Age and growth of the blackchin guitarfish Glaucostegus cemiculus (Geoffroy Saint-Hilaire, 1817) from Iskenderun Bay (Northeastern Mediterranean)

Between September 2010 and June 2012, a total 291 (166 females and 125 males) blackchin guitarfish Glaucostegus cemiculus were captured by a commercial bottom trawler (F/V Coşkun Reis) in Iskenderun Bay, Turkey (northeastern Mediterranean Sea). The total length (L) and total weight (W) of the female and male guitarfish ranged between 32.0–165.0 cm and 88 g–16.68 kg, and 34.3–128.3 cm and 112 g–6.00 kg, respectively. Vertebral age estimates ranged from 0 to 8 years for females and 0 to 5 years for males. The growth models of von Bertanlanffy and Gompertz were fitted to the length at age data using the nonlinear regression method. Model selection was based on the values of the residual standard error and the Akaike's information criterion corrected for small sample size (AIC_C) associated with each fit. The von Bertalanffy growth model provided the best fitting growth curves for each sex with parameters reaching L_∞ = 187.17 cm, K = 0.195 year^-1, t₀ = −1.38 year for females, and L_∞ = 144.85 cm, K = 0.321 year^-1, t₀ = −1.13 year^-1 for males. The W–L relationship parameters did not differ significantly between sexes, the estimated values of a and b were 0.0018 and 3.11, respectively. By using these values of a and b, and also respective estimates of L_∞, the values of W_∞ were obtained as 20.53 kg for females and 9.25 kg for males. The overall percentage ratios of females and males in the samples were 57% and 43% respectively.     

Unravelling growth trajectories from complicated otoliths – the case of Brazilian codling Urophycis brasiliensis

Uncertainty regarding the age determination of the Brazilian codling Urophycis brasiliensis has hampered its stock assessment. Transverse sections of otoliths displayed up to seven (in males) and 12 (in females) alternate opaque and translucent bands that could not be conclusively validated as annuli, resulting in unrealistically high ages of first maturity (A₅₀) (A_50male = 4·5 years and A_50female = 6 years). Therefore, growth was described by the von Bertalanffy (VB) model using an alternative approach that combined microstructure data (daily growth increments) and a fixed asymptotic total length (L_∞). This approach was supported by applying it to two other co‐occurring species, the whitemouth croaker Micropogonias furnieri and the king weakfish Macrodon atricauda, for which daily and annual ring formation has previously been validated. The sensitivity to realistic errors associated with the choice of the L_∞ and the daily increment readings was shown to be low. The results show that U. brasiliensis has a fast growth rate (K_male = 1·19 year^?1, K_female = 0·71 year^?1) and early maturation (A_50male = 1·1–1·5 years, A_50female = 1·6–1·8 years); typical life‐history traits for a sub‐tropical coastal gadiform. This novel study offers an alternative approach for age and growth reconstruction for species with complex patterns of opaque and translucent bands provided that daily growth increments in the yearlings can be counted and L_∞ reliably estimated.     

Geographic variation in life-history traits of the endemic kite skate Dipturus chilensis (Batoidea: Rajidae), along its distribution in the fjords and channels of southern Chile

Life-history traits of kite skates Dipturus chilensis were examined from two regions (c. 2286 km apart) in the sheltered fjords and channels of southern Chile. A total of 482 and 403 specimens were collected from the southern fjords (c. 42–46° S) and the fjords of Chilean Patagonia (c. 51–54° S), from September 2003 to 2004, respectively. Vertebra marginal increment analysis indicated an annual deposition of growth rings which was completed during the winter months. For each region, von Bertalanffy growth parameters showed that females attained a larger asymptotic size, L_∞, had a lower growth coefficient, K, and lived longer than males. Growth analysis indicated that D. chilensis from the Patagonian fjords had a longer life span (females: 22 v. 21 years; males 19 v. 17 years), attained a larger L_∞ (females: 150 v. 136 cm; males: 122 v. 118 cm total length, L_T) and had a lower K value (females: 0·087 v. 0·104; males: 0·110 v. 0·116) than their counterparts in the southern fjords. Comparisons with previous studies indicated that D. chilensis from both southern and Patagonian sheltered fjords had larger L_∞, and grew more slowly than their counterparts from central-southern Chile (L_∞= 119–123 cm, K= 0·123–0·127), suggesting latitudinal variations in growth. Females attained sexual maturity later than males in both regions. For both sexes, lengths at 50% maturity (L_50%) between regions were similar (females: c. 103 cm; males: c. 87 cm L_T); however, D. chilensis from Patagonia appeared to mature 1 year earlier (females: 13 v. 14 years; males: 10 v. 11 years). Specimens from Patagonia had a lower ovarian fecundity than those from the southern fjords. An increase in the proportion of mature females and males during summer, suggests that the reproductive peak occurs in this season, and no regional differences were found. The size of the egg cases increased with maternal L_T and these were longer in Patagonia. The information provided here represents the first evidence of regional variations in life-history traits for elasmobranchs in the south-eastern Pacific.     

Age, growth, and sexual maturity of the yellownose skate Dipturus chilensis in the south‐eastern Pacific

The age and growth parameters of Dipturus chilensis were estimated by counting growth rings from thin sections of vertebral centra from 400 fish (246 females and 154 males), ranging from 23 to 124 cm total length (L_T), and backcalculating fish lengths at previous ages. Marginal increment analysis lent support to the hypothesis of annual deposition of band‐pairs, which formed during the winter months. The oldest female D. chilensis aged in this study was 21 years and 117 cm L_T, whereas the oldest male was 18 years and 93 cm L_T. A 4·7% index of average per cent error (I_APE) suggested that this is a precise method for calculating the age of D. chilensis. Observed L_T were lower than backcalculated L_T, which implies the influence of Lee's phenomenon. The von Bertalanffy growth equations, based on mean length‐at‐age data, were estimated as L_t = 128·3 (1 ? e^{?0·112 (t + 0·514)}) for females and L_t = 107·8 (1 ? e^{?0·134 (t + 0·862)}) for males where t is age (years). Growth was significantly different between sexes: females reached a larger adult size. Ages and lengths at 50% maturity were estimated at 14 years of age and 106 cm L_T for females and 11 years of age and 86 cm L_T for males. At c. 14 years, there was a decline in growth rates in females. The factor most likely responsible for this was sexual maturity, which caused a discontinuity in growth of female fish. These results show that this species is slow‐growing, long‐lived, relatively large and of delayed maturity, characteristics that make it vulnerable to exploitation.     

Age,growth and maturity of the pelagic thresher Alopias pelagicus and the scalloped hammerhead Sphyrna lewini

Indonesia has the greatest reported chondrichthyan catches worldwide, with c.110,000 t caught annually. The pelagic thresher (Alopias pelagicus) and scalloped hammerhead (Sphryna lewini) together comprise about 25% of the total catches of sharks landed in Indonesia. Age and growth parameters were estimated for A. pelagicus and S. lewini from growth‐band counts of thin‐cut vertebral sections. Alopias pelagicus (n = 158) and S. lewini (n = 157) vertebrae were collected from three Indonesian fish markets over a 5 year period. A multi‐model analysis was used to estimate growth parameters for both species. The models of best fit for males and females for A. pelagicus was the three‐parameter logistic (L_∞ = 3169 mm L_T, k = 0·2) and the two‐parameter von Bertalanffy models (L_∞ = 3281 mm L_T, k = 0·12). Age at maturity was calculated to be 10·4 and 13·2 years for males and females, respectively, and these are the oldest estimated for this species. The samples of S. lewini were heavily biased towards females, and the model of best fit for males and females was the three‐parameter Gompertz (L_∞ = 2598 mm L_T, k = 0·15) and the two‐parameter Gompertz (L_∞ = 2896 mm L_T, k= 0·16). Age at maturity was calculated to be 8·9 and 13·2 years for males and females, respectively. Although numerous age and growth studies have previously been undertaken on S. lewini, few studies have been able to obtain adequate samples from all components of the population because adult females, adult males and juveniles often reside in different areas. For the first time, sex bias in this study was towards sexually mature females, which are commonly lacking in previous biological studies on S. lewini. Additionally, some of the oldest aged specimens and highest age at maturity for both species were observed in this study. Both species exhibit slow rates of growth and late age at maturity, highlighting the need for a re‐assessment of the relative resilience of these two globally threatened sharks at current high levels of fishing mortality throughout the eastern Indian Ocean.     

Life‐history strategies of the rock hind grouper Epinephelus adscensionis at Ascension Island

Epinephelus adscensionis sampled from Ascension Island, South Atlantic Ocean, exhibits distinct life‐history traits, including larger maximum size and size at sexual maturity than previous studies have demonstrated for this species in other locations. Otolith analysis yielded a maximum estimated age of 25 years, with calculated von Bertalanffy growth parameters of: L_∞ = 55·14, K = 0·19, t₀ = ?0·88. Monthly gonad staging and analysis of gonad‐somatic index (I_G) provide evidence for spawning from July to November with an I_G peak in August (austral winter), during which time somatic growth is also suppressed. Observed patterns of sexual development were supportive of protogyny, although further work is needed to confirm this. Mean size at sexual maturity for females was 28·9 cm total length (L_T; 95% C.I. 27·1–30·7 cm) and no females were found >12 years and 48·0 cm L_T, whereas all confirmed males sampled were mature, >35·1 cm L_T with an age range from 3 to 18 years. The modelled size at which 50% of individuals were male was 41·8 cm (95% C.I. 40·4–43·2 cm). As far as is known, this study represents the first comprehensive investigation into the growth and reproduction of E. adscensionis at its type locality of Ascension Island and suggests that the population may be affected less by fisheries than elsewhere in its range. Nevertheless, improved regulation of the recreational fishery and sustained monitoring of abundance, length frequencies and life‐history parameters are needed to inform long‐term management measures, which could include the creation of marine reserves, size or temporal catch limits and stricter export controls.     

Life histories of two deep‐water Australian endemic elasmobranchs: Argus skate Dipturus polyommata and eastern spotted gummy shark Mustelus walkeri

Two Australian endemic elasmobranchs, the Argus skate Dipturus polyommata and the eastern spotted gummy shark Mustelus walkeri, were collected from the by‐catch of a prawn Melicertus plebejus trawl fishery off Queensland. Age and growth parameters were estimated from growth band counts in vertebral sections of 220 D. polyommata and 44 M. walkeri. Dipturus polyommata males and females had an observed maximum age of 10 years and reached maximum sizes of 369 and 371 mm total length (L_T), respectively. Mustelus walkeri lived longer, with the oldest female aged 16 years and measuring 1050 mm stretched total length (L_ST), and oldest male aged 9 years and 805 mm L_ST. Dipturus polyommata grew relatively fast with a von Bertalanffy growth completion parameter of k = 0·208 year^?1 with males reaching maturity at 4·0 years (c. 278 mm L_T) and females at 5·1 years (c. 305 mm L_T). Mustelus walkeri grew more slowly with k = 0·033 year^?1 with males estimated to mature at 7–9 years (670–805 mm L_ST) and females at 10–14 years (833–1012 mm L_ST). Length at birth inferred from neonate D. polyommata was 89–111 mm L_T while for M. walkeri it was estimated to be 273 L_ST based on the value of L₀ from the von Bertalanffy growth model. Both species appeared to have continuous reproductive cycles and low fecundity with an average ovarian fecundity of eight follicles for D. polyommata and a litter size of five to seven pups for M. walkeri. Based on these life‐history traits, D. polyommata is more resilient to fishing pressure than M. walkeri.     

Age and growth of Carcharhinus leucas in the northern Gulf of Mexico: incorporating variability in size at birth

Age and growth rates of bull shark Carcharhinus leucas[n = 255; 555–2230 mm fork length (L_F)] from the northern Gulf of Mexico were estimated from ring counts on vertebral sections collected from fishery‐dependent and ‐independent surveys. Two growth models were fitted to observed data: the von Bertalanffy growth model (VBGM) with t₀ as the third parameter and a modified version of the VBGM using a fixed size‐at‐birth intercept as the third parameter. To address the variability in size‐at‐birth, a Monte Carlo simulation was incorporated into the size‐at‐birth intercept. The sex‐specific growth models were not significantly different, allowing a sexes combined model to be generated. The traditional VBGM predicted a theoretical maximum size (L_∞) of 3007·1 mm L_F, a growth coefficient (K) of 0·042 year^?1 and a theoretical age at zero length (t₀) of –6·844 years. The modified VBGM with a fixed size‐at‐birth intercept of 565 mm L_F predicted an L_∞ of 2289·2 mm L_F and a K value of 0·089 year^?1. When comparing model estimates to previously published information, the traditional VBGM predicted a significantly lower theoretical maximum size and a higher growth coefficient than those produced using data collected during the 1980s. Overall, results obtained using the VBGM with a fixed size‐at‐birth produced more biologically realistic parameters than that of the VBGM with t₀. The Monte‐Carlo simulation incorporating variability in size‐at‐birth produced similar results to the VBGM using a fixed size‐at‐birth. This study provides the first attempt to incorporate variability at size‐at‐birth and provide measurements of variability around the individual parameter estimates for an elasmobranch.     

Factors affecting estimates of size at age and growth in grey triggerfish Balistes capriscus from the northern Gulf of Mexico

Growth zones in dorsal spines of grey triggerfish Balistes capriscus from the northern Gulf of Mexico were utilized to estimate growth and examine factors that may affect estimates of size at age. Age was estimated from dorsal‐spine sections of 4687 individuals sampled from U.S. waters during 2003–2013, including both fishery‐independent (n = 1312) and fishery‐dependent (n = 3375) samples. Ninety‐six per cent (n = 4498) of these sections were deemed suitable for ageing; average per cent error between two independent readers was 10·8%. Fork length (L_F) ranged from 65 to 697 mm and age estimates from 0 to 14 years. Both sex and sample source (fishery‐independent v. recreational) significantly affected estimated size at age for 2–6 year‐old fish. Data were pooled between sources to fit sex‐specific von Bertalanffy growth functions. Results for the female model were L_∞ = 387 mm L_F, k = 0·52 year^?1 and t₀ = 0·01 year, while for males L_∞ = 405 mm L_F, k = 0·55 year^?1 and t₀ = 0·02 year. These results were significantly different between sexes and indicate clear sexual dimorphism. Thus, growth should be modelled separately by sex when examining population parameters or conducting stock assessment modelling. The positive bias in estimates of size at age computed for recreational v. fishery‐independent samples also has clear implications for stock assessment as growth functions computed with fishery‐dependent samples would tend to overestimate stock productivity.     

Reproductive biology,growth, and age composition of non‐native Indian glassy fish Parambassis ranga (Hamilton, 1822) in Haebaru Reservoir,Okinawa‐jima Island,southern Japan

Age composition, growth, and reproductive biology of the non‐native Indian glassy fish Parambassis ranga (Hamilton, 1822) were surveyed in the Haebaru Reservoir on Okinawa‐jima Island, southern Japan. Standard lengths (SLs) of males and females ranged from 19.7 to 44.0 mm and from 19.2 to 52.4 mm, respectively. The overall sex ratio was significantly female‐biased, with the monthly percentage of females ranging from 71.4 to 100.0. Marginal growth analysis of sectioned otoliths revealed opaque zones formed annually from November to May. Observed age ranged from 0 to 3 years for both sexes, although the 1‐year age class comprised the majority of the sampled population. Von Bertalanffy growth parameters were L_∞ = 48.8 mm (SL), K = 0.43 year^?1, and t₀ = ?1.47 years for males, and L_∞ = 43.7 mm, K =0.72 year^?1, and t₀ = ?1.29 years for females. Length at 50% maturity was estimated to be 25.8 mm SL, and maturation was within 1 year after hatching. The main spawning season of P. ranga was estimated to occur from February to October, peaking in April.     

Age and growth of the endemic Xingu River stingray Potamotrygon leopoldi validated using fluorescent dyes

Between 2003 and 2005, vertebrae of 151 Xingu River Potamotrygon leopoldi (Potamotrygonidae) (75 males and 76 females) were analysed to derive a growth curve for this species. The disc width (W _D) was significantly different between sexes, with females measuring 149–700 mm W _D and males 109–500 mm W _D. The average percentage error for vertebrae readings of the whole sample was 2·7%. The marginal increment ratio (R _MI) showed an increasing trend with the highest value in November, decreasing from December on. The majority of vertebrae displaying R _MI zero, occurred in September, but the annual periodicity of ring deposition throughout the year was not conclusive. Tetracycline (TCN) injected specimens were held in captivity for 13 months and displayed a fluorescent mark in vertebrae confirming a yearly periodicity of band pair formation with the translucent ring deposited in September–October. The Akaike information criterion (AIC) showed that, among the seven models considered, the best fit was obtained for the von Bertalanffy modified with W ₀ (where W ₀ = W _D at birth) for both sexes. Growth parameters for females were: W ₀ = 149 mm; W _∞ = 763·06 mm; k = 0·12 year^{– 1}, whereas for males: W ₀ = 109 mm; W _∞ = 536·4 and k = 0·22 year^?1. Maximal ages were 7·2 years in males and 14·3 years in females. The species shows sexual dimorphism expressed in the growth pattern, size at maturity, longevity and asymptotic sizes. Concern for sustainability is raised due to the construction of the Belo Monte Hydroelectric Power Plant (2015 and 2016) in the State of Pará causing changes to the habitat of this species, which is endemic to the Xingu River and two of its tributaries.     

Population structure and reproductive biology of a freshwater fish,Labeo boggut (Sykes, 1839), from two perennial rivers of Yamuna basin

Population structure and reproductive biology of an important and less studied freshwater carp, Labeo boggut (Sykes, 1839), from two perennial rivers of Central India were studied between January 2008 and December 2009. Maximum three annual rings were found and used to assess growth data in samples representing 0 to 3+ year classes. LWR indicated positive allometric growth in males and females of both rivers. Asymptotic length (L_∞) and growth co‐efficient (K) were 22.5 cm and 0.5 year^?1 for the Betwa River; and 23.6 cm and 0.6 year^?1 for the Ken River. Growth performance index (ø’) was higher in the Ken than in the Betwa. Reproduction was between June and September and GSI of both sexes were maximal in mid‐June, thereafter declining until September. Mean size at first sexual maturity was 12.2 cm (n = 12) for females and 13.2 cm (n = 8) for males in the Betwa, and 12.5 cm (n = 13) TL for females and 13.1 cm (n = 9) TL for males in the Ken. The exploitation level (E) and maximum allowable exploitation (E_max) limit of L. boggut was 0.23 and 0.36 in the Betwa, whereas it was 0.33 and 0.37 in the Ken. These presented biological traits and population characters of L. boggut from both rivers provide first basic information for use in future assessment and conservation planning.     

Age and growth of the gulf toadfish Opsanus beta based on otolith increment analysis

In the present study, sagittal otoliths of confirmed male and female specimens of the gulf toadfish Opsanus beta that were collected monthly over the course of a year from Biscayne Bay, Florida, U.S.A. were analysed. The timing and frequency of O. beta spawning seasons are reported by examination of the gonado‐somatic index. The estimated ages of males and females ranged from < 1 year to 6 and 5 years, respectively. Strong sexual dimorphism in growth was apparent with von Bertalanffy parameter estimates for males of L_∞ = 393·8 mm, K = 0·30, t₀ = 0·36 and females of L_∞ = 201·1 mm, K = 0·79, t₀ = 0·47. Comparison with previously published growth trajectories of the more northerly distributed conspecific Opsanus tau showed that O. beta males had a higher growth rate. Female O. beta and O. tau growth trajectories appear similar, with an indication that the former becomes asymptotic at least a year before the latter. Results are discussed in the context of temperature regimes, reproductive energy allocation and waste urea excretion in the two species.     

Age and growth in pink cusk-eel (Genypterus blacodes) off the Chilean austral zone: evaluating differences between management fishing zones

The von Bertalanffy (vB) growth parameters for pink cusk‐eel (Genypterus blacodes) were estimated for the Chilean austral‐zone (41°28′–57°00′S) by gender and management fishing zones. A total of 47 026 samples were collected between March 1982 and May 2004, with total length ranging from 19 to 154 cm. Age determinations, based on the reading of saggital otoliths, were between 1 and 14 years in males and between 1 and 16 years in females. Statistical differences in growth were found between the sexes and management fishing zones. For the combined sexes the vB growth parameters for the northern‐austral zone (41°28′–47°00′S) were: l_∞=111.452 cm, k = 0.186 year⁻¹, t₀ = −0.912 year; and for the southern‐austral zone (47°00′–57°00′S): l_∞ = 123.447 cm, k = 0.147 year⁻¹, t₀ = −1.779 year.     

Validated age and growth estimates for the shortfin mako, Isurus oxyrinchus, in the North Atlantic Ocean

Age and growth estimates for the shortfin mako, Isurus oxyrinchus, derived from vertebral centra of 258 specimens (118 males, 140 females), ranging in size from 64 to 340 cm fork length (FL) were compared with data from 22 tag–recaptured individuals (74–193 cm FL) and length–frequency data from 1822 individuals (1035 males, 787 females; 65–215 cm FL). Annual band-pair deposition, confirmed by a concurrent bomb radiocarbon validation study, was used as the basis for band interpretation. Validation was further confirmed with a tetracycline-injected male shortfin mako recaptured after being at liberty off South Africa for 1 year and aged at 18 years. Growth rates from tag–recapture analysis (GROTAG) were higher than those derived from vertebral annuli and were only available from sharks up to 193 cm FL at recapture. Modal length–frequency data were used to verify the first four age classes. Growth curves were fit using both von Bertalanffy and Gompertz models. The 3-parameter version of the von Bertalanffy growth function produced the most biologically reasonable values for males, based on observed data (L _∞  = 253 cm FL, K = 0.125 year^?1 (estimated longevity = 21 year), and L ₀ = 72 cm). The 3-parameter version of the Gompertz growth function produced the most biologically reasonable estimates, for females (L _∞  = 366 cm FL, K = 0.087 year^?1 (estimated longevity = 38 year) and L ₀ = 88 cm. Males and females were aged to 29 (260 cm FL) and 32 years (335 cm FL), respectively. Both sexes grew similarly to age 11 (207 cm FL, 212 cm FL for males and females, respectively) when the curve leveled in males and continued to rise in females. Age at 50% maturity was estimated at 8 years for males (185 cm FL) and 18 years for females (275 cm FL). The species grows slower, matures later and has a longer life span than previously reported in North Atlantic waters.     

Validated age,growth and maturity of the bonnethead Sphyrna tiburo in the western North Atlantic Ocean

The age, growth and maturity of bonnetheads Sphyrna tiburo inhabiting the estuarine and coastal waters of the western North Atlantic Ocean (WNA) from Onslow Bay, North Carolina, south to West Palm Beach, Florida, were examined. Vertebrae were collected and aged from 329 females and 217 males ranging in size from 262 to 1043 mm and 245 to 825 mm fork length, L_F, respectively. Sex‐specific von Bertalanffy growth curves were fitted to length‐at‐age data. Female von Bertalanffy parameters were L_∞ = 1036 mm L_F, k = 0·18, t₀ = ?1·64 and L₀ = 272 mm L_F. Males reached a smaller theoretical asymptotic length and had a higher growth coefficient (L_∞ = 782 mm L_F, k = 0·29, t₀ = ?1·43 and L₀ = 266 mm L_F). Maximum observed age was 17·9 years for females and 16·0 years for males. Annual deposition of growth increments was verified by marginal increment analysis and validated for age classes 2·5+ to 10·5+ years through recapture of 13 oxytetracycline‐injected specimens at liberty in the wild for 1–4 years. Length (L_F50) and age (A₅₀) at 50% maturity were 819 mm and 6·7 years for females, and 618 mm and 3·9 years for males. Both female and male S. tiburo in the WNA had a significantly higher maximum observed age, L_F50, A₅₀ and L_∞, and a significantly lower k and estimated L₀ than evident in the Gulf of Mexico (GOM). These significant differences in life‐history parameters, as well as evidence from tagging and genetic studies, suggest that S. tiburo in the WNA and GOM should be considered separate stocks.     

Life‐history characteristics of the large Amazonian migratory catfish Brachyplatystoma rousseauxii in the Iquitos region,Peru

The main life‐history traits of the dorado Brachyplatystoma rousseauxii, a large Amazonian catfish undertaking the largest migration known for a freshwater fish species (from the nursery area in the estuary of the Amazon to the breeding zones in the head waters of the western Amazon basin close to the Andes), were determined from a 5 year sampling of >15 000 specimens in the Peruvian Amazon. The breeding season occurred during the falling and low‐water periods, which is hypothesized to be an adaptation to maximize the chances of young stages to reach the estuary. The size at first sexual maturity was slightly larger for females than males, c. 91 and 83 cm standard length (L_S), respectively. Both males and females reproduce for the first time at >3 years old. The fecundity per spawning event ranged from 481 734 to 1 045 284 oocytes for females weighing 25 and 34 kg, respectively. Seasonal variations of body condition were similar among sexes, but differed between immature specimens that had a higher condition during the low‐water period and lower condition during rising waters, and mature individuals that showed the opposite pattern. The growth characteristics were estimated by L_S frequency analysis. For females, the best fitting models gave a mean birth date in August, during the height of the breeding cycle, with the following von Bertalanffy growth function parameters: L_S∞ = 153·3, K = 0·29 and t₀ =– 0·37 years. For males, the best fitting model gave a mean birth date in July, also during the height of the breeding period, with L_S∞ = 142, K = 0·30 and t₀ =– 0·36 years. At a given age, females were systematically larger than males and the size difference increased with age. The largest females sampled (148 cm L_S) was 11 years old and the largest male (134 cm L_S) was 9 years old. The mortality estimates were higher for males total (Z) = 1·34, natural (M) = 0·52 and fishing (F) = 0·82 than for females (Z = 0·98, M = 0·50, F = 0·48). The life‐history patterns of B. rousseauxii are discussed in light of the available knowledge about this species and the understanding of its complex life cycle.     

Age,growth and mortality of common two‐banded seabream,Diplodus vulgaris (Geoffroy Saint‐Hilaire, 1817), in the eastern Adriatic Sea (Croatian coast)

Age, growth and mortality were analysed for the common two‐banded seabream, Diplodus vulgaris, collected in the eastern Adriatic (Croatian coast) from commercial fishery catches by ‘tramata’ fishing (2005–2006) to obtain growth estimation. The oldest female was estimated to be age 11, the oldest male age 10 years. The von Bertalanffy growth parameters estimated by reading scales were: L_∞ = 48.60 cm (SE = 1.101), K = 0.112 (SE = 0.005) and t₀ = ?2.366 (SE = 0.060) for all specimens; L_∞ = 51.96 cm (SE = 2.153), K = 0.095 (SE = 0.007) and t₀ = ?2.837 (SE = 0.120) for females and L_∞ = 56.25 cm (SE = 2.662), K = 0.084 (SE = 0.067) and t₀ = ?2.920 (SE = 0.117) for males. The overall sex ratio was 1.22 : 1 in favour of males. Total mortality, corresponding to the slope of the descending limb of the catch curve, was Z = 0.81 per year for females and Z = 0.85 per year for males. Exploitation ratios were E = 0.68 for females and E = 0.73 for males.     

Population biology and assessment of the white-spotted spinefoot, Siganus canaliculatus (Park, 1797), in the southern Arabian Gulf

The age, growth, mortality, reproduction and resource status of Siganus canaliculatus in the southern Arabian Gulf were investigated using a combination of size frequency, biological and size‐at‐age data. Defined structural increments consisting of alternating translucent and opaque bands in transverse sections of sagittal otoliths were validated as annuli. The maximum absolute age estimate was 7.8 years. Parameter values of the von Bertalanffy growth function fit to size‐at‐age data (males and females combined) were: k = 1.0, L_∞ = 24.8 cm (L_F), t_o = −0.1 years. Fish in spawning condition were only observed between April and July although patterns in gonadosomatic indices suggested a second but less well defined spawning event in November. The mean sizes and ages at first sexual maturity were 21.5 cm L_F (1.9 years) for males and 25.7 cm L_F (2.1 years) for females. Fish were fully recruited to the fishery at a size (L₁₀₀ = 19.7 cm L_F) that was smaller than the sizes at which sexual maturity was attained. The annual instantaneous rate of fishing mortality (F = 0.85 year⁻¹) (0.26–1.44 year⁻¹ 95% CI) was considerably greater than the target (F_opt = 0.33 year⁻¹) and limit (F_limit = 0.44 year⁻¹) biological reference points, indicating that the stock is overexploited.     

Some biological parameters of the Mediterranean sand smelt Atherina (Atherina) hepsetus, Linnaeus, 1758 (Pisces: Atherinidae) from the middle eastern Adriatic (Croatian coast)

Data on the length–weight relationship, age, growth, sex ratio and mortality were analysed for the Mediterranean sand smelt, Atherina (Atherina) hepsetus L. (total = 2805; males = 1258; females = 1547) collected in the eastern middle Adriatic island area during the reproductive period (February to April) in 2002. The total length of sampled specimens ranged from 3.8 to 14.5 cm and the weight from 0.28 to 22.39 g. The overall sex ratio was 1.23 : 1 in favour of females, significantly different from the expected 1 : 1 ratio (χ² = 29.76; P < 0.05). All individuals >13.4 cm were females. The oldest collected male and female specimens were 5 years old. The von Bertalanffy growth formula was estimated for females (L_∞ = 15.79 (1−e^{−0.43(t+0.049)}) and males (L_∞ = 15.25 (1−e^{−0.43(t+0.018)}). The power values (b) of the length–weight relationship were very similar for both sexes (b = 3.14) and indicated a slightly allometric growth. The instantaneous rates of mortality for all collected fish were Z = 1.44 year⁻¹; M = 0.94 year⁻¹ and F = 0.50 year⁻¹. The exploitation ratio was E = F/Z = 0.35. The value for M is highly uncertain, however, as well as those values for F and E.