Coupling Lagrangian simulation models and remote sensing to explore the environmental effect on larval growth rate: The Mediterranean case study of round sardinella (Sardinella aurita) early life stages

Abstract

The relationship between environmental conditions and early life-history traits of Sardinella aurita are investigated using material collected in two sites of the Central Mediterranean Sea. Individual mean daily growth during the planktonic phase has been determined by using otolith microstructure analysis, while Lagrangian simulation models allowed to estimate the daily position in space and time of each specimen from the hatching to the catch. Generalized Additive Mixed Models (GAMMs) have been implemented to explore the impact of environmental conditions at time t, t-1 day and t-2 days on the mean daily growth rate occurring at time t. Spatial analysis evidenced a wide dispersion of eggs and larvae in the coastal area of both sampling sites in correspondence to relatively warmer and chlorophyll-a enriched waters. Lagrangian simulations detected a complementary larval dispersal pathway able to transport larvae to a known retention area. Temperature at time t was the most important driver affecting the mean daily larval growth, followed by the food availability. On the other hand, models performed on lagged environmental covariates (t-1 and t-2) did not show any significant effect on the growth rate at time t. In addition to the sub-linear positive correlation between temperature and mean daily larval growth, model highlighted a decrease in the otolith core width at higher temperature that can be linked to an earlier stage of ontogeny at hatching. This study provided a useful methodological approach that takes advantage of available remote sensing data to perform ecological studies in support to fisheries management.

A hierarchical Bayesian model to monitor pelagic larvae in response to environmental changes

“…Salinity was another relevant variable in the model for round sardinella species, with a significant positive linear effect on the presence of this species. For the abundance, a more complex relationship was considered, with a first-order random walk (RW1) effect that accounts for the role of a thermohaline front in shaping the spatial distribution of fish larvae in the study area (Torri et al 2023).…”

“…These authors have underscored the role of physical forces, such as currents, gyres, and fronts, in concentrating larvae born along the Sicilian coast in a larval retention area positioned to the southeast, precisely in the Capo Passero region. In contrast to the spawning areas situated in the northwestern coastal zone and characterized by elevated chlorophyll-a values associated with the upwelling phenomenon, the Capo Passero area typically exhibits a relatively lower concentration of food, although characterized by higher larval densities compared to the other areas (Russo et al 2021;Torri et al 2023). The model thus encapsulates a noteworthy pattern concerning the distribution of this species in the study area, namely the presence of larval concentration areas characterized by lower food availability compared to other egg deposition areas.…”

“…a greater effect for salinities above 37.6, highlights the fundamental role of the salinity front in controlling larval dispersion dynamics in this area. Indeed, this oceanographic structure arises from the encounter of the Atlantic Ionian Stream (AIS), typically less saline, with the water of the Ionian Sea and is therefore associated with a concentration of larvae originating from both the Strait of Sicily and the northern Ionian coastal zone (Torri et al 2023). Concerning the temperature, the mean posterior fixed effect on the probability of absence/presence shows a higher probability of observing sardines as the temperature increases with a probability equal to 0.55.…”

“…The causes of these oscillations can be multiple and linked to anthropic factors, such as the high fishing effort, and natural factors (Torri et al 2018). In particular, the biological and environmental dynamics that influence the survival of the first life stages of these species and the subsequent recruitment may be of fundamental importance in determining the annual declines and increases of the adult stock (Cuttitta et al 2006;Patti et al 2020;Torri et al 2023). Furthermore, the knowledge of the reproductive biology of these species gives insights into the impact of fishing efforts on the spawning fraction of the adult populations to avoid the risk of overfishing.…”

A Hierarchical Bayesian Model to Monitor Pelagic Larvae in Response to Environmental Changes

“…These authors have underscored the role of physical forces, such as currents, gyres, and fronts, in concentrating larvae born along the Sicilian coast in a larval retention area positioned to the southeast, precisely in the Capo Passero region. In contrast to the spawning areas situated in the northwestern coastal zone and characterized by elevated chlorophyll values associated with the upwelling phenomenon, the Capo Passero area typically exhibits a relatively lower concentration of food, although characterized by higher larval densities compared to the other areas (Russo et al, 2021;Torri et al, 2023). The model thus encapsulates a noteworthy pattern concerning the distribution of this species in the study area, namely the presence of larval concentration areas characterized by lower food availability compared to other egg deposition areas.…”