Field estimates of crayfish mortality associated with passive integrated transponder tagging

Abstract

Abstract Mark–recapture studies of crayfish using internally implanted passive integrated transponder (PIT) tags is a promising method for understanding details of crayfish ecology. The size of crayfish that can be marked is dependent on the size of the PIT tag. Several studies have examined mortality rates associated with the insertion of the smallest currently available PIT tags (Biomark MiniHPT8, 8.4 × 1.4 mm) using different insertion locations and husbandry conditions. Here, carapace length‐ and sex‐dependent mortality rates were evaluated for three ventral PIT tag insertion locations (central, pleopod and lateral) in a field experiment focusing on the northern crayfish (Faxonius virilis) in the Gila River Basin where it was introduced several decades ago. The central insertion method was the only treatment group that did not exceed background mortality in two trials for all individuals combined. When evaluated by sex, no insertion method exceeded control mortality in males, and only the lateral insertion method exceeded control mortality in females. The relationship between carapace length and mortality was different depending on the PIT tag insertion location and sex. Regardless of sex or size, F. virilis responded with lower mortality rates when the PIT tag was inserted using the central insertion method, and this method is preferred for tagging F. virilis of ≥20 mm carapace length. Crayfish are large‐bodied macroinvertebrate omnivores with important roles in freshwater ecosystems. This article identifies best practices for internal PIT tag placement, provides estimates of mortality associated with tagging, and thereby advances ecological research focused on the conservation of imperilled or sensitive crayfishes. It also provides useful guidance for studies of non‐native crayfish in communities where they have become invasive.