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Food-Web Implications for Pelagic Top Predators: from Guts and Isotopes to Models

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Food-web Implications for Pelagic Top Predators: from Guts and Isotopes to Models Robert J. Olson Inter-American Tropical Tuna Commission La Jolla, California Photo compliments of Dr. Frederic Menard, IRD, France Food webs and Ecosystem-based Fisheries Science • “Ecosystem” “Ecology”: multispecies approaches to management, reduction of bycatch, including environmental factors in stock assessment 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. 2005. New priorities for the 21st century: NOAA's strategic plan. NOAA, Washington, D.C. Mangel, M., and P.S. Levin. 2005. Regime, phase and paradigm shifts: making community ecology the basic science for fisheries. Phil. Trans. R. Soc. B, 360 (1453): 95-105. 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). • Review an assortment of information about food- web research in eastern Pacific, and (less-so) on modeling efforts. Eight ecosystem characteristics NMFS Ecosystem Principles Advisory Panel: 1. The ability to predict ecosystem behavior is limited 2. Ecosystems have thresholds and limits which, when exceeded, can effect major ecosystem restructuring 3. Once thresholds and limits have been exceeded, changes can be irreversible 4. Diversity is important to ecosystem functioning 5. Multiple scales interact within and among ecosystems 6. Components of ecosystems are linked 7. Ecosystem boundaries are open 8. Ecosystems change over time Components of ecosystems are linked How do we determine what the important components and linkages are? Critical food-web connections. •Keystone species •Dietary specialists •Models can help The tools for food-web research: •Diet studies (stomach-contents analysis) •Stable isotope analysis •Compound specific stable isotope analysis (amino-acids) •Fatty acid analysis Stomach-contents analysis (species identification) (and monitoring) V. Allain, SPC F. Galvan, CICIMAR IATTC, Manta, Ecuador Diet data for eastern Pacific predators (’92-’94) 100% 80% 60% weight 40% Percent 20% Dorado, Wahoo, R. Runner Billfishes 0% Sharks Dolphins Tunas Colleagues: •Felipe Galván-M, CICIMAR, La Paz, BCS, Mexico •Julio Martínez, Cumaná, Venezuela Diet data formulated food web (ETP) fico ó tr Nivel – Trophic level Trophic Olson, R.J., and G.M. Watters. 2003. A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission, Bulletin 22 (3): 133-218. Yellowfin tuna stomach-contents (1990s, 2000s) Set Locations 1990s 2000s 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 Trophic position: stable isotopes 15N 15 14 15 15 δ = [( N/ N) / Rstd – 1] x 1000 δ Npredator = 3.0 + δ Nprey (‰) Isotopic fractionation – the light 14N isotope is excreted more than the heavy 15N isotope, leaving the animal enriched by 3‰ in δ15N relative to its food source. Trophic position: stable isotopes, stomach contents 18 16 14 12 10 N (‰) 15 8 δ 6 Yellowfin tuna (5-deg areas) 4 Yellowfin tuna (outside 5-deg areas) Mesozooplankton (5-deg areas) 2 Mesozoopl. (outside 5-deg areas) CSIA samples 0 -15 -10 -5 0 5 10 15 20 25 30 Latitude (degrees) Mean TP = 4.5 PFRP, B. Popp, B. Graham, C. Hannides, F. Galván, G. López, B. Fry Yellowfin trophic position (TP) YFT δ15N = 13-16‰ Copepods δ15N = 6-12‰ ΔYFT-COP = 4.0 – 7.6 ‰ Gladis Lopez-I., CICIMAR, Mexico TP ≈ 4.3 - 5.3, spanning ~ 1 trophic level B. Popp, UH B. Graham, UH F. Galvan-Magana, CICIMAR C. Lennert-Cody, IATTC PFRP Popp, B.N., B.S. Graham, R.J. Olson, C.C.S. Hannides, M.J. Lott, G.A. López-Ibarra, F. Galván-Magaña, and B. Fry. 2007. Insight into the trophic ecology of yellowfin tuna, Thunnus albacares, from compound-specific nitrogen isotope analysis of proteinaceous amino acids. In Dawson, T.E., and R.T.W. Siegwolf (eds.), Stable Isotopes as Indicators of Ecological Change. Elsevier-Academic Press, Terrestrial Ecology Series, San Diego: 173-190. Yellowfintuna δ Bulk white muscle 15 N of Amino Amino of Acids N – eastern tropical Pacific (“Source” AA) (“Trophic” AA)(“Trophic” TL 4.5 TL E-W shift in trophic position in ETP TP shift≈1 Lipids as Dietary Tracers Traditional techniques problematic, e.g. gut content analysis Prey species have unique lipid / fatty acid compositions Many fatty acids readily transferred from prey to predator with minimal modification Constituent fatty acids therefore represent, to some extent, a temporal integration of diet Can be quantitative and allows temporal integration (cf gut content analysis) Signature fatty acids: combinations of fatty acids preserved as they pass up the food chain Complements other approaches * Jock Young, CSIRO Eight ecosystem characteristics NMFS Ecosystem Principles Advisory Panel: 1. The ability to predict ecosystem behavior is limited 2. Ecosystems have thresholds and limits which, when exceeded, can effect major ecosystem restructuring 3. Once thresholds and limits have been exceeded, changes can be irreversible 4. Diversity is important to ecosystem functioning 5. Multiple scales interact within and among ecosystems 6. Components of ecosystems are linked 7. Ecosystem boundaries are open 8. Ecosystems change over time Can models predict ecosystem behavior? • Nature is seldom linear, and often unpredictable (Francis et al. 2007) . • Ecosystem resilience depends on “stability domain” of existing food web: how broad is it, how resistant is it to change, how close is it to reorganizing? (Francis et al. 2007) Models are required. • How should components of the food web be represented in models? • Can models highlight key areas for field/lab studies? Francis, R.C., M.A. Hixon, M.E. Clarke, S.A. Murawski, and S. Ralston. 2007. Ten commandments for ecosystem-based fisheries scientists. Fisheries, 32 (5): 217-233. Taxonomy in models fico ó tr Nivel – Trophic level Trophic (Olson, R.J., and G.M. Watters. 2003. A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission, Bulletin 22 (3): 133-218.) Functional groups in models Epipelagic Epi Epi-Meso Meso Epi- Bathy Meso Bathy Meso-Bathy Bathy Qualitative analysis of Pacific Ocean predators 20 N South-Western Pacific Ocean Central-Eastern Pacific Ocean 5.0 77 5.0 76 169 106 75 124 74 43 44 115 121 165 65 170 122 110 168 134 77 152 4.5 33 109 108 159 31 45 157 32 160 154 126 125 4.5 74 75 76 124 106 169 121 115 44 211 85 198 127 173 215 66 70 65 122 165 168 149 172 83 155 163 156 157 114 108 112 126 167 120 161 23 219 37 36 24 12 151 14 2 13 68 4.0 26 4.0 210 212 174 215 116 177 119 117 127 209 38 5 4 147 123 3 113 28 20 18 197 193 37 192 219 196 191 195 25 69 153 27 15 35 34 52 3.5 57 60 51 59 58 64 56 194 178 Food webs 3.5 238 204 153 27 118 63 180 179 64 98 95 89 91 88 79 53 81 80 82 47 78 9 6 103 203 199 201 202 200 206 207 205 3.0 3.0 95 142 49 100 9396 140 92 72 105 102 94 23690 39 71 9 composed of 200+ 229 143 226 223 239 231 235 239 145 234 2.5 2.5 41 taxa level Trophic 245 242 222 247 237 244 246 217 216 2.0 2.0 182 241 232 185 228 1.5 1.5 183 1.0 1.0 243 Aggregated food webs composed of 24 nodes with similar predator prey relationships Can models highlight research needs? Sensitivity analysis of ETP Ecopath model Large marlinsLarge Marlins (5.5) Small sharksSmall Sharks (5.4) Small marlinsSmall Marlins (5.4) Toothed whalesToothed Whales (5.4) LargeLarge bigeye Bigeye Tuna (5.3) Spotted dolphinsSpotted Dolphins (5.2) Large sharksLarge Sharks (5.2) Large wahooLarge Wahoo (5.1) Large swordfishLarge Swordfish (5.1) Large sailfishLarge Sailfish (5.1) PursuitPursuit birds Birds (4.9) Small mahimahiSmall Mahimahi (4.8) Small sailfishSmall Sailfish (4.8) Large mahimahiLarge Mahimahi (4.8) Large Largeyellowfin Yellowfin Tuna (4.8) MesopelagicMesopelagic dolphins Dolphins (4.8) Small wahooSmall Wahoo (4.7) SmallSmall bigeye Bigeye Tuna (4.7) Small Smallyellowfin Yellowfin Tuna (4.7) SkipjackSkipjack Tuna (4.7) CephalopodsCephalopods (4.6) Small swordfishSmall Swordfish (4.6) Misc. piscivoresMisc. Piscivores (4.5) BluefinBluefin tuna Tuna (4.5) Auxis spp.Auxis spp. (4.1) Baleen whalesBaleen Whales (4.1) RaysRays (3.9) GrazingGrazing birds Birds (3.9) Sea turtlesSea Turtles (3.8) CrabsCrabs (3.6) Cephalopods Misc. mesopelagicMisc. Mesopelagic fishes Fishes (3.6) FlyingfishesFlyingfishes (3.6) Auxis spp. Misc. epipelagicMisc. Epipelagic fishes Fishes (3.3) Secondary consumersSecondary Consumers (3.0) Primary consumersPrimary Consumers (2.0) ProducersProducers (1.0) 0 20 40 60 80 100 120 140 160 Index of Sensitivity Eight ecosystem characteristics NMFS Ecosystem Principles Advisory Panel: 1. The ability to predict ecosystem behavior is limited 2. Ecosystems have thresholds and limits which, when exceeded, can effect major ecosystem restructuring 3. Once thresholds and limits have been exceeded, changes can be irreversible 4. Diversity is important to ecosystem functioning 5. Multiple scales interact within and among ecosystems 6. Components of ecosystems are linked 7. Ecosystem boundaries are open 8.
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  • Diet and Stable Isotope Analyses Reveal The

    Diet and Stable Isotope Analyses Reveal The

    RESEARCH ARTICLE Diet and stable isotope analyses reveal the feeding ecology of the orangeback squid Sthenoteuthis pteropus (Steenstrup 1855) (Mollusca, Ommastrephidae) in the eastern tropical Atlantic VeÂronique Merten1*, Bernd Christiansen2, Jamileh Javidpour1, Uwe Piatkowski1, Oscar Puebla1,3, Rebeca Gasca4, Henk-Jan T. Hoving1 a1111111111 a1111111111 1 GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, 2 UniversitaÈt Hamburg, Institute for Hydrobiology and Fishery Sciences, Hamburg, Germany, 3 Christian-Albrechts-UniversitaÈt zu Kiel, Kiel, a1111111111 Germany, 4 El Colegio de la Frontera Sur, Chetumal, Mexico a1111111111 a1111111111 * [email protected] Abstract OPEN ACCESS In the eastern tropical Atlantic, the orangeback flying squid Sthenoteuthis pteropus Citation: Merten V, Christiansen B, Javidpour J, (Steenstrup 1855) (Cephalopoda, Ommastrephidae) is a dominant species of the epipelagic Piatkowski U, Puebla O, Gasca R, et al. (2017) Diet nekton community. This carnivore squid has a short lifespan and is one of the fastest-grow- and stable isotope analyses reveal the feeding ecology of the orangeback squid Sthenoteuthis ing squids. In this study, we characterise the role of S. pteropus in the pelagic food web of pteropus (Steenstrup 1855) (Mollusca, the eastern tropical Atlantic by investigating its diet and the dynamics of its feeding habits Ommastrephidae) in the eastern tropical Atlantic. throughout its ontogeny and migration. During three expeditions in the eastern tropical PLoS ONE 12(12): e0189691. https://doi.org/ 10.1371/journal.pone.0189691 Atlantic in 2015, 129 specimens were caught by hand jigging. Stomach content analyses (via visual identification and DNA barcoding) were combined with stable isotope data (@15N Editor: Erik V. Thuesen, Evergreen State College, 13 UNITED STATES and @ C) of muscle tissue to describe diet, feeding habits and trophic ecology of S.
  • Behavior of Bluefin Tuna Schools in the Eastern North Pacific Ocean As Inferred from Fishermen's Logbooks

    Behavior of Bluefin Tuna Schools in the Eastern North Pacific Ocean As Inferred from Fishermen's Logbooks

    BEHAVIOR OF BLUEFIN TUNA SCHOOLS IN THE EASTERN NORTH PACIFIC OCEAN AS INFERRED FROM FISHERMEN’S LOGBOOKS, 1960-67’ J. MICHAELSCOTT’ AND GLENNA. FLITTNER3 ABSTRACT Fishermen’s records of 8,059 purse-seine sets made on TILunnus thynnus (bluefin tuna) were examined for the period 1960-67. A total of 3,538 sets were identified as to school type. The majority of these sets were made within 90 miles of the beach off southern and Baja California from lat 23ON to 34ON. The region was divided into a northern and southern area on the basis of biological and oceanographic factors. Significant differences were observed in the occurrence of the six most common school types between the northern and southern most areas of the fishery. The difference in occurrence of the jumping, boiling, and shining schools was related to the relative absence of red crabs (Pleuroncodes planipes) in the northern area and to differences in the for- aging behavior of T. thynnus on baitfish and red crabs. Differences in vulnerability to capture and catch per successful set were noted among the five most common daytime schools as well as with respect to time of day. Purse-seine sets made with the assistance of airborne spotters had larger catches and a greater percentage success than did unassisted sets. In addition the percentage of a particular school type taken with aircraft assistance was inversely proportional to the visibility of the schools from the mast. The existence of different school types in scom- schools commonly encountered in the eastern broid fishes has been noted by several authors.