Top Predators

Foragefauna

Zoo

Phyto

Data on trophic ecology of top predators

Stomach Content Analyses

Stable Isotope Analyses(Acoustics)

• To investigate feeding ecology& trophic structure in high-sea

ecosystems

• To document the diversityof the forage fauna

(micronekton)

stomachs are frozen

Stomachsare taken

from freshlycaught fishes

and analysed in the lab

Diet indices on preyOccurrence

Mean NumberMean Reconstituted Weight

DietFeeding rangeTrophic overlap

Prey size distributionsSize ratios

Stomach content data

INDIAN OCEAN: 2 databases

– YugNIRO 1962 to 1990 (Soviet Union)Low level of prey identification – Heterogeneity of data

– STOMAC 2000 to 2010 (IRD)Small spatial and temporal scales – High identification prey level

YugNIRO (Indian Ocean) STOMAC (West Indian Ocean)

> 20,000 stomachs6 main predators

300 prey taxa5 functional groups

6 main predators

Yellowfin tuna (Thunnus albacares)

Bigeye tuna (Thunnus obesus)

Skipjack (Katsuwonus pelamis)

Dolphinfish (Coryphaena hippurus)

Longnose lancetfish (Alepisaurus ferox)

Swordfish (Xiphias gladius)

Epi-Pel

Epi-Meso

Meso

Bathy

Meso-Bathy

Functional prey groups vs >300 prey taxa

dept

h

+ΔN +ΔN +ΔN +ΔN

15N = n‰ 15N = n + 4ΔN‰ΔN = Trophic enrichment

15Nbaseline

15Npredator

Stable isotope ratios of N in consumers reflect thoseof their prey as they are enriched in a predictable mannerd15N serve as indicators of consumer trophic position

Stable Isotope Analyses (d15N, d13C)

a tool to investigate trophic relationships (trophic tracers)

″ You are what you eat, plus a few per mil "

PRINCIPE : les processus biologiques, physiques et chimiques induisent une répartition différentielle des éléments légers et lourds

Cause : essentiellement dus aux différences de masse

- variation de certaines propriétés physico-chimiques

- modification des vitesses des réactions chimiques

réactivité différentielle

changement du rapport entre éléments lourds et légers

Nitrogen Isotope Fractionation

Rate of 14NH4+ excretion is

greater than the rate of 15NH4

+ excretion

δ15Npredator = ~3.0 + δ15Nprey (‰)NO3

-, NH4+ N2

14NH4+

14NH4+

14NH4+

14NH4+

14NH4+

2

4

6

8

10

12

14

16

-22 -21 -20 -19 -18 -17 -16d13C

d 15

N

Top predators

Micronekton

Gelatinous zooplankton

Tuna postlarvae

Fish

Crus Ceph

SWO

BET

YFT

• Multispecies trophic models of ecosystems depend on accurate depiction of trophic links

• Trophic level estimation using d15N

Stable Isotope Analyses (d15N, d13C): a tool to investigate trophic relationships

Latitudinal effect on d15N : differences in nitrogen dynamics existing at the base of the food web propagate along the food chain up to top predators

11

13

15

17

-30 -20 -10 0 10

Latitude

Pre

dic

ted

d15

N

YFT SWO Body Size = 160cm

• Isoscapes…

d15N isoscapes for bigeye (n = 196) and yellowfin (n = 387) tunaValues were normalized against the average within the study region (Graham et al.)

Residuals between the interpolated d15N values for the two

species

bigeye

yellowfin