Morphometric insights of least concern to vulnerable Elasmobranch in Tuban Waters, East Java: Baseline data and fisheries implications

¹ Coastal and Marine Resources Management Study Program, Department of Aquatic Resources Management, Faculty of Fisheries and Marine Sciences, IPB University, 16680 Bogor, Indonesia
² Department of Aquatic Resources Management, Faculty of Fisheries and Marine Sciences, IPB University, 16680 Bogor, Indonesia
³ Center for Coastal and Marine Resources Studies – International research Institute for Maritime, Ocean and Fisheries - IPB University, Bogor 16143, Indonesia
⁴ Department of Biology, University of Oxford, Oxford - OX1, United Kingdom
⁵ Mobula Project Indonesia, Pure 01/09, Krajan, Tembokrejo, Muncar, 68472 Banyuwangi, Indonesia
⁶ Department of Marine Science - Ronggolawe University, Manunggal Street No. 61, Wire, Kutorejo - Tuban, East Java 62391, Indonesia

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Indonesia is a mega biodiverse archipelagic nation with a high diversity of elasmobranch species (sharks and rays), yet it faces major challenges in their management. The northern coast of East Java, particularly Tuban Regency within Fisheries Management Area (FMA) 712, is a key landing site for these species. This study provides baseline morphometric data for elasmobranchs categorized as Least Concern (LC), Near Threatened (NT) and Vulnerable (VU) according to the IUCN Red List, and assesses their implications for sustainable fisheries management. Data were collected through daily observations of landings at Palang Fish Landing Base / Fish Landing Unit (PPI Palang) from May 2024 to April 2025. Shark landings consisted of 45.5% LC, 27.3% NT, and 27.3% VU species. Rays were composed of 38.5% LC, 30.8% NT, and 30.8% VU. Most individuals were below the known mature length (Lm), indicating that immature individuals were being harvested. These findings highlight the risk of silent collapse, where population declines progress unnoticed until a critical threshold is reached. Integrating biological considerations into fisheries management frameworks and fostering stronger collaboration between scientific and policy stakeholders is crucial to supporting the long-term sustainability of vulnerable species.