Dump those minnow buckets where they belong

February 27, 2021

Although it's illegal, too many anglers still release their leftover bait into lakes and rivers. The frequency of this behavior is concerning as it carries the risk of introducing fish pathogens to popular fishing waters.

Yet it continues to happen.

About 20 percent of anglers responding to a survey by the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota owned up to the practice, saying they did so on some of their fishing trips.

“It’s a fair guess the number is actually higher than 20 percent,” said Meg McEachran, a doctoral candidate at the Center whose work prompted the study. Not everyone wants to admit to a wrong-doing, she said.

The numbers that worry her, and should concern all of us, can be in the tens and hundreds of thousands. In a Feb. 17 webinar presentation the Center hosted and called “What’s in your bait bucket,” McEachran calculated the risks for introducing harmful pathogens to our favorite lakes based on a stochastic modeling technique.


The technique allows uncertainty to be considered in the models, and she calculated the risks for various scenarios with the knowledge that 20 percent of anglers are releasing bait fish on some of their fishing trips. She ran “what if” scenarios based on situations where no pathogens existed in the bait supply all the way up to situations where there were undetected outbreaks of pathogens in the supply.

The vast majority of the model runs showed no risk, but not all. The take-home message is this: The possibility of tens or even hundreds of thousands of disease introductions occurring is real, even at extremely low pathogen prevalence, according to McEarhan.

The greatest risk occurs in areas that are popular fishing destinations because that’s where the greatest number of fishing trips occur.

The good news is that she found that under current conditions, the transmission of certain pathogens, in particular the infamous Viral Hemorrhagic Septicemia Virus, is unlikely. This disease has not been found in our waters or bait supply, and we test for it.

Yet the virus is present in Lake Superior, and the risk exists that it could enter our bait supply.

She based her calculations on angler behavior using the survey that had gone out to 4,002 licensed anglers. It received 669 responses. Not a great response rate, but McEachran also pointed to other surveys that found similar, 20-percent-and-higher-rates of illegal dumping.

Most important, earlier research already demonstrated that there is the potential for many different types of pathogens to be present in the buckets of minnows we carry to our lakes and rivers.

Researchers purchased shiners at bait shops around Minnesota in 2014 and 2015. In total, they found pathogens present in almost 60 percent of the bait purchased, including some novel viruses. They found a fish parasite, Ovipleistophora ovariae, which damages the reproductive tissues of infected fish. They found different viruses and bacteria known to cause fatal hemorrhaging in fish.

About 60 percent of our baitfish are harvested in the wild, usually from shallow lakes. Another 40 percent are harvested from aquaculture, usually in small ponds. The minnows from various sources are gathered together and distributed to bait shops. There is minimal testing performed for the wide range of pathogens that exist. It is difficult to trace where the bait in any given bucket is sourced.

McEachran said there are 15 pathogens of concern in the state. Her research focused on the potential for three main pathogens. She calculated the prospects for carrying the Viral Hemorrhagic Septicemia Virus, Ovipleistophora avariae, and Asian Tapeworm.

For any of these pathogens to reach water bodies from bait fish, a series of events have to occur. A bait fish has to be infected, an angler must purchase the bait, take it to a lake or river, and release it.

Overall, she calculated that in most cases, well over 99 percent of fishing trips end without the risk of spreading pathogens. But consider: There are roughly 1 million licensed anglers in the state, and 70 percent of them use live bait fish. The survey also showed that many of them are making multiple fishing trips each year. The numbers add up fast when the probability exists for even a few of the bait fish to carry pathogens.

In one scenario, she modeled the probability for risky fishing trips based on the premise that VHSV is present in some of the baitfish purchased at shops in the Lake Superior Watershed. In that scenario, there is the probability for 22,000 “risky trips” a year where the virus could be released. In a scenario where VHSV is widespread and undetected in the bait supply, the average number of risky trips is over 400,000 per year.

Concern about the potential for spreading pathogens with live bait is the reason that the Minnesota Department of Natural Resources prohibits the importation of minnows from outside the state. All live bait sold in Minnesota is from state waters.

Live bait represents a $2.5 million a year industry in Minnesota, according to McEachran.

McEachran said there is some testing for pathogens that occurs before certain bait fish reach retail locations. Emerald and spottail shiners are subject to regular testing for the presence of VHSV, since it’s known these highly desired bait fish can be infected by the disease.

But she pointed out that fathead minnows, the most abundant bait fish in the market, are also susceptible to the disease. They are not subject to regular testing for VHSV.

She pointed out too that biosecurity is expensive. Adding more testing requirements and protocols for bait suppliers will raise the costs for bait.

The biggest worry is what is being called the “chink in the armor” in our defense system, angler release behavior.

“Angler release behavior was the primary driver of risk across all scenarios modeled,” said McEachran of her calculations.

In response to questions, she said anglers should not worry about the minnows on their hooks, even those that escape. The real risk of spreading pathogens occurs when live bait fish are released. The pathogens multiply in the host fish. These host fish can spread the pathogens by shedding the pathogens while in contact with native minnows and other fish, or when they are consumed by a predator.

McEachran said her next research will focus on why some anglers are illegally releasing their leftover bait. It’s believed one of the reasons is a misconception. Some anglers believe they are doing a good thing by tossing bait fish into the waters for their favorite game fish to eat.

Convenience is believed to be another reason that anglers release live bait.

McEachran emphasized in her presentation: “There is a lot of uncertainty and variability when it comes to fish pathogens and we need to embrace this, not avoid it.”

She also noted that we do not know the actual risk of an outbreak occurring when pathogen-contaminated bait fish are released in a body of water. This research focused on the probability for those introductions to occur.

The simple truth of the matter is that anglers just need to do the right thing and eliminate the risk by disposing of their leftover bait fish in a legal manner, either by tossing them in the trash, garden or lawn.

It’s also important to abide by the law and replace the water in bait buckets when moving from one lake to another. Not doing so brings the risk of transporting aquatic invasive species such as the veligers of zebra mussels, which are too tiny to see.