Neural Networks and Fuzzy Logic Reveal Overfished Spanish Mackerel Population off Syria

Off the Syrian coast, a large predatory fish that slipped through the Suez Canal barely two decades ago is being caught faster than it can grow old. A new stock assessment, published in the European Journal of Biology and Biotechnology, combines artificial neural networks with fuzzy logic to deliver the first formal evaluation of the narrow-barred Spanish mackerel (Scomberomorus commerson) in the eastern Mediterranean Sea, and the verdict is stark: the population is overfished, its age structure truncated, and its capacity to recover limited.

The narrow-barred Spanish mackerel is a fast-swimming pelagic predator that colonized the Mediterranean from its native range in the Indo-Pacific via the Suez Canal. First recorded near Rhodes in 2008, it has since spread across the eastern basin and become an increasingly important catch for small-scale fishers. The species is listed as Near Threatened on the IUCN Red List, yet until now no formal stock assessment existed anywhere in the Mediterranean, leaving managers blind to the state of a resource that supports coastal livelihoods in a region beset by conflict and institutional strain.

To fill that gap, a research team led by Hamwi and Ali analyzed 611 specimens collected between November 2023 and October 2024 from five fishing ports along the Syrian coast, from Ras al-Bassit in the north to Tartus in the south. Fishers were interviewed to determine where each fish was caught, and every specimen was measured for fork length and body weight immediately after landing. Because no validated ageing method, such as otolith analysis, was available, the researchers trained a custom artificial neural network to estimate age from body size, a proxy approach that achieved a coefficient of determination of 0.96 against the size-at-age data.

The results reveal a population under severe pressure. Fork lengths in the catch ranged from 48.73 to 109.58 centimeters, with a mean of 67.26 centimeters, and the oldest fish in the sample was just five years old. That figure pales beside populations elsewhere in the species’ range: Spanish mackerel in the Persian Gulf live up to 12 years and reach 160 centimeters, those off South Africa live up to 14 years and reach 161.5 centimeters, and those off Oman live up to 20 years and reach 166 centimeters. In Syrian waters, the fish simply do not survive long enough to attain such sizes or ages.

Growth analysis showed the population grows moderately fast, with a growth coefficient of 0.284 per year and a growth performance index of 3.65, but the body weight of fish increases more slowly than length alone would predict, a pattern of negative allometric growth. The critical finding, however, lies in the mortality estimates. Total mortality reached 1.22 per year, of which 0.73 per year was attributable to fishing, yielding an exploitation rate of 0.60. That figure exceeds the biomass-based reference point of 0.389, the threshold at which the spawning stock falls to half its unexploited level, providing strong evidence of overfishing.

The Beverton and Holt yield-per-recruit analysis reinforced the picture. Relative biomass-per-recruit has fallen to 38 percent of its unexploited level, and the marginal yield gain declines to one-tenth of its initial value at an exploitation rate of 0.764, meaning that any further increase in fishing effort would bring diminishing returns while continuing to erode the stock. Most individuals enter the fishery within their first year of life, often before completing their first spawning cycle, leaving few fish to reproduce more than once.

A sensitivity analysis confirmed the robustness of these conclusions. When growth parameters were varied by plus or minus 20 percent, the exploitation rate ranged from 0.55 to 0.68, always above the overfishing threshold. Even under the most favorable scenario, biomass-per-recruit remained below 45 percent of its unexploited level, well under the 50 percent benchmark.

To assess vulnerability beyond the catch data, the researchers applied a fuzzy logic system that translates qualitative biological knowledge into quantitative indices. The fishing vulnerability index came out at 50.9 on a 100-point scale, with membership degrees of 0.55 in the high category and 0.45 in the moderate category, closely matching the intrinsic vulnerability score of 52 assigned to the species in FishBase. The population growth potential index was estimated at 33.2, with membership degrees of 0.65 in the moderate category and 0.35 in the low category, reflecting limited recovery capacity under current exploitation.

The demographic pattern, with only 0.82 percent of fish reaching age five, mirrors the signature of overfished populations documented elsewhere: when fishing removes the older, larger individuals, the age structure collapses and the population loses the demographic buffer that once protected it from environmental fluctuations. Few fish survive to spawn multiple times, a pattern associated with heightened risk of collapse.

Based on these findings, the researchers propose three management measures. First, a minimum landing size of 75 centimeters fork length should be enforced, allowing fish to spawn at least once before capture. Second, fishing effort should be reduced, particularly during the spawning season, with seasonal closures from June to August to protect aggregating adults. Third, monitoring of small-scale fisheries should be strengthened, with regular collection of catch and effort data to enable ongoing assessment of the stock.

The study also demonstrates the value of computational tools in data-poor contexts. Where conventional stock assessment requires validated ageing structures, long time series, and substantial institutional capacity, the neural network and fuzzy logic approach can extract meaningful management signals from limited data. For conflict-affected regions where scientific infrastructure is strained, such methods offer a pragmatic path toward evidence-based fisheries management.

Whether Syrian managers adopt these recommendations remains uncertain amid ongoing conflict, but the study provides the first scientific foundation for conserving a resource that has become economically important in less than two decades. The narrow-barred Spanish mackerel arrived in the Mediterranean as a colonizer; without intervention, it risks becoming another cautionary tale of a resource exploited faster than it can replenish itself.

Subject of Research: Overfishing risk and population decline of Scomberomorus commerson (Actinopterygii, Scombriformes, Scombridae) in a data-poor fishery: First assessment from the eastern Mediterranean Sea

Article Title: Overfishing risk and population decline of Scomberomorus commerson ( Actinopterygii , Scombriformes , Scombridae ) in a data-poor fishery: First assessment from the eastern Mediterranean Sea

Article References: Hamwi, N. I., Altajer, H., & Salem, J. (2025). Overfishing risk and population decline of Scomberomorus commerson (Actinopterygii, Scombriformes, Scombridae) in a data-poor fishery: First assessment from the eastern Mediterranean Sea. Acta Ichthyologica et Piscatoria, 55, 369-377. https://doi.org/10.3897/aiep.55.170486

Image Credits: AI Generated

DOI: 10.3897/aiep.55.170486

Keywords: Overfishing, risk, population, decline, Scomberomorus, commerson, Actinopterygii, Scombriformes, Scombridae, data-poor, fishery, First