Discovery of an important aggregation area for endangered scalloped hammerhead sharks, Sphyrna lewini, in the Rewa River estuary, Fiji Islands

Abstract

The scalloped hammerhead shark, Sphyrna lewini, is endangered throughout its global distribution. Management and protection of this species is challenging in many locations because of limited scientific data and the vulnerable life-history traits of the species. Our study investigated anecdotal evidence that the Rewa River estuary in Fiji serves as an important nursery area for this shark. Research findings indicated that the average length of both males (60.6 ± 6.78 cm, n = 31) and females (60.4 ± 6.85 cm, n = 51) was well within published size limits of juvenile S. lewini studied in other locations (range = 38.0–89.5 cm). On the basis of published reference points for umbilical scar status we postulate that the first captured juveniles were born in January of the study year. Stomach content analysis found the following prey items: Decapoda (represented by prawns and shrimps), Stomatopoda, anguilliformes and osteichthyes. Decapods were the most numerous prey item by both count (59.17% of total prey items) and weight (60.25% of total weight). Our study provides strong support that the Rewa River estuary is an important aggregation area for S. lewini in Fiji.

Discovery of a multispecies shark aggregation and parturition area in the Ba Estuary, Fiji Islands

“…As exclusively juvenile sharks were encountered, it is likely that the studied nearshore environment constitutes another parturition ground in Fiji (Brown et al., ; Cardeñosa et al., ; Marie et al., ). Size ranges of C. limbatus and S. lewini (66 ± 4 and 52 ± 5 cm, respectively) were in accordance with size ranges of neonate and young‐of‐the‐year sharks from previously published studies (Castro, ; Castillo‐Géniz, Márquez‐Farias, Rodriguez de la Cruz, Cortés, & Cid del Prado, ; Brown et al., for S. lewini ). For example, size of newborn C. limbatus range between 55 and 65 cm total length (Castillo‐Géniz et al., ; Castro, ).…”

“…The significant time trend in healing of scars and increase in length observed over the study period for C. limbatus and S. lewini both suggest a seasonal monotonic growth of juveniles in the Ba Estuary from December to April, with births taking place rather at the beginning of this time frame. In Australia, births of S. lewini were observed between September and February (Miller et al., ), while another study conducted in the Rewa River Delta in southern Viti Levu describes individuals with semihealed scars caught in February and March (Brown et al., ). Although the current study did not sample during the months of May to November, the greatest numbers of individuals with an open umbilical scar were captured in December, followed by declining numbers in January and February, and zero catches in March and April.…”

“…Using data collected from dive operators, citizen scientists and local fishermen, an increasingly clear picture of shark species abundance throughout Fiji is emerging (Brunnschweiler, Abrantes, & Barnett, 2014; Glaus, Adrian-Kalchhauser, Burkhardt-Holm, White, & Brunnschweiler, 2015;Rasalato, Maginnity, & Brunnschweiler, 2010;Ward-Paige, 2014). Specific locations with confirmed species occurrence in the scientific literature are only available for Viti Levu (Brown, Seeto, Lal, & Miller, 2016;Brunnschweiler & Earle, 2006;Cardeñosa, Glaus, & Brunnschweiler, 2017;Marie, Miller, Cawich, Piovano, & Rico, 2017) and Vanua Levu (Goetze & Fullwood, 2013), the two largest islands of Fiji. In the former case, this has led to the establishment of the Shark Reef Marine Reserve, Fiji's first national marine park, and the Fiji Shark Corridor which comprises approximately 30 miles of coastline (Brunnschweiler, 2010).…”

Crossing lines: a multidisciplinary framework for assessing connectivity of hammerhead sharks across jurisdictional boundaries

“…This information is summarised below.

Size and sex structure data indicate that few adult females (and especially pregnant females) occur in northern Australia, but are regularly caught in Indonesia and PNG. Considering that hammerheads sharks in other regions move to shallow nursery areas to give birth314445, this population structure suggests that a proportion adult females may migrate from Australia to Indonesia and PNG, but return to give birth to their young in nursery areas in coastal areas of northern Australia4647.

There is genetic evidence of mixing between Australian and Indonesian animals48. Current genetic analysis only provides evidence of a connection on evolutionary time scales (although it does not discount connections at shorter time scales).…”

“…Considering that hammerheads sharks in other regions move to shallow nursery areas to give birth314445, this population structure suggests that a proportion adult females may migrate from Australia to Indonesia and PNG, but return to give birth to their young in nursery areas in coastal areas of northern Australia4647.…”