"Pope" Fish Invades Non-Native Land

Eurasian Ruffe is on the loose!

Classification

Common names: Ruffe or Pope

Scientific Names: Gymnocephalus cernua

Phylum/Division: Kingdom: Animalia

Class: Actinopterygii

Order: Perciformes

Family: Percidae

Identification:

  • colors and markings are similar to those of the walleye, an olive-brown to golden-brown color on its back, paler on the sides with yellowish white undersides.

  • 4–6 inches (10–15 cm) long and will never exceed 10 in (25 cm)

  • very aggressive

  • large, spiny dorsal fin likely distasteful to its predators

  • two fins on top

  • front fin has hard and sharp spines

  • back fin has soft spines called rays

  • large, continuous dorsal fin and its slightly downturned mouth.





Original Distribution:

Europe and northern Asia.


Modes of introduction:

1980s by the DNR. They suggest that the fish was introduced to the lake via ballast water that was dumped into the Duluth harbor by anchored freight ships.


Site and Date of Introduction:

Control Method:



Local fisherman have ried to control ruffe by increasing the number of its predators, especially walleye and northern pike. They did this by limiting sport catches of these species, and stocking walleye and northern pike.


Control Level Diagnosis:

Fisheries managers in Lake Superior first tried to control ruffe by increasing the number of its predators, To keep ruffe from spreading to the other Great Lakes, the Lake Carriers Association developed best management practice guidelines for handling ballast water in Great Lakes ships.


Reason why it is established:

The ruffe has already invaded Lake Superior and GARP modeling predicts it will find suitable habitat almost everywhere in all five Great lakes. GARP models are not able to make a prediction about some of the deeper waters of Lake Superior (U.S. EPA 2008). Established in western portion of Lake Superior since about 1988 and expanding in an easterly direction.


Ecological Role:

Gymnocephalus cernuus compete with native fish for food and habitat. Because of this, walleye, perch, and a number of small forage fish species are seriously threatened by continued expansion of the ruffe's range. Hajjar (2002), describes G. cernuus as prolific breeders and aggressive feeders.


Benefits:


Ruffe grow quickly, have a high reproductive capacity, and can live in a wide variety of environments.


Threats:


Based on population size and diet, ruffe should reduce food sources for many fish.
Ruffe grow quickly, have a high reproductive capacity, and can live in a wide variety of environments. These qualities give populations of ruffe the potential disrupt the delicate predator/prey balance vital to sustaining a healthy fishery.