374 
Fishery Bulletin 118(4) 
Table 4 
Estimated means of the parameters a (intercept) and 6 (slope or allome- 
tric coefficient) from the regression power model used for analysis of the 
length—weight relationship of Pacific hake (Merluccius productus) caught 
in the northern Gulf of California during the fishing season in 2015-2019, 
by year, sex, and maturity stage (juvenile [J] or adult [A]). Estimates also 
are provided for all years, both sexes, and both maturity stages combined. 
Degrees of freedom (df), the coefficient of determination (r”), and the stan- 
dard error of the mean (SE) are provided for each estimate. 
Regression parameter 
Maturity 
stage df 
All 18,101 
All 8588 
9511 
5075 
1,2941 
3323 
1100 
1487 
1613 
1057 
3923 
1406 
1595 
1461 
1118 
SSSSS757 3354 
a (SE) 
0.02 (0.00) 
0.02 (0.00) 
0.05 (0.00) 
0.02 (0.00) 
0.02 (0.00) 
0.01 (0.00) 
0.03 (0.00) 
0.02 (0.00) 
0.02 (0.00) 
0.02 (0.00) 
0.01 (0.00) 
0.03 (0.00) 
0.03 (0.00) 
0.02 (0.00) 
0.02 (0.00) 
b (SE) 
2.89 (0.01) 
2.93 (0.01) 
2.63 (0.01) 
2.90 (0.01) 
2.82 (0.02) 
3.06 (0.01) 
2.78 (0.02) 
2.86 (0.02) 
2.90 (0.02) 
2.90 (0.02) 
3.02 (0.01) 
2.74 (0.02) 
2.77 (0.02) 
2.87 (0.01) 
2.90 (0.01) 
in the NGC occurs during a transient spawning aggre- 
gation (Domeier, 2012). Additionally, spawning aggre- 
gations of Pacific hake have a male-biased sex ratio, as 
has been reported for the offshore population of Pacific 
hake (Saunders and McFarlane, 1997). Several explana- 
tions have been proposed for this phenomenon in other 
hake species, including early arrival and late departure of 
males to the spawning ground, females spawning in mid- 
water and a consequently higher proportion of males at 
the bottom, and a biological strategy to ensure fecunda- 
tion (Botha, 1986; Di Giacomo et al., 1993; Pajaro et al., 
2005; Bustos et al., 2007; Korta et al., 2015). 
It is essential to note that the sampling period (and the 
fishing season for Pacific hake) begins once fishermen 
obtain high catch rates and once Pacific hake reach com- 
mercial size (>40 cm SL). The season ends once the catch 
rate and mean SL diminish to unprofitable levels. Given the 
low ex-vessel prices of Pacific hake, with an average price 
of $0.61/kg (in 2019 US. dollars) during the study period, 
the profitability of the fishery for Pacific hake depends on 
achieving high catch rates with low fishing effort (i.e., few 
fishing days). In addition, the presence of other aggregated 
and more highly valued finfish species, such as the Gulf 
croaker (Micropogonias megalops), for which the fishing 
season occurs during March—August (Ramirez-Rodriguez, 
2017; Arzola-Sotelo et al., 2018), could offer a concomitant 
explanation for the shift in the species targeted by the 
trawler fleet during the spring. 
A pattern of catch rates of Pacific hake decreasing 
during January—March has been observed in other 
studies in the Gulf of California (Mathews et al., 1974; 
Grande-Vidal, 1983; Godinez-Pérez, 2016). The reduction 
in the catch rates in this study and in these other studies 
could be related to the end of the spawning aggregation 
of Pacific hake in the NGC. The progressive absence of 
large (in length and weight) adults reduces the number of 
individuals of Pacific hake in the fishing grounds and the 
mean size of the fish caught. 
In the NGC, the high concentrations of larvae of Pacific 
hake are related to the ephemeral presence of an anticy- 
clonic eddy during winter (Sanchez-Velasco et al., 2009). 
The presence of this eddy seems to influence the spawn- 
ing areas of other fish species that inhabit the Gulf of 
California (Contreras-Catala et al., 2012). Therefore, the 
spawning areas of Pacific hake could be associated with 
the winter eddy in this zone. The influence of oceano- 
graphic structures on spawning areas has been reported 
for other hake species (Di Giacomo et al., 1993; Marrari 
et al., 2019). 
Results from previous studies indicate that at depths 
>100 m, winter temperatures (<18°C) in the NGC remain 
vertically homogeneous (Lavin and Marinone, 2003). 
Water temperature homogeneity might partially explain 
the absence of a clear depth-dependent profile of catch 
rate or mean SL because the fleet deploys trawl nets at 
depths >200 m during the daytime, when fish have been 
