TY - JOUR
T1 - Food-web inferences of stable isotope spatial patterns in copepods and yellowfin tuna in the pelagic eastern Pacific Ocean
AU - Olson, Robert J.
AU - Popp, Brian N.
AU - Graham, Brittany S.
AU - López-Ibarra, Gladis A.
AU - Galván-Magaña, Felipe
AU - Lennert-Cody, Cleridy E.
AU - Bocanegra-Castillo, Noemi
AU - Wallsgrove, Natalie J.
AU - Gier, Elizabeth
AU - Alatorre-Ramírez, Vanessa
AU - Ballance, Lisa T.
AU - Fry, Brian
N1 - Funding Information:
This project was funded by Cooperative Agreement NA17RJ1230 between the Joint Institute for Marine and Atmospheric Research (JIMAR) and the National Oceanic and Atmospheric Administration (NOAA). The views expressed herein are those of the authors, and do not necessarily reflect the views of NOAA or any of its subdivisions. B.S. Graham was supported by a Pelagic Fisheries Research Program (PFRP) graduate assistantship. F. Galván-Magaña was supported by the Instituto Politécnico Nacional (COFAA and EDI), and N. Bocanegra-Castillo and V. Alatorre-Ramírez were supported by CONACYT and PIFI. We are grateful to NOAA Fisheries, Southwest Fisheries Science Center (SWFSC), USA, especially V. Andreassi, N. Bowlin, R. Dotson, D. Griffiths, C. Hall, M. Kelley, K. Kopitsky, and R. Pitman for collecting and making available the zooplankton samples on the STAR2003 cruises. Samples of tuna were collected by a team of observers in Ecuador and Mexico, with the valuable assistance of E. Largacha, H. Pérez, K. Loor, V. Fuentes, C. de la A.-Florencia, A. Basante, W. Paladines, F. Cruz, C. Maldonado, and the captains and crew of several purse-seine vessels. We thank J. Sibert, former program manager of the Pelagic Fisheries Research Program (PFRP), University of Hawaii at Manoa, for his support, and S. Hernandez-Trujillo, CICIMAR Project CGPI:20060472, for his support. We also thank J. Tanimoto, T. Rust, and A. Carter for their assistance with isotopic analysis, V. Allain for PFRP project leadership and advice, L. Duffy for assistance with the diet data, and C. Patnode, M. Román, and L. Duffy for assistance with the graphics. Assistance with stomach-content analysis was provided in Ecuador by L. Cedeño, J. Morales and M. Loor. The manuscript was improved by reviews of W. Bayliff and R. Deriso, IATTC, and by two anonymous reviewers. This is SOEST contribution number 7930.
PY - 2010/7
Y1 - 2010/7
N2 - Evaluating the impacts of climate and fishing on oceanic ecosystems requires an improved understanding of the trophodynamics of pelagic food webs. Our approach was to examine broad-scale spatial relationships among the stable N isotope values of copepods and yellowfin tuna (Thunnus albacares), and to quantify yellowfin tuna trophic status in the food web based on stable-isotope and stomach-contents analyses. Using a generalized additive model fitted to abundance-weighted-average δ15N values of several omnivorous copepod species, we examined isotopic spatial relationships among yellowfin tuna and copepods. We found a broad-scale, uniform gradient in δ15N values of copepods increasing from south to north in a region encompassing the eastern Pacific warm pool and parts of several current systems. Over the same region, a similar trend was observed for the δ15N values in the white muscle of yellowfin tuna caught by the purse-seine fishery, implying limited movement behavior. Assuming the omnivorous copepods represent a proxy for the δ15N values at the base of the food web, the isotopic difference between these two taxa, "ΔYFT-COP," was interpreted as a trophic-position offset. Yellowfin tuna trophic-position estimates based on their bulk δ15N values were not significantly different than independent estimates based on stomach contents, but are sensitive to errors in the trophic enrichment factor and the trophic position of copepods. An apparent inshore-offshore, east to west gradient in yellowfin tuna trophic position was corroborated using compound-specific isotope analysis of amino acids conducted on a subset of samples. The gradient was not explained by the distribution of yellowfin tuna of different sizes, by seasonal variability at the base of the food web, or by known ambit distances (i.e. movements). Yellowfin tuna stomach contents did not show a regular inshore-offshore gradient in trophic position during 2003-2005, but the trophic-position estimates based on both methods had similar scales of variability. We conclude that trophic status of yellowfin tuna increased significantly from east to west over the study area based on the spatial pattern of ΔYFT-COP values and the difference between the δ15N values of glutamic acid and glycine, "trophic" and "source" amino acids, respectively. These results provide improved depictions of trophic links and biomass flows for food-web models, effective tools to evaluate climate and fishing effects on exploited ecosystems.
AB - Evaluating the impacts of climate and fishing on oceanic ecosystems requires an improved understanding of the trophodynamics of pelagic food webs. Our approach was to examine broad-scale spatial relationships among the stable N isotope values of copepods and yellowfin tuna (Thunnus albacares), and to quantify yellowfin tuna trophic status in the food web based on stable-isotope and stomach-contents analyses. Using a generalized additive model fitted to abundance-weighted-average δ15N values of several omnivorous copepod species, we examined isotopic spatial relationships among yellowfin tuna and copepods. We found a broad-scale, uniform gradient in δ15N values of copepods increasing from south to north in a region encompassing the eastern Pacific warm pool and parts of several current systems. Over the same region, a similar trend was observed for the δ15N values in the white muscle of yellowfin tuna caught by the purse-seine fishery, implying limited movement behavior. Assuming the omnivorous copepods represent a proxy for the δ15N values at the base of the food web, the isotopic difference between these two taxa, "ΔYFT-COP," was interpreted as a trophic-position offset. Yellowfin tuna trophic-position estimates based on their bulk δ15N values were not significantly different than independent estimates based on stomach contents, but are sensitive to errors in the trophic enrichment factor and the trophic position of copepods. An apparent inshore-offshore, east to west gradient in yellowfin tuna trophic position was corroborated using compound-specific isotope analysis of amino acids conducted on a subset of samples. The gradient was not explained by the distribution of yellowfin tuna of different sizes, by seasonal variability at the base of the food web, or by known ambit distances (i.e. movements). Yellowfin tuna stomach contents did not show a regular inshore-offshore gradient in trophic position during 2003-2005, but the trophic-position estimates based on both methods had similar scales of variability. We conclude that trophic status of yellowfin tuna increased significantly from east to west over the study area based on the spatial pattern of ΔYFT-COP values and the difference between the δ15N values of glutamic acid and glycine, "trophic" and "source" amino acids, respectively. These results provide improved depictions of trophic links and biomass flows for food-web models, effective tools to evaluate climate and fishing effects on exploited ecosystems.
UR - http://www.scopus.com/inward/record.url?scp=77957134059&partnerID=8YFLogxK
U2 - 10.1016/j.pocean.2010.04.026
DO - 10.1016/j.pocean.2010.04.026
M3 - Artículo
AN - SCOPUS:77957134059
SN - 0079-6611
VL - 86
SP - 124
EP - 138
JO - Progress in Oceanography
JF - Progress in Oceanography
IS - 1-2
ER -