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MEPS 633:55-69 (2020)  -  DOI:

Variability in age of a Southern Ocean myctophid (Gymnoscopelus nicholsi) derived from scat-recovered otoliths

Angela D. Klemmedson1,*, Christian S. Reiss2, Michael E. Goebel2, Ronald S. Kaufmann1, Emmanis Dorval3, Tomasz B. Linkowski4, Renato Borras-Chavez5

1Department of Environmental and Ocean Sciences, University of San Diego, San Diego, CA 92110, USA
2Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, NOAA Fisheries, La Jolla, CA 92037, USA
3Ocean Associates Inc. under contract with National Marine Fisheries, Southwest Fisheries Science Center, La Jolla, CA 92037, USA
4Department of Fisheries Oceanography and Marine Ecology, National Marine Fisheries Research Institute, 81-332 Gdynia, Poland
5Center of Applied Ecology and Sustainability, Pontificia Universidad Católica de Chile, 8331150, Santiago, Chile
*Corresponding author:

ABSTRACT: Myctophids are ecologically important in the Southern Ocean, where they occupy a central trophic position and are a key energy resource for top predators. However, understanding their population dynamics is limited by a paucity of data due to sampling challenges. Antarctic fur seal Arctocephalus gazella scats provide large collections of otoliths and other prey remains that can be used to form time series for important mesopelagic taxa such as Gymnoscopelus nicholsi (Gn). Examination of otoliths from scats allowed for a reconstruction of Gn age and length structure from 8 selected sample years between 2000 and 2015. While mean reconstructed length did not change significantly over the time series, mean age declined. Older age classes were scarce in scat samples, and age-6 animals were not found after 2008. During the same time period, Gn otoliths in fur seal scats declined from approximately 2000 to fewer than 200. The decline in the number of otoliths in Antarctic fur seal scat samples coupled with the negative trend in mean age suggests declines in the availability of Gn on the South Shetland Island slope region between 2000 and 2015. This study demonstrates the utility of central-place foragers in assessing populations of unfished but ecologically important mesopelagic fishes, thus allowing evaluation of hypotheses about their population structure and dispersal.

KEY WORDS: Myctophidae · Gymnoscopelus nicholsi · Otolith · Mesopelagic · Southern Ocean · Antarctic fur seal · Krill

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Cite this article as: Klemmedson AD, Reiss CS, Goebel ME, Kaufmann RS, Dorval E, Linkowski TB, Borras-Chavez R (2020) Variability in age of a Southern Ocean myctophid (Gymnoscopelus nicholsi) derived from scat-recovered otoliths. Mar Ecol Prog Ser 633:55-69.

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