Trophic Signatures of Elasmobranchs:
a Comparison between Tropical and
Temperate Ecosystems.
Rainer Froese
IfM Kiel
rfroese@ifm.uni-kiel.de
Trophic Signatures: Methods
• Get diet composition or food items
• Troph = 1 + weighted mean troph of food
• Example:
50% fish of troph 3
+ 50% fish of troph 4
+
1
= predator troph 4.5
Trophic Signatures: Methods
• Diet composition by weight or volume
• Monte Carlo routine to estimate diet with s.e.
from known food items (TrophLab)
• If no food known, use mean troph of congeners
or of family (troph varies less than food items)
• Data, TrophLab and Trophic Pyramids available
in www.fishbase.org
Trophic Signatures: All Marine Fish
5
4.5
All marine fish
(13,442)
Trophic Level
4
3.5
3.2
3
2.5
2
1
10
100
Num ber of Species
1000
10000
Trophic Signatures: Elasmobranchs
5
All marine fish
(13,442)
4.5
Trophic Level
4
Elasmo
(886)
3.5
3
2.5
2
1
10
100
Num ber of Species
1000
10000
Trophic Signatures: Sharks & Batoids
5
All marine fish
(13,442)
4.5
Trophic Level
4
Elasmo
(886)
3.5
Sharks
(394) Batoidei
(492)
3
2.5
2
1
10
100
Num ber of Species
1000
10000
Size by Trophic Level
5
All marine fish
4.5
Trophic Level
4
Elasmobranchs
3.5
3
2.5
2
0
50
100
150
Mean m ax. Length of Fish Species (cm TL)
200
Temperate vs Tropical
Marine fish
Elasmos (%)
All
Oceans
Deep
Sea
13,442
2,794
886 (7)
Troph 4+ (%) 241 (20)
313 (11)
74 (23)
Temperate
Subtropical
Tropical
1,620
2,610
6,248
261 (10)
237 (4)
89 (26)
60 (13)
68 (4)
18 (15)
Large Marine Ecosystems
Large Marine Ecosystems: Issues
• Definition (boarders) of LMEs
• Usually no checklists available
• What to do with `rare guests´
Trophic Signatures in LMEs
South China Sea
5
4.5
Trophic Level
4
3.5
3
2.5
2
1
10
100
Num ber of Fish Species
1000
10000
Trophic Signatures in LMEs
Caribbean
5
4.5
Trophic Level
4
3.5
3
2.5
2
1
10
100
Num ber of Fish Species
1000
10000
Trophic Signatures in LMEs
North Sea
5
4.5
Trophic Level
4
3.5
3
2.5
2
1
10
100
Num ber of Fish Species
1000
10000
Trophic Signatures in LMEs
5
South China Sea
Caribbean
4.5
North Sea
New foundland
Trophic Level
4
Humboldt Current
3.5
3
2.5
2
1
10
100
Num ber of Fish Species
1000
Comparison of Ecosystems
All
South Caribbean Humboldt North NewOceans China S.
Current Sea foundland
Marine fish 13,442 2,488
Elasmo (%)
7
Troph 4+ (%) 20
1,467
724
186
141
7
8
11
13
12
21
31
24
26
20
Conclusions
• Elasmobranchs contribute about 7% to the diversity of
marine fishes
• Elasmobranchs constitute about 20% of the top
predators (troph 4+)
• No clear patterns of elasmobranch diversity emerge (yet)
from comaprisons between temperature zones or LMEs
• Trophic signatures of elasmobranchs are restricted to
higher trophic levels (>3), with most sharks above 3.5
and most batoids below 3.5
• Trophic signatures are evolutionary properties of
ecosystem with potential use for classifying LMEs
Acknowledgement
Thanks are due to the FishBase Team which
assembled the data used in this study.