Population Structure, Abundance and Movement of Whale Sharks in the Arabian Gulf and the Gulf of Oman

David P Robinson,Rima W Jabado,Katie Lee,Aaron C Henderson,Simon J Pierce,Christoph A Rohner,Simone Caprodossi,Mohammed Y Jaidah,James M Mair,Steffen Bach,Abi March,Rupert Ormond,Chaolun Allen Chen

doi:10.1371/journal.pone.0158593

Abstract

Data on the occurrence of whale sharks, Rhincodon typus, in the Arabian Gulf and Gulf of Oman were collected by dedicated boat surveys and via a public-sightings scheme during the period from 2011 to 2014. A total of 422 individual whale sharks were photo-identified from the Arabian Gulf and the northern Gulf of Oman during that period. The majority of sharks (81%, n = 341) were encountered at the Al Shaheen area of Qatar, 90 km off the coast, with the Musandam region of Oman a secondary area of interest. At Al Shaheen, there were significantly more male sharks (n = 171) than females (n = 78; X2 = 17.52, P < 0.05). Mean estimated total length (TL) for sharks was 6.90 m ± 1.24 (median = 7 m; n = 296). Males (7.25 m ± 1.34; median = 8 m, n = 171) were larger than females (6.44 m ±1.09; median = 7 m, n = 78; Mann-Whitney U test, p < 0.01). Of the male sharks assessed for maturity 63% were mature (n = 81), with 50% attaining maturity by 7.29 m and 100% by 9.00 m. Two female sharks of >9 m individuals were visually assessed as pregnant. Connectivity among sharks sighted in Qatari, Omani and UAE waters was confirmed by individual spot pattern matches. A total of 13 identified sharks were re-sighted at locations other than that at which they were first sighted, including movements into and out of the Arabian Gulf through the Strait of Hormuz. Maximum likelihood techniques were used to model an estimated combined population for the Arabian Gulf and Gulf of Oman of 2837 sharks ± 1243.91 S.E. (95% C.I. 1720–6295). The Al Shaheen aggregation is thus the first site described as being dominated by mature males while the free-swimming pregnant females are the first reported from the Indian Ocean.

Highlights

The whale shark, Rhincodon typus (Smith, 1828), is the world’s largest fish
Three hundred and forty-one individual whale sharks were identified from 980 useable identification photographs taken during fieldwork in Al Shaheen from 2011 to 2014
Excluding Al Shaheen, 81 individual whale sharks were identified from the Arabian Gulf and Gulf of Oman from records starting in 2004, including the Musandam (n = 46) and Daymaniyat Islands (n = 27) in Oman, and Fujairah (n = 8) in UAE (Fig 2)

Summary

Introduction

The whale shark, Rhincodon typus (Smith, 1828), is the world’s largest fish. This species is distributed throughout tropical and warm temperate seas [1]. Whale sharks form feeding aggregations in a number of regions around the world, including Western Australia [11], Belize [12], northern Mexico [13], the Philippines [14], Djibouti [15], Mozambique [16], Tanzania [17], the Maldives [18,19], the Seychelles [20,21], Red Sea [22] and Qatar [23]. The few places in the world where pregnant female whale sharks have been documented include sites off the Pacific and northwestern Caribbean Sea coasts of Mexico [13,33], Taiwan [34], and around the northern Galapagos Islands off Ecuador [32,35] Based on those limited data, size at maturity for females is approximately 9 m [36]

Methods

Results

Discussion

Conclusion