Using stable-isotope analysis and acoustic telemetry data to infer broad-scale migration patterns of Port Jackson sharks (Heterodontus portusjacksoni)

Context: Understanding migratory species’ habitat selection is complicated by variation in movement strategies. Stable-isotope analysis provides a powerful tool to investigate such variation.

Aims: We used acoustic telemetry and stable-isotope analysis to better understand the movement strategies of Port Jackson sharks.

Methods: We compared the δ¹³C and δ¹⁵N values of fin tissue from acoustically tracked individuals that undertook three distinct movement strategies. Hierarchical cluster analysis was then used to cluster movement strategies of a larger sample of sharks on the basis of δ¹³C and δ¹⁵N values.

Key results: Tracked individuals that remained in Jervis Bay were enriched in ¹³C, compared with those that migrated south after the breeding season. Individuals were assigned to six clusters and δ¹³C and δ¹⁵N values indicated that migrating males and females may utilise different geographical areas or niches during the non-breeding season.

Conclusions: By using stable isotope analysis and acoustic telemetry, we identified distinct groups of Port Jackson sharks with similar broad-scale movement strategies.

Implications: These variable movement strategies may lead to different reproductive fitness advantages on an individual and population level, having implications for the broader ecosystem, given the important role mesopredators play in southern reef marine ecosystems.