Environmental Engineering Reference
In-Depth Information
structure, since it removes preferentially the larger (older) individuals. In
fact, the length of fi sh species landed from coastal areas has been reduced
by 25% (Trites et al. 2006). For example, in the North Atlantic the maximum
length of the species landed from 1950 to 2000 decreased approximately
from 95 cm to 65 cm (Planque et al. 2010). As a consequence, the buffering
capacity of populations is constrained since a fi sh population with many
year classes can survive during long periods of adverse environment
conditions until the circumstances became favorable (Planque et al. 2010).
On the other hand, a population with few cohorts may collapse before the
onset of favorable conditions (Formentin and Fonteneau 2001).
One of the main repercussions of selecting the individuals at the edges
of the species range is that they are likely to have particular adaptations to
extreme conditions, therefore the genetic pool and the population plasticity
is greatly reduced (Brander 2010). The loss of sub-populations, alleles
and genotypes will reduce their surplus productivity potential and make
them more vulnerable to fi shing and climate variability (Brander 2010).
The alteration of life-history traits is another consequence of the fi shing-
associated acceleration of population turnover rates (Law and Rowell 1993,
Law 2000). As a consequence, the population replacement time is reduced
because there is an increment in the growth rate and a decrease in the age-
at-maturity (Perry et al. 2010b). It has been experimentally proved, that
fi sh species which present more rapid turnover of generations have faster
demographic responses to climate forcing and also have a faster tendency
of spatial redistribution (Perry et al. 2005).
The reproductive potential of fi sh populations is also affected by the
selectivity of fi sheries, since recruitment capacity is greater if larger/
older individuals are more abundant (Planque et al. 2010). Reducing
the average length and age of individuals may increase the recruitment
variability by diminishing the capacity of the population to cope with
short-term unfavorable environmental conditions (Barkley et al. 2004,
Hutchings and Reynolds 2004, Hutchings and Baum 2005, Hsieh 2006). In
addition, a population with fewer age classes could diffi cultly survive after
several years of poor recruitment (Perry et al. 2010b). On the other hand,
larger/older females present various adaptive advantages, such as longer
spawning period and over a larger vertically and horizontally area, higher
probability of egg survival and higher tolerance of their post-hatch larvae
to long periods of starvation (Barkeley et al. 2004, Secor 2007, Planque et
al. 2010).
Many fi sh species use bet-hedging strategies to increment the survival
of larvae in variable environmental conditions (Lambert 1987, Hutchings
and Myers 1993, Marteinsdottir and Steinarsson 1998). If the age structure
is truncated by fi shing, fi sh population become more unstable because
bet-hedging strategies are undetermined and are more infl uenced by short-
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