Lorenzo and Paiuelo: Biology of Pmmethichthys prometheus 



95 



O 



APE value was only 3.4%. A false hyaline 

 ring interrupting the normal growth pat- 

 tern of the otolith was identified within 

 the fourth annual opaque zone and in all 

 subsequent opaque zones. Marginal zone 

 analysis showed that one annulus was 

 formed per year (Fig. 5). The percentage 

 of otoliths with opaque edge was high in 

 the months from April to September, and 

 between June and August in particular. 



Fish aged 3 to 11 years were present in 

 the samples (Table 5). Growth parameters 

 determined for males, females, and the en- 

 tire population are shown in Table 6. No sig- 

 nificant differences in the growth param- 

 eters were found between sexes ( Hotelling's 

 r-^-test, r-^=5.29<T/o 05 3 666=7-88). 



The length converted catch curve is 

 shown in Figure 6. The rates of total mor- 

 tality, natural mortality, and fishing mor- 

 tality were Z=0.49/year, M=0.35/year, and 

 F=0. 14/ year, respectively. The size at first 

 capture was 51.57 cm TL. 



Discussion 



Promethichthys prometheus is distributed 

 along the slope to a depth of 800 m 

 (Nakamura and Parin, 1993). In waters 

 off the Canary Islands, greatest concen- 

 trations of this species are found between 

 400 and 700 m depth. Below this depth, 

 the species is replaced by other trichiuroid 

 fish present in the area, e.g. the black 

 scabbardfish, Aphanopus carbo Lowe, 

 1839(Uibleinetal., 1996). 



The roudi escolar off the Canary archipelago is a 

 gonochoristic species with no evidence of sexual di- 

 morphism. The sex ratio is clearly unbalanced in fa- 

 vor of females. This fact could be explained by the 

 differences between sexes in the spatial distribution. 

 The lowest discrepancy between sexes observed dur- 

 ing the reproductive season seems to confirm this 

 conclusion. Because of the space partitioning between 

 sexes and because females are fished more than 

 males, this species could be classed as vulnerable to 

 unrestrained fishing. Therefore, fishing for roudi es- 

 colar is an activity that has the potential to threaten 

 its target population compared with fishing for more 

 reliable and robust stocks (Csirke, 1988). This fishery 

 will require a prudent exploitation strategy to reduce 

 the potential risk of a collapse. 



The roudi escolar has a definite reproductive pe- 

 riod (extending from April to September, with a peak 



10 



Males 



10 



ASONDJFMAMJ JASONDJFMAMJ JASONDJFMAMJ J 

 1992 I 1993 I 1994 1995 



Females 



ASONDJFMAMJ JASONDJFMAMJ JASONDJFMAMJ J 

 1992 , 1993 I 1994 | 1995 | 



Month 



Figure 3 



Monthly evolution of the gonadosoniatic index ( GSI ) for males and females 

 of P. prometheus caught off the Canary Islands (August 1992-July 1995). 



in spawning activity in June— July) which agrees with 

 information reported by Parin ( 1986) and Nakamura 

 and Parin ( 1993). These authors pointed out that the 



