Evidence of Asian carp spawning above a key choke point in the Mississippi River: Data

Bighead Carp, Silver Carp and Grass Carp (collectively Asian carp) were introduced to North America in the 1960s and 70s and have established in the lower Mississippi River basin. Previously published evidence for spawning of these species has been limited in the upper Mississippi River to just below Dam 22 (near Saverton, MO). In 2013 and 2014, we sampled ichthyoplankton at 18 locations in the main stem of the upper Mississippi River from Dam 9 through Dam 19 and in four tributary rivers that empty into the Mississippi River (Des Moines, Skunk, Iowa and Wisconsin Rivers). We identified eggs and larvae using morphological techniques and then used genetic tools to confirm species identity. The spawning events we observed often included more than one species of Asian carp and in a few cases included eggs that must have been derived from more than one upstream spawning event. The upstream extent of genetically confirmed Grass Carp was Pool 12, while Bighead Carp and Silver Carp were observed in Pool 16. In all these cases, ichthyoplankton likely drifted downstream for several kilometers prior to collection. As has been observed elsewhere, no eggs or larvae were collected prior to water temperature reaching 17°C and discharge was usually high when eggs or larvae were observed. Several major spawning events were observed in 2013, but not in 2014. Although reproduction appears to be occurring for all three of these species above Dam 19, the recruitment success of these populations is unknown.

鳙鱼（Bighead Carp）、鲢鱼（Silver Carp）与草鱼（Grass Carp），三者合称为亚洲鲤（Asian carp），于20世纪60至70年代被引入北美，并已在密西西比河下游流域建立稳定种群。此前已发表的关于上述鱼类产卵的相关证据，在密西西比河上游区域仅局限于22号大坝下游（密苏里州萨弗顿附近）一带。2013年与2014年，研究团队在密西西比河上游干流从9号大坝至19号大坝间的18个采样点，以及汇入密西西比河的4条支流（得梅因河、斯坎克河、艾奥瓦河与威斯康星河）开展了鱼卵浮游生物（ichthyoplankton）采样工作。研究团队先通过形态学方法对采集到的鱼卵与仔鱼进行初步鉴定，随后借助遗传学工具确认其物种归属。本次观测到的产卵事件往往涉及不止一种亚洲鲤，少数案例中采集到的鱼卵甚至可能源自多次上游产卵事件。经遗传学确认的草鱼的上游分布边界为12号池段，而鳙鱼与鲢鱼的观测记录则出现在16号池段。所有采样案例中，采集到的鱼卵浮游生物均可能在被捕获前已顺流漂移了数公里。与其他区域的观测结果一致，当水体温度未达到17℃时，未采集到任何鱼卵或仔鱼；而在采集到鱼卵或仔鱼的时段，河道径流量通常处于较高水平。2013年观测到多次大规模产卵事件，但2014年未出现此类情况。尽管上述3种亚洲鲤在19号大坝上游区域均存在产卵繁殖现象，但相关种群的补充成功情况仍未明确。