Behavioural Responses of a Large, Benthic Elasmobranch to Catch-and-Release Angling

Abstract

Catch-and-release angling is widespread, but the impacts of this practice for captured individuals are understudied, especially among elasmobranchs. Studies on sub-lethal behavioural impacts are particularly sparse, despite their importance for the interpretation of biologging data and for assessments of species’ tolerance to capture. In this study, the behavioural responses of flapper skate (Dipturus intermedius) to catch-and-release angling were described for the first time, using archival observations (depth and temperature) for 21 tag deployment/retrieval events and five recreational angling events that occurred during tagged individuals’ time at liberty from charter vessels off the west coast of Scotland in 2016–17. During capture (8–50 minutes), the changes in depth and temperature experienced by individuals typically exceeded natural variability. Post-release, behavioural change was apparent from visual inspection, regression and functional data analysis of the time series. Immediately following release, movements into deeper water and short periods of low vertical activity (usually 1–2 hours in duration) were common. However, overall average vertical activity was typically around 38% higher in the 12 hours following release than in undisturbed activity. A small number of individuals (n = 3, 14%) exhibited irregular post-release behaviour in the form of rapid, transient re-ascents towards the surface following release. Collectively, the evidence for limited, short-term behavioural changes suggests that flapper skate behaviour is relatively resilient to catch-and-release angling from charter vessels, but irregular post-release behaviour in 14% of individuals is sufficiently notable to indicate that further research is required on the impacts of this practice. This study clearly demonstrates the value of biologging data and behavioural analyses for examining the impacts of disturbance and separating ‘disturbed’ and ‘undisturbed’ behaviours in studies of animal movement.

Benthic animal-borne sensors and citizen science combine to validate ocean modelling

“…This assumption is consistent with skate morphology and diet studies of the common skate species complex ( D. batis ), which includes flapper skate and the common blue skate ( D. batis ) 45 , that have revealed the exploitation of a wide range of benthic prey 46 – 48 . The way that flapper skate ‘dig’ into the sediment when hooked by recreational anglers also demonstrates benthic movements 40 . Moreover, recent research has shown that it is possible to reconstruct movement trajectories for flapper skate under the assumption that they remain near to the seabed (Lavender et al, in prep).…”

“…Temperature-depth profiles recorded during recreational angling events by tagged individuals that were pulled to the surface were used to validate modelled temperature-depth profiles. Angling events were identified in the mark-recapture database maintained by NatureScot, Marine Scotland Science and the Scottish Association for Marine Science 40 (see Supplementary Information Sect. 4.1).…”

“…4.1). Each angling event was defined from the time of the last depth observation preceding the capture ascent to the time of the first observation at the surface 40 (Fig. 2 ).…”

“…The flapper skate ( Dipturus intermedius ) is a Critically Endangered benthic elasmobranch 33 that is found off the west coast of Scotland where data from animal-borne tags have been collated to guide management of a 741 km 2 Marine Protected Area (MPA) established for its conservation 34 – 42 . Since the 1970s, a wealth of citizen-science mark-recapture data has been assembled from a recreational catch-and-release sport fishery that principally targets skate from anchored charter vessels over areas of relatively deep (> 100 m) water 34 – 40 . More recently (2016–17), the flapper skate became the focus of a major electronic tagging and tracking project that deployed passive acoustic telemetry and archival tags 39 – 41 , 43 .…”

An integrative modelling framework for passive acoustic telemetry

“…In the second stage, a particle filtering (PF) process is used to incorporate movement. Alongside the central framework, the coupling of the AC‐branch and PF‐branch algorithms collectively represents a new family of algorithms for inferring movements and patterns of space use termed the ‘flapper family’, following its motivation by research on the Critically Endangered flapper skate ( Dipturus intermedius ) (Dodd et al, 2022; Lavender et al, 2021a, 2021b; Lavender, Aleynik, Dodd, Illian, James, Smout, et al, 2022; Lavender, Aleynik, Dodd, Illian, James, Wright, et al, 2022; Thorburn et al, 2021). To support algorithm application, we introduce the flapper R package.…”