Histological Assessment of Sexual Maturity in Greenland Halibut in Div. 3LM

11 páginas, 6 tablas, 1 figura.-- Scientific Council Meetin

Histological Assessment of Sexual Maturity of the Flemish Cap Cod (Division 3M) in 1995

6 páginas, 5 tablas, 2 fisguras.-- Scientific Council Meetin

Sexual Maturity of Cod (Gadus morhua) in Flemish Cap (Div. 3M)

6 páginas, 3 tablas, 2 figuras.-- Scientific Council Meetin

Spawning biomass variation in Atlantic Cod (Gadus morhua) in Flemish Cap in Relation to Changes in Growth and Maturation

Drastic changes in both age- and length-at-maturity of cod (Gadus morhua) on Flemish Cap have been observed during this decade. In the present paper, growth by cohort in this period was analyzed and compared with the observed trend in maturation. Different cohorts displayed different growth rates, the strongest 1990 year-class showing fastest growth. The compensatory response to lower population density alone did not explain the decline in both age- and size-at-maturity. Strong changes in fishing pressure during the period could have provoked a size-selectivity for early maturity, i.e. genetic selection. An estimate of the spawning biomass, accounting for the corresponding size-at-age distributions, on a cohort basis is given. The influence of changes in spawning biomass and spawning stock biomass age structure on the probability of future stock rebuilding is also discussed. It is shown a low spawning biomass composed of young and recruited females will hardly rebuild the stock to historical levels

Histological Assessment of Sexual Maturity of the Flemish Cap Cod in 1995

In this paper the proportion of females with postovulatory follicles in their ovaries in July 1995 is used to determine the length- and age-at-maturity of cod (Gadus morhua) in the year 1995. The proportion of females in the cortical alveoli stage is then used to estimate the same parameters for 1996. This histological method allows to accurately detect the proportion of both adult and primiparous females in the population at the very beginning of the gonad development, as it happens in the summer, and few months after spawning, when it is very difficult to make a visual diagnosis of the sexual maturity stage. Length and age at 50% maturity obtained from the curves plotting the proportion of cortical alveoli were 39.07 cm and 3.1 years, respectively. The same parameters obtained from postovulatory follicle frequencies were 42.65 cm and 3.9 years, respectively. During the period from 1990 to 1995, a decrease in both length- and age-at-maturity was observed for cod on Flemish Cap. It seems likely that in those recent years the age-at-maturity of female cod was fixed around age 3. The possibility that these features could be a density-dependent response is discussed

Distribution and Abundance of Cod on the Flemish Cap, July 1988 and 1989

12 páginas, 5 tablas, 8 figuras.-- Scientific Council Meetin

Validation of Cod maturity ogive in NAFO 3M. Effect of the reproductive ccycle moment on ogive estimation.

The Flemish Cap (FC) survey is the source of the Atlantic cod maturity data for SSB estimation. FC survey takes place when females are resting and discrimination between spawning active and inactive females is still possible testing the presence of postovulatory follicles, that remains several months after spawning. However, the best moment for discriminate active spawning females is during the spawning season. For 2012 and 2014, the maturity ogives calculated during the spawning season and when females are resting were compared. Assuming a seasonal growth for cod in 3M, the moment in which maturity is estimated, had no effect on the ogives estimation. Thus, it is recommended to continue employing in the 3M cod assessment the maturity ogives produced with the FC survey information

Advances in methods for determining fecundity: application of the new methods to some marine fishes

Estimation of individual egg production (realized fecundity) is a key step either to understand the stock and recruit relationship or to carry out fisheries-independent assessment of spawning stock biomass using egg production methods. Many fish are highly fecund and their ovaries may weigh over a kilogram; therefore the work time can be consuming and require large quantities of toxic fixative. Recently it has been shown for Atlantic cod (Gadus morhua) that image analysis can automate fecundity determination using a power equation that links follicles per gram ovary to the mean vitellogenic follicular diameter (the autodiametric method). In this article we demonstrate the precision of the autodiametric method applied to a range of species with different spawning strategies during maturation and spawning. A new method using a solid displacement pipette to remove quantitative fecundity samples (25, 50, 100, and 200 milligram [mg]) is evaluated, as are the underlying assumptions to effectively fix and subsample the ovary. Finally, we demonstrate the interpretation of dispersed formaldehyde-fixed ovarian samples (whole mounts) to assess the presence of atretic and postovulatory follicles to replace labor intensive histology. These results can be used to estimate down regulation (production of atretic follicles) of fecundity during maturation