Evidence for seasonal cycles in deep-sea fish abundances: A great migration in the deep SE Atlantic?

Milligan, R.J. et al. (2020) Evidence for seasonal cycles in deep-sea fish abundances: A great migration in the deep SE Atlantic? Journal of Animal Ecology, 89(7), pp. 1593-1603. (doi: 10.1111/1365-2656.13215) (PMID:32198925)

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1. Animal migrations are of global ecological significance, providing mechanisms for the transport of nutrients and energy between distant locations. In much of the deep sea (>200 m water depth), the export of nutrients from the surface ocean provides a crucial but seasonally variable energy source to seafloor ecosystems. Seasonal faunal migrations have been hypothesized to occur on the deep seafloor as a result, but have not been documented. 2. Here, we analyse a 7.5‐year record of photographic data from the Deep‐ocean Environmental Long‐term Observatory Systems seafloor observatories to determine whether there was evidence of seasonal (intra‐annual) migratory behaviours in a deep‐sea fish assemblage on the West African margin and, if so, identify potential cues for the behaviour. 3. Our findings demonstrate a correlation between intra‐annual changes in demersal fish abundance at 1,400 m depth and satellite‐derived estimates of primary production off the coast of Angola. Highest fish abundances were observed in late November with a smaller peak in June, occurring approximately 4 months after corresponding peaks in primary production. 4. Observed changes in fish abundance occurred too rapidly to be explained by recruitment or mortality, and must therefore have a behavioural driver. Given the recurrent patterns observed, and the established importance of bottom‐up trophic structuring in deep‐sea ecosystems, we hypothesize that a large fraction of the fish assemblage may conduct seasonal migrations in this region, and propose seasonal variability in surface ocean primary production as a plausible cause. Such trophic control could lead to changes in the abundance of fishes across the seafloor by affecting secondary production of prey species and/or carrion availability for example. 5. In summary, we present the first evidence for seasonally recurring patterns in deep‐sea demersal fish abundances over a 7‐year period, and demonstrate a previously unobserved level of dynamism in the deep sea, potentially mirroring the great migrations so well characterized in terrestrial systems.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Scott, Professor Marian and Bailey, Dr David
Authors: Milligan, R.J., Scott, E.M., Jones, D.O.B., Bett, B.J., Jamieson, A.J., O'Brien, R., Pereira Costa, S., Rowe, G.T., Ruhl, H.A., Smith Jr., K.L., de Susanne, P., Vardaro, M.F., and Bailey, D.M.
College/School:College of Science and Engineering > School of Mathematics and Statistics > Statistics
College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Journal Name:Journal of Animal Ecology
ISSN (Online):1365-2656
Published Online:21 March 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Journal of Animal Ecology 89(7):1593-1603
Publisher Policy:Reproduced under a Creative Commons License
Data DOI:10.1594/PANGAEA.909448

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
163674NERC DTG 2010 - 2014: FBLSMorven BarlassNatural Environment Research Council (NERC)NE/I528369/1MVLS - Finance