Long-term insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910–2018)

Zara L R Botterell,Rod Penrose,Brendan J Godley,Matthew J Witt

doi:10.1017/s0025315420000843

Abstract

AbstractWith over a century of records, we present a detailed analysis of the spatial and temporal occurrence of marine turtle sightings and strandings in the UK and Ireland between 1910 and 2018. Records of hard-shell turtles, including loggerhead turtles (Caretta caretta, N = 240) and Kemp's ridley turtles (Lepidochelys kempii, N = 61), have significantly increased over time. However, in the most recent years there has been a notable decrease in records. The majority of records of hard-shell turtles were juveniles and occurred in the boreal winter months when the waters are coolest in the North-east Atlantic. They generally occurred on the western aspects of the UK and Ireland highlighting a pattern of decreasing records with increasing latitude, supporting previous suggestions that juvenile turtles arrive in these waters via the North Atlantic current systems. Similarly, the majority of the strandings and sightings of leatherback turtles (Dermochelys coriacea, N = 1683) occurred on the western aspects of the UK and the entirety of Ireland's coastline. In contrast to hard-shell turtles, leatherback turtles were most commonly recorded in the boreal summer months with the majority of strandings being adult sized, of which there has been a recent decrease in annual records. The cause of the recent annual decreases in turtle strandings and sightings across all three species is unclear; however, changes to overall population abundance, prey availability, anthropogenic threats and variable reporting effort could all contribute. Our results provide a valuable reference point to assess species range modification due to climate change, identify possible evidence of anthropogenic threats and to assess the future trajectory of marine turtle populations in the North Atlantic.

Highlights

Understanding the status of marine turtle populations and anthropogenic threats that may impact their survival is important for effective conservation (Hamann et al, 2010)
For loggerhead and Kemp’s ridley turtles, the patterns of decadal records potentially reflect the historical events that have impacted the number of nesting females, the total number of clutches laid and subsequently the number of hatchlings recruited each year (Mazaris et al, 2017)
From the 1980s onwards we observed a significant increase in the decadal totals of loggerhead turtle sightings and strandings, which could be the result of increased hatchling recruitment due to successful conservation measures

Summary

Introduction

Understanding the status of marine turtle populations and anthropogenic threats that may impact their survival is important for effective conservation (Hamann et al, 2010). Leatherback turtles, the majority adults, seasonally frequent the waters around the UK and Ireland during the boreal summer and autumn as it is a foraging ground for their gelatinous prey (Godley et al, 1998; Witt et al, 2007a) This species nests on tropical and subtropical beaches, with adults undertaking extensive migrations across oceans before returning to their nesting beaches every 2–4 years (McDonald & Dutton, 1996; Fossette et al, 2010). Juvenile oceanic marine turtles are rarely observed and as such this stage of their life cycle remains the least described in terms of occurrence, distribution and abundance These turtles are likely to originate from rookeries in the North-west Atlantic (loggerhead turtles) and the Downloaded from https://www.cambridge.org/core.

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