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dc.contributor.authorWilhelm, Margit R.
dc.contributor.authorBlack, Bryan A.
dc.contributor.authorLamont, Tarron
dc.contributor.authorPaulus, Sarah C.
dc.contributor.authorBartholomae, Chris
dc.contributor.authorLouw, Deon C.
dc.date.accessioned2020-11-07T01:27:51Z
dc.date.available2020-11-07T01:27:51Z
dc.date.issued2020-05-08
dc.identifier.citationWilhelm, M. R., Black, B. A., Lamont, T., Paulus, S. C., Bartholomae, C., & Louw, D. C. (2020). Northern Benguela Merluccius paradoxus annual growth from otolith chronologies used for age verification and as indicators of fisheries-induced and environmental changes. Frontiers in Marine Science, 7, 315.en_US
dc.identifier.issn2296-7745
dc.identifier.doi10.3389/fmars.2020.00315
dc.identifier.urihttp://hdl.handle.net/10150/648136
dc.description.abstractIn this study we develop a 32-year (1982-2013) otolith biochronology of the commercially important deepwater hake Merluccius paradoxus in the northern Benguela, Namibia. Mean annual growth (mm) calculated from 140 thin-sectioned M. paradoxus otoliths were compared with change in mean length at age 3 to age 4 determined from Namibian whole-otolith-read age-length keys (ALKs). Annual growth rates calculated from the two methods (overlapping 2000-2013) were strongly positively correlated (rho = 0.730, n = 14, p < 0.01). This indirectly validated annual age determination of M. paradoxus, the accuracy of otolith chronologies, and the ability of ALKs to capture annual variability in fish growth. Annual M. paradoxus growth rates were significantly positively correlated with the July-September upwelling index 1982-2013 at 30 degrees S, (rho = 0.414, n = 32, p < 0.05) and positively correlated with August mean chlorophyll-a concentrations (as indicator for primary production) 2002-2013 in the 28-30 degrees S area (rho = 0.734, n = 12, p < 0.01). Annual M. paradoxus growth rates significantly negatively correlated with October (austral spring) sea surface temperatures in the 24-28 degrees S area (rho = -0.381, n = 32, p < 0.05). This Orange-River Namaqua upwelling cell corresponds to the area where juvenile and young adult M. paradoxus live, suggesting growth rate strongly responds to local forcing. We also determined that mean length-at-age 3 calculated from ALKs (current and literature) significantly increased from 1977 through 2016 at 0.075 cm.year(-1) (t = 3.04, df = 41, p = 0.004), while length-at-age 8 significantly decreased at 0.25 cm.year(-1) (t = -3.59, df = 30, p = 0.001). Both trends may indicate fisheries-induced adaptive changes. M. paradoxus occurring at >300 m bottom depth, are thus strongly influenced by fisheries. As an upper-level demersal predator, this species integrates signals throughout the food web to provide a unique "view from the top" of long-term changes in the northern Benguela upwelling system. These results provide background ranges of growth variability and context for what will likely be negative impacts of predicted decreases in future upwelling.en_US
dc.language.isoenen_US
dc.publisherFRONTIERS MEDIA SAen_US
dc.rightsCopyright © 2020 Wilhelm, Black, Lamont, Paulus, Bartholomae and Louw. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).en_US
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en_US
dc.subjectclimate changeen_US
dc.subjectdeepwater hakeen_US
dc.subjectfishery-induced adaptive changeen_US
dc.subjectinter-annual variabilityen_US
dc.subjectsclerochronologyen_US
dc.subjectupwellingen_US
dc.titleNorthern Benguela Merluccius paradoxus Annual Growth From Otolith Chronologies Used for Age Verification and as Indicators of Fisheries-Induced and Environmental Changesen_US
dc.typeArticleen_US
dc.contributor.departmentUniv Arizona, Lab Tree Ring Resen_US
dc.identifier.journalFRONTIERS IN MARINE SCIENCEen_US
dc.description.noteOpen access journalen_US
dc.description.collectioninformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.en_US
dc.eprint.versionFinal published versionen_US
dc.source.journaltitleFrontiers in Marine Science
dc.source.volume7
refterms.dateFOA2020-11-07T01:28:07Z


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Copyright © 2020 Wilhelm, Black, Lamont, Paulus, Bartholomae and Louw. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).
Except where otherwise noted, this item's license is described as Copyright © 2020 Wilhelm, Black, Lamont, Paulus, Bartholomae and Louw. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).