Seasonal changes in growth and condition of anchovy late larvae explained with a hydrodynamic-biogeochemical model simulation

Abstract

We studied seasonal changes in otolith and somatic growth and condition of anchovy Engraulis encrasicolus late larvae (8−55 mm) from the North Aegean Sea (eastern Mediterranean), hatched during the peak (summer) and end (autumn) of, and also after (winter), the regular anchovy spawning period in the area. Mean growth rate and somatic condition were compared with abiotic and biotic parameters collected in situ (current environment). Additionally, we used the output of a coupled 3D hydrodynamic−biogeochemical model implemented over the broader sampling area to reconstruct the potential conditions that the larvae experienced during their development (environmental history). Growth in length was similar for larvae in summer and autumn (0.80 mm d ). Larval and otolith size at hatching were larger in winter. Otolith microstructure was faint in winter with very narrow increments. Otolith and somatic growth were coupled in autumn and winter, but in summer, when temperature was high, otoliths were significantly larger for the same fish length, age and weight. The biogeochemical model simulation implied that mean plankton productivity was significantly higher during the development of larvae in summer, explaining their higher growth in weight and somatic condition compared to autumn and winter. In situ measured environmental parameters represented a snapshot of ambient conditions at the site and time of sampling and did not adequately explain the seasonal differences in growth and condition.

Disentangling the effects of inherent otolith growth and model-simulated ecosystem parameters on the daily growth rate of young anchovies

“…The sagittal otoliths were removed and processed following the methodology described in Schismenou et al (2013) for the treatment of otoliths of large larvae. The right or left otolith was randomly selected from each fish and analysed under a light microscope coupled with an image analysis system (Image-Pro Plus 3.0, Media Cybernetics).…”

“…Uncoupling is known to occur, for example, when environmental conditions such as food availability or temperature change, and during transitions between ontogenetic stages (e.g. Molony & Choat 1990, Hare & Cowen 1995, Folkvord et al 2000, Otterlei et al 2002, Fey 2006, Schismenou et al 2013. In these instances, the speed and magnitude of change in growth can be different between the soma and otolith.…”

“…In this study, we used 3 seasonal samples (July, December and February) of juvenile European anchovy Engraulis encrasicolus from the North Aegean Sea and a daily dataset of environmental parameters (Schismenou et al 2013) to study the variability in daily growth based on otolith microstructure analysis. The environmental dataset was derived from the simulation of a coupled hydrodynamic-biogeochemical model (POM-ERSEM) over the period of growth of the sampled fish.…”

“…The environmental dataset was derived from the simulation of a coupled hydrodynamic-biogeochemical model (POM-ERSEM) over the period of growth of the sampled fish. The use of simulated ecosystem parameters has been recently proposed as a useful approach to represent the environmental history of growing individuals (Schismenou et al 2013). We constructed a GAM with daily increment widths as the response variable (Hinrichsen et al 2010) and examined the effect of a suite of environmental parameters.…”

European anchovy (Engraulis encrasicolus) age structure and growth rate in two contrasted areas of the Mediterranean Sea: the paradox of faster growth in oligotrophic seas

“…Such studies have been based both on in situ experiments (in tanks) and on field-collected specimens, and highlighted the huge variability in growth among fish species and life history stages (Pauly, 1980). In short-lived species, such as small pelagic fishes, particular effort has been devoted to understanding the growth-mortality mechanism as it is considered the most important driver of recruitment variability of sardine and anchovy stocks (e.g., Jacobson & MacCall, 1995;Sinovčić, 1998;Allain et al, 2001;La Mesa et al, 2009;Schismenou et al 2014). On the contrary, only few studies have focused on the growth of adults, underlining the importance of growth on biomass production of populations (Van Beveren et al, 2014;Cerna & Plaza, 2016;Uriarte et al, 2016).…”