Jesse E. M. Cochran

Movement Patterns of Juvenile Whale Sharks Tagged at an Aggregation Site in the Red Sea

Conservation efforts aimed at the whale shark, Rhincodon typus, remain limited by a lack of basic information on most aspects of its ecology, including global population structure, population sizes and movement patterns. Here we report on the movements of 47 Red Sea whale sharks fitted with three types of satellite transmitting tags from 2009–2011. Most of these sharks were tagged at a single aggregation site near Al-Lith, on the central coast of the Saudi Arabian Red Sea. Individuals encountered at this site were all juveniles based on size estimates ranging from 2.5–7 m total length with a sex ratio of approximately 1∶1. All other known aggregation sites for juvenile whale sharks are dominated by males. Results from tagging efforts showed that most individuals remained in the southern Red Sea and that some sharks returned to the same location in subsequent years. Diving data were recorded by 37 tags, revealing frequent deep dives to at least 500 m and as deep as 1360 m. The unique temperature-depth profiles of the Red Sea confirmed that several whale sharks moved out of the Red Sea while tagged. The wide-ranging horizontal movements of these individuals highlight the need for multinational, cooperative efforts to conserve R. typus populations in the Red Sea and Indian Ocean.

Whale sharks target dense prey patches of sergestid shrimp off Tanzania

Large planktivores require high-density prey patches to make feeding energetically viable. This is a major challenge for species living in tropical and subtropical seas, such as whale sharks Rhincodon typus. Here, we characterize zooplankton biomass, size structure and taxonomic composition from whale shark feeding events and background samples at Mafia Island, Tanzania. The majority of whale sharks were feeding (73%, 380 of 524 observations), with the most common behaviour being active surface feeding (87%). We used 20 samples collected from immediately adjacent to feeding sharks and an additional 202 background samples for comparison to show that plankton biomass was ∼10 times higher in patches where whale sharks were feeding (25 vs. 2.6 mg m−3). Taxonomic analyses of samples showed that the large sergestid Lucifer hanseni (∼10 mm) dominated while sharks were feeding, accounting for ∼50% of identified items, while copepods (<2 mm) dominated background samples. The size structure was skewed towards larger animals representative of L.hanseni in feeding samples. Thus, whale sharks at Mafia Island target patches of dense, large, zooplankton dominated by sergestids. Large planktivores, such as whale sharks, which generally inhabit warm oligotrophic waters, aggregate in areas where they can feed on dense prey to obtain sufficient energy.

The abundance of herbivorous fish on an inshore Red Sea reef following a mass coral bleaching event

A healthy herbivore community is critical for the ability of a reef to resist and recover from severe disturbances and to regain lost coral cover (i.e., resilience). The densities of the two major herbivorous fish groups (the family Acanthuridae and scarine labrids) were comparatively studied for an inshore reef that was severely impacted by a mass coral bleaching event in 2010 and an unaffected reef within the same region. Densities were found to be significantly higher on the affected reef, most likely due to the high algal densities on that reef. However, densities of herbivores on both reefs were found to be on average about 1–2 orders of magnitude lower than previously published reports from some Pacific reefs and from Red Sea reefs in the Gulf of Aqaba and only slightly higher than Caribbean reefs. Thus, it is predicted that recovery for this reef and similarly affected reefs may be very slow. The protection of herbivores from overfishing and the introduction of other management strategies that maximize reef resilience in Saudi Arabian waters are highly recommended.

First record of the Pigeye Shark, Carcharhinus amboinensis (Müller & Henle, 1839) (Carcharhiniformes: Carcharhinidae), in the Red Sea

The shark fauna of the Red Sea is believed to be remarkably depauperate with three orders, 10 families and highly variable species richness estimates (29 by COMPAGNO 1983, 31 by BONFIL & ABDALLAH 2004 and 40 by STAFFORD-DEITSCH 1999). The most recent reappraisal describes 28 species, of which 16 are Carcharhinids (GOLANI & BOGORODSKY 2010). Data available in the literature are very poor and result almost exclusively from research conducted in the Gulf of Aqaba, including studies on shark taxonomy (BARANES & SHAHRABANYBARANES 1986) and occurrence (e.g. BARANES & BEN-TUVIA 1978a, b, c, GOHAR & MAZHAR 1964). Information essential for stock management, e.g. data on their ecology and life histories, is non-existent. This apparent lack of both historic as well as recent shark research in the Red Sea may have led to incomplete species accounts. In October 2010, a small male specimen of a Pigeye Shark (also known as Java Shark), Carcharhinus amboinensis (Müller & Henle 1839) (Fig. 1), was encountered at the fish market in Jeddah, Saudi Arabia, and purchased for further examination. The shark’s vendor stated that it was originally landed in Al-Qunfudah (approximately 19°07’N, 41°05’E), about 330 km south of Jeddah. Fleets landing their catches in Al-Qunfudah consist exclusively of Red Sea artisanal fishermen who fish national waters between Jizan (16°53’N, 42°33’E) and the Farasan islands (16°47’N, 42°5’E) (Talal ABUSHUSHA, KSA Fisheries Research Center, pers. comm.). The specimen measured 89 cm total length (PCL: 68 cm, FL: 74 cm), first and second dorsal fin heights were 95 mm and 27 mm, respectively. 11 teeth were counted on either side of the lower jaw (Fig. 2) and a vertebral count, made by dissection, revealed 92 precaudal vertebrae. Based on the fishing hook found during the dissection, the specimen was most likely caught on a hand line. An undigested fusilier species (Caesionidae), which is thought to have served as bait fish, together with unidentified pieces of fish in various states of digestion, were contained in its stomach.

Population structure of a whale shark Rhincodon typus aggregation in the Red Sea.

The presence of whale sharks Rhincodon typus were recorded around Shib Habil, a small, coastal reef off the Red Sea coast of Saudi Arabia, from 2010 to 2015. A total of 267 suitable photographs resulting in the identification of 136 individuals, were documented from 305 encounters. Sharks were divided evenly between the sexes with no evidence of temporal or spatial segregation. All individuals were immature based on size estimates and, for males, juvenile clasper morphology. Scars were reported for 57% of R. typus with 15% showing evidence of propeller trauma. Estimates of population size and patterns of residency were calculated by modelling the lagged identification rate. Multiple models were run simultaneously and compared using the Akaike information criterion. An open population model was found to best represent the data and estimates a daily abundance between 15 and 34 R. typus during the aggregation season, with local residence times ranging from 4 to 44 days. Residence times away from Shib Habil range from 15 to 156 days with a permanent emigration-death rate between 0·07 and 0·58 individuals year(-1) . These results are broadly similar to those from other aggregations of R. typus, although the observed sexual parity and integration found at this site is unique for the species and needs further study.