The effect of quality feeding resources versus quantity was demonstrated in the
larvae of the Mediterranean bluefin tuna in which three annual larval cohorts from
2003 to 2005 were analyzed from both the growth and condition standpoint. The
greatest larval growth of bluefin tuna larvae was attained in 2003, under extreme
temperature changes and extremely low production caused by the historical Mediterranean heat wave (García et al. 2013).
13.5.2 Larval Growth and Larval Condition Research Studies
Ramírez et al. (2001) revealed that the growth strategy of the ELHS of the winterspawned sardine larvae in the northwestern Alboran Sea is characterized by a
decrease of length increment growth rates with increasing larval ages, while growth
in somatic mass gain tends to increase with age. This sardine larval growth strategy
was corroborated by other studies conducted with northern Alboran Sea sardine
larvae (Ramírez et al. 2004). However, studies conducted with sardine larvae in postflexion stages (García et al. 2006a, b; size range from about 16 to 28 mm) found that
size at age followed a linear pattern rather than a power pattern and thereby, the
resulting growth rates for those size classes are constant (around 0.32 mm/day). The
results of all these studies indicate that there is an inflection in sardine somatic
growth rates, both in length and weight, which could be due to ontogenic changes of
larvae during its development and by the changes in larval food items. Thus,
Conway et al. (1994) based on the analysis of the gut content reported an increase
in copepodites in the diet of sardine larvae larger than 15 mm collected in the north
Iberian continental shelf.
Otolith growth also provides important information to understand the variability
in recruitment. Thus, for the northern Alboran Sea sardine, Ramírez et al. (2001)
reported that otolith larval growth was faster for older age groups in comparison with
younger larvae. These differences could be attributed to growth-dependent mortality
during the earlier stages of sardine larval development (Ramírez et al. 2001).
Likewise, growth-dependent mortality could explain the observed increase in nutritional condition with larval length (Ramírez et al. 2001), since well-fed larvae would
also have more survival rates than poor feed or starved larvae.
The studies conducted in the Alboran Sea have also allowed further insights on
how larval growth, otolith growth, and nutritional condition are related. Under ideal
conditions, a close relationship between larval somatic growth and nutritional
condition is expected. Thus, previous studies with other species related recent
somatic fish larval growth with RNA/DNA (Buckley 1984; Hovenkamp and Whitte
1991; Westerman and Holt 1994). However, the studies conducted with field-caught
sardine larvae suggest that RNA/DNA is not a good indicator of somatic growth in
length or age. Thus, Ramírez et al. (2001) found that the RNA/DNA and protein/
DNA ratios were weakly related to somatic larval growth in mass as well as to recent
otolith growth. On the other hand, previous studies have used the width of the last
three-six otolith daily microincrements as a proxy of recent larval growth in some
13 Evolving from Fry Fisheries to Early Life Research on Pelagic Fish Resources
507
larvae of the Mediterranean bluefin tuna in which three annual larval cohorts from
2003 to 2005 were analyzed from both the growth and condition standpoint. The
greatest larval growth of bluefin tuna larvae was attained in 2003, under extreme
temperature changes and extremely low production caused by the historical Mediterranean heat wave (García et al. 2013).
13.5.2 Larval Growth and Larval Condition Research Studies
Ramírez et al. (2001) revealed that the growth strategy of the ELHS of the winterspawned sardine larvae in the northwestern Alboran Sea is characterized by a
decrease of length increment growth rates with increasing larval ages, while growth
in somatic mass gain tends to increase with age. This sardine larval growth strategy
was corroborated by other studies conducted with northern Alboran Sea sardine
larvae (Ramírez et al. 2004). However, studies conducted with sardine larvae in postflexion stages (García et al. 2006a, b; size range from about 16 to 28 mm) found that
size at age followed a linear pattern rather than a power pattern and thereby, the
resulting growth rates for those size classes are constant (around 0.32 mm/day). The
results of all these studies indicate that there is an inflection in sardine somatic
growth rates, both in length and weight, which could be due to ontogenic changes of
larvae during its development and by the changes in larval food items. Thus,
Conway et al. (1994) based on the analysis of the gut content reported an increase
in copepodites in the diet of sardine larvae larger than 15 mm collected in the north
Iberian continental shelf.
Otolith growth also provides important information to understand the variability
in recruitment. Thus, for the northern Alboran Sea sardine, Ramírez et al. (2001)
reported that otolith larval growth was faster for older age groups in comparison with
younger larvae. These differences could be attributed to growth-dependent mortality
during the earlier stages of sardine larval development (Ramírez et al. 2001).
Likewise, growth-dependent mortality could explain the observed increase in nutritional condition with larval length (Ramírez et al. 2001), since well-fed larvae would
also have more survival rates than poor feed or starved larvae.
The studies conducted in the Alboran Sea have also allowed further insights on
how larval growth, otolith growth, and nutritional condition are related. Under ideal
conditions, a close relationship between larval somatic growth and nutritional
condition is expected. Thus, previous studies with other species related recent
somatic fish larval growth with RNA/DNA (Buckley 1984; Hovenkamp and Whitte
1991; Westerman and Holt 1994). However, the studies conducted with field-caught
sardine larvae suggest that RNA/DNA is not a good indicator of somatic growth in
length or age. Thus, Ramírez et al. (2001) found that the RNA/DNA and protein/
DNA ratios were weakly related to somatic larval growth in mass as well as to recent
otolith growth. On the other hand, previous studies have used the width of the last
three-six otolith daily microincrements as a proxy of recent larval growth in some
13 Evolving from Fry Fisheries to Early Life Research on Pelagic Fish Resources
507