Qualitative analysis of food webs in the Pacific Ocean

Transcription

1 Qualitative analysis of food webs in the Pacific Ocean Wealth from Oceans J Young, J Dambacher, R Olson, V Allain, F Galvan-Magana, M Lansdell, N Bocanegra- Castillo, V Alatorre-Ramirez, S Cooper, L Duffy

2 Acknowledgements

3 Origins of the study

4 Reports also in PFRP Newsletter, GLOBEC newsletter

5 Skipjack tuna trophic links Prey Fam Tot Wt g % Wt 'Other Teleostei' Scombridae 'Other Cephalopoda' Ommastrephidae 'Unidentified' Exocoetidae Engraulidae Gempylidae Carangidae Thalassocarididae 'Caridea' 'Hyperiidea' Alepisauridae Bramidae Monacanthidae Acanthuridae 'Decapoda' 'Stomatopoda' Argonautidae Serranidae 6 0.2

6 Multiple predators

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

8 Bray-Curtis you are who you eat , Social network you are who you eat and who eats you! 5-7

9 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

10 Stomach collections CSIRO (PESCI) data base Stomachs collected : CSIRO 3102, SPC 1691, IATTC 3882 Sampling area ~ 35 million km2 Prey taxa 651 overall 248 taxa > 1% wet weight

11 Qualitative analyses: method flow chart Full diet matrix (after removal of weak links and isolates Role equivalence (social network theory) Key player analysis Reduced model/ Aggregation (REGE) Fragmentation the species/group that, when removed, causes the most disruption or fragmentation is the key player Reach the influence of a species/group Qualitative dynamics Perturbations of species/groups to positive or negative inputs e.g. temperature

12 SW Pacific Food Web: Key Player Analyses Removal/Fragmentation yellowfin tuna

13 Key players - identified from their reach through, and their ability to fragment, a food web sw cw ce Lancetfish + + Mahi + Opah + Skipjack + Albacore + Yellowfin + + swordfish + tripletail + squid + + Insert presentation title

14 Southwest Pacific Ocean 5.0 Key players yellowfin tuna Swordfish lancetfish squid small fish swordfish yft lancetfish squid S = Small fish TL=

15 Central Western Pacific Ocean 5.0 Key players albacore mahi mahi squid, small fish S = TL=

16 Central Eastern Pacific Ocean yft Key players yellowfin tuna Triple tail mahi mahi skipjack small fish S = 91 TL=

17 Aggregated food webs of three regions of the Pacific Ocean. South Western Pacific Ocean Central Western Pacific Ocean Central Eastern Pacific Ocean Predation Trophic Level Tier T 1 mean 4.3 SD 0.02 T T T T T T T T T 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. T

18 SW Pacific Food Web: climate change scenarios -+: mako shark + - +: yellowfin tuna -: bigeye tuna - -: swordfish, albacore, southern bluefin tuna -: squid

19 Perturbation response of increasing yellowfin tuna on other commercial fish species South western Pacific Central western Pacific Central eastern Pacific Mahi mahi Skipjack Albacore Bigeye tuna na swordfish

20 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 studies Caveats 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