Conference Proceedings - IAD

39th IAD Conference, August 2012, Szentendre, Hungary
comparatively weakest sensitivity to the spawning frequency and age at first
spawning. As can be seen in Figure 1, influence of the age at first spawning in
the Model 2 (Navodaru et al. 1992) was substantially higher than in the other
four model setups. As it was previously discussed, this population represented a
heavily exploited population. In such a population, few fish survive long enough
to spawn and contribute to the population growth, so the age of their maturation
becomes a very important parameter. Results indicate that in highly exploited
populations maturation represents one of the most important life history
parameters. The selective pressure of fishery towards the earlier maturation is a
widely observed phenomenon (Kuparinen et al. 2008), which requires attention
of the scientific community due to the long-term negative effects it might produce
on economically important fish species.
The age at first spawning and fecundity were more influential in the model
setups representing exploited populations (i.e., those based on Prodanov et al.
1997 and Navodaru et al. 1992). Spawning frequency was more influential in
populations without any fishery pressure (Fig. 1, models 3-5). This is probably a
result of low number of fish surviving to their second spawning in exploited
populations, which renders this parameter less important in the presence of
fishery.
Figure 2. Change in population growth rate (λ) with increasing survival rate of each age
class by 10%.
The change in the population growth rate (λ) based on the increase of survival
rate of each age class is presented in Fig. 2. As can be observed in the Figure,
general pattern was consistent among all models. It is evident that the influence
of age classes before the first spawning (≤3) on population growth rate and
population sensitivity is greater than the influence of subsequent age classes.
This is a result of two distinct processes. Firstly, high mortality rates result in a
low abundance of older age classes, which decreases their influence on
population dynamics. Secondly, mature age classes have already reproduced
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