Publication Abstract

Egg production estimates in the Irish Sea: The effects of modelling choices and assumptions.

David Maxwell*, Mike Armstrong*, Steven Beggs and John Aldridge*

During 2006 and 2008, the annual egg production of cod (Gadus morhua), plaice (Pleuronectes platessa) and haddock (Melanogrammus aeglefinus) in the Irish Sea was estimated from five ichthyoplankton surveys carried out each year during the spawning season. Generalized additive models (GAMs) were used to model the spatial patterns and temporal trends and to estimate total annual production of stage 1 eggs. The method presented develops previous work by using 2-D spatial smoothing and automatic selection of the degree of smoothing. We explore the sensitivity of the estimates to different modelling choices and assumptions, considering practical issues faced when carrying out egg production modelling, such as outlying observations, missing data and boundary effects. The results are compared to a design-based method that derives estimates from spatial strata and the advantages and disadvantages of the GAM-based approach are discussed.

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