Qualitative analysis of food webs in the Pacific Ocean

J Young, J Dambacher, R Olson, V Allain, F Galvan-Magana, M Lansdell, N Bocanegra-Castillo, V Alatorre-Ramirez, S Cooper, L Duffy

Wealth from Oceans

Acknowledgements

http://www.frdc.com.au/�

Origins of the study

Reports also in PFRP Newsletter, GLOBEC newsletter

Prey Fam Tot Wt g % Wt'Other Teleostei' 2049 56.3Scombridae 557 15.3'Other Cephalopoda' 308 8.5Ommastrephidae 153 4.2'Unidentified' 145 4.0Exocoetidae 76 2.1Engraulidae 59 1.6Gempylidae 59 1.6Carangidae 40 1.1Thalassocarididae 26 0.7'Caridea' 17 0.5'Hyperiidea' 16 0.4Alepisauridae 15 0.4Bramidae 13 0.4Monacanthidae 10 0.3Acanthuridae 9 0.3'Decapoda' 8 0.2'Stomatopoda' 7 0.2Argonautidae 7 0.2Serranidae 6 0.2

Skipjack tunatrophic links

Multiple predators

Understanding complexity through system structure or if this is all we know then what do we know?

Bray-Curtisyou are whoyou eat.

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Social networkyou are whoyou eat andwho eats you!

Aim

Perturb an influential species (yellowfin tuna) that could be directly affected by ocean warming and trace the effects to commercially important species in three different regions of the Pacific Ocean

Stomach collections

Stomachs collected : CSIRO 3102, SPC 1691, IATTC 3882Sampling area ~ 35 million km2Prey taxa 651 overall248 taxa > 1% wet weight

CSIRO (PESCI) data base

Key player analysis

Fragmentationthe species/group that, when removed, causes the most disruption or fragmentation is the key player

Qualitative analyses: method flow chart

Perturbationsof species/groups to positive or negative inputs e.g. temperature

“Full” diet matrix (after removal of weak links and isolates

Reachthe influence of a species/group

Reduced model/Aggregation (REGE)

Qualitative dynamics

Role equivalence(social network theory)

SW Pacific Food Web: Key Player AnalysesRemoval/Fragmentation

yellowfin tuna

Key players - identified from their reach through, and their ability to fragment, a food web

Insert presentation title

sw cw ceLancetfish + +Mahi +Opah +Skipjack +Albacore +Yellowfin + +swordfish +tripletail +squid + +

Southwest Pacific Ocean

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swordfishyft

lancetfishsquid

Small fish Key players•yellowfin tuna•Swordfish•lancetfish•squid•small fish

S = 109TL=3.6

Central Western Pacific Ocean

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Key players•albacore•mahi mahi•squid, •small fish

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Central Eastern Pacific Ocean

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yft

Key players•yellowfin tuna•Triple tail•mahi mahi•skipjack •small fish

S = 91TL=3.5

Aggregated food webs of three regions of the Pacific Ocean.

T1 4.30.02

South Western Pacific Ocean

Predation Trophic Level

Tier mean SD

T2 4.20.31

T3 3.40.66

T1 4.40.13

T2 4.00.47

T3 3.80.55

T4 3.20.63

T1 4.20.27

T2 4.20.29

T3 3.60.65

T4 3.00.76

Central Western Pacific Ocean

Central Eastern Pacific Ocean

•Nodes represent groups of taxa with similar predator–prey relationships and are arranged in predation tiers (Tn)

•Groups with asterisks contain key players. Shown for each tier are mean and standard deviation of trophic levels of taxa in each group.

•These network structures were used to create qualitative models of each pelagic ecosystem, which were used for perturbation analyses.

+: yellowfin tuna

-: swordfish, albacore,southern bluefin tuna

-: bigeye tuna

-: squid

--+: mako sharkSW Pacific Food Web: climate change scenarios

+

-

Perturbation response of increasing yellowfin tuna on other commercial fish species

Mahimahi

Skipjack Albacore Bigeye tuna

swordfish

South western Pacific

- + - - -

Centralwestern Pacific

+ - - + +

Central eastern Pacific

+ - - - na

Conclusions, caveats and future research

•Identified species that were “key players” in the three regions•Positive perturbation of yellowfin tuna impacted commercially important species in SW Pacific, varying results in other regions•Sharks not keystone species (support from quantitative studies)•Response of a species to a change in ocean conditions (e.g. ocean warming) depends on food web structure – importance of detail in trophic studiesCaveats•Sampling methodology (Lancetfish longline caught v rainbow runners purse seine)Future research•Fisheries exploitation and feedbacks that drive fishing fleet•Direct comparisons with quantitative models

Qualitative analysis of food webs in the Pacific OceanAcknowledgementsOrigins of the studySlide Number 4Slide Number 5Multiple predatorsSlide Number 7Slide Number 8AimStomach collectionsSlide Number 11Slide Number 12Key players - identified from their reach through, and their ability to fragment, a food webSouthwest Pacific OceanCentral Western Pacific OceanCentral Eastern Pacific OceanAggregated food webs of three regions of the Pacific Ocean.Slide Number 18Perturbation response of increasing yellowfin tuna on other commercial fish speciesConclusions, caveats and future research