also used upstream habitat at a higher percentage, but otherwise exhibited relatively similar migratory patterns. Proportional weight loss displayed a strong positive relationship with both cumulative water temperature during residence time and number of days spent upstream, and to a lesser extent, minimum distance the fish traveled in the river. Surviving emigrating males lost up to 30% of their initial weight and females lost up to 50% of their initial weight, indicating there are potential survival thresholds. Survival for the spawning season was low and estimates ranged from 0.07 to 0.17; no distinct factors (e.g., sex, size, migration distance) that could contribute to survival were detected. Sampled and estimated American Shad abundance increased from 2007 through 2009, but was lower in 2010. Our study provides substantial new information about American Shad spawning that may aid restoration efforts.