有时，关于自然界的最佳消息会以微小的痕迹形式出现。美国国家海洋和大气管理局渔业局（NOAA Fisheries）表示，科学家发现迹象表明，河鲱鱼正在利用马里兰州帕塔普斯科河（Patapsco River）中原本对它们封闭的栖息地。转折点出现在2018年大坝拆除之时。数年后，微量的DNA痕迹和两条成鱼显示，鲱鱼正在找到回归之路。
Sometimes the best news about nature can show up in tiny traces. NOAA Fisheries says scientists have found signs that river herring are using habitat in Maryland’s Patapsco River that had been closed to them. The turning point came with the removal of the large dam in 2018. Years later, tiny traces of DNA and two adult fish show herring finding their way back.
这是一个虽小却充满希望的迹象，表明如果我们扫清障碍，河流是可以恢复的。一座阻隔帕塔普斯科河的大坝布洛德大坝（Bloede Dam）位于巴尔的摩附近的帕塔普斯科河上。官员称，一百多年来，它是鱼类从切萨皮克湾（Chesapeake Bay）逆流而上时遇到的第一道障碍。这座老旧大坝多年来也一直是对公共安全的重大威胁。
It's a small but hopeful sign that rivers can recover if we clear the way.A dam that blocked the Patapsco RiverThe Bloede Dam was located on the Patapsco River near Baltimore. For over 100 years, it was the first obstacle that fish met when swimming upstream from the Chesapeake Bay. The old dam had also been a significant threat to public safety for many years, officials say.
2018年，美国国家海洋和大气管理局与合作伙伴，连同美国河流组织（American Rivers）及其他机构，拆除了这座大坝。据报道，该局在该项目及后续监测上投入了超过930万美元。其他资金来源包括国家鱼类和野生动物基金会（National Fish and Wildlife Foundation）和美国鱼类和野生动物管理局（U.S. Fish and Wildlife Service）。
In 2018, NOAA and partners removed the dam, along with American Rivers and other organizations. The agency reportedly spent more than $9.3 million on the project and monitoring there. Other funding sources included the National Fish and Wildlife Foundation and the U.S. Fish and Wildlife Service.
科学家如何追踪看不见的鱼河鲱鱼是两种小型银色鱼类——花鳞鲱（alewife）和蓝背鲱（blueback herring）的统称。每年有数百万条鱼洄游至产卵和育苗栖息地。大坝和涵洞等障碍物会阻挡它们。如果鱼无法到达栖息地，就无法繁殖，种群数量就会下降。科学家利用环境DNA（eDNA）来判断鲱鱼是否回归。鱼类不断将鳞片、组织和其他遗传物质脱落入水。
How scientists tracked fish they couldn't seeRiver herring are the collective name for two small, silvery fish, the alewife and the blueback herring. Millions of fish migrate to spawning and rearing habitat every year. Barriers such as dams and culverts can block them. If fish cannot get to their habitat, they cannot reproduce, and their populations can decline. Scientists used eDNA, or environmental DNA, to see if the herring were returning. Fish constantly shed scales, tissue, and other genetic material into the water.
研究人员采集水样并检测其中近期造访者的遗传信息。史密森尼环境研究中心（Smithsonian Environmental Research Center）和马里兰大学环境科学中心（University of Maryland Center for Environmental Science）的一个团队已在该地点使用这种方法。研究发现了什么研究结果来自2023年发表在《PLOS ONE》上的一项研究。
Researchers take a sample of water and test it for recent visitors. A team from the Smithsonian Environmental Research Center and the University of Maryland Center for Environmental Science has used this method at the site. What the study foundThe results came from a 2023 study in PLOS ONE.
研究发现，在大坝拆除前的四年里，即使设有鱼道，在大坝上游也未发现成年河鲱鱼、河鲱鱼环境DNA（eDNA）或鱼卵。鱼道基本上是一种帮助鱼类越过大坝的建筑结构。大坝拆除后，情况发生了变化。三年内，在上游发现鳞片鲱（alewife）环境DNA的几率从0上升到5%。对于青背鲱（blueback herring），这一几率从0上升到13%。
The study found that in the four years before the removal of the dam, no adult river herring, eDNA, or eggs were found upstream of the dam, even with a fish ladder. A fish ladder is basically a structure built to help fish pass a dam. After the dam came down, it was different. Within three years, the chance of finding alewife eDNA upstream went from 0 to 5 percent. For blueback herring, it went from 0 to 13 percent.
2021年，马里兰州自然资源部的生物学家在上游记录到两条成年河鲱鱼，一条鳞片鲱和一条青背鲱。充满希望的开端，但故事尚未结束研究显示出早期迹象，表明鲱鱼正在利用旧大坝上方新开放的栖息地。然而，这仅占河流中鱼类种群的一小部分。未观察到鱼卵数量的变化，拆除大坝后上游也未检测到标记鱼。作者指出，需要持续的长期监测以了解种群的任何变化。
In 2021, biologists with the Maryland Department of Natural Resources recorded two adult river herring upstream, one alewife and one blueback herring.A hopeful start, but not a finished storyThe research showed early signs that herring were making use of the new habitat above the old dam. However, this was the case for only a small proportion of the fish population in the river. No change in egg numbers was noted, and no tagged fish were detected upstream after removal.
所以这是一个早期的胜利；这并不能证明鲱鱼数量已经恢复。不仅仅是一条河的事布卢德大坝（Bloede Dam）并非唯一被拆除的大坝。在国家海洋和大气管理局（NOAA）支持的早期项目中，位于更上游的联合大坝（Union Dam）和西姆金斯大坝（Simkins Dam）已于2010年拆除。这三座大坝的拆除共同开放了超过65英里的栖息地供青背鲱、鳞片鲱、美洲鲱（American shad）和山楂鲱（hickory shad）使用，以及超过183英里供美洲鳗（American eel）使用。
The authors note that continued long-term monitoring is needed to understand any change in the population. So that’s an early win; it’s not proof that herring numbers have come back. Bigger than just one riverBloede wasn't the only dam that was removed. Previous NOAA-supported projects removed Union Dam and Simkins Dam further upstream in 2010. The three removals, together, have opened up more than 65 miles of habitat to blueback herring, alewife, American shad and hickory shad, and more than 183 miles for American eel.
国家海洋和大气管理局的社区恢复计划已在超过4400英里的溪流和河流中恢复了鱼类通道。2022年12月，该机构还宣布为全国36个新的鱼类通道项目提供资金。对于洄游鱼类而言，通畅的河流只是开始，但这是必须首先到来的部分。
NOAA’s community-based restoration program has reopened fish passage in over 4,400 miles of streams and rivers. In December 2022, the agency also announced funding for 36 new fish passage projects around the country. For migrating fish, an open river is only the beginning, but it’s the part that needs to come first.