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Daily Egg Production (daily + egg_production)
Selected AbstractsSpawning habitat and daily egg production of sardine (Sardina pilchardus) in the eastern MediterraneanFISHERIES OCEANOGRAPHY, Issue 4 2006S. SOMARAKIS Abstract Spawning habitats of two eastern Mediterranean sardine, Sardina pilchardus (Walbaum, 1792), stocks (coastal waters of central Aegean and Ionian Seas) are characterized from daily egg production method (DEPM) surveys conducted during the peak of the spawning period. The latter occurs earlier in the Aegean Sea (December) than in the less-productive Ionian Sea (February). Single-parameter quotient analysis showed that the preferred bottom depth for spawning was 40,90 m in both areas but sardine selected sites of increased zooplankton in the Aegean Sea during December and increased fluorescence in the Ionian Sea during February. Estimates of daily egg production (P) and spawning stock biomass (B) were about four times lower for the Ionian Sea (P = 7.81 eggs m,2, B = 3652 tonnes) than the Aegean Sea (P = 27.52 eggs m,2, B = 16 174 tonnes). We suggest that zooplankton biomass might not be sufficient to support sardine reproduction in the highly oligotrophic Ionian Sea where the very small sardine stock may rely on the late-winter phytoplankton bloom. Actively selecting sites with increased zooplankton or phytoplankton and feeding plasticity (the well-known switching from selective particle feeding to non-selective filter feeding in sardines) are interpreted as adaptations to grow and reproduce optimally at varying prey conditions. Despite differences in temperature and productivity regimes, reproductive performance of sardine in the Ionian Sea was very similar to that in the Aegean Sea during the peak of the spawning period. In comparing adult parameters from DEPM applications to Sardina and Sardinops stocks around the world, a highly significant linear relation emerged between mean batch fecundity (F) and mean weight of mature female (W, g) (F = 0.364W, r2 = 0.98). The latter implies that, during the peak of the spawning period, mean relative batch fecundity (eggs g,1) of sardine is fairly constant in contrasting ecosystems around the world. [source] Validation of macroscopic maturity stages according to microscopic histological examination for European anchovyMARINE ECOLOGY, Issue 2009Rosalia Ferreri Abstract The identification and classification of macroscopic maturity stages plays a key role in the assessment of small pelagic fishery resources. The main scientific international commissions strongly recommend standardizing methodologies across countries and scientists. Unfortunately, there is still a great deal of uncertainty concerning macroscopic identification, which remains to be validated. The current paper analyses reproductive data of European anchovy (Engraulis encrasicolus L. 1758), collected during three summer surveys (2001, 2005 and 2006) in the Strait of Sicily, to evaluate the uncertainty in the macroscopic maturity stage identification and the reliability of the macroscopic adopted scale. On board the survey vessels, the maturity stage of each fish was determined macroscopically by means of an adopted maturity scale subdivided in six stages. Later, at the laboratory, the gonads were prepared for histological examination. The histological slides were analysed, finally assigning the six maturity stages for macroscopic examinations. A correspondence table was obtained with the proportion and number of matches between the two methods. The results highlight critical aspects in the ascription of macroscopic maturity stages, particularly for the present research aim. Different recommendations were evaluated depending on the scope of the study conducted on maturity (e.g. daily egg production, fecundity and maturity ogive computation). The most interesting results concern the misclassification of stage IV and stages III and V (the most abundant), which confirms their macroscopic similarity. Although the results are based on a small number of samples, the advantages and disadvantages of macroscopic and histological methods are discussed with the aim to increase the accuracy of correct identification and to standardize macroscopic maturity ascription criteria. [source] Effects of diapause duration on future reproduction in the cabbage beetle, Colaphellus bowringi: positive or negative?PHYSIOLOGICAL ENTOMOLOGY, Issue 2 2006Xiao-Ping Wang Abstract., Cabbage beetles, Colaphellus bowringi, undergoing an imaginal summer and winter diapause in the soil, show a great difference in diapause duration (from several months to more than 3 years) under natural conditions. The effects of diapause duration on future reproduction in the beetle are investigated at 25 °C with an LD 14 : 10 h photoperiod and under natural conditions. The fecundity of postdiapause adults with a short diapause of 5 months and nondiapause adults is similar, showing that a short diapause has no affect on reproduction, whereas the longevity of postdiapause adults with a short diapause of 5 months is significantly shorter than nondiapause adults, showing that a short diapause has a negative affect on longevity. The mean total egg production per female and longevities of postdiapause adults with long diapause periods of 16, 22, 29 and 34 months are similar to nondiapause adults, but the mean daily egg production per female is significantly higher than nondiapause adults, showing that extended diapause has a positive effect on postdiapause reproduction. The offspring of postdiapause parents require a relatively shorter time for egg development compared with the offspring of nondiapause parents, showing that diapause has a positive effect on their offspring's performance. However, there are no significant differences among offspring performance in terms of survival, adult longevity, mean egg production per female and mean daily egg production per female. [source] | ||||||||||