Lake Superior Benthic Fish Community Structure
ByMichael H. Hoff
U.S. Geological SurveyGreat Lakes Science Center
Lake Superior Fish Community Objectivesand
Joint Strategic Plan for Management of Great Lakes Fisheries
“The Parties must…meet the biological, chemical, and physical needs of desired fish communities.”
Lake Whitefish
Background
•Great Lakes fishery managers agreed to change from fish species to community management approaches
in 1987.
•The Lake Superior Committee developed the Fish Community Objectives to manage Lake Superior fish communities
Lake herring
Background
•A community is an ecological unit that is structured with unique, quantifiable attributes.
•Statistical analysis has been used in community ecology to; Discover community data structureGraph community data Test for differences in communities
Rainbow smelt
•Dynamics of fish communities can be used to evaluate effects of management changes and ecosystem perturbations (e.g. invasions)
Background
Spoonheadsculpin
Deepwater sculpin
Slimysculpin
•Using statistical analyses, only two fish communities have been described from Lake Superior-
both reside in Chequamegon Bay.
•Fish communities have not been described from Lake Superior’s main basin.
Background
Burbot
Report Objective
To quantitatively describe the summer, benthic fish community structure and habitat associations in Lake Superior by examining the on-contour, bottom-trawl data set.
On-contour trawl tows Cross-contour trawls
Lake Superior
Ship
Trawl
Fishing with a bottom trawl.
Mouth of bottom trawl – side view.
Methods
Sampling
•22 locations sampled during mid-June to mid-September
•937 bottom-trawl tows were taken
•Fish densities (no./hectare) computed from catches and the area swept by trawls
N Ontario
Michigan
Wisconsin
Minnesota
Locations of on-contour bottom-trawl stations sampled during 1972-1995.
Lake Superior
Methods
Data Analysis
•4 statistical procedures 3 multivariate (many variables used)1 univariate (one variable used)
Kiyi
Why all of those statistics?
• No single test exists that examines communitystructure
• An integrated set of procedures was needed for a thorough exploration, examination, and portrayal of the
existence and structure of communities.
Round whitefish
Results
•937 on-contour bottom trawl tows at 22 stations captured 396,390 fish from
26 taxa23 species and stocked lake trout, wild lake trout, siscowet lake troutsplake
Siscowet lake trout
Lake trout
•Only four or less shortjaw ciscoes, splake, pink salmon, white suckers, spottail shiners, and yellow perch were caught in all tows.
•15 taxa were represented by at least 300 specimens.
Shortjaw cisco
5-9.
9
10-1
9.9
20-2
9.9
30-3
9.9
40-4
9.9
50-5
9.9
60-6
9.9
70-7
9.9
80-8
9.9
90-9
9.9
100-
109.
9
110-
119.
9
120-
141
0
50
100
150
200
250
300
Depth (meters)
No.
of
tow
sSample sizes of bottom-trawl tows, by depth group.
•Analysis of densities of 26 taxa accounted for only 30% of the data variation,
•Analysis of densities of 9 taxaaccounted for 65% of the variation.
•Densities of 9 taxa used in further statistical analyses
Ninespine stickleback
Trawl tows classified to depth groups
•Highest overall correct classification rate (80%) was to 5.0-39.9 meters (82% correct) 40.0-79.9 meters (77% correct) > 80.0 meters (56% correct)
•All depth groups classified at rates greater than were possible by chance
Bloater
Differences of 9 taxa densities across depths
•Multivariate analysis showed that densities of the 9 taxa were different across
shallow (5.0-39.9 meters), intermediate (40.0-79.9 meters), and deep (80.0-141 meters) trawl depths.
•Therefore, 3 communities existedand habitats were their depth ranges.
Pygmy whitefish
rainbow smelttrout-perch
ninesp. stickleback
slimy sculpinlake whitefish
siscowet troutbloater
kiyideepw. sculpin
0 10 20 30 40 50
Shallow (5.0-39.9 m) Intermediate (40.0-79.9) Deep (80.0-141 m)
shallow > intermediate > deepshallow > intermediate, deepshallow, intermediate > deepshallow, intermediate > deep
intermediate > deep
deep > shallow, intermediate
deep > intermediate > shallowdeep > shallow, intermediatedeep > intermediate > shallow
Significance testComparison of densities of 9 fish taxa across depths.
No./hectare
Significant Depth Associations of Other 17 Taxa
None found – 10 taxaalewife splake pink salmon lake chub spottail shiner white suckerlongnose sucker burbot yellow perchspoonhead sculpin
Sample sizes small (< 216) of all but alewife and spoonhead sculpin
Rainbo
w smelt
Trout
-per
ch
Round
whit
efish
Pygm
y whit
efish
John
ny d
arte
r
Ninesp
. stic
kleba
ck
Slimy s
culpi
n
Wild
lake
trou
t
Stock
ed la
ke tr
out
Lake
her
ring
Lake
whit
efish
Siscow
et la
ke tr
out
Bloate
rKiyi
Deepw
ater
sculp
in
Shortj
aw ci
sco
0123456
Density (no./hectare)5.0-39.9 40.0-79.9 80.0-141.0
Densities, by depth, of 16 taxa in Lake Superior.
Depth (meters)
Shallow Shallow &Intermed.
Intermediate Deep
Conclusions
•Lake Superior contained 3 summer, benthic fish communities.
•Their habitats were described by depth ranges Shallow (5.0-39.9 meters)Intermediate (40.0-79.9 meters)
Deep (80.0-141 meters) Trout-perch
Lake Superior bays, and main basin depth zones.
Bays
Bays
< 80 m > 80 m
•Although a gradient of densities occurred across all depths for some taxa,
densities changed abruptly with depth for:
wild lake trout siscowet lake trout round whitefish pygmy whitefish
bloater kiyi slimy sculpin deepwater sculpintrout-perch ninespine stickleback
johnny darter
Johnny darter
Recommendations
1. Lake Superior fish populations have changedsince much of the data were collected
A study of the present structure of benthic fish communities is needed.
2. Agencies need to consider fish communities when implementing management strategies to achieve Fish Community Objectives.
Recommendations
Recommendations
3. Fish community structures should be documented in;bays harbors estuaries tributariesAreas of Concern, and pelagia (above bottom) of main basin.
Except pelagia, all those habitats are highly vulnerable to pollution and habitat degradation.
Recommendations
4. Need to construct models that relate fish population & community data to habitat measures
Model outputs will better enable managementto rehabilitate damaged ecosystems(Remember: Ecosystem = community + its habitat).
Recommendations
Areas of Concern (AOC)•7 of the 8 have degraded fish populations and habitats.
•Comparisons of community structures in AOCs, with similar areas not damaged, will help managers refine AOCfish community and habitat objectives.
Areas of Concern (continued)
•Monitoring structures of communities in AOCs will track progress in rehabilitating their degraded
populations, communities, and habitats.
Recommendations
Acknowledgements
Thanks to G. Cholwek, M. Burnham-Curtis, and J. Lyons for some of the photographs.
Rainbo
w smelt
Trout
-per
ch
Round
whit
efish
Pygm
y whit
efish
John
ny d
arte
r
Ninesp
. stic
kleba
ck
Slimy s
culpi
n
Wild
lake
trou
t
Stock
ed la
ke tr
out
Lake
her
ring
Lake
whit
efish
Siscow
et la
ke tr
out
Bloate
rKiyi
Deepw
ater
sculp
in
Shortj
aw ci
sco
0123456
Density (no./hectare)5.0-39.9 40.0-79.9 80.0-141.0
Densities, by depth group, of 16 taxa in Lake Superior.
Depth (meters)
Shallow Shallow &Intermed.
Intermediate Deep