REPRODUCTION IN MALE ATLANTIC WALRUSES (ODOBENUS ROSMARUS ROSMARUS) FROM THE NORTH WATER (N BAFFIN BAY)

Age at sexual maturity and timing of the mating season were determined in male Atlantic walruses ( Odobenus rosmarus rosmarus , L.) from the "North Water" subpopulation in northern Baffin Bay. Testes and epididymides of 174 male walruses (between 0 and 30 yr old) from NW Greenland (1987–1990) were studied macroscopically and a subset of 57 specimens was analyzed microscopically. In physically mature bulls ( i.e. , ≥12 yr old), sperm or apparently ripe spermatids were found between 9 November and 12 July. In younger walruses these signs of fertility were found in a few specimens (7–11 yr old) collected between 9 January and 28 May. The mating season seems to peak in January—April. The youngest sexually mature individual was 7 yr old and the oldest apparently immature individual was 13 yr old. Average age of sexual maturity was 10.9 yr (95% C.I.: 9–6–12.2 yr) and all were sexually mature by the time they were 14 yr old. The non-spermiogenetic testes and epididymides showed accelerated growth between about the 5–6th and about the 12–15th year of life, indicating that sexual maturation occurs during these years. The length of the baculum increased gradually until about 12–15 yr of age, when physical maturity was reached.     

Population features of Microphrys bicornutus Latreille, 1825 (Brachyura, Majidae) from Isla Margarita, Venezuela

The aim of this study is to characterize the population biology (sex ratio, size structure, relative growth of reproductive characters and realised fecundity) of the crab Microphrys bicornutusfrom Isla Margarita, Venezuela. Nearly 100 crabs were collected and fixed monthly during 1998. In the laboratory, crabs were sexed and measured: maximum carapace length, chelae length, chelae and abdomen width for females and first pleopod length for males. Additionally, 96 ovigerous females were collected to determine fecundity. The following measurements were taken for each female: body wet weight (BWW), body dry weight (BDW), egg wet weight (EWW), egg dry weight (EDW) and number of eggs (NE). The following determinations were made: relative fecundity (RF) = NE/BDW and reproductive output (RO) = (EDW/ BDW) × 100. Relative size at the onset of maturity (RSOM) was calculated as minimum ovigerous female/female's maximum size. The results indicate that the sex ratio is nearly 1:1 during the entire year. Ovigerous females and moulted males and females were observed throughout the year. Size frequency distribution and size at the onset of sexual maturity, estimated by relative growth of the sexual secondary characters and RSOM value, differed from those estimated in studies done in Jamaica and Buchuaco, Venezuela.     

AGE, GROWTH, AND REPRODUCTION OF THE FINLESS PORPOISE, NEOPHOCAENA PHOCAENOIDES, IN THE COASTAL WATERS OF WESTERN KYUSHU, JAPAN

Abstract: In the coastal waters of western Kyushu, Japan, a total of 97 incidentally taken or stranded finless porpoises, Neophocaena phocaenoides , was collected for studying age, growth and reproduction. An additional 17 specimens from the Inland Sea were used for a comparison of life history. Mean neonatal body length was 78.2 cm. Both males and females grew to around 140 cm by 5 yr of age. The maximum body lengths of males and females in western Kyushu were 174.5 cm and 165.0 cm, respectively, which were smaller than those recorded in other Japanese waters. Females probably attain sexual maturity at ages of 6–9 yr and at body lengths of 135–145 cm. Males probably mature sexually at ages of 4–6 yr, at body lengths of 135–140 cm and at weight of testis of 40–150 g. The lack of females aged 5–6 yr and males aged 4–5 yr precluded firm conclusions on ages at sexual maturity. Parturition in western Kyushu was estimated to be prolonged from autumn to spring, whereas in the Inland Sea and Pacific waters it was restricted from spring to summer with a peak in April. These geographical differences and available information on distribution implies that the finless porpoises in western Kyushu constitute a local population.     

Reproduction of the summer flounder, Paralichthys dentatus (L.)

The reproduction of summer flounder, Paralichthys dentatus (L.), occurring in the Middle Atlantic Bight was studied from 1974–1979. Males dominated the length interval between 21–35 cm t.l. and were essentially absent in samples >55 cm t.l. Females were more abundant in all length intervals >45 cm t.l. Length at maturity ranged from 24–27 cm t.l. for males and from 30–33 cm t.l. for females which coincided with length at age two. Ovarian egg diamerter frequencies indicated summer flounders are serial spawners and the trend in mean and maximum maturity indexes (% ovary weight of total fish weight) indicated spawning began in September and continued through February in 1975 and probably into March in 1976. Annual condition cycle of males peaked in September and was lowest in April while females' cycle reached a maximum in October which coincided with peak spawning time. Fecundity was related to length, weight and ovary weight for 1974–1977 and the length-fecundity equation F = 0.0007975 L ^3.402 was found to be the best predictive relationship. The overall reproductive strategy of summer flounder was discussed and apparently tends to maximize reproductive potential through an extended spawning season, early maturation, high fecundity, serial spawning and extensive spawning migrations.     

Probabilistic reaction norm reveals family-related variation in the association between size,condition, and sexual maturation onset in Atlantic salmon (Salmo salar)

This study investigated the relationship between the size, condition, year class, family, and sexual maturity of Atlantic salmon (Salmo salar) using data collected in an aquaculture selective breeding programme. Males that were sexually mature at 2 years of age (maiden spawn) have, on average, greater fork length and condition factor (K) at 1 year of age than their immature counterparts. For every 10-mm increase in fork length or 0.1 increase in K at 1 year of age, the odds of sexual maturity at 2 years of age increased by 1.48 or 1.22 times, respectively. Females that were sexually mature at 3 years of age (maiden spawn) have, on average, greater fork length and K at 2 years of age than their immature counterparts. For every 10-mm increase in fork length or 0.1 increase in K at 2 years of age, the odds of sexual maturity at 3 years of age increased by 1.06 or 1.44 times, respectively. The family explained 34.93% of the variation in sexual maturity among 2-year-old males that was not attributable to the average effects of fork length and K at 1 year of age and year class. The proportion of variation in sexual maturity among 3-year-old females explained by the family could not be investigated. These findings suggest that the onset of sexual maturation in Atlantic salmon is conditional on performance (with respect to energy availability) surpassing a threshold, the magnitude of which can vary between families and is determined by a genetic component. This could support the application of genetic selection to promote or inhibit the onset of sexual maturation in farmed stocks.     

Reproductive aspects of male franciscana dolphins (Pontoporia blainvillei) off Argentina

As the first study to investigate reproductive aspects of male franciscana dolphin -Pontoporia blainvillei - in Argentine waters, the aim of this paper was to assess sexual maturity by using histological and morphometric methods. P. blainvillei was labeled as "Vulnerable" by the IUCN in 2008. The specimens analyzed were either incidentally caught in artisanal fishing nets (n=47) or found stranded on the beach (n=3). Testis weight and testicular index of maturity were reliable indicators of sexual maturity, being their values: MTW: 1.14 ± 0.60-4.49 ± 1.94; IM: 0.03 ± 0.01-0.09 ± 0.03, for immature and mature specimens' respectively. It was found that the hierarchical cluster analysis (HCA) might be appropriate for establishing sexual maturity stage, based on both the body morphometric measurements and age. The values for age, standard length and total weight at attainment sexual maturity were 2.92-3.54 years, 126.19-126.27 cm and 23.47-23.75 kg. Considering the extremely low relative testis weight, the reversed sexual length dimorphism, the absence of secondary sexual characteristics, and the lack of scars from intrasexual combats in males, the hypothesis that sperm competition does not occur in the species, and male combats for accessing female reproductive may be rare for P. blainvillei is reinforced. All these features fit the species within a serial monogamous mating system.     

The ovaries and reproduction in Pontoporia blainvillei (Cetacea: Platanistidae)

The ovaries of 113 Pontoporia blainvillei (Franciscana dolphin) were examined and their characteristics related to season, body length of the animals and, in some individuals, foetal length. The following conclusions were drawn from the results: most females attain sexual maturity when they reach 136–146 cm body length; most conceptions occur in the period December to February, with a peak in the first half of January; usually only one ovulation occurs, and no animal ovulated more than twice, in a season; postpartum ovulation may occur, and evidence is presented that this is probably followed by conception and that animals may breed once a year but most females breed every other year; body length at birth is greater than 70 cm and less than 85 cm, and probably nearer the smaller figure; the gestation period is 10.5–12 months (depending on what is the actual figure for length at birth, but probably less than 11 months); lactation lasts at least nine months; the corpus luteum contains two morphologically distinct, but apparently functional cell types; there is no apparent morphological difference between corpora lutea which are not associated with pregnancy, and corpora lutea of pregnancy; corpora albicantia may persist for a maximum of four years before being reabsorbed completely.     

Size distribution,length–weight relationship and size at the onset of sexual maturity of the orange mud crab,Scylla olivacea,in Malaysian waters

The size distribution, length–weight relationship and size at the onset of sexual maturity of the orange mud crab (Scylla olivacea) from four geographically distinct locations (Taiping, Setiu, Kota Marudu and Lundu) representing Malaysian waters were analysed and estimated. Scylla olivacea was found in the size range of 47–134?mm carapace width. Males were significantly smaller in size but heavier than females. Geographical variation in carapace width and body weight were significant, but no interaction was found between sexes and locations. As shown by the length–weight relationships of S. olivacea, the males exhibited positive growth allometry whereas the females exhibited negative growth allometry. Males mature physiologically prior to attaining morphometric sexual maturity. Females, however, achieve physiological and morphometric sexual maturity in synchrony. No significant variation was found in the estimates of size at the onset of sexual maturity of males and females among different locations. We recommend the use of the third right walking leg merus length and carapace width to estimate the size at the onset of sexual maturity (morphometric maturity) for S. olivacea. Data obtained in this study serve as important baseline data for future mud crab resource management in Malaysia and were used to recommend minimum landing sizes for S. olivacea in each respective location based on the largest size at the onset of sexual maturity estimates were suggested.     

The biology of the scaldfish, Arnoglossus laterna (Walbaum) on the west coast of Scotland.

The biology of a Scottish population of the small bothid flatfish, Arnoglossus laterna , was studied from January 1975 until September 1976. The data were taken from monthly samples totalling over 500 fish trawled in 18–36 m on a soft mud bottom. Otoliths were used for age determination and a growth curve was constructed which showed that most growth occurs in the first 2–3 years of life. The maximum age recorded was 8+ years. The fish first mature sexually in their second year at a standard length of 6–7 cm and the short spawning season lasts from the late June to August. Fecundity is length-dependent and the relationship could be described by the regression equation: log fecundity = 3·3472 log standard length (mm) -2·1064. The diet consists mainly of decapod crustaceans (particularly crangonid shrimps), polychaetes, mysids and small fish.     

The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

(1) The pattern of absolute atid relative gonad growth during the life-span and the seasonal gotiad cycle were determined from monthly samples of chub taken from two tributaries of the Herefordshire Wye. (2) A marked change in the pattern of absolute gonad growth was thought to indicate the attainment of sexual maturity. This was found to occur synchronously with corresponding changes in the pattern of body growth described previously and was in agreement with the age at which a seasonal gonad cycle was detectable. (3) Sexual maturity was attained during the eighth year of life (7+) in female chub and in males from the Afon Llynfi, but most males from the River Lugg matured a year earlier. (4) The chub gonads continued to increase in relative size after the attainment of sexual maturity. This was more evident in female chub. (5) Seasonal changes in the gonad condition and weight were followed. Gonad maturation occurred during spring and the gonad mass increased rapidly just prior to spawning. (6) Spawning occurred during June.     

Age, growth, length–weight relationship, sex ratio and food habits of the Argentine pejerrey, Basilichthys bonariensis (Cuv. and Val.), from Lake Peñuelas, Valparaíso, Chile

Argentine pejerreys were collected in Lake Peñuelas during January 1973. Calculated growth rate was maximum during the 3rd year of life. The length–weight relationship was: log W =-5.69395+3.25248 log L where W =weight (g), and L =total length (mm). Agegroup I was sexually mature. The sex ratio was 85 males (54%) to 73 females (46%). Young-of-the-year pejerreys fed primarily on copepods, but cladocerans [ Bosmina sp. (Baird), Diaphanosoma brachyurum (Liéven), Simocephalus serrulatus (Koch)], ostracods, and dipterans were also represented. Feeding occurred during daylight.     

Maturation in chinook salmon, Oncorhynchus tshawytscha (Walbaum): early identification based on the development of a bimodal weight-frequency distribution

Male chinook salmon, orhynchus tshawytscha (Walbaum), are known to mature sexually after one summer in sea water, one year earlier than any of the females. Two year classes of first generation domestic chinook salmon stock reared to sexual maturity on a commercial salmon farm in British Columbia, Canada were sampled for wet weight at various times during the spring after their first winter in the sea. Frequency distributions of wet weight were developed for both year classes. The weight-frequency distributions for both cohorts became statistically bimodal in May of their first year in the sea. The fish from the two modal groups for both cohorts were sorted and kept separate over the summer. The difference in the mean weight for the two groups increased throughout the summer in both years. The higher weight group in each cohort proved to be >95% early maturing males, and represented 64–46% of all the early maturing males evident in the September following the sort. The potential use of this information for commercial salmon growers and fisheries scientists interested in sexual maturation of the chinook salmon is discussed.     

Growth and reproduction in the Icelandic common seal (Phoca vitulina L., 1758)

Length, weight and maturity were studied in relation to age in the common seal (Phoca vitulina vitulina L., 1758), collected during the periods 1979-1983 and 1990-2000 in Icelandic waters. The maximum age of common seal observed was 36 years for females and 30 years for males. For common seal females and males, asymptotic length and weight were 161 cm and 93 kg and 174 cm and 97 kg, respectively, showing slight sexual dimorphism in size. The condition of adult females, measured as fat thickness at the lower end of the sternum, was lower in the period 1979-1983 than in 1990-2000 during June-September, the breeding and mating time of the Icelandic common seal. Males reached sexual maturity between 5 and 7 years, whereas 50% of females did so at age 4 years. Including the length and age interaction term in the logistic regression model for the maturity of females significantly improved it. Thus, body size matters in the onset of maturity. The mean birthing date for the Icelandic common seal was found to be in early June. A comparison of animals collected in the two periods 1979-1983 and 1990-2000 did not show significant differences in growth and the average age of sexual maturity for either males or females. The observed decline of the Icelandic common seal population is most probably caused by increased mortality, due to exploitation and accidental by-catch in gill-nets, rather than a decrease in fecundity.     

LIFE HISTORY OF FRASER'S DOLPHIN, LAGENODELPHIS HOSEI, BASED ON A SCHOOL CAPTURED OFF THE PACIFIC COAST OF JAPAN

Life history of Fraser's dolphin, a little known delphinid species, was examined based on 108 specimens from a school captured by the driving fishing method in Japan. The sex ratio was approximately 1:1, and mature dolphins of both sexes formed the bulk of the school. The oldest animals were two males and a female of 17.5 yr. Age and body length at sexual maturity were estimated at 7–10 yr and 220–230 cm in males and 5–8 yr and 210–220 cm in females. Mature males were larger in body length than mature females and showed apparent secondary sexual features: deepening of the tail stock and widening and darkening of the lateral dark stripe. The annual ovulation rate was 0.49. The estimated neonatal length (110 cm) predicts a gestation period of about 12.5 mo and calving peaks in spring and probably also in fall. The calving interval was estimated to be about 2 yr. These life history parameters are similar to those of the striped and pantropical spotted dolphins, except for longevity. The reproductive rate of this species may be lower than that of other pelagic delphinids, if the observed shorter longevity is real.     

Reproduction in the male sub-Antarctic fur seal Arctocephalus tropicalis

The reproductive tracts of male sub-Antarctic fur seals Arctocephalus tropicalis ( n = 123), taken at Gough Island (40° 20'S, 9° 54'W) between November 1977 and October 1978, were examined. The presence of spermatozoa in the epididymal tubules showed that all males ≥4 years old had reached puberty, and the marked slower increase in mean testis weight and baculum length suggested that sexual (social) maturity was approached by 8-year-olds. Full adulthood was attained at 10–11 years of age based on the peak in mean testis and prostate weights, and mean baculum length. Secondary sexual characteristics were only fully developed in males ≥9 years old. A significant decline in mean testosterone concentration, and in testis, epididymis and prostate weights showed that adult males were reproductively quiescent during winter from May to July when seminiferous and epididymal tubules had lowest mean diameters with no spermatozoa present. Both the mean plasma testosterone concentration and mean testis weight peaked twice during the austral summer. The first peak coincided with the breeding season, and the second peak with the moulting period when adult males were impotent. Photoperiodic cueing might explain this seasonal trend.     

Variation of reproductive traits in a population of the lizard Lacerta vivipara

Variation in reproductive traits (sexual maturity, clutch size, clutch weight, mean egg mass, newborn weight) was studied during a four year period in a population of the live-bearing lizard Lacerta vivipara . Sexual maturity was associated with attaining a minimum body size. Clutch size increased with female body length and litter weight increased with clutch size. A major component of the within year variation in these reproductive traits was attributable to female size. Analysis of successive clutches in individual females indicated that a significant fraction of the variation in litter size, adjusted for female length, was due to consistent differences between individuals. Newborn weight varied within and among litters, but no relations between hatchling mass or mean egg mass in a litter and other traits were detected.
Size-adjusted reproductive performances remained constant during the course of this study, even though environmental conditions (weather factors, food availability) varied annually. Observed among year variations in reproductive characteristics were attributable to differences in the body size distributions of the adult females.     

Observations on the age, growth, reproduction and food of the roach Rutilus rutilus (L.) in two rivers in southern England

Scales and opercular bones from 632 roach from the River Stour were used for age and back-calculated growth determinations. The scales had clearer inner annuli but operculars clearer outer annuli in fish more than nine years old. The annuli were laid in late May or early June at the beginning of the growth period. Growth was minimal between November and April. Roach from both rivers grow faster than those in most other European waters. Female roach grow faster than males; River Frome roach faster than those from the Stour. Spawning occurred in May and elaboration of gonads between September and May. Immature roach have an annual cycle in condition with a maximum in June and a minimum in early Spring. The condition of mature females is affected by the gonad cycle. The fecundity of Stour roach is represented by the formula: log egg number=4.43 log length (mm)—1.69. Approximately half of the Stour males attained sexual maturity at age III and most of the rest by age IV. Half of the females were mature at age IV and the remainder by age V. Both brood success and growth rate varied from year to year but independently of one another. Most Stour roach ate aquatic insect larvae and molluscs but algae were more frequent in the diet of larger fish.     

Gonadosomatic index‐based size at first sexual maturity and fecundity indices of the Indian River shad Gudusia chapra (Clupeidae) in the Ganges River (NW Bangladesh)

The present study aims to estimate the size at first sexual maturity and fecundity for female Gudusia chapra from the lower Ganges River, northwestern Bangladesh. A total of 250 female specimens, 3.60–13.70 cm in standard length (SL) and 1.00–43.60 g in body weight (BW), were collected during March–August 2006. The gonadosomatic index (GSI) for females was calculated by the equation, GSI (%) = (GW/BW) × 100. The size at first sexual maturity of females was estimated by the relationship between their gonadosomatic index and standard length. The specimen larger (≥8.00 cm in SL) than first size at sexual maturity was used for the estimation of fecundity. The size at first sexual maturity for female G. chapra was considered to be 8.00 cm SL in the Ganges River. The mean total fecundity was 20200 ± 6500 and ranged from 10800 to 36200. This study should be useful for fisheries biologists/managers to impose adequate regulations for sustainable‐fishery management in the Ganges River and elsewhere in Bangladesh.     

Biology of the annular seabream, Diplodus annularis (Sparidae), in coastal waters of the Canary Islands

The biology of the Canary Islands annular seabream Diplodus annularis (Linnaeus 1758) was studied from samples collected between January and December 1998. Fish ranged from 82 to 209 mm total length in size and from 8.7 to 137.1 g in weight. The mean length showed an increase with increasing water depth. Males showed a negative allometric growth and females isometric growth. The species was characterized by protandric hermaphroditism. The overall sex ratio was unbalanced in favour of males (1 : 0.79). The reproductive season extended from January to May, with a peak in spawning activity in March–April. Males reached maturity at a smaller length (103 mm, 1-year-old) than females (128 mm, 2-year-old). Fish aged 0–6 years were found. The von Bertalanffy growth parameters for all individuals were: L_∞=247.9 mm, k=0.268 years^–1, and t₀=–0.879 years.     

Sex‐specific reproductive investment of summer spawners of Illex argentinus in the southwest Atlantic

Energy investment in reproduction and somatic growth was investigated for summer spawners of the Argentinean shortfin squid Illex argentinus in the southwest Atlantic Ocean. Sampled squids were examined for morphometry and intensity of feeding behavior associated with reproductive maturation. Residuals generated from length‐weight relationships were analyzed to determine patterns of energy allocation between somatic and reproductive growth. Both females and males showed similar rates of increase for eviscerated body mass and digestive gland mass relative to mantle length, but the rate of increase for total reproductive organ weight relative to mantle length in females was three times that of males. For females, condition of somatic tissues deteriorated until the mature stage, but somatic condition improved after the onset of maturity. In males, there was no correlation between somatic condition and phases of reproductive maturity. Reproductive investment decreased as sexual maturation progressed for both females and males, with the lowest investment occurring at the functionally mature stage. Residual analysis indicated that female reproductive development was at the expense of body muscle growth during the immature and maturing stages, but energy invested in reproduction after onset of maturity was probably met by food intake. However, in males both reproductive maturation and somatic growth proceeded concurrently so that energy allocated to reproduction was related to food intake throughout the process of maturation. For both males and females, there was little evidence of trade‐offs between the digestive gland and reproductive growth, as no significant correlation was found between dorsal mantle length‐digestive gland weight residuals. The role of the digestive gland as an energy reserve for gonadal growth should be reconsidered. Additionally, feeding intensity by both males and females decreased after the onset of sexual maturity, but feeding never stopped completely, even during spawning.