Hydrographic variability and biomass fluctuations of European anchovy (Engraulis encrasicolus) in the Central Mediterranean Sea: Monetary estimations and impacts on fishery from Lagrangian analysis

During the last decades, scientific community has been investigating both biological and hydrographic processes that affect fisheries. Such an interdisciplinary and synergic approach is nowadays giving a fundamental contribution, in particular, in connecting the dots between hydrographic phenomena and biomass variability and distribution of small pelagic fish. Here we estimate impacts of hydrographic fluctuations on small pelagic fishery, focusing on the inter-annual variability that characterizes connectivity between spawning and recruiting areas for the European anchovy (Engraulis encrasicolus, Linnaues 1758), in the Northern side of the Sicily Channel (Mediterranean Sea). Results show that coastal transport dynamics of a specific year largely affect the biomass recorded the following year. Our work, moreover, quantifies the specific monetary impacts on landings of European anchovy fishery due to hydrodynamics variability, connecting biomass fluctuations with fishery economics in a highly dynamic and exploited marine environment as the Sicily Channel. In particular, we build a model that attributes a monetary value to the hydrographic phenomena (i.e., cross-shore vs. alongshore eggs and larvae transport), registered in the FAO Geographical Sub-Area (GSA) 16 (Southern Sicily). This allows us to provide a monetary estimation of catches, derived from different transport dynamics. Our results highlight the paramount importance that hydrographic phenomena can have over the socio-economic performance of a fishery.

💡 Research Summary

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This paper investigates how hydrographic variability influences the biomass and economic performance of the European anchovy (Engraulis encrasicolus) in the northern Sicily Channel (FAO GSA 16). Using ichthyoplankton surveys conducted between 1999 and 2012, the authors estimate the total number of eggs produced each summer by integrating measured egg densities over a 10‑meter surface layer across the spawning area. To quantify the transport of eggs and larvae, they apply a Lagrangian Transport Index (LTI), which represents the percentage of virtual particles released from the Sciacca spawning zone that cross an imaginary Malta‑Sicily line and reach the recruitment area off Cape Passero within 25 days. The LTI varies markedly among years, reflecting changes in coastal currents and wind events such as Mistral bursts that can either retain larvae near the coast or advect them offshore.

The “survived eggs” metric is obtained by multiplying the estimated egg production by the LTI, providing a proxy for the number of larvae that successfully reach the nursery. The authors then link this biological output to fishery economics. They calculate an exploitation rate as the ratio of annual catches to biomass (using GFCM data) and assume a 5 % discard rate for trawl and purse‑seine fisheries operating mainly out of Sciacca. Because 95 % of the catch consists of 1‑ and 2‑year‑old anchovies, the model distributes the survived cohort into two successive catch components, each scaled by the exploitation rate and a survival factor that assumes un‑caught fish persist to the next year.

Catch weight is derived by multiplying the number of fish by an average adult weight of 13.2 g, and monetary value is obtained by applying annual market prices from the Aci Trezza market (ISMEA) and adjusting for inflation using the Italian consumer price index (ISTAT). The resulting monetary estimates are not intended as actual market revenues but as a measure of how hydrographic fluctuations translate into economic variability.

Statistical analysis includes Pearson correlations between next‑year biomass and three lagged predictors: total eggs, LTI, and survived larvae. Multicollinearity is examined, and generalized linear (GLM) and additive (GAM) models are fitted, with Akaike’s Information Criterion (AIC) used for model selection. Models incorporating LTI and survived larvae consistently outperform those using egg abundance alone, indicating that the physical transport process is the dominant driver of inter‑annual biomass changes.

The findings demonstrate that years with favorable coastal currents—enhancing on‑shore transport of eggs and larvae—lead to higher recruitment, larger catches, and greater monetary returns. Conversely, years dominated by strong offshore jets reduce the survived cohort, depress catches, and diminish economic returns. By converting oceanographic variability into a monetary metric, the study provides a novel framework for integrating physical oceanography, population dynamics, and fisheries economics, offering valuable insights for management under climate‑driven changes. Limitations include the restriction of egg estimates to the upper 10 m, omission of the full spawning season, and the neglect of natural mortality and predation, which likely render the monetary impacts conservative. Future work should incorporate full depth profiles, extended spawning windows, and explicit mortality processes to refine the bio‑economic linkage.