Electro Sensory and Turbidity: American Paddlefish’s Decline and Outlook

Polyodon spathula

Figure 1: American Paddlefish (image courtesy of U.S. Fish and Wildlife Service)


The American Paddlefish (Polyodon spathula) or spoonbill as they are often referred to due to their paddlelike snout, is a large and ancient fish that has survived relatively unchanged since the late cretaceous period around 68 million years ago when dinosaurs walked the earth. They can be found throughout North American in the Mississippi River Basin. While they are a protected and rare state threatened species in Ohio, they are found most commonly in Ohio River tributaries downstream of the first dams; particularly in the Scioto River south of Columbus (Rice and Zimmerman 2019). In Ohio, they can grow to a maximum size of 5′ and 184lbs, however fish ranging from 2-4′ and around 20-30lbs are much more common (Rice and Zimmerman 2019). The cause for their decline was attributed to increased turbidity, or suspended particles like clay and silt, and being cutoff from suitable spawning areas to reproduce due to the construction of dams (Rice and Zimmerman 2019). In order to understand why turbidity has impacted these fish so much and why their populations are beginning to rebound as water quality improvements t0 the rivers has been made, you must first understand how they feed.

Filter Feeding:

Despite their massive size and tough exterior, these fish are filter feeders that prey mostly on small plankton crustaceans, which are small organisms that float freely in the water. You may be wondering how it is possible for the paddlefish to eat enough of these organisms to grow to such a large size. Luckily for the paddlefish, they are excellent filter feeders like Humpback Whales. Having been described by early naturalists as “A living plankton net” these fish have hundreds of gill rakers that form a tight mesh that collects plankton as they swim around with their large gaping mouths open as seen in Figure 2.

Figure 2: Paddlefish gill rakers (Courtesy of John Lyons of Virigina Tech)

But what purpose does the paddle serve?


The paddle or rostrum was once thought to have been used to dig through the stream substrate foraging for food, but research has proven that it is actually an electro sensory organ covered in sensory pores (Figure 3) used by the paddlefish to detect the weak electrical currents plankton give off (Wilkens and Hofmann 2007). In a study published in 2007, researchers ran feeding experiments on juvenile paddlefish where they placed the paddlefish in dark tanks and witnessed them able to seek out single small crustaceans that were placed in the tank (Wilkens and Hofmann 2007). They also noted that they would avoid metallic objects in the tank, even in the dark, as this likely interfered with their perception of electrical currents which may also hint at a further impact locks and dams could have on paddlefish by disrupting their ability to navigate rivers and access spawning habitat after dams were constructed (Wilkens and Hofmann 2007). If paddlefish can locate food even in the dark or muddy waters, then why has increased turbidity impacted them so much?

Figure 3: Paddlefish rostrum and closeup of electro sensory pores (Helfman et al. 2007)


The issue with increased turbidity is largely due to their ability to finely filter feed. Some studies have shown that 50% of the gut content of some paddlefish was detritus (decomposing organic material like small leaves) and sand (Pyron et al 2019). Under highly turbid conditions, paddlefish gill rakers may become clogged with materials that are suspended in the water, making them unable to filter feed plankton effectively. In addition to not being able to filter feed as effectively, other studies have linked high turbidity to reduced growth of plankton species (Kirk and Gilbert 1990). Despite the paddlefish’s ability to find food solely using electroreception, they’d still struggle to find food as plankton growth can be reduced, leaving them less food in water with high turbidity.


At present, water quality in Ohio has been steadily improving after legislation like the Clean Water Act in 1972 and many fish species have since begun to bounce back after having been impacted by habitat and water quality degradation (Pyron et al 2019). As water quality continues to improve and many old and outdated dams are removed; granting these fish access to places to spawn, we can be hopeful that conservation efforts to protect this ancient Ohio fish will be successful and future paddlefish will be free to filter feed all they want.



Helfman, G., Collette, B. B., Facey, D. E., & Bowen, B. W. (2009). The diversity of fishes: biology, evolution, and ecology. John Wiley & Sons.

Kirk, K. L., & Gilbert, J. J. (1990). Suspended clay and the population dynamics of planktonic rotifers and cladocerans. Ecology71(5), 1741-1755. Lon A. Wilkens, Michael H. Hofmann, The Paddlefish Rostrum as an Electrosensory Organ: A Novel Adaptation for Plankton Feeding, BioScience, Volume 57, Issue 5, May 2007, Pages 399–407.

Pyron, M., Mims, M. C., Minder, M. M., Shields, R. C., Chodkowski, N., & Artz, C. C. (2019). Long-term fish assemblages of the Ohio River: Altered trophic and life history strategies with hydrologic alterations and land use modifications. Plos one14(4), e0211848.

Rice, D. L., Zimmerman, B.. (2019). A naturalist’s guide to the fishes of Ohio. Ohio Biological Survey.


How does noise impact marine whales?


We all know that it’s difficult for light to transmit in the water, especially in deep water areas. Compared to being in the air on land, the visibility underwater is so low that sight is not that important for creatures living in the water. Therefore, sound has become the only tool they can explore and communicate. Water is a very good conductor of transmission, and sound can travel very long distances in water (Jensen et al., 2009). Many marine mammals, such as whales and dolphins, use sound to see this marine environment. They use the auditory system to discover food, find mates, communicate and explore the surrounding terrain (Peng et al., 2015). However, the increasing amount of anthropogenic noise created below sea level is having a huge impact on whales.

After searching the news and information on the internet, two large whale stranding struck me. One occurred off the coast of the Bahamas in 2000, where about 17 cetaceans were spotted on the shore in two days (Nevala, 2008). The enthusiastic people tried to drive these poor animals back to the open ocean, but they kept swimming back to the shore. Some of the whales unfortunately died. The marine biologists dissected and found that the whales had severe bleeding near their brains. After investigation, it was found that the U.S. Navy’s sonar system had caused a huge, explosion-like sound in the sea, resulting in serious damage to the whales’ hearing system (Nevala, 2008). That’s the reason why these cetaceans wanted to flee away from their habitats. Massive noise altered their behaviors.

There are two classifications of anthropogenic noise. One is impulsive noise like blasting caused by sonar and air guns, and another is stationary noise (Peng et al., 2015). Commercial transportation vessels similarly interfere with whale communication by this kind of low-frequency stationary noise. The communication signals of these mammals are masked and interfered with by the loud noise sound from the ship’s oars, reducing their sensitivity to sound signals (Peng et al., 2015). Without receiving signals that bounce back, young whales may be lost in the ocean, unable to find their families, or even eventually come to their deaths. A defunct auditory system may make it difficult for the whales to find food and miss their mates in the near distance. What sad results these are.

The good news is that industries started to develop quieter ships and enhance the shapes of ships to reduce the noise. Also, with more and more attention on this issue, more policies and requirements have been established for cooperation (Dolman & Jasny, 2015). It is our responsibility to protect the ecological health of the ocean. We should do all we can to reduce the damage and maintain the ecological balance.



Dolman, S., & Jasny, M. (2015). Evolution of Marine Noise Pollution Management. Aquatic Mammals, 41, 357–374. https://doi.org/10.1578/AM.41.4.2015.357
Jensen, FH., Bejder, L., Wahlberg, M., Aguilar Soto, N., Johnson, M., & Madsen, PT. (2009). Vessel noise effects on delphinid communication. Marine Ecology Progress Series, 395, 161–175.https://www.int-res.com/abstracts/meps/v395/p161-175/

Peng, C., Zhao, X., & Liu, G. (2015). Noise in the Sea and Its Impacts on Marine Organisms. International Journal of Environmental Research and Public Health12(10), 12304–12323. https://doi.org/10.3390/ijerph121012304

Nevala, A. (2008). The Sound of Sonar and the Fury about Whale Strandings. Oceanus.https://www.whoi.edu/oceanus/feature/the-sound-of-sonar-and-the-fury-about-whale-strandings/