Jackson Cephalopod reproductive investment 



263 



tern observed in males, which had reached maturity 

 in winter, and suggested that female maturity was out 

 of phase with males during this period of the year. 



All females aged in summer with an ovary weight 

 >1.161g were mature, and the ovary filled much of the 

 mantle cavity. The youngest mature female was 83 d, 

 while the oldest immature female was the oldest fe- 

 male aged, 100 d. 



Gonad-soma relationships Comparing gonad weight 

 to individual age (Fig. 1A,B) revealed a different pat- 

 tern than in the gonad weight/mantle length analysis 

 (Fig. 1C,D). Despite the fact that there was a notice- 

 able difference in the testis weight/age scatter plot 

 (Fig. 1A), due to the older winter males, the testis 

 weight/mantle length relationship was similar for both 

 seasons (Fig. 1C). Thus gonad increase was propor- 

 tional to the squid length rather than its age. 



A different pattern emerged when comparing ovary 

 weight/mantle length relationships for female L. 

 chinensis (Fig. ID). Although the lack of maturity was 

 still obvious in winter females, the gonad weight/mantle 

 length relationship for both seasons resulted in a single 

 curvilinear relationship, suggesting that maturity oc- 

 curred at 100-120 mmDML, regardless of age. Fur- 

 thermore, although this ageing study indicated that a 

 large proportion of the winter females were older than 

 their summer counterparts, many of the winter imma- 

 ture females were smaller than squids captured in the 

 summer. As with the males, squid size rather than age 

 may be a better indicator of maturity. 



CO 



Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct 



I ee I 89 



MONTH 



B 



N-107 



i 



-+- 



> 



-+- 



-i 





■+- 



i 



■+- 



Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct 

 68 69 



MONTH 



Figure 2 



Mean monthly gonadosomatic index for Loligo chinensis over 

 the study period for (A) males and (B) females. Bars = SE. 



Reproductive indices Although it was possible to de- 

 termine the ages of only a small number of individuals 

 in two seasons (rc=64), changes in the gonad weight/ 

 soma weight relationship throughout the year were 

 examined. For both males and females, a seasonal trend 

 could be detected in the GSI (Fig. 2). In males, GSI 

 values were low, with <1.2% of the total body weight 

 consisting of gonad. In contrast, female GSI values 

 were more variable and generally higher than in males, 

 with the gonad comprising as much as 8% of total 

 body weight. 



Mature males were found in all months sampled. 

 However, a regular seasonal oscillation in relative go- 

 nad weight was apparent (Fig. 2A). There was an in- 

 crease in relative gonad weight from April to October 

 in both years. Over the two years, the testis accounted 

 for its greatest percentage (>1%) of body weight in 

 October, while its lowest values were recorded in April. 



A similar pattern of fluctuation also existed with 

 the female GSI values (Fig. 2B). In October, females 

 consistently had GSI values that were considerably 

 higher than for other months. Mature females were 

 present in all months except July 1989. As discussed 



previously, females aged from the 1989 summer sample 

 showed a considerable range in gonad size and level of 

 maturity, despite similarities in both size and age. This 

 range in gonad size was also reflected in the female 

 GSI values, in that the mean values had large stan- 

 dard errors (Fig. 2B) in nearly every month. This was 

 due to the fact that for many months, a proportion of 

 the individuals was immature. 



The seasonal trend in the NGL/ML index (Fig. 3) 

 was similar to the trend in the female GSI (Fig. 2B). 

 This index also indicated a greater investment in re- 

 production during October, with lowest values in July. 

 Furthermore, standard errors were generally less for 

 this index than for the GSI. 



The monthly mean mantle lengths for males and 

 females were plotted for the 2yr period (Fig. 4A,B). 

 Although there was some variation in mantle lengths 

 for the different samples, these could not be related to 

 the seasonal peaks or troughs in the GSI values. For 

 example, the largest females were captured from Feb- 

 ruary to July 1988 (Fig. 4B). However, GSI values 

 dropped considerably over this period. Furthermore, 

 mean mantle length was not highest in October for 



