On reconstructing the (once) living population from osteological age data

It is shown how the sex and age distribution of the (once) living population can be calculated from estimated mortalities. Fertility calculations and estimations of the number of children per woman are provided as well. The method is applied to two materials from the Middle Ages: Westerhus and Helgeandsholmen.     

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.     

Monitoring population productivity in the saiga antelope

Effective conservation requires a good understanding of factors causing variation in population growth rate. We here analyse the relationship between female age and fecundity in the saiga antelope Saiga tatarica tatarica , a critically endangered ungulate of the Eurasian steppes and semideserts, at both individual and population levels. Annual variation in age structure and twinning rates was investigated using long-term datasets, sampling a total of 3308 females in four populations over more than 40 years. Further, a new non-invasive method is presented, estimating twinning rates from both calves and placentas encountered during calving aggregation transects. At an individual level, the most parsimonious model for twinning rates included three age classes (1, 2 and ≥3 years); however, the model with only two classes (1 and ≥2 years) was competitive and particularly useful for monitoring because these two age classes can reliably be determined by direct observation in the field. Among yearlings, 77.4% were fecund and 11.7% twinned, whereas among older females 94.6% were fecund and 72.6% twinned. At a population level, annual variation in age structure (proportion ≥2 years) correlated well with annual variation in twinning rate except in the north-west Pre-Caspian population. Our results suggest that the recent poaching-driven collapse in saiga numbers has potentially resulted in reductions in fecundity, which will have an impact on population growth rate. Our results highlight the potential for monitoring of twinning rate using non-invasive calving aggregation transects as a cost-effective additional tool to population counts for monitoring the status of this critically endangered species. These monitoring methods are also potentially transferable to other ungulate species.     

On the life-history of Atractoscion aequidens, a migratory sciaenid off the east coast of southern Africa

East coast geelbek exist as a single stock comprising three distinct age/size structured subpopulations. The subadults (1-4 years) occur in the SW Cape, South Africa. They feed principally on anchovy Engraulis capensis , which they follow inshore in summer and offshore in winter. The adults (5-9+ years) undergo a seasonal inshore and longshore migration to Natal where they spawn offshore in spring. During this migration they feed mainly on the pilchard Sardinops sagax , which also move north-eastwards during this time, facilitated by regional oceanographic conditions. 'Adolescent' fish (4/5 years) appear to undergo limited gonadal growth and partially accompany the spawning stock on their migration. It is suggested that the eggs, larvae and early juveniles are transported southwards by the peripheral inshore waters of the Agulhas Current. Juveniles (<2 years) use the SE Cape region as a nursery area for about 1 year, initially feeding on mysids and then switching to anchovy, before moving south-westwards to join the Subadults in the SW Cape region.     

Biology of the Sand Smelt, Atherina presbyter (Teleostei: Atherinidae), Off the Canary Islands (central-east Atlantic)

Atherina presbyter is a common fish off the Canary Islands. Age, growth, reproduction, and mortality of the species are studied based on sampling carried out from July 1995 to June 1996. The parameters of the total length–total weight relationship are: a=0.004521, and b=3.0771. Otoliths age readings indicate that the sampled population consists of four age groups (0–III years). The von Bertalanffy growth parameters for all individuals are: L=122mm total length, k=0.79year^–1, and t₀=–0.21 years. Individuals grow quickly in their immature first year, attaining approximately 60% of their maximum length. After the first year, the annual growth rate drops rapidly, because the energy is probably diverted to reproduction. It is a gonochoristic species with no evidence of sexual dimorphism. The gonad is present as a single diffuse testis in males and as a single discrete ovary in females. The overall ratio of males to females is not significantly different from 1:1. The reproductive period of the species is protacted (February to June). The peak of the reproductive effort occurs in April–May. The size at first maturity is 68mm. The population is being heavily exploited.     

Biology of the mysid Mesopodopsis slabberi (van Beneden, 1861) (Crustacea, Mysidacea) in a coastal lagoon of the Ebro delta (NW Mediterranean)

Aspects of the population and reproductive biologyof the mysid Mesopodopsis slabberi were studiedin the western Mediterranean (Encanyissada coastallagoon, Ebre delta, Spain). Misids were sampling atmonthly intervals from August 1993 to June 1995. InDecember 1994 and February 1995 any individuals werefound. The relationship between carapace length (Lc)and total length (Lt) was isometric:logLt = 1.0612logLc + 0.9411 (n = 178,r = 0.9411). Thesize of mature males and females was at a maximum inthe winter, and a minimum in the summer. The longevityof individuals changed throughout the year; those withthe longest life expectancy were members of theoverwintering generation. Brooding females wererecorded throughout the year, except in December 1993and April 1994; they were most numerous in spring andautumn. The number of embryos or larvae (N) carried byfemales was related to the size of the females (range:1–22, mean value: 4.8): logN = 1.8705logLc–0.0985(n = 361, r = 0.4097, P < 0.01). Thesize of the eggs(maximum diameter, Le) was related to the size of thefemales (range: 0.35–0.6 mm in total length):logLe = 0.3404logLc–0.4820 (n = 277, r = 0.5420, P < 0.01).     

尖膀胱螺的生物学特征及光照对其生长繁殖影响的初步研究

尖膀胱螺Physa acuta是世界广泛分布的淡水螺类,在我国属外来入侵种.本文着重对该螺的形态特征、繁殖、发育及光照对螺生长和繁殖发育的影响等进行了实验观察和研究.尖膀胱螺个体中等,左旋,壳口无厣.喜聚居于水生植物较多、营养丰富的淡水区域.尖膀胱螺为雌雄同体,异体受精,有时也可自体受精.性成熟个体在条件适宜的情况下(温度、食物和光照)每天都可产卵,卵孵化率近100％.尖膀胱螺胚胎发育共经历卵裂期、囊胚期、原肠期、担轮幼虫期、面盆幼虫期、仔螺形成及出膜期7个时期.一般情况下,螺卵7～10 d可孵化,60 d即可性成熟.25℃、24 h连续光照条件下,尖膀胱螺体重明显增加,40 d就可以性成熟并产卵.     

人工油松种群生长与生殖分配关系的研究

植物种群营养生长和生殖生长的关系是植物生殖生态学研究的重要内容之一,自本世纪70年代,国外已有大量报道,但国内的研究报道很少。本文在种群水平上研究了人工油松种群一年生雌性枝条和雄性枝条在枝长、直径、叶数、叶生物量、枝生物量及新生枝条在大小孢子球生物量、雌雄枝条长度和生物量等方面的差异,结果表明,一年生枝条除在西方向上雌雄枝条直径差异显著和在东、西方向上雌雄枝条生物量差异显著外,其它处理条件下雌雄枝条在长度、直径、叶数、叶生物量和枝生物量等方面差异均不显著;而对新生枝条的取样分析表明同方向上雌雄枝条在大小孢子球生物量、雌雄枝条长度、雌雄枝条生物量等方面差异均显著或极显著。无论是一年生枝条,还是新生枝条,在东、西、南、北四个方向上其各项指标差异显著或极显著。     

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.