Aspects of the Life History of the Salema, Sarpa salpa (Pisces, Sparidae), off the Canarian Archipelago (Central-East Atlantic)

Life history of the salema, Sarpa salpa, off the Canarian archipelago was studied from samples collected between January 1998 and December 1999. Fish ranged from 119 to 452 mm in total length and from 24.9 to 1491.7 g in weight. The species was characterized by a protandric hermaphroditism. The overall sex ratio was unbalanced in favour of males (1 : 0.41). The reproductive season extends from September to March, with a peak in spawning activity in December–January. Males reached maturity at a smaller length (226 mm, 2 years old) than females (294 mm, 3 years old). Males, females and all fish showed an isometric growth. The morphometric relationship between length and mass for the whole population was described by the parameters: a = 0.0000134 and b = 3.01. A concentric pattern of opaque and translucent zones was readily distinguishable on the otoliths. Two rings, one opaque and one translucent, were laid down each year on the otoliths; the opaque zone was formed during the summer months, and the translucent zone during the winter months. Individuals aged 0 to 11 years were found. The parameters of the von Bertalanffy growth equation for all individuals were: L = 479 mm, k = 0.212 year^–1, and t₀ = –1.08 year.     

Recruitment mechanism of the eel, Anguilla japonica, to the Japanese coast

A total of 149 Anguilla japonica elvers collected at 10 locations along the Japanese coast were aged according to otolith daily increments. The interrelationships among age, birth date, body size, pigmentation stage, sampling location and the timing of recruitment were examined in order to determine the recruitment mechanism of elvers to coastal waters.
First catches of eels were earlier in the locations at lower latitudes. Age at recruitment was roughly constant, 218 ± 29 (mean ± s.d.) days old, disregarding the localities, but a weak positive correlation was obtained between age and sampling date or timing of recruitment. Body length at recruitment was also constant, 56.3 ± 2.3 mm s.l., and showed no significant correlation with either locality or recruitment timing. Estimated birth date ranged from April to November, the mean ± s.d. being 22 July 1982 ± 42 days, suggesting a peak season spawning in summer. Birth date was closely related with both the latitude of location and sampling time. Pigmentation developed more at lower latitude. Recruitment mechanism of the Japanese eel was summarized as follows: the earlier-born individual recruits earlier at lower latitude and at younger age, but at a constant body size.     

Diet, growth and reproduction of the Arctic charr in a high alpine lake

The Arctic charr of Muzelle lake, at 2105 m in the Oisans massif (French Alps) feed most actively, essentially on Chironomidae, during the 6 or 7 weeks following the melting of the ice. The period of maximum growth corresponds to the time when food availability is at its highest, and it does not overlap with the period of maximum temperatures. Males and females mature at age 3 years but only half of the females of age 3 years spawn each year. This ratio of spawning females is constant from 3 to 6 years, the latter being maximum age observed in this lake. Each female spawns only twice at the most during its lifetime.     

Age structure, growth and reproduction of Leuciscus pyrenaicus in an intermittent stream in the Guadalquivir river basin, southern Spain

The age, growth and reproduction of Leuciscus pyrenaicus (Günther, 1868), an endemic cyprinid from the Iberian Peninsula, was studied from November 1987 to September 1989 in a small seasonal tributary of the Guadalquivir river basin. Maximum fork lengths observed were a 160 mm male with six scale annuli and a 171 mm female aged 7 +. Maximum ages observed were 7 + in males and 8 + in females. There were no significant differences in the annual growth increments between sexes. Seasonal growth period started in March and continued for 5 to 6 months. Mean lengths of 1 + specimens onwards diminished during summer and/or autumn. Males and females matured in their third and fourth year of life respectively. The overall sex ratio (272 males: 310 females) differed significantly from equality. Spawning began in May and ended in July. L. pyrenaicus is a multiple spawner that releases a minimum of two batches of eggs per female each year. Eggs in each batch were similar in both size (egg diameter) and number released. The relationship between fecundity (Fee) and fork length (mm) was represented by the formula: Fec=1.96 10⁻³ L^2.50.     

Geographic variation in the growth of white croaker,Pennahia argentata,off the coast of northwest Kyushu,Japan

We examined geographic variation in the growth of white croaker,Pennahia argentata, off the coast of northwest Kyushu, Japan, Ariake Sound, Tachibana Bay, Omura Bay and the Goto Sea by examination of otoliths. The outer margins of the otoliths showed that a opaque zone was formed once a year, with its peak in June, and could be used as an annulus. White croaker caught during this study reached a maximum age of 10years in the Goto Sea. The growth curves for both sexes in all localities were expressed by the von Bertalanffy growth equations from back-calculated total length of fish. We found significant sexual differences in growth curves in Ariake Sound, Tachibana Bay and the Goto Sea. For both sexes, white croaker in the Goto Sea reached the largest length at each estimated age of the four localities. The growth curves for both sexes showed significant differences among four localities, suggesting that several stocks may exist in the study area although the greatest distance between each locality was at most 30 km.     

Effect of river regulation on the life-history patterns of Barbus sclateri in the Segura river basin (south-east Spain)

The age structure, growth and reproduction of Barbus sclateri in a non-regulated section of the Segura River were similar to previously studied populations of undisturbed areas. Differences in the duration of the growth period or the reproductive cycle are considered evidence of the plasticity of the species as it adapts to different latitudes and local habitat characteristics. However, this population differed from one in a section with artificial water flow regulation. The non-regulated river population had a greater number of age groups, displayed a regular condition cycle, reached maturity earlier at lower ages and lengths and showed greater fecundity than the regulated river population. The mean lengths at age were longer in the regulated river population, possibly owing to the longer river section studied and/or to selective mortality of smaller specimens within a particular age group from the high water velocity when sluices are opened.     

On the biology of female Epiplatys bifasciatus (Cyprinodontidae) from southern Sudan

The biology of female Epiplatys bifasciatus (Steindachner, 1881) from the Sudd region of southern Sudan was investigated. The population was dominated by females whose growth in body dimensions relative to total length was found to be linear. The reproductive system differs from that of oviparous teleosts in having a portion of the ovary (anterior) modified for carrying the developing brood. Gradual development of oocytes towards the nursing portion of the ovary, and low absolute fecundity of the brood, suggests a rather long breeding season (June to September).A large variety of food organisms belonging to three main groups, viz. insects, crustaceans and arachnids, were taken by Epiplatys collected from the littoral zones of two rivers, the Bahr El Ghazal and the White Nile. Little variation occurred in the food of these two populations. Chironomid larvae showed the highest occurrence frequency in the fish food for both localities, and insects in general constituted over 80% of all organisms eaten.     

Age and growth of Trisopterus luscus (Linnaeus, 1758) (Pisces,Gadidae) off the coast of Asturias

The age and growth of an Asturian population of the bib Trisopterus luscus L. were studied based on 990 bibs from monthly catches from October 1986 until October 1988.Using the estimates of age taken from otolith readings, it was possible to construct a growth curve for the whole range of ages and demonstrate that most growth takes place during the first two years of life. The maximum age was found to be 5 years. The largest fish caught during the investigation measured 430 mm in standard length.The different growth rates of males and females show that in most cases the mean standard length of females was equal to or greater than that of the males.     

The marine algae of Hluleka (Transkei) and the warm temperate/sub-tropical transition on the east coast of southern Africa

The marine flora of the transition region between the warm temperate south coast and sub-tropical east coast of southern Africa is very poorly documented. The seaweeds of Hluleka Nature Reserve, centrally placed along this transition, are described. 178 species (120 rhodophytes, 33 chlorophytes and 25 phaeophytes) are recorded, including 28 new records for the region, and a new combination,Tiffaniella schmitziana (Barton) nov. comb. A biogeographical analysis of those species whose distribution is sufficiently known reveals that 65% are warm water species, also occurring in tropical seas. Hluleka is thus towards the warmer end of the transition, and the major discontinuity is sharply defined, occurring in the ca 130 km of coastline between Hluleka and the mouth of the Kei River. It is probable that a rapid temperature gradient along this stretch of coast (change of 2°C in annual mean) is responsible for the discontinuity.     

The effects of age at mating on female life-history traits in a seed beetle

Age at first reproduction is an important component of lifehistory across taxa and can ultimately affect fitness. Becausegenetic interests of males and females over reproductive decisionscommonly differ, theory predicts that conflict may arise overthe temporal distribution of matings. To determine the potentialfor such sexual conflict, we studied the direct costs and benefitsassociated with mating at different times for females, usingseed beetles (Acanthoscelides obtectus) as a model system. Virginfemales were resistant to male mating attempts at a very earlyage but subsequently reduced their resistance. Although we foundno difference in life span or mortality rates between femalesmated early in life and those mated later, females that matedearly in life suffered a 12% reduction in lifetime fecundity.Thus, there are direct costs associated with mating early inlife for females. Yet, males mate even with newly hatched females.We suggest that these data indicate a potential for sexual conflictover the timing of first mating and that female resistance tomating, at least in part, may represent a female strategy aimedat delaying mating to a later time in life.     

Site fidelity and association patterns of Indo-Pacific humpback dolphins off the east coast of Zhanjiang,China

This study examined the population of Indo-Pacific humpback dolphins, Sousa chinensis, inhabiting the waters off the east coast of Zhanjiang, China. A total of 116 dolphins were identified during 147 boat-based surveys, completed between June 2005 and June 2007. Abundance estimates indicated that a small population of 268 dolphins (95% CI = 189–413) inhabited this coastal area. The sighting frequencies of identified dolphins varied between one and five when the 2006 and 2007 data were organized into six occasions. Twenty-three percent (27 individuals) of the cataloged dolphins were identified in more than one calendar year. The two animals (ZJ001, ZJ011) with the highest degree of site fidelity were present in the study area for a period of 23 months. The most frequently (15 times) sighted dolphin (ZJ046) was recorded in nine (56%) of the 16 months surveyed. This evidence indicates the interannual site fidelity of S. chinensis to the area off the eastern coast of Zhanjiang City. Range sizes of eight identified individuals calculated by the minimum convex polygon varied from 2.07 to 331.20 km². Associations between 34 individuals sighted at least three times and more than three times were measured by the half-weight index and SOCPROG program. The majority of these dolphins (80.57%) were not seen together during surveys and the mean association rate between dyads was low at 0.05. Temporal analyses for all the individuals were conducted using a lagged association rate. The results indicated a non-random social structure made by constant companions.     

Early ontogeny of Galeichthys feliceps from the south east coast of South Africa

The early development of Galeichthys feliceps (Valenciennes, 1840) was investigated using a combination of incubator-reared embryos and embryos removed from the buccal cavities of wild-caught parents. The eggs were 15·7 mm in diameter and the average brood size was 49. Hatching occurred at an advanced developmental state after approximately 75–80 days, when branchial and fin differentiation were complete. Exogenous feeding began within the adult buccal cavity shortly after hatching. The young were released as juveniles after approximately 140 days, at a total length of 54 mm.     

Life-history changes in exploited reef fishes on the east coast of South Africa

Synopsis The impact of exploitation on various life-history characteristics of two sex changing, reef-dwelling sparid species was examined by comparing populations protected in a large marine reserve with those adjacent to the reserve. Like other sparids, Chrysoblephus laticeps and C. cristiceps grow slowly and are long lived, reaching ages of 17 and 21 years, respectively. No significant differences in the growth rate of C. laticeps were measured, but growth in C. cristiceps was significantly slower in the exploited population. Observed data showed that sex ratios outside the marine reserve were skewed towards the females, a result of size selective exploitation. Size at sex change was also significantly smaller for C. cristiceps in the exploited area, but not so for C. laticeps. This difference between the species was explained as a function of the size at recruitment into the fishery and the degree of protection afforded both large females and male fish. Considering the possibility that reproduction could be impaired as a result of changes in population structure, the tactic of protection through marine reserves is supported as a hedge against recruitment failure.     

Life History of Black Seabream, Spondyliosoma cantharus, off the Canary Islands, Central-east Atlantic

Black seabream, Spondyliosoma cantharus, caught off the Canary Islands is characterized by a protogynous hermaphroditism. The size range of the catches is between 8 and 40cm, with a main distribution between 16 and 24cm. The mean length of the individuals shows an increase with increasing depth. Males:females ratio is unbalanced in favour of females (1:2.18). The reproductive season extends from late autumn to mid spring, with a peak in spawning activity in January–February. A dichromatism is found between males and females during the spawning season. Males reach maturity at a larger total length, 22.7cm (3 years old), than females, 17.3cm (2 years old). Morphometric relationship between length and mass for the whole population is described by the parameters: a=0.00732, and b=3.24747. Otoliths age readings indicate that the exploited population consists of eleven age groups (0–X years), including a very high proportion of individuals between 2 and 3 years old. The von Bertalanffy growth parameters for the whole population are: L=43.35cm, k=0.24 year–1, and t0=–0.11 year. The rates of total, natural and fishing mortality are 1.36, 0.52 and 0.84 year–1, respectively. The length at first capture is 16.8cm. The exploitation rate indicates that the stock is overfished.     

Age, growth and reproduction of the cyprinid Rutilus lemmingii (Steindachner, 1866) in the River Huebra, Central Spain

Age, growth and reproduction of the R. lemmingii population of the River Huebra, Duero basin are analysed. Females dominated older age classes and lived up to 6 years (5+) while males only reached 5 years (4+). The growing season extended from April to September; growth rates were similar for both sexes. 0+ fish condition increased during their first summer and spring. In older fish, condition cycle was related to gonad development and showed some differences between sexes. The number of females reaching maturity at age 1 + almost doubled that of males; females also matured at smaller size. Both fecundity and egg size increased with female length: mean egg counts varied between 974 for 1 + individuals and an estimated 10491 for 5+ fish. Eggs were produced as a single batch, but were released fractionally during April and May.     

Life history of the cownose ray, <Emphasis Type="Italic">Rhinoptera bonasus</Emphasis>, in the northern Gulf of Mexico,with comments on geographic variability in life history traits

Synopsis We determined age and growth, size at maturity, and fecundity for cownose rays, Rhinoptera bonasus, collected from the northern Gulf of Mexico. Vertebral age estimates ranged from 0+ to 18+ years for females and 0+ to 16+ years for males. Annual deposition of growth increments was verified with marginal increment analysis. Likelihood ratio tests indicated that the growth of the cownose ray was best described by a combined sexes Gompertz model. Median size at 50% maturity was determined to be 642 mm DW for males and 653 mm DW for females, or 4–5 years of age. Median pup size-at-birth was estimated to be 350 mm DW, with a gestation period of 11–12 months. In all cases, gravid females contained only one pup. Statistically significant differences were detected between growth curves for the Gulf of Mexico and the western Atlantic Ocean. Cownose rays in the Gulf of Mexico had lower estimates of DW_∞ and K, and a higher theoretical longevity than their conspecifics in the western Atlantic Ocean. Cownose rays in the Gulf of Mexico also attain maturity at a smaller size and earlier age than their counterparts in the western Atlantic Ocean.     

Age structure,growth and reproduction ofRutilus lemmingii in an intermittent stream of the Guadalquivir river basin,southern Spain

The age, growth and reproduction ofRutilus lemmingii (Steindachner, 1866), an endemic cyprinid from the Iberian Peninsula, was studied for over a period of two years in a small seasonal tributary of the Guadalquivir river basin. Approximately 65 % of the total growth in length occured in the first year of life. Males reached a maximum age of 3+ yr (Fork Length, F.L. = 114 mm) and females 4+ yr (F.L. = 144 mm). Both sexes matured during their second year of life (1 +). The overall sex ratio (334 males to 389 females) differed significantly from unity. Somatic condition decreased markedly during the reproductive period of March to May.R. lemmingii is a multiple spawner and releases two batches of eggs per female each year. Mean egg diameter of the first batch was larger than the second one. The regression between fecundity and Fork Length (mm) was: Fec = 0.014 F.L.Z.^2.858 Compared with available information, thisR. lemmingii population, located at a lower latitude, is characterized by fast growth, early maturity, high level of reproductive effort, and a short life-span. These life-history characteristices are typical of species in unstable environments, where adult mortality is high, variable or unpredictable.     

Comparisons of life-history traits between clonal and sexual fish (Poeciliopsis:Poeciliidae) raised in monoculture and mixed treatments

Summary Clonal and sexual co-existence is common in a number of vertebrate taxa, even though the cost of sex makes such co-existence theoretically unlikely. The frozen niche-variation (FNV) model explains this co-existence on the basis of differences in overall niche breadth and competition between clones and sexuals. In the present study I examined two predictions of the FNV model. First, I examined the prediction that genetically variable populations have higher relative fitness when compared with monoclonal populations by comparing the performances of clonal and outcrossed sexual strains ofPoeciliopsis in monocultures at two densities. The prediction of increased overall productivity for the sexuals was verified, with net reproductive rates for the sexuals being between two and four times as high as the clones. Second, I tested the prediction that derived clones will successfully compete with their sexual progenitor(s) in the narrow range to which the clones are adapted, while the sexuals should co-exist because of their ability to use a wider range of resources than any single clone. I examined this prediction by comparing performance variables (e.g. growth, fecundity and survival) of each strain in pure culture with their partitioned performance from the mixed treatments. Clonal performance increased in mixtures compared to monocultures, as expected. However, the expectation that the sexual's performance would be less affected by mixtures than the clones' performance, was not met. The sexuals had reduced growth and fecundity on a par with the increase in both variables in the clones. Therefore, support for the FNV model was mixed. Although the performance in monocultures suggests that the sexuals have a wider niche breadth than the clones, performances in mixtures do not indicate such a relationship. Switching of behaviours or resource-use patterns between mixed and pure cultures may have caused the equivocal results.     

Aspects of the Ecology of the Fishes of Holyrood Pond: A Coastal Lake with Occasional Access to the Sea Located in St. Mary's Bay,Newfoundland

Physical and chemical conditions and fish were studied during spring and summer in 1974 and 1975 in Holyrood Pond, Avalon Peninsula, Newfoundland. It is a landlocked body of water lying at sea level (length = 21.72 km; maximum width = 1.55 km; maximum depth = 100.0 m) which is occasionally opened to the sea. The landlocked condition is caused by prevailing southwest winds and wave action which create a beach barrier that effectively isolates the mouth from St. Mary's Bay. Under landlocked conditions, there was a continual decrease in salinity and dissolved oxygen at all depths. Temperature profiles were of a dichothermic nature; a certain amount of temporal variability was noted in lower lying water. When the barrier was opened (by bulldozer) and the pond came under tidal influence, there was a replenishment of salt water and dissolved oxygen. Temperature profiles retained the same overall shape but were more erratic, and compared with the closed barrier condition, showed greater variability with time especially in the deeper water. A small amount of commercial fishing is carried out in the pond during both open and closed barrier conditions. A total of 30 species of fish was encountered during the sampling period. Of these, Salvelinus fontinalis, Gadus morhua, Urophycis tenuis, Pseudopleuronectes americanus and Alosa pseudoharengus were studied in detail. Aspects of their biology are compared with other populations and discussed in the context of environmental conditions peculiar to Holyrood Pond.