Spring Signals Spawning Season

With air temperatures on the rise, it won’t be long before maple sap isn’t the only thing running. Each spring, as the ice on our lakes and rivers goes out, a number of fish species begin their spawning runs. Many people in the region are familiar with the spawning runs of rainbow smelt (Osmerus mordax) and walleye (Sander vitreus), but few give much consideration to another spring spawner: suckers. This month we put the spotlight on the underappreciated sucker family (Catostomidae). 

Warming water temperatures are a cue to suckers to begin their annual trip from the waters of Georgian Bay into tributaries to spawn. White sucker, one of the most common and widespread fish species in Ontario, are well known for their large spawning migrations into even the smallest streams in the spring. Schools of hundreds to thousands of suckers can be seen in creeks and rivers with suitable spawning habitat.

Suckers are broadcast spawners meaning they do not build nests. Instead, fertilized eggs settle and adhere to the gravel or cobble substrate and hatch out within a couple weeks with no parental care.

Although it is not the most flattering name, the common name for species in the family Catostomidae comes from the fact that most have downturned mouths on the underside of the head, the perfect adaptation for sucking food (aquatic insects, small crustaceans, molluscs, or plants) off the bottom of a lake. Their mouths are described as having thick, fleshy lips that are touch and taste sensitive. These lips are covered in either folds or ridges (plicae) or bumps (papillae), and are a helpful aid in identifying suckers.

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Of the 14 species in the sucker family that occur in Ontario, you are most likely to find 6 of these species in or around eastern Georgian Bay. 

The sucker spawning run is not only important for maintaining healthy sucker populations, it also plays a key role in the food web of the tributary. With spawning suckers comes sucker waste. Fish poop is a great fertilizer providing much needed nutrients for algae, the very base of the food web. Algae is eaten by aquatic insects which are then eaten by fish or birds. The nutrients from sucker waste make their way up through the food web, supporting a healthy aquatic ecosystem.

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Common species, uncommon research subject

Although sucker species are common throughout the Great Lakes, like other non-game species, they are relatively understudied. A research biologist at the Shedd Aquarium in Chicago is endeavouring to change this. Karen Murchie’s research aims to improve our understanding of sucker migratory habits. 

Murchie is three years into a study looking at spawning site fidelity – whether suckers return to the same spawning habitat year after year. Three hundred suckers found in the same creek were microchipped in 2018. In 2019, their team found that 204 of the 300 tagged fish returned to the same creek to spawn.

Murchie’s research is also asking whether climate change is having an influence on the timing of sucker spawning. With the help of volunteer citizen scientists, the timing of the spring arrival of suckers in a number of tributaries is being documented. By comparing current migration timing to historical records, it will be possible to determine whether or not suckers are on the move earlier in the year due to warming.

To learn more about this research, visit: https://www.sheddaquarium.org/care-and-conservation/shedd-research/investigating-great-lakes-sucker-migrations.

Report your sightings!

Have you seen a sucker? Report it! Join the Georgian Bay Biosphere iNaturalist project and share your observations! All species observations (fish and others) help us to gather more information about the species on the eastern coast of Georgian Bay in order to better understand threats and where efforts into research and mitigation should be directed. These observations will help guide research questions, mitigation projects, and other conservation initiatives.

iNaturalist shares your findings with scientific data repositories like the Global Biodiversity Information Facility to help scientists find and use your data. All you have to do is:

1. Download the free app or register online
2. Take photos of fauna and flora, even if if you don’t know the species
3. Upload them to iNaturalist, and add information about date and location
4. Add it to the “Georgian Bay Biosphere” Project!