370 
Fishery Bulletin 118(4) 
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6.51) 
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7.08) 
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Partial effect (edf 
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Partial effect (edf 
3.7 4.7 i 
Tow speed (km/h) 
=3,53) 
=3,24) 
Partial effect (edf 
Partial effect (edf 
6 8 10 12 14 16 18 20 
Hour of the day (24 h) 
3.7 
Tow speed (km/h) 
=3.35) 
Partial effect (edf 
83 9 10 11 
Mesh size (cm) 
150 200 250 300 
Depth (m) 
=3.44) 
Partial effect (edf 
150 200 250 300 
Depth (m) 
Art — @pi/ 
Figure 3 
Partial effect plots of generalized additive models fit to the (A-D) natural logarithm of catch per unit of effort, (E) mean 
standard length, and (F) natural logarithm of sex ratio of Pacific hake (Merluccius productus) in the northern Gulf of 
California in Mexico. Explanatory variables in the models include speed of trawl tow, mesh size of trawl net, depth of 
trawl tow, and hour of the day of trawl tow (with hours expressed as numerals between 1 and 24). Data used in models 
are from Pacific hake caught in 2015-2019 during the fishing season from January through March. The gray shaded 
area in each plot represents the 95% confidence interval, and black lines just above the x-axis represent the density 
of observations for each covariate. edf=effective degrees of freedom. 
Variability of mean length 
The final model for mean SL did not include mesh size, the 
hour of the day, or depth (Table 1). This model explained 
15% of deviance and used just a smoother for tow speed 
as well as the factors of month and year without inter- 
action. The smoother for speed indicates that tows made 
slower and faster than the interval of 4.00—5.00 km/h 
(2.16—-2.66 kt) caught Pacific hake with sizes under the 
mean SL of fish caught in this study (Fig. 3E). 
The minimum annual mean SL occurred in 2015 
(45.7 cm [95% CI: 44.2—47.1 cm]), and the maximum was 
observed in 2018 (51.8 cm [95% CI: 50.5-53.2 cm]). 
Although yearly differences in mean SL were significant 
