Ecosystem Models: Food webs

Transcription

1 Ecosystem Models: Food webs How should components of the food web be represented in models? Ecosystem: a geographically specified system of organisms, including humans, the environment, and the processes that control its dynamics (NOAA 2005). The time has come for community ecology to replace population ecology as the fundamental ecological science underlying fisheries (Mangel and Levin 2005). Communities are assemblages of species. Interactions makes the community more than the sum of its parts. Communities interact via the food web. NOAA New priorities for the 21st century: NOAA's strategic plan. NOAA, Washington, D.C. Mangel, M., and P.S. Levin Regime, phase and paradigm shifts: making community ecology the basic science for fisheries. Phil. Trans. R. Soc. B, 360 (1453):

2 Food web of pelagic ETP Trophic level Nivel trófico Olson, R.J., and G.M. Watters A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission, Bulletin 22 (3):

3 Functional groups in models Epi Epipelagic Epi-Meso Meso Epi- Bathy Meso Bathy Meso-Bathy Bathy

4 Food web of pelagic EPO (a hypothesis) Trophic level Nivel trófico Olson, R.J., and G.M. Watters A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission, Bulletin 22 (3):

5 TROPHIC STRUCTURE AND TUNA MOVEMENT IN THE COLD TONGUE-WARM POOL PELAGIC ECOSYSTEM OF THE EQUATORIAL PACIFIC PFRP project # PRINCIPAL INVESTIGATORS Valerie ALLAIN Robert Olson Felipe Galvan-Magaña Brian Popp Secretariat of the Pacific Community, New Caledonia Inter-American Tropical Tuna Commission Centro Interdisciplinario de Ciencias Marinas, Mexico University of Hawaii COLLABORATOR Brian Fry Louisiana University Three-year project to begin in January 2003

6 Diet contrast: 1990s versus 2000s (node 15, n=1332) (node 14, n=479) Vinciguerria lucetia 2000s: Mesopel. fishes 90s: Epipelagic fishes Auxis spp. Frigate/bullet tuna

7 Two trophic pathways Auxis, cephalopods Epipelagic Mesopelagic Watters, G.M., R.J. Olson, R.C. Francis, P.C. Fiedler, J.J. Polovina, S.B. Reilly, K.Y. Aydin, C.H. Boggs, T.E. Essington, C.J. Walters, and J.F. Kitchell Physical forcing and the dynamics of the pelagic ecosystem in the eastern tropical Pacific: simulations with ENSO-scale and global-warming climate drivers. Can. J. Fish. Aquat. Sci. 60 (9):

8 Prey size distributions Daily rations Predator size range cm Predator size range cm Frequency Prey Size (mm) Olson, R. J., and A. J. Mullen Recent developments for making gastric evacuation and daily ration determinations. Environmental Biology of Fishes. 16: Food consumption per day (% of body weight)

9 Stock Assessment: YFT Summary The population may have recently switched from a high to a lower productivity regime Compliments of Alexandre Aires-da-Silva, IATTC

10 Summary: Ecosystem change (without caveats) 1990s 2000s High YFT recruitment ( ) Intermediate YFT recruitment ( ) Higher productivity regime Less jumbo squid, smaller range Abundance of highly productive epipelagic prey (i.e. Auxis spp.) Higher daily rations Larger prey sizes Shorter food webs (greater transfer efficiency) Lower productivity regime More jumbo squid, range expansion Increase in highly productive mesopelagic prey (e.g. mesopel. fishes, cephalopods) Lower daily rations Smaller prey sizes Longer food webs (lower transfer efficiency)

11 Food web of pelagic EPO Trophic level Nivel trófico Olson, R.J., and G.M. Watters A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission, Bulletin 22 (3):

12 Feeding Ecology of Surface Migrating Myctophid Fishes in the eastern Tropical Pacific Joel Van Noord, Univ. of San Diego Jessica Redfern et al., NMFS SWFSC

13 Chai, F., R.C. Dugdale, T.-H. Peng, F.P. Wilkerson, and R.T. Barber One-dimensional ecosystem model of the equatorial Pacific upwelling system. Part I: model development and silicon and nitrogen cycle. Deep-Sea Research II. 49 (13-14): Food Web equatorial Pacific 3.45 Misc. mesopelagic fishes Myctophidae, Phosichthyidae ETP EwE model (Olson & Watters 2003) (64%) 2.0 (36%) Microzooplankton Heterotrophic nanoflagellates, heterotr. dinoflagellates, ciliates, crustacean nauplii. (100%) (70%) Mesozooplankton Copepods, euphausiids, pteropods, amphipods, ctenophores (30%) Small Producers Pico- nanophytoplankton Large Phytoplankton diatoms 1.0

14 Chai, F., R.C. Dugdale, T.-H. Peng, F.P. Wilkerson, and R.T. Barber One-dimensional ecosystem model of the equatorial Pacific upwelling system. Part I: model development and silicon and nitrogen cycle. Deep-Sea Research II. 49 (13-14): Food Web equatorial Pacific 3.7 Misc. mesopelagic fishes Myctophidae, Phosichthyidae (Van Noord et al. In review) (~100%) 2.0 Microzooplankton Heterotrophic nanoflagellates, heterotr. Dinoflagellates, ciliates, crustacean nauplii (100%) (70%) Mesozooplankton Copepods, euphausiids, pteropods, chaetognaths, ctenophores (30%) Small Producers Pico- nanophytoplankton Large Phytoplankton diatoms 1.0

15 Key Data for Ecosystem Models Spatial scope of model. Definition of food web components (keystone species, dietary specialists). Aggregation/disaggregation (Pinnegar et al. 2005) Do critical food-web connections exist? Distribution & abundance of managed stocks, non-target species, and forage base. Spatiallyexplicit models. Pinnegar, J.K., J.L. Blanchard, S. Mackinson, R.D. Scott, and D.E. Duplisea Aggregation and removal of weak-links in food-web models: system stability and recovery from disturbance. Ecological Modelling. 184:

16 Understanding changes in pelagic ecosystems: 1. Monitoring Issue: Fisheries-independent surveys of micronekton forage communities using nets or acoustics expensive and difficult. Recommendation: Low-level, carefully-designed, continuous stomach sampling program of tunas to monitor changes in mid-trophic levels. Generalist predators as biological samplers: Ubiquitous in EPO High energy requirements Energy limited (bioenergetics, growth) Low prey size selectivity (large yellowfin) Diversity in YFT diet in EPO mirrors broad-scale species diversity patterns described in literature.

17 Why study food webs? Trophic structure represented in food webs is thought to be the central organizing concept in ecology (Martinez 1995). Knowledge of pelagic food webs is still rudimentary, in many aspects. Better food-web models are needed (preferably, spatially-explicit).

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19 Can models highlight research needs? Sensitivity analysis of ETP Ecopath model Large marlins Large Marlins Small sharks Small Sharks Small marlins Small Marlins Toothed whales Toothed Whales Large bigeye Large Bigeye Tuna Spotted dolphins Spotted Dolphins Large sharks Large Sharks Large wahoo Large Wahoo Large swordfish Large Swordfish Large sailfish Large Sailfish Pursuit birds Pursuit Birds Small mahimahi Small Mahimahi Small sailfish Small Sailfish Large mahimahi Large Mahimahi Large yellowfin Large Yellowfin Tuna Mesopelagic Mesopelagic dolphins Dolphins Small wahoo Small Wahoo Small Bigeye bigeye Tuna Small yellowfin Small Yellowfin Tuna Skipjack Tuna Cephalopods Cephalopods Small swordfish Small Swordfish Misc. piscivores Misc. Piscivores Bluefin Bluefin tuna Tuna Auxis spp. Auxis spp. Baleen whales Baleen Whales Rays Rays Grazing Grazing birds Birds Sea turtles Sea Turtles Crabs Misc. mesopelagic fishes Misc. Mesopelagic Fishes Flyingfishes Misc. epipelagic fishes Misc. Epipelagic Fishes Secondary Consumers Secondary consumers Primary consumers Primary Consumers Producers (5.3) (5.2) (5.1) (5.1) (5.1) (4.9) (4.8) (4.8) (4.8) (4.8) (4.8) (4.7) (4.7) (4.7) (4.6) (4.5) (4.5) (4.1) (3.9) (3.9) (3.8) (3.6) (3.6) (3.6) (1.0) (5.2) (5.5) (5.4) (4.7) (2.0) (5.4) (3.3) (3.0) (5.4) (4.1) Cephalopods Auxis spp. (4.6) Index of Sensitivity

20 Pelagic ommastrephid squids (e.g. Dosidicus gigas): Ecosystem indicators? Olson, R.J., M.H. Román-Verdesoto, and G.L. Macías-Pita Bycatch of jumbo squid Dosidicus gigas in the tuna purse-seine fishery of the eastern Pacific Ocean and predatory behaviour during capture. Fish. Res. 79(1-2):

21 Percent frequency of cephalopods in the stomach contents of yellowfin tuna in the eastern Pacific Ocean 100 Percent frequency of occurrence Unidentified Octopus Squid All cephalopods PFRP, F. Galvan, N. Bocanegra, V. Alatorre, J. Martinez, F. Alverson Hunsicker, Essington, Olson, Duffy. Manuscript in prep. Evidence of increased cephalopod production in a large marine ecosystem.