Multidecadal analysis of beach loss at the major offshore sea turtle nesting islands in the northern Arabian Gulf

Rommel H Maneja,Jeffrey D Miller,Wenzhao Li,Rejoice Thomas,Hesham El-Askary,Sachi Perera,Ace Vincent B Flandez,Abdullajid U Basali,Joselito Francis A Alcaria,Jinoy Gopalan,Surya Tiwari,Mubarak Al-Jedani,Perdana K Prihartato,Ronald A Loughland,Ali Qasem,Mohamed A Qurban,Wail Falath,Daniele Struppa

doi:10.1016/j.ecolind.2020.107146

Abstract

Undocumented historical losses of sea turtle nesting beaches worldwide could overestimate the successes of conservation measures and misrepresent the actual status of the sea turtle population. In addition, the suitability of many sea turtle nesting sites continues to decline even without in-depth scientific studies of the extent of losses and impacts to the population. In this study, multidecadal changes in the outlines and area of Jana and Karan islands, major sea turtle nesting sites in the Arabian Gulf, were compared using available Kodak aerographic images, USGS EROS Declassified satellite imagery, and ESRI satellite images. A decrease of 5.1% and 1.7% of the area of Jana and Karan islands, respectively, were observed between 1965 and 2017. This translated to 14,146 m2 of beach loss at Jana Is. and 16,376 m2 of beach loss at Karan Is. There was an increase of island extent for Karan Is. from 1965 to 1968 by 9098 m2 but comparing 2017 with 1968, Karan Is. lost as much as 25,474 m2 or 2.6% of the island extent in 1968. The decrease in island aerial extent was attributed to loss of beach sand. The southern tips of the island lost the most significant amount of sand. There was also thinning of beach sand along the middle and northern sections that exposed the rock outcrops underneath the beach. The process of beach changes of both islands was tracked by the satellite imagery from Landsat 1,3,5,7 and Sentinel-2 during 1972 to 2020. Other factors including the distribution of beach slope, sea level changes, as well as wind & current from both northward and eastward components were analyzed to show its impact on the beach changes. The loss of beach sand could potentially impact the quality and availability of nesting beach for sea turtles utilizing the islands as main nesting grounds. Drivers of beach loss at the offshore islands are discussed in the context of sea level rise, dust storms, extreme wave heights and island desertification.

Highlights

Nesting beaches for sea turtles around the world are facing major beach erosion
A decrease of 5.1% and 1.7% of the area of Jana and Karan islands, respectively, were measured between 1965 and 2017 (Table 3, Fig. 3). This translated to 14,146 m2 of beach loss at Jana Is. and 16,376 m2 of beach loss at Karan Is
There was an increase of island extent for Karan Is. from 1965 to 1968 by 9098 m2, which could be attributed to natural dynamics of island erosion and accretion

Summary

Introduction

Nesting beaches for sea turtles around the world are facing major beach erosion. Historic nesting beaches of hawksbill and green sea turtles have been reduced and impacted by humans with the remaining beach areas facing risks of further loss (McClenachan et al, 2006; Seminoff et al, 2015). Four of the six offshore islands in the Saudi waters of the Arabian Gulf host the largest aggregation of nesting hawksbill and green sea turtles in the Gulf (Gasperetti et al, 1993; Miller, 2011a; Pilcher, 1999, 2000). Around 1000 green sea turtles and 500 hawksbill turtles nest annually at these offshore islands (Miller, 1989; Al Merghani et al, 2000; Pilcher, 1999, 2000; Pilcher et al, 2015). No studies have been done to assess the status of the nesting beach at the islands in particular on the aspect of beach erosion

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Conclusion