January 14th, 2021
The article I read this week is “A Comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River” by Christopher Sullivan, Michael Weber, Clay Pierce, and Carlos Camacho. The purpose of this article was to conduct a study “to compare the relative abundance, size structure, condition, growth, and recruitment variability of Grass Carp collected upstream and downstream of [Lock and Dam 19].”¹ The hypothesis regarding a potential difference in characteristics was formed because the dam prevents fish from moving upstream and reduces the quality of spawning habitats downstream¹. This study was necessary because the Grass Carp is an invasive species, and knowing the different characteristics of Grass Carp populations at different points of the river could help create more effective control measures. Some of the key terms of this article were Grass Carp, population characteristics, dam, Mississippi River, downstream versus upstream.
Two of the authors of the article are Christopher J. Sullivan and Michael J. Weber. Sullivan is a Ph.D. student at the University of Connecticut. He’s located in the Department of Natural Resources and the Environment and has published 13 works (articles, technical reports, and a thesis) since 2015, done in conjunction with other authors. He has studied Forestry at Purdue University and Fisheries Biology at Iowa University in the past. Michael J. Weber is an associate professor at Iowa State University in the Department of Natural Resource Ecology and Management. Alongside having a Ph.D. in Fisheries Science, Weber has also published 97 works (articles, technical reports, and conference papers) since 2007. Sullivan and Weber, alongside Clay Pierce and Carlos Camacho, have already published an article together in the past regarding the strength of Silver Carp in the Mississippi River.
The study was conducted at nine different sites both upstream and downstream of Lock and Dam 19 in the upper Mississippi River. While this dam is considered a semi-permanent barrier, it still limits upstream migration of fish populations, which was what was needed for the experiment. The results were summarized as downstream Grass Carp “tend[ing] to be smaller, younger, of lower body condition, ha[ving] a higher mortality rate, and...slower growing compared with fish collected upstream.”¹ The mean weight and length of downstream carp were 4.4 kilograms and about 732 millimeters¹. On the other hand, the mean weight and length of the upstream carp were about 6.8 kilograms and 806 millimeters¹. The stark difference between upstream and downstream is obvious. The only reason something of the same fish species would be so different both weight and size is due to a difference in environmental conditions, usually being less favorable for the smaller fish.
While last week’s article focused more on the fluvial impacts of dams, this week’s article takes a closer look at the impact dams have on fish populations. This includes the differences in characteristics when comparing upstream and downstream populations, which last week’s article mentioned that downstream fish populations tend to suffer more. One important thing to note about Grass Carp is that it is an invasive species. Originally from the Amur River basin (located near northern Vietnam), this fish species was introduced to the United States between the 1960s and 1990s as a way to control the growth of aquatic vegetation in lakes and reservoirs¹. However, Grass Carp can eat a variety of aquatic plants, travel large distances, and live in various environmental conditions, so they have spread to inhabit rivers as well, including the Mississippi River¹. If this invasive species is having negative impacts on the ecosystem is yet to be investigated since it appears that their numbers are low despite their widespread distribution¹. However, this presents a flaw in this article. Although this article clearly presented how dams have negative effects on fish populations, this fish population itself is deemed as “invasive”, which always has a negative connotation. Invasive species typically thrive in the environments that they get introduced to, so, while these fish might suffer the effects of the dam like any other fish, these fish still have a natural advantage over all the aquatic animals. They can out-compete all other fish for food, can reproduce at a quicker rate, and are more adaptable to different environmental conditions so seeing the impact a dam has on these fish doesn’t give the whole picture of how the dam impacts the whole aquatic ecosystem.
The database I used to find this article was Gale in Context: Science, with the search terms “dams”, “downstream”, and “aquatic”
Sullivan, Weber, Pierce, and Camacho "A comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River".
Bibliography:
Sullivan, Christopher J., Michael J. Weber, Clay L. Pierce, and Carlos A. Camacho. "A Comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River." Journal of Fish and Wildlife Management 11, no. 1 (2020): 99+. Gale In Context: Science (accessed January 11, 2021). https://link.gale.com/apps/doc/A629811843/SCIC?u=nysl_ca_guild&sid=SCIC&xid=92169c75.
“Dr. Michael J Weber.” Natural Resource Ecology and Management. Iowa State University, 2021. https://www.nrem.iastate.edu/people/michael-weber.