Temperature effects on fish production across a natural thermal gradient

• Published in: Global Change Biology
• Main Authors: O'Gorman, Eoin J., Olafsson, Olafur P., Demars, Benoit O. L., Friberg, Nikolai, Gudbergsson, Gudni, Hannesdottir, Elisabet R., Jackson, Michelle C., Johansson, Liselotte S., Mc Laughlin, Orla, Olafsson, Jon S., Woodward, Guy, Gislason, Gisli M.
• Other Authors: Department of Life Sciences Trieste, Università degli studi di Trieste = University of Trieste, Institute of Life and Environmental Sciences, University of Iceland Reykjavik, The James Hutton Institute, Norwegian Institute for Water Research (NIVA), Institute of Freshwater Fisheries, Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria South Africa, Department of Bioscience, Aarhus University Aarhus, Agroécologie Dijon, Institut National de la Recherche Agronomique (INRA)-Université de Bourgogne (UB)-AgroSup Dijon - Institut National Supérieur des Sciences Agronomiques, de l'Alimentation et de l'Environnement, NERC NE/L011840/1, NE/I009280/2, Royal Society RG140601, British Ecological Society 4009-4884, Fisheries Society of the British Isles; Grand Challenges in Ecosystems; Environment initiative at Imperial College London; Scottish Government Rural and Environment Science and Analytical Services (RESAS); Salmonid Fisheries Management Fund in Reykjavik; Assistantship and Research Funds from the University of Iceland GMG2006, GMG2007
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: natural experiment; Arctic; Hengill; freshwater; Salmo trutta fario; PIT tag; mark-recapture; ecosystem services; [SDV]Life Sciences [q-bio]; Global warming; Iceland
• Online Access: https://hal.science/hal-01604316; https://hal.science/hal-01604316/document; https://hal.science/hal-01604316/file/2016_O%27Gorman_Global%20Change%20Biology_1.pdf; https://doi.org/10.1111/gcb.13233

Global warming is widely predicted to reduce the biomass production of top predators, or even result in species loss. Several exceptions to this expectation have been identified, however, and it is vital that we understand the underlying mechanisms if we are to improve our ability to predict future trends. Here, we used a natural warming experiment in Iceland and quantitative theoretical predictions to investigate the success of brown trout as top predators across a stream temperature gradient (4-25 degrees C). Brown trout are at the northern limit of their geographic distribution in this system, with ambient stream temperatures below their optimum for maximal growth, and above it in the warmest streams. A five-month mark-recapture study revealed that population abundance, biomass, growth rate, and production of trout all increased with stream temperature. We identified two mechanisms that contributed to these responses: (1) trout became more selective in their diet as stream temperature increased, feeding higher in the food web and increasing in trophic position; and (2) trophic transfer through the food web was more efficient in the warmer streams. We found little evidence to support a third potential mechanism: that external subsidies would play a more important role in the diet of trout with increasing stream temperature. Resource availability was also amplified through the trophic levels with warming, as predicted by metabolic theory in nutrient-replete systems. These results highlight circumstances in which top predators can thrive in warmer environments and contribute to our knowledge of warming impacts on natural communities and ecosystem functioning.