ISRA FACTSHEETS
ISRA FACTSHEETS
WESTERN INDIAN OCEAN REGION
Kilindoni Bay
Summary
Kilindoni Bay is located on the western side of Mafia Island in Tanzania. The Rufiji River Delta on the nearby mainland of Tanzania influences the area by discharging nutrient-rich waters into the bay. The area is characterised by shallow waters with sandy substrate, mangroves, and patches of subtidal seagrass. Highly dense patches of sergestid shrimp zooplankton form in the area. The area overlaps with the Rufiji-Mafia-Kilwa Ecologically or Biologically Significant Marine Area, and partly overlaps with the Mafia Island Key Biodiversity Area, and the Mafia Island Marine Park. Within the area there are: threatened species (e.g., Jenkins’ Whipray Pateobatis jenkinsii); feeding areas (Whale Shark Rhincodon typus); and undefined aggregations (Jenkins’ Whipray).
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Kilindoni Bay
DESCRIPTION OF HABITAT
Kilindoni Bay is on the western side of Mafia Island in Tanzania. The bay faces the Rufiji River Delta and the Tanzanian mainland to the west. Most of the shore is lined by mangroves, and subtidal seagrass beds in some areas. The main substrate of the area is shallow <30 m sand, with some small coral rubble areas interspersed. The area is mainly influenced by the East African Coastal Current and monsoon winds. Southern monsoon winds (May–September) are stronger than northeast monsoon winds (November–March) and lead to higher productivity (Painter 2020). In addition, nutrient- and sediment-rich water discharge from the Rufiji River Delta influences patterns of productivity in the area, and the underwater visibility is often poor (Temple & Sundborg 1972). Sergestid shrimp zooplankton regularly form dense patches in the area, particularly in October–February, supporting abundant schools of small- to large planktivorous pelagic fishes (Rohner et al. 2015a).
Kilindoni Bay overlaps with the Rufiji-Mafia-Kilwa Ecologically or Biologically Significant Marine Area (EBSA; CBD 2023). A small part in the south of the area overlaps with the Mafia Island Key Biodiversity Area (KBA; KBA 2023) and with the Mafia Island Marine Park. The area falls under the Dokichunda Community Collaborative Fishing Management Area (CFMA) (URT 2023).
This Important Shark and Ray Area is benthopelagic and extends from inshore and surface waters (0 m) to 30 m, based on the distribution of the Qualifying Species.
CRITERION A
VULNERABILITY
Two Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened SpeciesTM regularly occur in the area. These are the Endangered Whale Shark (Pierce & Norman 2016) and the Vulnerable Jenkins’ Whipray (Manjaji Matsumoto et al. 2020).
CRITERION C
SUB-CRITERION C2 – FEEDING AREAS
Kilindoni Bay is an important feeding area for one shark species.
Whale Sharks aggregate in the area to feed on sergestid shrimp zooplankton (Rohner et al. 2015a). Boat-based surveys were conducted each year from 2012 to 2022 during October to February. All Whale Sharks encountered were photographically identified in-water, their sex was determined, and the total length (TL) visually estimated. Over the 385 surveys, 2,148 encounters (mean = 5.6 per survey) of 222 individuals were recorded. Whale Sharks ranged from 250–950 cm TL with a mean of 610 cm TL, and 88% were males (C Rohner unpubl. data, updated from Rohner et al. 2015b).
Up to 49 photographically identified individuals were seen feeding in an aggregation and on 75% of all encounters (C Rohner unpubl. data 2023). When the sharks were feeding, the size of their aggregation was larger (mean = 8.7 individual per survey) than when they were not feeding (2.6 individuals). Feeding was recorded in all surveyed months and every year. A dedicated zooplankton study in 2012–2013, consisting of 202 background zooplankton and 20 Whale Shark feeding samples, showed that Whale Shark target dense prey patches of the sergestid shrimp Belzebub hanseni (Rohner et al. 2015a). Background samples collected at four stations in Kilindoni Bay when no feeding individuals were present had ~10-times less biomass and were dominated by copepods. The same sergestid prey has consistently been recorded in opportunistic samples collected for biochemical analyses since that study (C Rohner unpubl. data 2023). Additional information from local ring-net fishers operating outside the bay in an area between Mafia Island and the mainland suggest that Whale Sharks are rarely feeding in the southern part of the area. It is possible that the onset of the north-east monsoon, which coincides with the start of the Whale Shark season, influences this feeding aggregation by concentrating the sergestid zooplankton in Kilindoni Bay.
Individual Whale Sharks show high residency in Kilindoni Bay, indicating that this feeding aggregation is important for them. Compared to most other areas, Whale Sharks are unusually resident to this small bay off Mafia Island (Cagua et al. 2015, Rohner et al. 2020). A passive acoustic telemetry study from 2012–2018 with 20 receivers and 67 tags (mean tracking duration = 307 days, up to 4.5 years) showed that Whale Sharks were detected in Kilindoni Bay throughout the year (Rohner et al. 2020). A higher proportion of tagged Whale Sharks (> 85%) were detected at least once per month from October–February, when feeding aggregations were observed. Nevertheless, > 67% of tagged individuals were still detected in the other months over three consecutive years while at least five individuals were tagged. On a daily scale, tagged Whale Sharks were detected in Kilindoni Bay on a mean of 39% of days while their tag was attached. Many of the tagged animals continued to be photographically identified in the area after their tag had fallen off, further demonstrating the high importance of Kilindoni Bay to their ecology. Monthly kernel utilisation distributions showed that their hotspot of activity shifted from inshore in October–February to ~6 km offshore in March–September (Rohner et al. 2020). This shift supports the idea that the northeast monsoon plays a role in concentrating prey in the area during October–February when feeding aggregations have been observed.
CRITERION C
SUB-CRITERION C5 – UNDEFINED AGGREGATIONS
Kilindoni Bay is an important area for undefined aggregations of one ray species.
Based on fisheries landings monitoring between 2017–2018 and local ecological knowledge from fishers operating in Kilindoni Bay, Jenkins’ Whiprays are targeted in the area. Target locations are especially near Bwejuu island, mostly between November and March (Matiku 2018, 2020). The growing demand for their meat and liver oil has fuelled a targeted fisheries by these artisanal fishers. Animals are targeted in coastal sites where the species is known to occur and where aggregations are found (B. Kuguru pers. obs. 2023). Fishers report catches of 20–50 individuals at each location in a single net setting. This suggests that this species is aggregating in the area, but the function of these aggregations remains unknown. In addition, dozens of Jenkins’ Whipray can be landed in a single day in the area. According to surveys in mainland Tanzania and the Zanzibar Archipelago, much lower numbers are captured and landed in those areas, confirming the importance of Kilindoni Bay for this species.
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