Contrasting post-ovulatory follicle production in fishes with different spawning dynamics (original) (raw)
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Fisheries Research, 2012
The estimation procedures of the spawning fraction (S) of the Bay of Biscay anchovy (Engraulis encrasicolus), a species with short spawning intervals, have been revised using the samples collected in 14 surveys for the application of the daily egg production method in the period 1990-2007. Towards this aim, the procedure to assign mature females to daily spawning classes was first improved by incorporating all the available knowledge on final oocyte maturation and degeneration of post-ovulatory follicles (POFs) in a matrix system which defines the probabilities of females with either of these histological indicators belonging to pre-and post-spawning daily classes according to the time of capture. Subsequently several S estimators and their biases were evaluated: The proportion of day 0 and day 1 spawners showed a high consistency over a 24-hour cycle around the mean S value of 0.395 (CV = 18%), although some oversampling of day 0 females, up to 0.48, was observed around peak spawning time (at 23:00 hours). Individual daily spawning classes had a clumped distribution, resulting in strong negative correlation (−0.73) between day 0 and day 1 spawners. For all these features the mean proportion of day 0 and day 1 S(0 + 1), was practically unbiased and slightly more precise than the traditional S(1) corrected estimator (based upon the proportion of day 1 females, corrected for oversampling of day 0). The new estimates were very similar throughout the study period and were independent of the fishing gear or sampling time. Female size had a small but significant influence on S. In support of the high spawning fraction recorded, it is shown that many females received a double allocation to a pre and a post spawning daily class; this allowed an alternative estimation of S based upon the reciprocal of the individual spawning frequencies of females which produced a result very consistent with the other S estimators.
Atlantic mackerel daily spawning dynamics and implications for batch fecundity estimations
ICES Journal of Marine Science, 2018
The present study contributes to a better understanding of the daily spawning dynamics of southern NEA mackerel (Scomber scombrus) with implications for the estimation of batch fecundity. It shows that there is a time window during the day, mainly in the afternoon, during which the advanced oocyte mode in imminent spawners separates from the remaining, smaller oocytes. This synchronicity in the separation of the spawning batch amongst imminent spawners corroborates evidence for the existence of daily spawning synchronicity in the population. This is particularly important for applications of the daily egg production method, DEPM, because such pattern facilitates both the ageing of eggs for the estimation of the daily egg production at sea and the ageing of postovulatory follicles for the estimation of spawning frequency. For NEA mackerel, batch fecundity could only be measured when a clear hiatus was established between the spawning batch and the smaller oocytes. Hydrated females th...
A new ageing method for eggs of fish species with daily spawning synchronicity
Canadian Journal of Fisheries and Aquatic Sciences, 2001
A new method for ageing staged eggs of fish is presented. The method is intended for species that show spawning synchronicity and for which the egg phase can be classified into development stages, each of which lasts less than a day, such as sardines and anchovies. It combines biological information on the daily frequency of spawning and egg development rates, via a probabilistic resampling method. A general methodology that allows the use of models of daily spawning frequency and egg development as a function of temperature is provided and applied to sardine egg data from three surveys in northern Spain. Unlike previous ageing methods, the proposed method allows for the variability of egg ages in a way that reflects the extent of the assumed daily spawning period, and estimates of the uncertainty in the stage-to-age conversion can be obtained. These estimates of uncertainty can be incorporated into subsequent analyses that involve age as a covariate, such as in the daily egg production method (DEPM), thus allowing more reliable estimates of the variance of egg production.
Journal of Northwest Atlantic Fishery Science, 2003
Appraisal of reproductive strategy and fecundity is necessary to evaluate the reproductive potential of individual fish species. To estimate reproductive potential, one needs to consider a variety of attributes including onset of maturity, fecundity, atresia, duration of reproductive season, daily spawning behaviour and spawning fraction. In this contribution, we review several methods currently used to estimate fecundity of marine fishes collected in the field in relation to their reproductive strategy. The advantages and disadvantages of each method are provided. Requirements are given to appropriately sample gonadal tissue that will enable researchers to establish incidence of sexual maturity and estimate fecundity.
The daily fecundity reduction method: a new procedure for estimating adult fish biomass
ICES Journal of Marine Science, 1992
A new method was developed for estimating adult fish biomass from the daily decline in reproductive potential of the population and the numbers of planktonic eggs. Decline in reproductive potential was estimated from the product of the daily decline in the standing stock of advanced oocytes in ovaries and the daily decline in the numbers of females with reproductively active ovaries. Daily production of planktonic eggs was estimated from the number of eggs in quantitative oblique plankton tows. The method is restricted to fishes in which the potential annual fecundity becomes fixed prior to the onset of the spawning season, that is, fishes with determinate annual fecundity. The method was applied to data for Microstomus pacificus, commonly known as Dover sole, a pleuronectid flatfish of the upper continental shelf (200-1500 m) of the west coast of North America.
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Stock reproductive potential is determined by the number of fish at age, sex ratio, proportion of mature female at age and fecundity. Fecundity data, which are fundamental in estimating egg production are not collected routinely for most fish stocks. Thus, variability in fecundity is largely ignored in the estimations of reproductive potential. The objective of this study was to identify patterns of spatial and temporal variation in the fecundity within and between different stocks of Atlantic cod (Gadus morhua) in the North Atlantic and Baltic Sea. A review of fecundity data for cod of different stocks and years was made. The examination of fecundity at size indicated a very large variability in the fecundity of cod between stocks and years. The fecundity of a 60 cm cod varied from 210 000 eggs to 2 250 000 eggs. Baltic and North Sea cod stocks were very distinct from the others, highest fecundity-at-size notwithstanding years being observed for these stocks. A different pattern of variation was observed for the other stocks. Temporal variation in fecundity appeared as important as or even more important than differences associated with stocks. Without excluding genetic differences, variations in the environmental conditions and fishing pressure could possibly explain much of the variation in the fecundity of these stocks. At a smaller scale, it also appears that the increase in the reproductive investment with age/size can differ between stocks and years. Thus, routine measurement of fecundity should be essential in estimating reproductive potential of cod.
Using environmental and biological indices as proxies for egg and larval production of marine fish
J. Northw. Atl. Fish. …, 2003
Several biological and environmental factors have direct or indirect influence on maturation, fecundity and egg viability of marine fishes. The relationships observed between these reproductive characteristics and specific biological and/or environmental indices may provide alternative methods of estimating annual variations in the reproductive potential of fish stocks in the absence of specific data, or represent a more rapid and less costly method of monitoring egg production. The utility of these relationships to serve as proxies for egg production will depend on the predictive power of the relationships, the effort required to measure selected proxies, the scale of application, and the availability of pre-existing target data. We believe that alternative methods to measure reproductive output could be developed for some reproductive characteristics needed to estimate egg/larval production using data already available. This review, largely based on gadoid fish species, indicates that relationships between indices of nutritional condition (e.g. condition factor, liver index) and potential fecundity meet the criteria of predictability and low effort and thus are candidate proxies for measuring egg production. No relationship examined was a suitable proxy for egg/larval viability and age-and size-at-maturity. The development of alternative measures of reproductive characteristics of fish could result in more precise estimates of reproductive potential of fish stocks that could be used for hindcasting and predicting egg and/or larval production and viability.