In our Research Highlights blog series, we debut newly published fisheries research by our women of fisheries colleagues. If you have research you would like to highlight and share with our readers, submit a nomination form here!
This Month’s Research Highlight:
Lenaerts, Allison W., Alison A. Coulter, Kevin S. Irons, and James T. Lamer. 2023. A Quick Method for Estimating Batch Fecundity in Bigheaded Carp. North American Journal of Fisheries Management 43:3-11.
Lenaerts, Allison W., Alison A. Coulter, Kevin S. Irons, and James T. Lamer. 2023. Examination of Bigheaded Carp Ovaries Indicates Batch Spawning. North American Journal of Fisheries Management 43:25-34.
Lenaerts, Allison W., Alison A. Coulter, Kevin S. Irons, and James T. Lamer. 2023. Plasticity in Reproductive Potential of Bigheaded Carp along an Invasion Front. North American Journal of Fisheries Management 43:92-100.
As you probably guessed from the title, this month’s research highlight is all about carp, invasive Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis to be specific. Since their importation from Asia in the 1970s, these bigheaded carp have established populations in several large river basins in the United States. It’s a big deal – and not just because of their size or impressive acrobats. As efficient filter feeders that can quickly outgrow native piscivores, they have become major disruptors of our river ecosystems and continue to expand their range. This isn’t just a problem in the United States either, with introduced populations recorded in over 70 other countries.
(Photo Credit: Allison Lenaerts)
So, what makes them such successful invaders?
To help answer this question, we look to research by Allison Lenaerts, Large River Ecologist with the Illinois Natural History Survey, and her colleagues. Their carp reproductive studies were recently featured in a special section Invasive Carp Early Life History in North American Journal of Fisheries Management. After learning about their work, I think you will agree, it’s an “Oh carp!” situation.
Allison was first introduced to the world of carp reproduction at Purdue University, first as a fisheries technician and then graduate student focusing on the commercial harvest of Silver and Bighead Carp in the upper Mississippi River. Given the importance of reproduction and recruitment to a species’ invasion potential, this work is vital to the control and management of bigheaded carp.
For this series of studies, fish were collected by commercial harvesters from the upper Mississippi River during the summer spawning period. In one study, Allison and her colleagues sought to find a shortcut method for estimating batch fecundity for these species. With up to an estimated 3.7 million eggs observed in a single Silver Carp and 2.7 million eggs in a single Bighead Carp, it is not hard to imagine why fisheries scientists would want to bypass the traditional method of manually counting egg samples. Although they were successful in creating an equation to estimate the number of eggs in Silver Carp based on fish length, weight, relative weight, and ovary weight, Bighead Carp proved to be too variable. In another related study, the researchers found evidence that these fish can spawn multiple times during the spawning period in this river system, but the reproductive strategy – ranging from protractive over two or more months to single batch spawning – can vary among rivers. Even more, they found the number or size of eggs varied by fish density, meaning along an “invasion front” where numbers are low, these fish can adapt to increase their reproductive potential.
(Photo Credit: Allison Lenaerts)
So, what makes them such successful invaders? To summarize Allison and her colleagues’ work, it is because along with fast growth, these species have flexible spawning strategies and high fecundity. It is an “Oh carp!” situation indeed.
News like this can make the future seem bleak, but all is not lost. There are a number of methods being used to try to control these species and limit their range expansion, from electric barriers to commercial harvesting. In some areas like the lower Illinois River, commercial fishers are subsidized for their harvest of these species. Efforts are also underway to expand the market for them. By purchasing or requesting “copi” – a collective term being used for invasive carps – at your local grocery or fish market, you, too, can support control efforts like these.
(Photo Credit: Allison Lenaerts)
We are in a race of sorts, a race to protect some of our largest freshwater resources. Allison explains, “Current concerns about future range expansion include establishment in the Great Lakes because they could have detrimental impacts on those fisheries, such as competition with native species or disruption of complex food webs. They also pose a risk to boaters because they jump out of the water when startled and can injure boaters (from personal experience, it’s not fun).”
With the help of research like this, managers have the best opportunity to minimize the impacts in current carp strongholds and prevent future carp invasions. Our message of hope for the future is not “Oh carp!” but “No carp!”
When I started as an undergraduate, I was majoring in wildlife rather than fisheries. My first technician position…was my first look into fisheries and I really enjoyed being out on the water every day. I also enjoyed the research we were doing, and it got me interested in the idea of studying reproduction. Studying invasive species is appealing to me because there is so much we can learn from doing basic research, like looking at fecundity and growth within newly invaded areas.
Allison Lenaerts
Allison Lenaerts is continuing her invasive carp reproduction work by collecting ovarian samples from these species in the Upper Illinois River to monitor egg development during the spawning season.
The full manuscripts can be found or downloaded here:
doi.org/10.1002/nafm.10651
doi.org/10.1002/nafm.10633
doi.org/10.1002/nafm.10583