A unified paradigm for defining elasmobranch aggregations

Abstract

Elasmobranchs are highly diverse in movement, sensory capacity, and behavioural responses to the environment, leading to differences in the function and nature of associations and interactions between individuals, populations, and species. The term "aggregation"has been widely and variably used to describe co-occurrence across elasmobranch species, but its defining criteria remain vague and indeterminate. The lack of standardized terminology hinders comparisons across studies, species, and systems. It can cause misinterpretation about the drivers of aggregation formation or grouping behaviour and limits the impact of elasmobranch behavioural research. Here, we propose generalizable definitions of aggregation and supporting terms, adapted from more mature socioecological theory in other systems, which can be applied across elasmobranchs. We discuss the drivers and types of elasmobranch aggregations, detail the criteria required to identify an aggregation based on our definition, and offer direction on future methods and reporting to advance the field. These proposed definitions and reporting protocols standardize the study of elasmobranch socioecology, will generate greater understanding of the mechanisms underlying behaviour and distribution across species, and support more cross-system comparisons. Finally, this information can offer greater predictive power into when and how aggregations may form, leading to more proactive management strategies to mitigate anthropogenic threats.