Abstract-The roudi escolar Pro- Biology of a deep benthopelagic fish, methichthys prometheus is common in deep hook-and-line and longline catches roudi escolar Promethidtfhys prometheus of a small-scale fishery along the slope off the Canary Islands. Population (Gempylidae), off the Canary Islands structure, reproduction, growth, and mortality of the species were studied from sampling undertaken from August José M. Lorenzo 1992 to July 1995. Range of length of José G. Pajuelo fish in the catches was between 36 and Departamento de Biología (Universidad de Las Palmas de Gran Canaria) 80 cm TL, with a main distribution be- tween 56 and 66 cm. The overall ratio Edificio de Ciencias Básicas, Carnpus Universitario de Tafira of males to females was 1:1.74. Females 35017 Las Palmas, Spain predominated in al1 sizes. The sex ra- E-mail address (for J. M. Lorenzo): [email protected] tio varied throughout the period of study; the lowest discrepancy between males and females, however, was dur- ing the reproductive penod. A vertical space partitioning among sexes was ob- served, with males predominating from 600 to 800 m depth, females from 300 to 500 m. The reproductive penod of the The family Gempylidae consists of in addition to al1 those aspects, species was from April to September, 16 genera and 23 species. Only population structure and mortality. with a peak in spawning in JuneJuly. seven species are found off the Ca- The roudi escolar is common in The size at first maturity was 47.41 cm. nary Islands, one of which is the the catches of the deep hook-and- Tho paramotors ef the !en@h-weight roudi escolar Promethichthys pro- line and longline small-scale fish- relationship for al1 fish were a=0.004521 and b=2.98932. Age read- metheus (Cuvier, 1832), the only ery over the slope off the Canary ings of otoliths indicated that the ex- species recognized to date in the Islands. In this area, this species is ploited population consisted of nine age genus Promethichthys (Nakamura captured year round without signifi- groups (111-XI years). The von and Parin, 1993). cant seasonal differences in landings. Bertalanffy growth parameters for al1 The roudi escolar is a bentho- individuals were L-=93.61 cm, k=O.l8/ years, and t, =-1.54 years. She rates of pelagic marine fish that has a mortality for al1 fish were Z=0.49/years, worldwide distribution in tropical Materials and methods M=O.35lyears, and F=0.14/years. The and warm temperate waters. This length at first capture for the whole species generally inhabits waters Between August 1992 and July population was 51.57 cm. between 100 and 800 m in depth 1995, the TL (cm) of 1879 specimens over seamounts and continental of roudi escolar was measured and insular slopes. It migrates up- monthly from commercial catches of ward at night, probably forming the small-scale fleet. Fish were schools (Nakamura, 1981; Parin, caught with baited hook-and-lines 1986; Nakamura and Parin, 1993). and longlines at depths of 285-870 Published information on P. m around the islands of the Canary prometheus is very scarce. The ma- archipelago (Fig. 1). jority of studies describe its morpho- A subsample was taken by a ran- logical characteristics, geographical dom stratified method from each and depth distribution, and ecology sample for biological examination. In (Nakamura, 1981; Parin, 1986; total, 776 individuals were analyzed. Nishikawa, 1987; Nakamura and For each fish, the TW (0.1 g) and the Parin, 199.1). On!y L~rer?znand weight of the g~nads(0.01 g) wzrs Pajuelo (1995) have studied some measured, and sex and stage of matu- biological aspects of the species. ration were ascertained macroscopi- These authors carried out a prelimi- cally. The latter was classified as fol- nary study on the sex ratio, repro- lows: 1 = immature; 11 = resting; 111 = duction, and age and growth of ripe; IV = ripe and running; V = spent. roudi escolar off the Canary Islands Sagittal otoliths of the fish were ex- (central-east Atlantic) on the basis tracted, cleaned, and stored dry. The =fa sma!! mmber of specimeris dur- ~erig@h-frequericy&str&uiion "fin&- Manuscript accepted 23 April 1998 ing one life cycle. This paper is an viduals in catches was calculated. Fish. Bull 97:92-99 (1999). extension of their work, analyzing, Data were pooled for 1992-95. Lorenzo and Pajuelo: Biology of Promefhkhihyspromefheus 93 - ___.--___ - .-~ ... 7-7r......- -- ..-.___________~-~~._A CANARY ISLANDS n Lanzzrote La Palma - 2 8" Fueneventui a Hiemoa 0 Figure 1 Location of sampling areas (8)in the Canary Islands The sex ratios (ma1es:females) for the whole total mortality (2)was calculated from the length sample, for different size clases, for quarters of a converted catch curve by using ELEFAN program year, and for depth strata were calculated. The re- (Gayanilo et al., 1988). The rate of'natural mortaiity productive season was determined on the basis of (M) was determined,from the equation of Pauly monthly variations of the gonadosomatic index (GSI) (1980). Following estimation of Z and M, the rate of according to Anderson and Gutreuter (1983). The fishing mortality (F)was calculated by substraction. length at sexual maturity (length at whch fiRy per- The length at first capture was estimated from the cent of the specimens became mature) was estimated selection ogive generated from the length converted by means of a logistic function that was fitted to the catch cupe (Pauly, 1984). proportion of the mature individuals (stages 111, IV,and V) by using a nonlinear regression (Saila et al., 1988). The ratio of total length to total weight was calcu- lated over the whole period for males and females separately, as well as for the population as a whole, The size-frequency distribution showed a length by applying a linear regression (Ricker, 1973). Age range of 36 to 80 cm TL in the catches, with a main was determined by interpreting growth rings on the distribution between 56 and 66 cm (Fig. 2). otoliths; whole otoliths were placed in a watch glass Of the 776 fish examined, 282 (36.3%)were male, with a blackened bottom and containing glycerin and 491 (63.3%)female. The sex of the remaining 3 (0.4%) examined under a compound microscope with re- individuals could not be identified macroscopically flected light. Counts for each specimen were per- because they were immature and had very thin, formed at least twice and only coincident readings translucent gonads. The overall ratio of males to fe- were accepted. An index of average percent error males was 1:1.74 and x2 analysis revealed this to be (ME) developed by Beamish and Fournier (1981) significantly different from a 1:l ratio (Table 1).Fe- was used to compare the precision of age determina- males predominated in al1 size intewals. Sex ratios tions Ageing was validated indirectly by examina- for males and females grouped into 5-cm length tinn d menthly chlnges in ippearance of the margins classes had sip-ifirant departures from t.he 1:1 ratin of the otoliths (Morales-Nin, 1987).The date 1July was for al1 size intervals (Table 1).The ratio of males to considered as birthdate to assign the individual ages females varied throughout the period of study, but to age groups. The von Bertalanffy growth curve was there were no significant differences from the 1:l ratio fitted to data of the resulting age-length key by means during the spring and summer months (Table 2). of the Marquardt's algorithm for nonlinear least There was a relationship between the sex of roudi es- squares parameter estimation (Saila et al., 1988). colar and depth; males predominated at 600 to 800 m Length-frequency data were converted to age fre- depths, females at 300 to 500 m (Table 3). qüeíicies by ~siagthe estimated voi; Eei.ta!ai;ffi. The GS! shvwec! higher va!ües f~rfemales thai, growth parameters (Pauly, 1983, 1984). The rate of for males (Fig. 3). The same temporal variation pat- BBE value was only 3.4%.A false hyaline ring intempting the normal growth pat- te- 9f the etelith wus identified withiri the fourth annual opaque zone and in al1 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 sampIes (Table 5). Growth parameters determined formales, females, and the en- tire population are shown in Table 6. No sig- nificmt diflereiices the giüwth piaii- eters were found between sexes (Hotelling's- p-test, ~=5.29<To20.05,3,,,,=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 2=0.49/year, M=0.35/year, and F=O.l4/ year, respectively. The size at first capture was 51.57 cm SL. Promethichthys prometheus is distributed o / I , ,,,,.,,, 1, along the slope to a depth of 800 m ASONDJFMAMJJASONDJFMAMJJASONDJFMAMJJ (Nakamura and Parin, 1993). In waters 1992 l 1993 1994 1 1995 1 off the Canary Islands, greatest concen- Month trations of this species are found between 400 and 700 m depth. Below this depth, Figure 3 the species is replaced by other trichiuroid Monthly evolution of the gonadosomatic index (GSI) for males and females of P prornetheus caught off the Canary Islands (August 1992July 1995) fish present in the area, e.g.