Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 4382
Title: Among-year variation in growth of Antarctic krill (Euphausia superba) based on length-frequency data
Author: Andrew Olaf Shelton, Douglas Kinzey, Christian Reiss, Stephan Munch, George Watters, Marc Mangel
Publication Year: 2013
Journal: Marine Ecology Progress Series
Keywords: Krill,growth,kernel density estimator,von Bertalanffy,temporal variation,Southern Ocean

Understanding the temporal variability in vital rates (e.g. growth and survivorship) of wild populations is practically and statistically difficult but vital for connecting such variation to mechanistic drivers and to population consequences.  For somatic growth, empirical estimates of variation are rare because they often require expensive long-term tag-recapture programs. In marine pelagic ecosystems, where many species are difficult to sample and not amenable to tagging studies, researcher have relied on estimating growth from length-frequency distributions. We develop a novel and general approach for estimating growth from observed length-frequency samples by combining kernel density estimates of the length-frequency distribution and the von Bertalanffy growth function. Our approach is conceptually straightforward and easy to implement. We apply our methods to Antarctic krill (Euphausia superba) collected from the Southern Ocean over a span of 19 years to document among year variation in krill growth during the Austral summer. Our estimates of growth align closely with existing estimates of growth but we also provide the first estimates of among year variation in krill growth.  We estimate very high among year variation in growth (annual estimates for a 30mm krill in the Elephant Island region ranged from 0.00 to 0.17 mm day^{-1}; among year CV ~ 0.8). Growth rate variation was correlated to estimates of ocean chlorophyll, but not to other oceanographic indices contrasting with results from previous studies. Our study has substantial implications for the management of the Southern Ocean ecosystem.

Theme: Ecosystem Approach to Management for the California Current Large Marine Ecosystem
Foci: Characterize linkages between climatic conditions and biotic responses.