m456p001 - MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser...

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MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 456: 1–6, 2012 doi: 10.3354/meps09785 Published June 7 INTRODUCTION Mesopelagic (200 to 1000 m depth) fishes are important planktivores and prominent prey for higher trophic levels in all the world’s oceans (Gjøsæter & Kawaguchi 1980, Lam & Pauly 2005) and, because of pronounced diel vertical migrations (DVM), contribute to the biological pump whereby organic material is transported from upper layers down to the waters at depth (Hidaka et al. 2001, Hernández-León et al. 2010). The current global bio- mass estimate of mesopelagic fishes, primarily based on catches by micronekton sampling gears prior to 1980, amounts to approximately 1 gigatonne (10 9 t wet weight) (Gjøsæter & Kawaguchi 1980, Lam & Pauly 2005). This is likely an underestimate (Gjøsæter & Kawaguchi 1980) because mesopelagic fishes are not captured quantitatively by sampling gear. Subse- quent gear intercomparisons have revealed marked differences in catch efficiency of mesopelagic fish between different trawl types, due to various influ- ences from extrusion through meshes and net avoid- © Inter-Research 2012 · www.int-res.com *Email: [email protected] FEATURE ARTICLE: NOTE Efficient trawl avoidance by mesopelagic fishes causes large underestimation of their biomass Stein Kaartvedt 1,2, *, Arved Staby 3,4 , Dag L. Aksnes 3 1 King Abdullah University of Science and Technology, Red Sea Research Center, Thuwal 23955-6900, Saudi Arabia 2 Department of Biology, University of Oslo, 0316 Oslo, Norway 3 Department of Biology, University of Bergen, 5020 Bergen, Norway 4 Present address : Institute of Marine Research, 5817 Bergen, Norway ABSTRACT: Mesopelagic fishes occur in all the world’s oceans, but their abundance and consequently their ecological significance remains uncertain. The current global estimate based on net sampling prior to 1980 suggests a global abundance of one gigatonne (10 9 t) wet weight. Here we report novel evidence of efficient avoidance of such sampling by the most common myctophid fish in the Northern Atlantic, i.e. Benthosema glaciale . We reason that similar avoid- ance of nets may explain consistently higher acoustic abundance estimates of mesopelagic fish from dif - ferent parts of the world’s oceans. It appears that mesopelagic fish abundance may be underestimated by one order of magnitude, suggesting that the role of mesopelagic fish in the oceans might need to be revised. KEY WORDS: Mesopelagic fish · Avoidance behavior · Trawling · Acoustics Resale or republication not permitted without written consent of the publisher Mesopelagic fishes show efficient avoidance behavior in response to sampling gears. Image: Hege Vestheim O PEN A CCESS
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Mar Ecol Prog Ser 456: 1–6, 2012 ance behavior (Pakhomov & Yamamura 2010, Heino et al. 2011). However, regardless of trawl type, acoustic abundance estimates always appear to be consistently higher than the net-based estimates (Koslow et al. 1997, Kloser et al. 2009, Pakhomov & Yamamura 2010).
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