Table 1. Variables and model selection.

A)
Variables	Description
Depth	Measured from sea surface to the ocean floor (meters)
Sea surface salinity (SSS)	Average salinity from each station from 0–50 meters (parts "per mille"—ppt)
Sea surface temperature (SST)	Average temperature from each station from 0–50 meters (°C)
Zooplankton biomass	Dry weight from WP2 hauls at each station (mg/m3)
Fulton's K	Fulton's condition factor (K = 100(W/L3)
Latitude and longitude	Geographical marker of stations
Total catch	Log transformed total mackerel catch (ton) per station
Week	week number during the survey
Time of day	Day divided into four time periods with 6 hours in each (00:00–05:00, 06:00–11:00, 12:00–17:00, 18:00–23:00)
Year	Data collected from 2011–2014
Distance to shore	From isobath lines (≤100m, ≤200m, ≤500, >501m)
B)
Model #	Response variable Explanatory variable	Factorial variables	AIC	ΔAIC	wi	Deviance explained	R2 adjusted	DF
1	log(stomach weight) zooplankton + (longitude,latitude)+ Fulton´s K+ depth + SSS + SST + log(total catch)	time period+distance to shore+week+year	-1854	8.92	0.007	48.50%	0.44	153
2	log(stomach weight) zooplankton + (longitude,latitude)+ depth + SSS + SST + log(total catch)	time period+distance to shore	-1863	0	0.58	48.60%	0.44	150
3	log(stomach weight) zooplankton + (longitude,latitude) + SSS + SST + log(total catch)	time period	-1862	1	0.35	48.50%	0.44	148
4	log(stomach weight) zooplankton + (longitude,latitude)+ depth+ SSS + SST	time period	-1860	4.4	0.06	48.30%	0.42	147

A) List of explanatory variables considered in analyses of Northeast Atlantic mackerel stomach weight in Icelandic waters in 2011–2014 using generalised additive models (GAMs). B) GAMs selection table, the model marked in bold was found to be the best-fitted model based on Akaike Information Criterion (AIC) from the R package “MuMIn” (see Table 6).