Presentation Sections

1
Presentation Sections

• Introduce the ruffe
• Describe why we were initially concerned
• Explore if that concern still exists

2
from MN Sea Grant (G. Cholwek)
Ruffe (Gymnocephalus cernuus formerly G. cernua
Acerina cernua)
3
European Distribution
Native
4
Large Range Increase in 1986
5
Why we were initially concerned

• ... an undesirable component of a fish fauna
  ... -- Neja (1988)
• categorized with undesirable fish -- Bonar
  (1977)
• in trash fish cluster -- Salojarvi Ekholm
  (1990)
• ... disparagingly referred to as a ruff lake.
  and ... ruff ... and other worthless small fish
  ... -- Pihu Maemets (1982)

• Ruffe is generally despised!!

6
Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Broad physiological and ecological tolerances

7
Popova et al. (1998) said it best ...
Ruffe have a variety of traits, both at the
population and individual level, which allow them
to perform successfully in a broad range of
ecological situations and be adaptable to
fluctuations in both biotic and abiotic factors.
8
Example - Broad Tolerances

• 0-30oC
• Fresh and Brackish waters
• Lakes and Rivers
• Depths from 0.25 - 85 m
• Montane and Sub-Montane
• Oligotrophic to Eutrophic

9
Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Broad physiological and ecological tolerances
• Flexible diet

10
Example -- Diet in a Baltic Archipelago(from
Hansson 1984)
100
other
Isop
80
Gamm
Pont
60
Volume
40
Chiro
Bival
20
Trich
0
1
6
Inner Site
Outer Site
11
Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Broad physiological and ecological tolerances
• Flexible diet
• Reduced vulnerability to predation

12
Example -- Pike Predation in Norway(Vollestad et
al. 1986)
Roach
Ruffe
Volume
Smelt
Og
Ro
Lake
13
Anti-Predator Adaptations

• Large spines (many predators prefer soft-rayed
  prey)

14
There must be more than just the spines!
15
Anti-Predator Adaptations

• Large spines (many predators prefer soft-rayed
  prey)
• Sensitive detection devices
• Lateral-line system
• Tapetum lucidum

16
Anti-Predator Adaptations

• Large spines (many predators prefer soft-rayed
  prey)
• Sensitive detection devices
• Difficult to detect
• Usually active at twilight or night

17
Example -- Diel Activity(from Ogle et al. 1995)
Adults
300
2 m
200
Number Caught
100
0
0
1000
2000
Surface Light (?mol)
18
Anti-Predator Adaptations

• Large spines (many predators prefer soft-rayed
  prey)
• Sensitive detection devices
• Difficult to detect
• Usually active at twilight or night
• Use of benthic habitats

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Example -- Bottom-dwellers(modified from Bergman
1988)
100
80
60
Bottom
of time
40
20
0
0
0.02
1
10
Light Level (lux)
20
Anti-Predator Adaptations

• Large spines (many predators prefer soft-rayed
  prey)
• Sensitive detection devices
• Difficult to detect
• Usually active at twilight or night
• Use of benthic habitats
• Cryptic coloration

21
Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Broad physiological and ecological tolerances
• Flexible diet
• Reduced vulnerability to predation
• Fast growth

22
Example -- Range of Growth Rates
Holker Hammer (1994)
Lind (1977)
Length (mm)
Age
23
Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Broad physiological and ecological tolerances
• Flexible diet
• Reduced vulnerability to predation
• Fast growth
• Reproductive behavior
• Early maturation
• Extended or continuous breeding
• Multiple clutches

24
Reproduction -- Generalities

• Ruffe may mature at age I
• L. IJssel -- 50 mature (Willemsen 1977)
• Spawn mid-April to July, temps from 6-18oC
• Nadym R. -- June, 6-8oC (Kolomin 1977)
• L. Aydat -- April-June, 15-18oC (Jamet Desmolls
  1994)
• Spawning season may be prolonged
• mid-April to June in Lake Ilmen (Kovalev 1963)

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Reproduction -- Generalities (Cont)

• Batch spawners in some instances
• spawn one to three batches of ova over a 2-mo
  spawning season in Lake Glubokoe, USSR (Koshelev
  (1963), as reported by Hokanson (1977))
• Absolute fecundity between 5000 82000
• compare to 36000-109000 for yellow perch (15-25
  cm)
• compare to 7200-38000 for bluegill (14-18 cm)

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Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Suggested negative effects on other species

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Example - Ruffe Density Perch Growth(from
Bergman Greenberg 1994)
2
1
Log Perch Growth (g)
0
-1
0
5
10
15
20
25
Ruffe Density (g/m2)
28
Example - C. lavaretus Egg Predation(Loch Lomond
from Adams Tippett 1991)
Occurrence
by Weight
29
Example - C. lavaretus Egg Predation(Lake
Constance from Rosch Schmid 1996)
Whitefish Started Spawning
60
40
Occurrence in Ruffe
20
0
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Why we were initially concerned

• Ruffe is generally despised!!
• High potential to be a pest!!
• Suggested negative effects on other species
• Rapid population growth upon invasion

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Example -- Loch Lomond(from Adams and Maitland,
1998)
14000
12000
10000
8000
Number Fish Impinged
6000
4000
2000
0
82
84
86
88
90
92
94
96
Year (19__)
32
Recall why we were concerned?

• Ruffe is generally despised!!
• High potential to be a pest!!
• Suggested negative effects on other species
• Rapid population growth upon invasion

Are we still concerned?
33
Density in the St. Louis River(from Bronte et
al. 1998)
Density (Geo. Mean)
89
90
91
92
93
94
95
96
Year (19__)
34
North American Distribution(from U.S. Fish
Wildl. Serv.)
Superior
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What have we learned?

• Benthophagous (Ogle et al. 1995)
• Consume fish eggs in Lake Superior (Selgeby 1998)
  
• Ruffe might compete with yellow perch (Savino
  Kolar 1996)
• Few ruffe are consumed (Ogle et al. 1996, Mayo et
  al. 1998)
• 100 mature in early invasion (Selgeby 1992)
• spawn late April to late June (Brown et al. 1998)
• Even minimal impacts will be costly (Leigh 1998)
• AND MORE WE WILL LEARN TODAY!!!

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Not Everyone Agrees
The general conclusion from the International
Symposium on the Biology and Management of Ruffe
is that ruffe may not be as great a threat to
yellow perch, walleye, and Coregonus spp in the
Great Lakes as was first thought.
37
Not Everyone Agrees
38
Not Everyone Agrees
biologists contend that healthy sport and
forage fish populations are being sustained in
ruffe-infested areas. Ohio Sea Grant Extension
Specialist Fred Snyder agrees with Lake Superior
biologists who believe that if ruffe were going
to wipe out fisheries they would be doing it by
now. Researchers are finding that ruffe diets and
yellow perch diets do not have much overlap a
major fear over the last ten years.
39
Not Everyone Agrees
Although we need to resist further invasions of
exotics and do our best to minimize spreads and
impacts, Snyder adds, the available information
indicates that Lake Erie is likely to absorb the
ruffe invasion eventually without major
consequences.
40
A Ruffe Introduction
Derek H. Ogle Mathematics Department Northland
College Ashland, WI