Occurrence of Microplastic-like Particles in Opisthonema libertate and Sardinops sagax from the Gulf of California: Seasonal Patterns, Morphophysiological Responses, and Fisheries Management Implications

The proliferation of microplastics in marine environments threatens coastal ecosystems via ingestion by planktivorous fish. This study evaluated the occurrence of microplastic-like particles (MPLPs), characterized morphologically, in the digestive tracts of Opisthonema libertate and Sardinops sagax in the Gulf of California. Blue and green fibers dominated the assemblages. O. libertate exhibited peak abundance in autumn (74.08 particles/individual), while S. sagax peaked in winter (78.10 particles/individual). Species-specific analysis revealed distinct patterns: S. sagax showed a strong positive correlation between MPLP abundance and both total length (r = 0.71, p < 0.01) and body weight (r = 0.68, p < 0.05), indicating ontogenetic accumulation. Furthermore, a significant negative correlation between MPLPs and triglycerides in S. sagax (r = −0.38, p < 0.05) suggests a potential metabolic cost. Conversely, ingestion in O. libertate appeared incidental. These findings document chronic exposure in key forage fish, with high fiber prevalence suggesting abandoned fishing gear as a likely source. While spectroscopic validation is needed, these results highlight the necessity of integrating microplastic monitoring into sustainable fisheries management to ensure food security in the region.