Effect of the significant smoothing functions (solid line) on the discard rate of plaice in the Kattegat demersal trawl fishery.

<p>Plaice </p

Effect of the significant smoothing functions (solid line) on the discard rate of Norway lobster in the Kattegat demersal trawl fishery.

<p>Norway lobster </p

The official Danish landing statistics (www.fvm.dk) for the Kattegat: 1997 to 2008.

<p>Species are ranked according to their relative importance by weight. Average value in thousands with standard deviation for the 12 years investigated.</p

Map of the study area with the location of discards observer hauls used in the analysis.

<p>Locations represent the mid-way point of each haul.</p

Final models together with each covariates degrees of freedom, significance level and the deviance explained by the model.

<p>Significance levels: 0.001 ‘**’ 0.01 ‘*’, α = intercept, mesh = mesh size category, quarter = quarter of the year, Yr = year, catch = Total catch weight, JuvAb = Juvenile abundance, lon = longitude, lat = latitude, quota = species quota utilisation, vessel kW = vessel power, depth = mean fishing depth, vessel = individual vessel id.</p

Several different GAMs were fitted to each of the data sets and best models were chosen by the GCV scores.

<p>Model effects of the best model of SREAS data (<b>a–b</b> H7, CPUE ∼ te(Year,Area) + s(CPUE_t–1)+ ε) and VCD data (<b>c–f</b>, L1, CPUE∼ te(Year,Area) + s(DY) + s(SST) + s(SST5) + ε). <b>a</b>) shows the effect of the interaction term on CPUE and <b>b)</b> the effect on CPUE of CPUE lagged one year. <b>C–f</b> shows model effects of best model on VCD data (L1). Effects on CPUE from <b>c</b>) the interaction term, <b>d</b>) fishing day, <b>e</b>) lagged summer temperature SSTX and <b>f</b>) temperatures during fishing, SST_AUT.</p

Summary of variables included in Generalised Additive Models of factors influencing discards.

<p>Based on data collected as part of the discard sampling programme 1997–2008.</p>1<p>Juvenile abundance was only available for cod.</p>2<p>Quota utilisation was only assessed for cod and plaice. The quota for Norway lobster is not restrictive and therefore does not affect discards.</p

Wavelet analyses of periodicity of the two sets of lobster data.

<p><b>a</b>) displays the wavelet power spectrum of the SREAS data where the dominant periodicity of ∼20 years becomes less pronounced as well as shorter through the time series. The color symbolizes the strength of the periodicity. Blue is weak, red is strong and contours indicate statistically significant periodicities. The cone of influence is drawn and suggests that any periods above are doubtful due to time series length. <b>b</b>) displays the global wavelet spectrum and the dotted line shows the corresponding confidence interval indicating the significance of the periodicities. <b>c</b>) and <b>d</b>) are the global power spectrum and the wavelet power spectrum of the VCD data respectively, showing no significant periodicity.</p

Autocorrelation, and partial autocorrelation, functions were used to analyze temporal lags in the time-series.

<p>We calculated ACF and PACF for linearly de-trended aggregated SREAS CPUE data (a, b), residuals of model H3 (c, d) and residuals of model L1 (e, f). Dashed lines are Bartlett bands showing approximate 95% confidence limits. For the SREAS data ACF and PACF was performed both on linearly de-trended CPUE values and the residuals of GAM model H3. In the case of VCD, showing non-stationary structuring, the ACF and PACF were performed only on the residuals of the GAM model L1.</p

Effect of the significant smoothing functions (solid line) on the discard rate of cod in the Kattegat demersal trawl fishery.

<p>Cod </p