Occurrence of juvenile bull sharks (Carcharhinus leucas) in the Navua River in Fiji

Cardeñosa, Diego; Glaus, Kerstin B. J.; Brunnschweiler, Juerg M.

doi:10.1071/mf16005

Cited by 12 publications

(18 citation statements)

References 29 publications

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“…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 ).…”

Section: Discussionmentioning

confidence: 99%

“…While only two could be measured (76.1 cm, 78.2 cm), fishermen confirmed fairly regular catches of small sharks of different species within the river during informal discussions and interview sessions. Bull sharks are classified as “Near Threatened” (Simpfendorfer & Burgess, ) and despite having been documented in other river systems of Fiji (Cardeñosa et al., ), no scientific record had been made in the study area before.…”

Section: Discussionmentioning

confidence: 99%

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

Vierus

Gehrig

Brunnschweiler

et al. 2018

Ecology and Evolution

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Population declines in shark species have been reported on local and global scales, with overfishing, habitat destruction and climate change posing severe threats. The lack of species‐specific baseline data on ecology and distribution of many sharks, however, makes conservation measures challenging. Here, we present a fisheries‐independent shark survey from the Fiji Islands, where scientific knowledge on locally occurring elasmobranchs is largely still lacking despite the location's role as a shark hotspot in the Pacific. Juvenile shark abundance in the fishing grounds of the Ba Estuary (north‐western Viti Levu) was assessed with a gillnet‐ and longline‐based survey from December 2015 to April 2016. A total of 103 juvenile sharks identified as blacktip Carcharhinus limbatus (n = 57), scalloped hammerhead Sphyrna lewini (n = 35), and great hammerhead Sphyrna mokarran (n = 11) sharks were captured, tagged, and released. The condition of umbilical scars (68% open or semihealed), mean sizes of individuals (±SD) (C. limbatus: 66.5 ± 3.8 cm, S. lewini: 51.8 ± 4.8 cm, S. mokarran 77.4 ± 2.8 cm), and the presence of these species over recent years (based on fishermen interviews), suggest that the Ba Estuary area is a critical habitat for multiple species that are classified as “Near Threatened” or “Endangered.” Specifically, the area likely acts as a parturition ground over the studied period, and potentially as a subsequent nursery area. We identified subareas of high abundance and found that temperature, salinity and depth acted as small‐scale environmental drivers of shark abundance. The data suggests a tendency for species‐specific spatial use, both horizontally (i.e., between sampling areas) and vertically (i.e., across the water column). These results enhance the understanding of shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of these threatened species.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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

Vierus

Gehrig

Brunnschweiler

et al. 2018

Ecology and Evolution

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“…The large majority of the species found in small fins (93.1%) inhabit coastal habitats (Yokota & Lessa, ; Carlson et al ., ; Yates et al ., ) and were either small species (62.9%), or large species captured as juveniles (at least 91.8% of the fins identified from large species). Many of the large species found in our small fin survey have been reported to use shallow coastal areas as juveniles, which frequently overlap with habitats used by small shark species (Simpfendorfer & Milward, ; Carlson & Brusher, ; Duncan & Holland, ; Yokota & Lessa, ; Yates et al ., ; Cardeñosa et al ., ). Therefore, it is possible that many of the small fins found in this preliminary survey are sourced from multi‐species fisheries in shallow, coastal habitats used by large species and also occupied by small species.…”

Section: Discussionmentioning

confidence: 99%

Small fins, large trade: a snapshot of the species composition of low‐value shark fins in the Hong Kong markets

Cardeñosa

Shea²,

Zhang³

et al. 2019

Animal Conservation

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The international fin trade is a major source of mortality for many threatened shark species but most of what it is known about this trade comes from assessments of large fins commanding high prices in trade hubs. There is growing international trade in ‘small, low‐value’ fins in Southeast Asia, which are used for inexpensive shark fin soup products. These fins could be derived from small species, juveniles of large species, or a combination of both. Resolving the species identification of these small fins has important conservation implications, because large sharks tend to be more vulnerable (VU) to overexploitation than small ones. Here we describe the first species‐specific assessment of the small, low‐value fins in the shark fin retail markets of Hong Kong. A total of 475 randomly collected samples were genetically identified using a portion of the cytochrome oxidase I, revealing at least 29 species. Around a third (34.5%) of the species found are in threatened International Union for the Conservation of Nature Red List categories, and 21.2% of the samples were from four species listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). The size of the analyzed fins and the species composition found suggests that small fins come from a combination of small (62.9 %) and large (37.1%) species, with the majority of small fins coming from suspected juveniles of large species. We suggest the sources of most of these fins are likely to be multi‐species fisheries in shallow, coastal habitats used by large species and also occupied by small species. Our results represent the first step to better understand the trade in small shark fins on a species‐specific basis and highlight the need for market surveys and increased inspection of this fin category at border control check points for CITES‐listed species.

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“…Subsequently, sampling sites within the Rewa and Sigatoka Rivers (see below in the fishery‐independent surveys) were chosen following fishermen's local ecological knowledge (Rasalato et al, ) who suggested areas where they previously caught sharks and upon recommendations by the Ministry of Fisheries and Forests. The sampling scheme in the Navua River was similar to the one applied in Cardeñosa et al ().…”

Section: Methodsmentioning

confidence: 99%

“…The latter study documented three juvenile bull sharks caught several kilometers upstream in the Ba River. Juvenile bull sharks were also confirmed in the Navua River close to the Shark Reef Marine Reserve (SRMR) where large adult bull sharks are abundant (Brunnschweiler, Abrantes, & Barnett, ; Cardeñosa, Glaus, & Brunnschweiler, ). In addition to these observed occurrences, results from an interview‐based survey documented small sharks in all of Fiji's major rivers (Rasalato, Maginnity, & Brunnschweiler, ) suggesting that in particular Fiji's largest riverine systems, the Rewa and Sigatoka Rivers on the southern coast of Viti Levu represent EFH for young bull sharks.…”

Section: Introductionmentioning

confidence: 99%

Essential waters: Young bull sharks in Fiji's largest riverine system

Glaus

Brunnschweiler

Piovano

et al. 2019

Ecology and Evolution

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Coastal and estuarine systems provide critical shark habitats due to their relatively high productivity and shallow, protected waters. The young (neonates, young‐of‐the‐year, and juveniles) of many coastal shark species occupy a diverse range of habitats and areas where they experience environmental variability, including acute and seasonal shifts in local salinities and temperatures. Although the location and functioning of essential shark habitats has been a focus in recent shark research, there is a paucity of data from the South Pacific. In this study, we document the temporal and spatial distribution, age class composition, and environmental parameters of young bull sharks ( Carcharhinus leucas ) in the Rewa, Sigatoka, and Navua Rivers, Fiji's three largest riverine systems. One hundred and seventy‐two young bull sharks were captured in fisheries‐independent surveys from January 2016 to April 2018. The vast majority of the captures were neonates. Seasonality in patterns of occurrence of neonate individuals suggests a defined parturition period during summer. Environmental parameters between the Rewa and the Sigatoka River differed significantly, as did the recorded young bull sharks abundance. According to the surveys, young bull sharks occur in all three rivers with the Rewa River likely representing essential habitat for newly born bull sharks. These results enhance the understanding of bull shark ecology in Fiji and provide a scientific basis for the implementation of local conservation strategies that contribute to the protection of critical habitats.

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Occurrence of juvenile bull sharks (Carcharhinus leucas) in the Navua River in Fiji

Cited by 12 publications

References 29 publications

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

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

Small fins, large trade: a snapshot of the species composition of low‐value shark fins in the Hong Kong markets

Essential waters: Young bull sharks in Fiji's largest riverine system

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