Overexploitation of the Atlantic Sharpnose Shark (Rhizoprionodon terraenovae) in Marine Priority Regions of Tamaulipas, Mexico: Implications for Wetland Conservation and Data-Limited Fisheries Management

Artisanal fisheries in Mexico frequently operate under data-limited conditions, lacking historical time series of catch and effort. The Atlantic sharpnose shark (Rhizoprionodon terraenovae) is caught by artisanal fisheries in Marine Priority Regions 45-46 and the influence area of the Playa Tortuguera Rancho Nuevo Wetland of International Importance, Tamaulipas, where it acts as a natural predator of Kemp's ridley sea turtle (Lepidochelys kempii) hatchlings, a critically endangered species. In this data-limited context, the population status of R. terraenovae was assessed for the first time using length-frequency based methods. Between November 2018 and February 2020, 541 organisms from the artisanal fishery in La Barra del Tordo were analyzed using FISAT II. The von Bertalanffy growth parameters for combined sexes were: L∞ = 105 cm, k = 0.59 yr⁻¹, t₀ = -0.195 yr. Total (Z), natural (M), and fishing (F) mortality rates were 4.13, 0.467, and 3.22 yr⁻¹, respectively. The mean exploitation rate (E = F/Z) was 0.78 (95% CI: 0.745-0.805), exceeding the reference point of 0.5 (Gulland, 1971), indicating severe overexploitation. The parameters showed biological consistency (Ø' = 3.81; M/k = 0.79), and natural mortality (0.467 yr⁻¹) fell within the range reported for the species. This finding, in a priority conservation region under the Conservation Sector regime of the Marine Ecological Zoning Program, evidences the urgent need to implement ecosystem-based fisheries management. The study demonstrates that, even with limited data, it is possible to obtain robust estimates that reconcile fisheries sustainability with L. kempii conservation in protected natural areas.