Tracks, Maps and Gaps: A Testable Research Definition for Critical Chondrichthyan Areas, European Atlantic Insights

Abstract

Designing effective spatial management for chondrichthyans (sharks, skates, rays and chimaeras) requires incorporating critical areas, sites essential for population maintenance, such as reproductive and feeding areas. Yet most area-based measures have been developed without consideration of chondrichthyan habitat use. The Important Shark and Ray Area (ISRA) initiative has been pivotal in designating priority areas through a rigorous, consultative process. To complement this, our study offers researchers a testable definition for generating robust evidence to strengthen future critical area delineations and related management decisions. We define critical areas using three criteria: 1) relative frequency of use, (2) extended within-year occupancy and (3) repeated use across years. This framework enables objective comparison among candidate sites and is generalisable across different critical area types. The definition builds upon established early-life-stage habitat concepts and applies these to broader life-history functions. The utility of this framework is then demonstrated through a systematic review of contemporary peer-reviewed literature of critical chondrichthyan areas in the European Atlantic. The review highlighted 62 critical areas with Strong evidence and 41 areas of Moderate strength evidence, which informed the European Atlantic ISRA selection process. Research effort was concentrated in inshore areas, particularly around the British Isles and Portugal, with biases towards large, threatened and commercially valuable species, whilst chimaeras were notably underrepresented. Early-life stage areas were most frequently identified, whereas resting areas were rarely documented. Evidence patterns and biases are examined in the context of evolving critical area concepts to advance their development and improve the quality and breadth of future research. By outlining a testable definition, identifying key knowledge gaps, and proposing research and reporting guidelines, this work enhances the consistency, comparability, and spatial coverage of future chondrichthyan habitat research to support its application to conservation planning.