Aspects of Age and Growth of Bluemouth, Helicolenus Dactylopterus Dactylopterus (Delaroche, 1809) from the Azores

ASPECTS OF AGE AND GROWTH OF BLUEMOUTH, HELICOLENUS DACTYLOPTERUS DACTYLOPTERUS (DELAROCHE, 1809) FROM THE AZORES EDUARDO ESTEVES, JAIME AN~BAL,HELENA KRUG & HELDER MARQUES DA SILVA ESTEVES,EDUARDO, JAIME AN~BAL,HELENA KRUG & HELDERMARQUES DA SLvA 1997. Aspects of age and growth of bluemouth, Helicolenus dactylopterus dactylopterus (Delaroche, 1809) from the Azores. Arquipdago. Lie and Marine Sciences 15A: 83-95. Ponta Delgada. ISSN 0873-4704. Bluemouth, Helicolenus dactylopterus dactylopterus (Delaroche, 1809), age and growth were studied by whole-view examination of left sagittae (n = 401) obtained from specimens (14-47 cm in total length) caught off the Azores. Opaque rings observed on the anti-sulcd surface of sagittae were enumerated as age estimates. Ages ranged from 3 to 14 years in males and 3 to 12 years in females. The von Bertalanffy growth equation was fitted . - - to average length at age data, and compared between sexes and methods (direct examination of otoliths, backcalculation and length-frequency analysis). No important differences in growth between sexes were found. Results are different from published literature for the region. The causes and implications of the results are discussed. ESTEVES, EDUARDO,JAIME AN~BAL,HELENA KRUG & HELDERMARQUES DA SILVA 1997. Idade e crescimento do boca-negra, Helicolenus dactylopterus dactylopterus (Delaroche, 1809) dos Aqores. Arquip6lago. Ciencias Biolbgicas e Marinhas 15A: 83-95. Ponta Delgada. ISSN 0873-4704. A idade e o crescimento de boca-negra, Helicolenus dactylopterus dactylopterus (Delaroche, 1809), foram estudadas pela obsema@io dos ot6litos (sagittae) esquerdos inteiros (n = 401) obtidos de exemplares (14-47 cm de comprimento total) capturados em 6guas A~oreanas.Enurneraram-se os antis opacos obsewados na face anti-sulcd dos ot6litos. 0s intemalos de idades foram 3-14 anos para machos e 3-12 anos para femeas. Estimaram-se e compararam-se os parfimetros da equa@o de crescimento de von Bertalanffy, entre sexos e entre mttodos (leitura directa de ot6litos, retroc6lculo e anaise de distribui~Besde frequencias de comprimentos). N5o se verificaram diferen~asimportantes. 0s resultados sbdiferentes da literatura publicada para a regi5io. Discutem-se as causas e implica~6esdos resultados obtidos. Eduardo Esteves (e-mail: [email protected])& Jaime Anfbal, UCTRA, Universidade do Algarve, Campus de Gambelas, PT-8000 Faro, Portugal. - Helena Krug & Helder Marques da Silva, Universidade dos Agores, Departamento de Oceanografia e Pescas, PT- 9900 Horta, Portugal. INTRODUCTION Azores, Madeira and Canaries, and in the Mediterranean Sea (Q~CRO1984; HUREAU& The bluemouth, Helicolenus dactylopterus LITVINENKO1986). It is one of the three dactylopterus (Delaroche, 1809), is a benthic scorpaenid species of economic value captured (200-1000 m) fish species common in the by the Azorean artisanal that fishes for Atlantic ocean from Norway to South-Africa, blackspot seabream (Pagellus bogaraveo) (ISmRO 1987b). The captures of bluemouth was determined macroscopically, and the increased from 29% weight of the blackspot otoliths (sagittae) were extracted, cleaned and seabream landings reported in 1986 to 67% in stored dry. Otoliths were then sorted into four 1995 (LOTACOR198511995). size classes (<25 cm, 25-30 cm, 31-35 cm, and Information on age and growth of Atlantic >35 cm). In each class, about 100 otoliths were bluemouth is sparse, being the aim of two chosen randomly with the aid of a random study reports (ISIDRO1987~1, b). This author numbers table (YAMANE 1964). Whole left examined whole otoliths from monthly sagittae (n = 401, 228 males and 173 females) samples, and evidences of annual ring were examined in 96% ethanol under a deposition and of differential growth between compound stereoscope with reflected light and males and females were presented. a dark background. Opaque rings were counted The aims of this study were to investigate on the anti-sulcal surface and around the the age and growth of the bluemouth, otolith, mainly on the rostrum, antirostru~nand Helicolenus doctylopterus dactylopterus ventral planes (Fig. 1). The otoliths were (Delaroche, 1809), from the Azores using the examined without the knowledge of length. sagittae otoliths and to compare the results The type of edge (translucent or opaque) of the with published findings for the region. otolith along the axis of measurement was also noted. Whenever interpretation of the otoliths MATERIAL AND METHODS imposed doubts the otoliths were discarded. A sub-sample of 183 sagittae previously read (1 12 males and 71 females) was chosen for FISH SAMPLINGAND OTOLITH PREPARATION ring measurement, according to assigned age, fish length and sex. Otoliths were analysed A total of 912 bluemouth specimens were using image analysis software linked to a caught at stations across the Azores compound stereoscope equipped with a video archipelago, using bottom longline, aboard camera. Measurements were made along the RN "ArquipClago": in March-April 1995. rostrum from the focus to the edge of the From the fish sampled, total length (TL, to the otolith (otolith radius, OR), and to the outer lowest cm) was measured with a calliper, sex margin of each opaque ring (ring n radius, On). ventral path Fig. 1. Diagram of the anti-sulcal surface of a left sagitrae of bluemouth. Helicolenus dactylopterus dactylopterus. Opaque rings are represented by fine lines and counting paths are indicated with arrows. Rostra1 length of otoliths observed varicd between 3.15 mm and 10.06 mm. 17 - focus. VENEMA (1992)). and the coefficient of determination (r2)were chosen. Age-length keys (ALK) based on the readings were constructed for males, females and both RESULTS sexes combined. Mean TL (LSD) were calculated for each age. Female bluemouth specimens ranged in length The relationships between TL and otolith (TL) from 14 cm to 46 cm and were estimated radius, and between otolith radius and ring to be 3 to 12 years, while males ranging in counts were examined by regression analyses length from 15 to 47 cm were estimated to be 3 and the significance of the regressions values to 14 years. Age-length keys (ALK) and mean was tested (SOKAL& ROHLF 1981). Intercept TL at age (observed length) are presented in and slope values were compared between Tables 1 and 2. For succeeding years the males and females using the t-Test (SOKAL& observed length increments were 3.4, 3.4, 3.5. ROHLF 1981). Lengths at age for individual 4.0, 2.3, 1.4, 4.5, -1.0 and 2.8 cm (12th year), fish were back-calculated using the Fraser-Lee and 2.2, 2.7, 2.0, 3.6, 3.1, 3.0, 3.8, 4.5 and 0.7 linear method (FRANCIS1990). Mean TL (k cm (12th year), in males and females SD) was computed for each age. respectively. Almost all otoliths, both male and Modes in the length-frequency distribution female, presented translucent borders (97.7% of specimens sampled during the cruise (11 = of the females and 98.7% of the males). 882, 487 males and 395 females) were The eight components identified in the separated using Bhattacharya's method (see length-frequencies distributions of males and SPARRE& VENEMA1992) implemented in the females and the results of the analysis are LFSA-FA0 package (SPARRE 1988). Two summarised in Tables 3 and 4. The values criteria were used to identify the modes, the calculated for the Separation Index (SI) were separation index (SI), a ratio based on the greater than 2.0. Expected and observed difference between the means of the distributions were significantly different components and the average of correspondent (~~0.05).The first component identified in the standard deviations, and the correlation distribution was considered to be the third age coefficients of the regression lines. group. Components showing a SI greater than 2.0 The relationships between sngittne radius were considered to be meaningfully separated. (OR) and TL, for males, females and sexes The observed and expected distributions were combined, were best described by significant compared by the Chi-square Test (SOKAL& positive linear equations (p<0.001) (Table 5 ROHLF1981). and Fig. 2). Between males and females, Von Bertalanffy growth equations intercepts were not significantly different (t' = (BAGENAL& TESCH 1978) were fitted to mean 0.18, p>0.05), whereas equality of slopes was lengths at age derived from age-length keys, rejected (t' = 0.69, p<0.05). Ring counts (RC) backcaiculation analysis, and length-frequency increased with otolith growth. The analysis using the FiSAT computer software relationships RC:OR were linear and (GAYANILOet al. 1994). To avoid possible statistically significant (p<0.001) (Table 5 and biases, ages that represented less than 5% of Fig. 3). Neither intercepts nor slopes differed total number of specimens aged were discarded between males and females (t = 1.67, p>0.05, from the analysis. Constraints were and t = 1.39, p>0.05, respectively). Mean back- automatically set by the software. Equations calculated lengths at age (BL) ranged from maximising the Phi-prime ($') Test's value (a 15.8 cm to 43.4 cm in females (ages 3 to 12) maximum likelihood test for the comparison of and from 16.6 cm to 4 1.9 cm in males (ages 3 overall growth performance. See SPARRE & to 14) (Tables 6 and 7). Table 1 Age-length key for female bluemouth. H. dactylopter~udactylopterus. CL - length classes (midpoint); N - number of individuals from which sagittae were examined; Mean TL - mean total length; and SD - standard deviation. Estimated age - Ring counts CL. 123456789 10 11 12 (... 14.5 1 15.5 1 16.5 211 17.5 1 1 18.5 1 1 19.5 1 20.5 111 21.5 3 1 22.5 1323 23.5 235 24.5 1333 25.5 4 3 26.5 2 8 4 1 27.5 14541 28.5 6421 29.5 1412 30.5 123 3 1.5 1321 32.5 1461 33.5 112 34.5 112 35.5 331 36.5 2 2 1 37.5 1 38.5 3 39.5 2 1 1 40.5 1 1 41.5 2 42.5 13 2 43.5 1 44.5 1 45.5 1 Mean TL, cm 19.9 22.1 24.8 26.8 30.4 33.5 36.5 40.3 44.8 45.5 SD 2.75 3.65 4.99 2.64 3.44 3.96 4.02 2.23 1.25 0.00 The von Bertalanffy growth parameters equations derived from the age-length keys, computed for males and females, using data backcalculation analysis and length-frequency derived from length frequency analysis (LFA), analysis are similar in males and in females age-lengths keys (ALK) and backcalculation (Fig.

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