Summary: Estimating and decomposing total uncertainty for survey-based
abundance estimates of Norwegian spring-spawning herring
Anders Løland, Magne Aldrin, Egil Ona, Vidar Hjellvik, and Jens Christian Holst
Løland, A., Aldrin, M., Ona, E., Hjellvik, V., and Holst, J. C. 2007. Estimating and decomposing total uncertainty for survey-based abundance
estimates of Norwegian spring-spawning herring. ICES Journal of Marine Science, 64: 13021312.
A method is developed to quantify the uncertainty of abundance and age-specific abundance estimates of Norwegian spring-spawning
herring, accounting for the combined effect of several error sources. We present an abundance estimate adjusted for vessel avoidance,
acoustic shadowing, and depth-dependent target strength, and highlight the potentially dramatic combined effect of these adjust-
ments. Uncertainty in this estimate is affected by the precision of the adjustment formulae as well as by the sampling errors in acoustic
and trawl measurements. This total uncertainty is decomposed into contributions from each source. Here, the method is applied to
data from surveys on the overwintering stock in the Vestfjord system and off Vesteraalen in northern Norway in November/December
of the years 20012004.
Keywords: acoustic abundance estimation, total estimation uncertainty, uncertainty decomposition.
Received 6 October 2006; accepted 5 July 2007.
A. Løland and M. Aldrin: Norwegian Computing Center, Gaustadalle´en 23, PO Box 114, Blindern, NO-0314 Oslo, Norway. E. Ona, V. Hjellvik,
and J. C. Holst: Institute of Marine Research, PO Box 1870, Nordnes, N-5817 Bergen, Norway. Correspondence to A. Løland: tel: þ47 22 85 25 00;
fax: þ47 22 69 76 60; e-mail: email@example.com.
The Norwegian spring-spawning herring (Clupea harengus) stock
has been, at times, the largest fish stock in the Northeast