Reproductive biology of the fat snook Centropomus parallelus Poey, 1860 (Teleostei,Centropomidae) and implications for its management in the southern Atlantic Ocean

The reproductive biology of Centropomus parallelus was described from 589 individuals captured in estuarine and coastal waters in Southern Brazil. Length-frequency distribution showed the dominance of males in smaller length-classes (132–290 mm L_T), whereas females were dominant in larger length-classes (>290 mm L_T). Total length at maturity (L₅₀) was 180 mm L_T and corresponded to 29% of the maximum length recorded. Histological sections revealed one hermaphrodite (205 mm L_T) and few immature females. Life history traits provided herein can contribute to sustainable fisheries management practices.     

Catch composition and reproductive biology of Sphyrna lewini (Griffith & Smith) (Carcharhiniformes, Sphyrnidae) in Indonesian waters

Data on the length compositions and reproductive biology have been collected for Sphyrna lewini in Indonesian waters, in which this species makes an important contribution to the biomass of its artisanal and small‐scale fisheries. These data were obtained by recording relevant body measurements and counts for this species while visiting Indonesian fish landing sites. The fish, which had been caught by gillnetting and longlining, covered a wide length range and included substantial numbers of immature, maturing and mature individuals. The vast majority of S. lewini <1100 mm total length (L_T) had been caught by gillnetting, whereas most of those above this length had been obtained through longlining. The number of embryos in pregnant females, which ranged from 14 to 41, with a mean of 25, was positively correlated with the L_T of those females. Birth occurred at c. 400 mm L_T and predominantly in October and November. The number of females was similar to that of males among smaller fish, but far greater than that of males among larger fish. This presumably reflects a faster growth and greater longevity of females, selectivity of longlining for females and a tendency for males to move outside the area fished. For males, the relationships between clasper length and the extent of its calcification, and also with sexual maturation and L_T have been determined. Females attained maturity (L_T50) at a far larger size (2285 mm) than males (1756 mm). The L_T of virtually all females and all males taken by gillnetting were less than their respective L_T50 at maturity, and c. 67 and 51% of the longline catches of females and males, respectively, were likewise immature. This feature, together with the substantial catches of S. lewini and the life cycle traits of elasmobranchs, suggest that this species is likely to be prone to overfishing in Indonesian waters. Furthermore, the removal of large numbers of this apex predator will presumably be affecting the trophic structure in the waters in which it is fished.     

Reproductive parameters of the Pacific angel shark Squatina californica (Selachii: Squatinidae)

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (L_T) and body mass (M_T). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm L_T; the median size at maturity (L_T50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm L_T; the estimated L_T50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non‐gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter.     

Reproductive aspects of the Atlantic angel shark Squatina dumeril in the southern Caribbean Sea

The maturity and reproduction of the Atlantic angel shark Squatina dumeril were assessed using 77 females (29·2–110·4 cm total length; L_T) and 269 males (58·7–108·2 cm L_T) harvested by artisanal gillnetters off Venezuela. The biased sex ratio implied segregation or sex‐specific gear selectivity. Based on the development of the reproductive tract, 50% L_T at sexual maturity (L_T50, mean ± s.e .) for females and males were estimated at 86·14 ± 0·64 and 81·55 ± 0·12 cm, respectively. Uterine fecundity ranged between one and six and with a maximum embryo size of 25·7 cm L_T. Gravid females were observed from August to December, including those close to parturition and while the gestation period was not confirmed, the size of ovarian follicles among some specimens implied protraction. The low fecundity of the species supports close monitoring of catches.     

Reproductive biology of the greeneye spurdog Squalus chloroculus (Squaliformes,Squalidae)

The reproduction of the greeneye spurdog Squalus chloroculus was studied based on animals caught in the multispecies and multi‐gear southern and eastern scalefish and shark fishery on the upper continental slope off southern Australia. One hundred and ninety‐nine females (502–990 mm, total length, L_T) and 189 males (515–810 mm L_T) were examined. The female reproductive cycle, based on 41 breeding animals, is continuous and triennial, with the pregnancy period estimated to be 31–34 months, seasonal and synchronous with the ovarian cycle; a third of the breeding female population is estimated to give birth between September and December each year. The estimated L_T at which 50% of females are mature is 799 mm (95% c.i. : 794, 804), whereas the L_T at which 50% are maternal is 825 mm (95% c.i. : 817–833), but these estimates are probably biased by the phenomenon of apparent change of L_T at maternity and L_T at maturity following severe length‐selective fishing mortality. Litters ranged from four to 15 embryos with a 1:1 sex ratio, and litter size increased with maternal length. The breeding cycle of males is neither seasonal nor synchronous with the female cycle. The estimated L_T of males where 50% are mature was 629 mm (95% c.i. : 603, 645).     

Maturation and sexual ontogeny in the spangled emperor Lethrinus nebulosus

The reproductive development and sexual ontogeny of spangled emperor Lethrinus nebulosus populations in the Ningaloo Marine Park (NMP) were investigated to obtain an improved understanding of its evolved reproductive strategy and data for fisheries management. Evidence derived from (1) analyses of histological data and sampled sex ratios with size and age, (2) the identification of residual previtellogenic oocytes in immature and mature testes sampled during the spawning season and (3) observed changes in testis internal structure with increasing fish size and age, demonstrated a non‐functional protogynous hermaphroditic strategy (or functional gonochorism). All the smallest and youngest fish sampled were female until they either changed sex to male at a mean 277·5 mm total length (L_T) and 2·3 years old or remained female and matured at a larger mean L_T (392·1 mm) and older age (3·5 years). Gonad masses were similar for males and females over the size range sampled and throughout long reproductive lives (up to a maximum estimated age of c. 31 years), which was another correlate of functional gonochorism. That the mean L_T at sex change and female maturity were below the current minimum legal size (MLS) limit (410 mm) demonstrated that the current MLS limit is effective for preventing recreational fishers in the NMP retaining at least half of the juvenile males and females in their landed catches.     

Reproductive biology of the crocodile shark Pseudocarcharias kamoharai

From February 2005 to September 2007, a total of 490 crocodile sharks Pseudocarcharias kamoharai, caught as by‐catch in the swordfish and tuna longline fishery that operates in the tropical western Atlantic Ocean, was studied in regard to their reproductive biology. Maximum observed total lengths (L_T) were 1220 and 1090 mm for females and males respectively, with a high proportion of the catch being composed of mature specimens. Sexual maturity was attained at 760–810 mm L_T for males (L_T50 = 800 mm) and 870–980 mm L_T for females (L_T50 = 916 mm). The size at birth was estimated at 415 mm L_T. Temporal variation in gonad morphology and mass suggests that in this region P. kamoharai, an aplacental viviparous species with oophagy, does not show a well‐defined reproductive seasonality, with mating and parturition occurring possibly over an extended period of the year. Mean ±s.d . fecundity was estimated to be 3·9 (± 0·6) pups per reproductive cycle.     

Living on the edge: latitudinal variations in the reproductive biology of two coastal species of sharks

Differences in the reproductive biology of both the Australian weasel shark Hemigaleus australiensis and the Australian sharpnose shark Rhizoprionodon taylori were apparent between individuals from the southern‐most extent of their range in eastern Australia (Moreton Bay) and those from northern Australia. For H. australiensis from Moreton Bay the total length (L_T) at which 50% of individuals were mature (L_T50) was 759 mm for females and 756 mm for males, values that were respectively 17–26% larger than reported for the species in northern Australia. The relatively low percentage (63%) of pregnant mature females and presence of small, similar‐sized, embryos in utero in both May and November suggested a semi‐synchronous, annual reproductive cycle in Moreton Bay, whereas a synchronous, biannual reproductive cycle occurred in northern Australia. It is likely that H. australiensis has a resting phase between gestation cycles at the southern‐most extent of its range. For R. taylori from Moreton Bay the L_T50s were 588 and 579 mm for females and males, respectively, values 2–3% larger than for individuals from the mid‐Queensland coast and 31–35% larger than for individuals from northern Australia. The length at which 50% of the females were maternal (611 mm L_T) in Moreton Bay was greater than the L_T50, indicating that not all sharks mate immediately after maturing. Rhizoprionodon taylori in the south had an annual reproductive cycle incorporating a 7–8 month embryonic diapause, with pups probably born in February. A mean fecundity of 7·5 was almost double that reported from northern Australia. Regional variations in the reproductive characteristics of H. australiensis and R. taylori may influence their resilience to fishing and other anthropogenic pressures. The substantial differences reported here highlight the importance of region‐specific life‐history parameters to successful management and conservation.     

Biological observations on the bristly catshark Bythaelurus hispidus from deep waters off the south‐west coast of India

Biological data are presented for the poorly known bristly catshark Bythaelurus hispidus based on specimens collected from the by‐catch of the commercial deep‐sea shrimp trawl fishery operating in the Arabian Sea at depths of 200–500 m off the south‐west coast of India. One hundred and sixty‐two individuals, which ranged from 120 to 366 mm total length (L_T), were collected for this study. Size‐at‐maturity (L₅₀) for females and males was estimated at 252 and 235 mm L_T, respectively. The reproductive mode of B. hispidus was aplacental viviparity, which is the rarest reproductive mode within the Scyliorhinidae and is considered to be the most advanced of the three reproductive modes occurring within this family. Dietary analysis of stomach contents revealed B. hispidus feeds on a variety of prey, primarily fishes.     

Geographical variability in life‐history traits of a midslope dogfish: the brier shark Deania calcea

Deania calcea (n = 420) were collected from the catch of deep‐water trawlers in the southern and eastern scalefish and shark fishery in southern Australia during the years 2008–2011. The total length (L_T) range varied between sexes, females being larger (n = 264; 280–1530 mm) than males (n = 156; 310–921 mm). The reproductive cycle in this population is non‐continuous and asynchronous. The estimated L_T at which 50% of males are mature is 807 mm and is 914 mm for females. Populations of D. calcea in higher latitudes appear to mature at a larger size than conspecifics in lower latitudes, in both the northern and southern hemispheres. Litters ranged from three to 10 embryos with a 1:1 sex ratio, but litter size does not increase with maternal L_T. Deania calcea shows geographical variability in its biological parameters and gathering information on life‐history traits of populations is vital to understand the trade‐offs made by this species in response to environmental conditions and to predict intraspecific spatial differences. Such information is a basis for specific spatial management to protect populations from excessive fishing.     

Reproductive biology and feeding habits of the prickly dogfish Oxynotus bruniensis

The reproductive biology and diet of prickly dogfish Oxynotus bruniensis, a deep‐sea elasmobranch, endemic to the outer continental and insular shelves of southern Australia and New Zealand, and caught as by‐catch in demersal fisheries, are described from specimens caught in New Zealand waters. A total of 53 specimens were obtained from research surveys and commercial fisheries, including juveniles and adults ranging in size from 33·5 to 75·6 cm total length (L_T). Estimated size‐at‐maturity was 54·7 cm L_T in males and 64·0 cm L_T in females. Three gravid females (65·0, 67·5 and 71·2 cm L_T) were observed, all with eight embryos. Size‐at‐birth was estimated to be 25–27 cm L_T. Vitellogenesis was not concurrent with embryo development. Analysis of diet from stomach contents, including DNA identification of prey using the mitochondrial genes cox1 and nadh2, revealed that O. bruniensis preys exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans. Based on spatial overlap with deep‐sea fisheries, a highly specialized diet, and reproductive characteristics representative of a low productivity fish, the commercial fisheries by‐catch of O. bruniensis may put this species at relatively high risk of overfishing.     

Reproductive biology of the tarpon snook Centropomus pectinatus (Perciformes,Centropomidae) in estuarine waters in the south‐western Atlantic

The reproductive biology of Centropomus pectinatus is described from an artisanal fish landings collaborative monitoring programme between May 2012 and April 2013 in estuarine waters in north‐eastern Brazil. The total length (L_T) at which 50% are mature was 24 cm, corresponding to 37·7% of the maximum recorded L_T. Gonado‐somatic indices were variable, but highest values were in June and August 2012. Length‐frequency distributions showed male dominance in smaller length classes (15–30 cm) and females in larger length classes (>30 cm).     

Reproductive and population parameters of spiny dogfish Squalus acanthias in the south‐western Atlantic Ocean

The objective of this study was to estimate reproductive and population parameters of the spiny dogfish Squalus acanthias for the south‐western Atlantic Ocean. In total, 2714 specimens (1616 males and 1098 females) were collected from surveys carried out using research vessels. Males ranged from 225 to 861 mm total length (L_T) and females from 235 to 925 mm L_T. The size at maturity of females (651 mm) was significantly greater than that of males (565 mm). The maximum proportion of mature individuals (P_max) of the gestation ogive was <1, which indicates that a proportion of mature females was not in gestation. This inactivity may be explained by the occurrence of resting periods between cycles or by the asynchrony of the reproductive cycle. The estimated P_max for the maternity ogive suggested that about one third of mature females were in the maternity stage (i.e. with embryos >156 mm). The temporal and spatial co‐occurrence of non‐gravid adult females at different stages of ovarian development, as well as gravid females at all embryonic development stages would indicate that the female reproductive cycle in the south‐western Atlantic Ocean is asynchronous. The results indicate that S. acanthias is susceptible to fishing pressure on account of its length at maturity, extended reproductive cycles and low fecundity.     

Effects of exploitation on reproductive capacity of blackspot snapper, Lutjanus fulviflamma (Pisces: Lutjanidae) in Mafia Island, Tanzania

There is paucity of information on the effects of exploitation on reproductive characteristics of blackspot snapper, Lutjanus fulviflamma (Forsskål 1775) in Tanzanian coastal waters. We compared size at first sexual maturity (L_M50), sex ratio, fecundity, and breeding season of L. fulviflamma in least fished Mafia Island Marine Park (MIMP) and intensively fished areas (IFA) between May 1999 and April 2001. Fish in MIMP matured at significantly smaller size (female: L_M50 = 206.3 mm; male: L_M50 = 195.5 mm) than in IFA (female: L_M50 = 216.7 mm; male: L_M50 =212.1 mm) total body length. Sex ratio was balanced at 1.03 : 1 (female : male) in MIMP, but it was skewed 0.9 : 1 (female : male) in IFA. Size‐related differences in sex ratio were observed with males predominating in the smaller sizes and females in the larger sizes. Total fecundity of fish in MIMP was determined at 45,200–430,200 oocytes in females of between 207 and 293 mm total length. Lutjanus fulviflamma in MIMP has a prolonged spawning season lasting from September to March peaking in December. None of the fish from IFA were in breeding state, suggesting recruitment overfishing is an added matter of concern for the long‐term sustainability of the fishery at the current exploitation level.     

Reproductive biology of the southern thorny skate Amblyraja doellojuradoi (Chondrichthyes,Rajidae)

The total lengths (L_T) of 193 males (209–556 mm) and 130 females (275–515 mm) of Amblyraja doellojuradoi, a commercial by‐catch species on the Argentinean continental shelf, which are increasingly retained, were analysed. No sexual dimorphism was observed in the L_T at which 50% of individuals were sexually mature; males matured at 448 mm and females at 411 mm, c. 80 and 82% of maximum L_T. The hepato‐somatic index was similar among sexes, but significantly different between maturity stages, being lower in mature than immature specimens. Males had no seasonal difference in the hepato‐somatic index and females had the lowest index in autumn. The gonado‐somatic index was lower in males than in females and significantly higher in mature than immature specimens of both sexes. Males had the highest index in autumn and females had no seasonal difference. Collectively, these results would indicate that A. doellojuradoi breeds in autumn.     

Sex ratios,sexual maturity,fecundity, and spawning seasonality of Metapenaeus dobsoni off the western coastal waters of Sri Lanka

The reproductive biology of Metapenaeus dobsoni, the most abundant species caught in coastal trawls off Sri Lanka, was studied from samples collected from two main fishing grounds during January 2009 to April 2010. This information is important for developing scientifically sound management measures, as current management is based only on artisanal knowledge. Data obtained included sex ratios, fecundity, gonadosomatic index (%GSI), and morphometric characters with respect to maturity. Size at 50% sexual maturity (L _50m) and size at 50% insemination (L _50in) were estimated for females. In males, L _50m was determined based on the presence of spermatophores in the terminal ampoule. Synchronous seasonal gametogenesis with some asynchrony among individuals was found. Impregnated females were found throughout the year. The GSI and histological examination suggested a prolonged spawning season in M. dobsoni, reaching peaks in August–January and March. Sex ratio, defined as the proportion of females to the total, increased steadily in size beyond 2.35?cm carapace length (CL) and reached 100% at sizes >3.8?cm CL. Estimated population parameters of the species will be important for the sustainable management of this resource.     

Size and age estimates at sexual maturity for the little skate Leucoraja erinacea from the western Gulf of Maine,U.S.A.

Size and age estimates at sexual maturity were determined for 162 male and 273 female little skates Leucoraja erinacea collected from the western Gulf of Maine. Maturity ogives suggest that 50% maturity in females occurs at age 9·5 years and 480 mm total length (L_T), whereas 50% maturity in males occurs at a slightly younger age of 7·7 years and smaller size of 460 mm L_T. Age estimates were made from 389 L. erinacea ranging in size from 93 to 570 mm L_T. The index of average per cent error and age‐bias plots indicated that the ageing methods were precise and non‐biased. Additionally, annual periodicity of band formation was validated with oxytetracycline in eight individuals (three males and five females) ranging in age from 3 to 12 years. In conclusion, results from this study indicate that L. erinacea exhibits characteristics that make other elasmobranch populations highly susceptible to overexploitation.     

Sex identification and PIT‐tagging: tools and prospects for studying intersexual differences in freshwater fishes

This study evaluated a technique to allow the long‐term monitoring of individual fishes of known sex in the wild using sex confirmation in close proximity to the reproductive period combined with individual tagging. Hundreds of partially migratory roach Rutilus rutilus were tagged with passive integrated transponders (PIT) following sex determination in spring and various performance measures were compared with fish tagged outside the reproductive period in autumn. Short‐term survival was >95% for R. rutilus sexed and tagged under natural field conditions. Total length (L_T) did not affect the probability of survival within the size range tagged (119–280 mm), nor were there differences in timing of migration the following season between individuals sexed and tagged in spring and individuals tagged in autumn (i.e. outside the reproductive period). Also, a similar per cent of R. rutilus sexed and tagged in spring and tagged in autumn migrated the following season (34·5 and 34·7%). Moreover, long‐term recapture data revealed no significant differences in body condition between R. rutilus individuals sexed and tagged in spring, individuals tagged in autumn and unmanipulated individuals. The observed sex ratio of recaptured fish did not differ from the expected values of equal recapture rates between males and females. Hence, there is no observable evidence for an adverse effect of tagging close to the reproductive period and therefore this method is suitable for studying intersexual differences and other phenotypic traits temporarily expressed during reproduction at the individual level in fishes.     

Catch composition,reproductive biology and diet of the bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae) from the south‐eastern Arabian Sea

Fishery and biological data are presented for the poorly known bramble shark Echinorhinus brucus (Squaliformes: Echinorhinidae), from the deep waters of the south‐eastern Arabian Sea. A total of 5318 individuals from by‐catch landings of deep‐water bottom set longlines, gillnets and shrimp trawl fisheries operating at depths of 200–1200 m were recorded between January 2008 and December 2011 at the Kochi Fisheries Harbour (Kerala). A total of 431 individuals, from 46 to 318 cm total length (L_T) and 0·8 to 132 kg total mass (M_T), were examined to determine biological data for this species. The L_T at which 50% were mature (L_T50) for females and males was estimated at 189 and 187 cm L_T. Litter size ranged from 10 to 36 and size at birth was between 42 and 46 cm L_T. Dietary analysis of stomach contents revealed E. brucus feeds on a variety of prey including crustaceans (69% index of relative importance, I_RI), teleosts (25·8% I_RI), cephalopods (1·7% I_RI) and elasmobranchs (0·7% I_RI). This study provides the first detailed biological data for this species and also highlights the extent of the by‐catch fishery for this species in Indian waters.     

Biological observations on the broadfin shark Lamiopsis temminckii (Carcharhiniformes: Carcharhinidae)

Biological information was collected from 214 individuals of the broadfin shark Lamiopsis temminckii measuring 418 to 1782 mm total length, L_T. Size at maturity (L₅₀) for females and males was estimated at 1430 and 1368 mm L_T, respectively, while mature and gravid females were observed from 1350 mm L_T with litter sizes 2–8 and size at birth 418–650 mm L_T. Analysis of stomach contents revealed a variety of prey, primarily crustaceans (54·0%), teleosts (42·7%) and cephalopods.