Seasonal and Ontogenetic Variation in Depth Use by a Critically Endangered Benthic Elasmobranch and Its Implications for Spatial Management

James Thorburn,Jane Dodd,Mark James,Edward Lavender,Caroline Lynam,Peter J Wright,Julien G A Martin,Francis Neat

doi:10.3389/fmars.2021.656368

Abstract

Seasonal and ontogenetic variations in depth use by benthic species are often concomitant with changes in their spatial distribution. This has implications for the efficacy of spatial conservation measures such as marine protected areas (MPAs). The critically endangered flapper skate (Dipturus intermedius) is the designation feature of an MPA in Scotland. This species is generally associated with deeper waters &gt;100 m; however, little is known about its seasonal or ontogenetic variation in habitat use. This study used archival depth data from 25 immature and mature flapper skate tagged in the MPA over multiple years. Time series ranged from 3 to 772 (mean = 246) days. Generalised additive mixed models and highest density intervals were used to identify home (95%) and core (50%) highest density depth regions (HDDRs) to quantify depth use in relation to time of year and body size. Skate used a total depth range of 1–312 m, but home HDDRs typically occurred between 20 and 225 m. Core HDDRs displayed significant seasonal and ontogenetic variations. Summer core HDDRs (100–150 m) suggest high occupancy of the deep trenches in the region by skate of most size classes. There was an inverse relationship between body size and depth use and a seasonal trend of skate moving into shallow water over winter months. These results suggest that flapper skate are not solely associated with deep water, as skate, especially large females, are frequently found in shallow waters (25–75 m). The current management, which protects the entire depth range, is appropriate for the protection of flapper skate through much of its life history. This research demonstrates why collecting data across seasonal scales and multiple ontogenetic stages is needed to assess the effectiveness of spatial management.

Highlights

Marine protected areas (MPAs) are increasingly being established globally to conserve and recover species, habitats, biodiversity, and ecosystem functions (Edgar et al, 2007)
These variations in habitat use can impact the efficacy of spatial management measures, both seasonally and throughout an individual’s lifetime (Martell et al, 2000; Speed et al, 2010)
Seasonal and ontogenetic variations in depth use are poorly understood for flapper skate, yet identifying these changes could be essential to implement effective management (Grüss et al, 2011; Doherty et al, 2017). To address this knowledge gap, this study aimed to investigate the seasonal and ontogenetic depth use of flapper skate within LStSoJ marine protected areas (MPAs) by deploying data storage tags (DSTs) on immature and mature flapper skate over multiple seasons and years

Summary

Introduction

Marine protected areas (MPAs) are increasingly being established globally to conserve and recover species, habitats, biodiversity, and ecosystem functions (Edgar et al, 2007). Intraspecific variation in habitat use may be driven by variation in resource requirements and hunting capabilities between different life-history groups (Economakis and Lobel, 1998; Hurst et al, 1999; Pratt and Carrier, 2001; Grubbs, 2010; Wearmouth and Sims, 2010; Papastamatiou et al, 2015; Thorburn et al, 2019) These variations in habitat use can impact the efficacy of spatial management measures, both seasonally and throughout an individual’s lifetime (Martell et al, 2000; Speed et al, 2010). An understanding of a species’ spatial ecology, including movement and habitat preferences, is required at ontogenetic and seasonal scales in order to implement effective management strategies (Martell et al, 2000; Speed et al, 2010)

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