Reproductive biology of Psammobatis extenta

Psammobatis extenta collected from the commercial bottom trawl fishery operating in Puerto Quequén, Argentina, between 2000 and 2001, had a sex ratio of 1:1 (535 specimens). Both the largest male and female measured 313 mm total length ( L _T). The relationship between total body mass and L _T was significantly different between sexes; mature females weighed more than mature males for a given L _T. The size at which 50% of males were sexually mature was 262 mm L _T (83·6% of the maximum size), whereas 50% of females were mature at 249 mm L _T (80·0% of the maximum size). The gonadosomatic index in mature males and females was slightly higher during summer, but did not show significant variation over the sampling period. The hepatosomatic index of males and females was higher during the autumn and winter and followed a distinct seasonal pattern. Evidence suggested a continuous reproductive cycle during the year, with a maximum number of females carrying egg-cases in summer.     

Reproductive biology of the milk shark Rhizoprionodon acutus and the bigeye houndshark Iago omanensis in the coastal waters of Oman

Female Rhizoprionodon acutus were found to mature between 62 and 74 cm total length ( L _T) whereas males matured between 63 and 71 cm L _T. The L _T at 50% maturity was 64·3 cm for females and 64·7 cm for males. Litter size varied from one to six embryos, and was positively correlated with maternal L _T. Female embryos outnumbered males by a ratio of 2·3:1. The size at birth was c . 37 cm L _T. Full‐term embryos and post‐partum females were observed during all seasons although their occurrence was highest in spring. Spermatozoa were rarely recorded in the oviducal gland, indicating that this species does not store sperm. It was not possible to generate maturity curves for Iago omanensis but it was evident that females matured by the time they reached 35 cm and males were mature by 31 cm L _T. This species displayed a clearly defined reproductive cycle with parturition occurring primarily in spring, after a gestation period of c . 1 year. Maximal embryo size was 19 cm L _T while maximal litter size was 24 embryos. The oviducal gland appeared to act as a seminal receptacle and it appeared that females may utilize these stores by not mating every year.     

Reproductive biology of the smooth-hound shark Mustelus mustelus (L.) in the Gulf of Gabès (south-central Mediterranean Sea)

The reproductive biology of the smooth-hound shark Mustelus mustelus was studied in the Gulf of Gabès (southern Tunisia). Females were found to mature between 1075 and 1230 mm total length ( L _T) whereas males matured between 880 and 1120 mm L _T. The L _T at which 50% of the population reached maturity was 971 and 1172 mm for males and females, respectively. Male gonads were symmetrical in terms of mass and both functional, whereas in females only the right ovary was functional. The seasonal changes in the oocytes and testes development, embryo length and the occurrence of near-term and post-partum females showed that this species displayed a clearly defined annual reproductive cycle with parturition occurring during late April and early May, after a gestation period of 10–11 months. Mating took place during May and early June and fertilization occurred from early June to early July. The embryo sex ratio was not significantly different from unity. Litter size varied from four to 18 embryos and was positively correlated with maternal L _T. The young were born with a L _T of 340–420 mm.     

A comparison of the maturation and growth of female flathead sole in the central Gulf of Alaska and south‐eastern Bering Sea

Female flathead sole Hippoglossoides elassodon maturity appears not to be area dependent since the total length ( L _T) at which 50% were mature ( L _T50) was similar for the central Gulf of Alaska (333 mm) and south‐eastern Bering Sea (320 mm) areas. Likewise the age at which 50% were mature ( A ₅₀) was similar in the south‐eastern Bering Sea (9·7 years) and central Gulf of Alaska (8·7 years). The timing of female flathead sole spawning may also be similar between areas. Batch or serial spawning was indicated for flathead sole. Female flathead sole grew at a similar rate in both the Gulf of Alaska and Bering Sea. In contrast, males grew faster in the Bering Sea than in the Gulf of Alaska. Males grew more slowly than females in both areas after 5 years of age, and reached a smaller maximum L _T. The growth of both sexes was similar during 1993 and 1996 in the Gulf of Alaska.     

Age and growth of Anguilla anguilla in the Camargue lagoons

Age and total length ( L _T) data from a 11 year monitoring of the Anguilla anguilla eel population of the Camargue lagoons (Rhône delta, southern France) were collected for glass, yellow and silver eels. Three distinct models were calibrated to describe the growth process of undifferentiated eels, females and males, respectively. Uncertainty of parameter estimates was evaluated by bootstrapping. Females were characterized by larger asymptotic body size ( L _T) than males (580 ± 50 v . 388 ± 13 mm) and faster growth, whilst the Brody growth coefficient was larger for males than for females (means ±  s . d . 3·00 10⁻³ ± 1·68 10⁻³ v . 1·73 10⁻³ ± 0·50 10⁻³). Sexual differentiation was estimated to begin at 204 ± 38 mm mean ±  s . d ., i.e . at the end of the second year in the lagoons, well before the L _T at which macroscopic differentiation became possible ( c . 300 mm). Males probably leave the lagoon or die (due to either natural or fishing mortality) within the first 3 years, whilst females can remain up to 5 years. Sexual differentiation and maturation have a major role in shaping the L _T structure of the population. The L _T and mass ( M ) data were fitted by allometric curves     . The calibration of distinct curves for data from different years indicated that the allometric coefficient a was subject to wider interannual fluctuations than the allometric exponent b . A negative correlation linked the average L _T and the allometric exponent ( r  = −0·58, P  < 0·01).     

Reproductive biology and population variables of the Brazilian sharpnose shark Rhizoprionodon lalandii (Müller & Henle, 1839) captured in coastal waters of south-eastern Brazil

Throughout 1 year, from October 2003 to September 2004, 88 visits to the landing site of a small urban fishery (APREBAN) in Rio de Janeiro city were conducted and 816 specimens of Rhizoprionodon lalandii were analysed. The sample, mostly females, was composed of two cohorts: young-of-the-year were abundant in spring and summer and adults predominated in autumn and winter. Gravid females were most abundant from April to June, whereas post-partum females composed most of the catch in August to September. Adult males were present all year although were more abundant between February and July. No neonates were captured during the study and most embryos collected measured slightly below the reported total length ( L _T) at time of birth ( L ₀) for the species, suggesting that parturition may occur slightly outside the main fishing grounds or that neonates were not captured in commercial gillnets set at this time of the year. The mean L _T at maturity ( L _T50) for males was 578 mm and females matured between 620 and 660 mm, although a precise estimate of L _T50 for females could not be determined. The total length ( L _T) and total mass ( M _T) relationship     was calculated for both sexes and showed no significant differences. The mean condition factor increased steadily from February to July followed by a steep decrease in values relative to females in August and September, suggesting a pupping season. The present study area can be classified as a coastal juvenile habitat and a probable mating ground for R. lalandii .     

Maturation, spawning and growth of rock soles off Kodiak Island in the Gulf of Alaska

Northern rock sole Lepidopsetta polyxystra females from the Kodiak Island area, Alaska, reached 50% maturity at 328 mm L _T and an average age of 7 years. In contrast, southern rock sole Lepidopsetta bilineata females reached 50% maturity at 347 mm L _T and an average age of 9 years. Spawning started in midwinter for northern rock sole and peaked during the spring, while spawning for southern rock sole occurred during the summer. The bottom depth for spawning northern rock sole ranged from 43 to 61 m and averaged 45 m; spawning depth for southern rock sole ranged from 35 to 120m and averaged 78m. Both species appeared to develop a single stock of oocytes and to ovulate them in a single spawning. Northern rock sole females grew faster overall ( K =0.24) than southern rock sole females ( K =0.12) but reached a smaller maximum length ( L _∞=430 mm) than southern rock sole ( L _∞=520mm). Males of both species grew more slowly than females after 5 years of age and reached a smaller maximum length.     

Using the composite variables of reproductive morphology, histology and steroid hormones to determine age and size at sexual maturity for the thorny skate Amblyraja radiata in the western Gulf of Maine

Age at size was linked to sexual maturity in 77 male and 93 female thorny skates Amblyraja radiata from the western Gulf of Maine using three criteria: 1) gross reproductive morphology, 2) histology and 3) steroid hormone concentrations. Age-bias plots and the coefficient of variation from vertebral band counts suggested that the ageing method represented a non-biased and precise approach to the age assessment of A. radiata . Maturity ogives for males, based on data gathered for clasper length, circulating testosterone concentrations and proportion of mature spermatocysts within the testes, predicted that 50% maturity occurred at a total length ( L _T) of 865 mm and c. 10·90 years of age. For females, maturity ogives, based on data gathered for ovary mass, shell gland mass, follicle size and circulating oestradiol concentrations, predicted that 50% maturity occurred at 875 mm L _T and c. 11·00 years of age. Collectively, the results suggest that analysis of several contemporaneous reproductive variables offers an accurate determination of sexual maturity in the thorny skate.     

The reproductive biology of Scyliorhinus canicula in the Bristol Channel, U.K.

Among 972 Scyliorhinus canicula , the overall sex ratio (males:females) was 1:1·23. Males matured between 490 and 540 mm L _T with 50% maturity at 520 mm. Females matured between 520 and 640 mm L _T with 50% maturity at 550 mm. Female gonadosomatic index peaked in May. Fecundity increased with fish length. The egg laying season lasted 10 months with a peak in June and July. The importance of erect, sessile invertebrates such as bryozoans, poriferans and hydroids as egg-case deposition sites has been established. Recently hatched fish were born in an equal sex ratio and at a mean length of 100·5 mm and mean weight of 3·07 g. One intersexual fish is described.     

Age and size compositions, growth and reproductive biology of the breaksea cod Epinephelides armatus, a gonochoristic serranid

Details of the reproductive biology, size and age compositions and growth of the breaksea cod Epinephelides armatus , the sole representative of Epinephelides , were obtained by collecting monthly samples of a wide total length ( L _T) range of individuals from coastal marine waters at 31–32° S on the lower west coast of Australia. Although the modal L _T class of females (250–299 mm) was markedly less than that of males (400–449 mm), the modal ages of the two sexes were similar, i.e. 4 v. 5 years, respectively. The similarity in the age compositions and the histological demonstration that the gonads of all E. armatus consist solely of either ovarian or testicular tissues demonstrate that this species is gonochoristic, which is highly unusual for an anthiinine serranid. The absence of a central, membrane-lined 'ovarian' lumen in the testes of juveniles would account for adult testes containing neither this ovarian remnant nor the peripherally located sperm sinuses that are found in the mature testes of almost all other serranids. The results demonstrate that E. armatus exhibits a very unusual pattern of sexual development for a serranid. The spawning period of E. armatus lasts for c. 9 months, which is long for a species in temperate Western Australian waters, but comparable with that of many other relatively small serranids elsewhere. Females grow slower than males, attaining L _T at 3, 5 and 10 years of c. 200, 285 and 420 mm, respectively, compared with c. 215, 315 and 450 mm, respectively. Females, however, attain maturity at a greater L _T and older age than males.     

Reproductive cycle and sex inversion in razor fish, a protogynous labrid in the southern Mediterranean Sea

The reproductive biology of the Mediterranean razor fish Xyrichthys novacula was investigated by demographic data and histological analysis of the female, intersexual and male gonads. Specimens were collected by bottom trawl on a monthly basis between June 2000 and July 2001 in a sandy bay in southern Thyrrenian. Gonad histology confirmed that the Mediterranean razor fish is a monandric, protogynous hermaphrodite. Females reached first sexual maturity at 100 mm ( L _T) and the estimated mean L _T at first maturity ( L ₅₀) was 125 mm. Females exhibited asynchronous ovarian development and multiple ovulations occurred over the spawning period. Vitellogenesis started in early May and spawning occurred from late May until late September. Sexual transition involved a large‐scale atresia of all oocyte stages and a massive degeneration of ovarian tissue followed by primordial germ cells proliferation. Sex change began at spawning time (June) but transitional individuals tended to cluster at the end of the reproductive period (September). They accounted for 17·1% of the population sampled and were found in a broad size range (105–150 mm L _T).     

Life‐history variation among local populations of Atlantic cod from the Norwegian Skagerrak coast

Small‐scale spatial variation in life history was found among genetically distinct local populations of Atlantic cod Gadus morhua from the Norwegian Skagerrak coast. Among populations, age at 50% maturity varied from 2·6 to 3·8 years, total ( L _T) length at 50% maturity from 35 to 60 cm, annual survival from 33 to 64%, mean L _T at age 4 years from 43 to 63 cm, and mean backcalculated L _T at age 1 year from 8 to 12 cm.     

The biology of the bigeye grenadier at South Georgia

The biology of the bigeye grenadier Macrourus holotrachys caught as by‐catch in the Patagonian toothfish Dissostichus eleginoides longline fishery conducted around South Georgia was investigated to improve data available for fisheries management. Age estimates suggest that M. holotrachys is a moderately slow growing species ( K  = 0·10), reaching ages of >30 years and attaining total lengths ( L _T) >80 cm ( L _∞ = 33). The size at which 50% of females had started to mature ( L _int50) for M. holotrachys was 21 cm pre‐anal length ( L _PA) and occurred at c . 9 years old. Estimates of natural mortality and Pauly's growth performance index were found to be low ( M  = 0·09 and Φ = 2·82 respectively). Gonad maturity stage was described from macroscopic and histological investigation. Mature ovaries had oocytes at all developmental stages with between 22 and 55% likely to be spawned each year. Absolute fecundity ranged from 22 000 to 260 000 eggs and was positively correlated with both pre‐anal length and mass. A highly skewed sex ratio of 32 : 1, females : males, was found for specimens caught by longlines but not for a small sample of shallower trawl‐caught specimens. It is suggested that females are far more susceptible to longline capture than males. Macrourus holotrachys is a bentho‐pelagic predator and scavenger that feeds on a wide range of fishes and invertebrates. The fish are long lived, slow‐growing species typical of deep‐water grenadiers; fisheries management strategies should reflect their probable susceptibility to overfishing.     

Diet of brown trout in relation to variation in abundance and size of pelagic fish prey

The seasonal diet of a predator, brown trout Salmo trutta [total length ( L _T) 17–69 cm] and simultaneous density and size‐structure of prey populations, vendace Coregonus albula and smelt Osmerus eperlanus (4–16 cm L _T), in a large boreal lake were analysed and compared in 2001 and 2002. The upper L _T limit for consumed prey was c . 40% of the predator L _T. All brown trout, however, preferred small (<10 cm L _T) and avoided large (≥10 cm L _T) prey. The results also suggested that equal densities of similar‐sized (4–10 cm L _T) fish of the two prey species led to random foraging on these species by brown trout, but if either one of the prey species predominated (>50%) in the lake, brown trout shifted to foraging on this species almost exclusively. Brown trout diets thus reflected the density dynamics of the two alternative prey species.     

Reproductive biology of the South West Atlantic marbled sand skate Psammobatis bergi Marini, 1932 (Elasmobranchii, Rajidae)

The reproductive biology of Psammobatis bergi was investigated based on 92 males and 136 females skates taken from the coastal bottom trawl fishery at Puerto Quequén, Argentina. The relationship between total body mass and total length (TL) was not significantly different between sexes, but females were heavier than males. Minimum length at maturity in males was 451 mm TL with a length ratio of 74%, whereas females were 415 mm TL with a length ratio of 74%. TL at which 50% of males were mature was 457.6 mm (75.6% of the largest male) and for females was 441.6 mm (79.1% of the largest female). The results indicate a continuous reproductive cycle during the year, with a maximum number of females carrying egg cases in warmer seasons.     

Reproductive biology and implications for management of the orange-spotted grouper Epinephelus coioides in the southern Arabian Gulf

The reproductive biology of Epinephelus coioides was determined from the examination of 1455 individuals collected between July 2005 and June 2007 in the southern Arabian Gulf. Histological preparations of gonads indicated that males were either derived from a juvenile phase or the transition of postspawning females, confirming a diandric protogynous sexual pattern. The spawning season was well defined, occurring once a year during April and early May. Peaks in spawning occurred after the full and new moons and was completed within a single lunar cycle. The presence of mature males over the entire size and age range and the absence of inactive mature females during the spawning season suggested that the population was not constrained by sperm limitation. While specimens undergoing sexual transition were only observed in size and age ranges of 335–685 mm total length ( L _T) and 5–6 years, patterns in the proportion of males in size and age classes suggested that sex change occurred at a relatively constant rate after female maturation up to the maximum size (1002 mm L _T) and age (11 years). Relationships between reproductive output and capacity with size and age indicated that conventional regulations that equate the mean size at first capture to sexual maturation are unsuitable for the management of E. coioides . The maximum age, small size and young age at sexual maturation ( L _min= 320 mm L _T, 2 years, for females and 242 mm L _T, 1 year, for males) conflict with the general pattern for large epinepheline groupers and may be a direct result of the intensive demersal fishery in the southern Arabian Gulf.     

Size-dependent predator–prey relationships between perch and their fish prey

Size-dependent interactions between piscivorous perch Perca fluviatilis (age ≥1 year) and their fish prey age 0 year perch, pikeperch Sander lucioperca and roach Rutilus rutilus in the biomanipulated Bautzen Reservoir indicated that the highest ratio of prey total length ( L _T) to predator L _T was 59%. Perch L _T and prey fish L _T were positively and linearly related. Perch L _T was strongly related with both gape width and gape height. Within the range 80–110 mm L _T, the gape height of perch exceeded gape width, while beginning at 120 mm L _T the gape width exceeded gape height. The minimum, maximum and mean prey L _T and prey body depths of all three prey species increased with increasing predator size, but the increases in mean sizes of perch and pikeperch as prey were less than that of roach. The low limit of the 'predation window' observed in this study coupled with results of previous studies on perch in the Bautzen Reservoir indicated that perch had a major impact on the population dynamics of both perch and pikeperch.     

Population variables and life-history characteristics of the alligator pipefish Syngnathoides biaculeatus, in Papua New Guinea

Population structure and life-history variables of the widely distributed alligator pipefish Syngnathoides biaculeatus were characterized in Bootless Bay, Papua New Guinea over the course of 11 months. There was little evidence of seasonality with four focal populations showing no significant change in abundance. Similarly, the sex ratio remained 1:1 for all but 1 month. Reproductive males carrying eggs (148–278 mm in total length, L _T) were found in all months. Brood size was significantly, positively related to male L _T for newly laid broods only. Maximum observed brood size was 351 and mean ± s . d . brood size was 238 ± 57 for newly laid broods. Juveniles and males showed no change in mean L _T over the year while slightly smaller females were captured in November 2006 and September 2007. Males were significantly longer than females so von Bertalanffy growth coefficients were estimated separately for each sex: males L _∞= 285 mm, K = 0·82 year⁻¹ and females L _∞= 261 mm, K = 1·10 year⁻¹. These estimates suggest that this species grows rapidly and has a short-life span. In the context of growing concern about overexploitation of syngnathids, a rapid growth rate combined with year round reproductive activity suggests that the tropical S. biaculeatus may be relatively resilient with regard to fishing pressure.     

Reproductive biology of Carcharhinus acronotus in the coastal waters of South Carolina

The reproductive biology of blacknose sharks Carcharhinus acronotus in the western North Atlantic Ocean was studied by examining specimens collected in the coastal waters of South Carolina. Males begin the maturation process between 875 and 910 mm fork length ( L _F), as indicated by the presence of functional claspers and siphon sacs. The presence of vitellogenic oocytes and developing oviducal glands and uteri indicated that females begin to mature at c . 870 mm L _F. Length at which 50% of the population reached maturity was 896 and 964 mm L _F, equivalent to 4·3 and 4·5 years, for males and females, respectively. Gonado‐somatic indices suggested that spermatogenesis and vitellogenesis began after December. Mating took place during the end of May and the beginning of June. Fertilization occurred during late June and early July, suggesting that female blacknose sharks were capable of sperm storage. Based on the timing of fertilization and occurrence of females carrying near‐term pups in late May and early June, the gestation period for blacknose sharks was c . 11 months. Female blacknose sharks reproduced biennially based on the absence of vitellogenic oocytes in near‐term females and there being no indication of vitellogenesis in postpartum females. Male blacknose sharks were capable of reproducing annually as indicated by turgid genital ducts, which were observed in all mature males collected during late May and early June.