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ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

Pagan Island ISRA

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Pagan Island ISRA

Pagan Island

Summary

Pagan Island is located on the volcanic Mariana Arch, in the northwestern Pacific Ocean. It is part of the Commonwealth of the Northern Mariana Islands, a self-governing commonwealth in association with the United States of America. The habitat is characterised by hard substrates and soft sediment. This area holds the greatest coral assemblage richness of the Northern Mariana Islands. Within this area there are: threatened species and reproductive areas (Grey Reef Shark Carcharhinus amblyrhynchos).

Pagan Island

Pagan Island

DESCRIPTION OF HABITAT

Pagan Island is located on the volcanic Mariana Arch, in the northwestern Pacific Ocean. It is part of the Commonwealth of the Northern Mariana Islands, a self-governing commonwealth in association with the United States of America. This uninhabited island, 52 km north of Alamagan and 65 km south of Agrihan, is isolated by steep slopes which extend to depths >3,000 m (Brainard et al. 2012). It is one of the most active volcanic islands in the Mariana Archipelago and is the fourth-largest island of the Northern Mariana Islands. Two large cone-shaped volcanoes formed this island, and a low-lying, narrow isthmus connects them (Brainard et al. 2012). The narrow isthmus that separates the two parts of this island is dominated by a narrow ridge with very steep slopes on either side. In general, habitats in the north and east regions consist of hard substrates supported by a moderate cover of live corals, and, in contrast, the south and west seabed is characterised by soft-sediment habitats that support very low levels of live coral cover (Brainard et al. 2012). Along with Agrihan Island, this area holds the greatest coral assemblage richness of the Northern Mariana Islands (Houk & Starmer 2009).

This Important Shark and Ray Area is delineated from surface waters (0 m) to 50 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

One Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occurs in the area. This is the Endangered Grey Reef Shark (Simpfendorfer et al. 2020).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Pagan Island is an important reproductive area for one shark species.

Observations of Grey Reef Sharks have been made from historical and contemporary towed-diver surveys (TDS) and stationary point count (SPC) surveys conducted around the island. The TDS method involves two divers being towed behind a boat (~2.2 km track). The diver at ~15 m depth recorded the number, size (TL), and species of all fishes measuring >50 cm total length (TL) within a 20,000 km2 area (Brainard et al. 2012). The SPC method involves two divers counting fish in 15-meter-diameter plots each, covering smaller areas (~350–600 m2). The SPC survey is a comprehensive small-scale survey approach, thus, aggregations, and rare and patchily distributed species are not well surveyed (Brainard et al. 2012). Aggregations of neonates and young-of-the-year (YOY) Grey Reef Sharks were recorded in the area. These were determined to be neonates and YOY based on the size-at-birth of this species (45–60 cm total length [TL]; Ebert et al. 2021).

Between 2009–2017, 59 TDS were conducted in the area (April 2009 = 15 dives; April 2011 = 14; April 2014 = 11; May 2017 = 5; June 2017 = 19) (CREP PIFSC 2017a, 2017b, 2017c). In 2017, a total of 58 Grey Reef Sharks were counted during the surveys (range 50–90 cm TL) of which the majority (n = 51) were part of three aggregations recorded in different dives. The first comprised 41 YOY (range 75–85 cm TL), and the other two were formed by five neonates and YOY each (range 50–75 cm TL, average 60.5 cm TL) (CREP PIFSC). During an SPC survey in 2017, an aggregation of 30 YOY Grey Reef Sharks (75–85 cm TL) was recorded (CREP PIFSC 2017d), and one additional aggregation of five juveniles was recorded (range 130–150 cm TL) (CREP PIFSC 2017d). In 2009, two small juveniles (80 cm TL) were recorded together in one TDS (CREP PIFSC 2017a).

Only two Grey Reef Sharks larger than 150 cm TL were reported in the area, and except for one aggregation of larger juveniles in 2017, all other aggregations observed were formed by neonates or YOY (50–85 cm TL) (CREP PIFSC 2017a, 2017b, 2017c). Considering the depth range of the Grey Reef Shark, the coral reef association and the estimated 6.2 km2 (1.4–10.8 km2) home range (Bonnin et al. 2021), aggregations of neonates and YOY in the area support the critical importance of the area the reproductive success of Grey Reef Sharks. However, further information is required to understand the timing of pupping in this area since all surveys were conducted between April–July (CREP PIFSC 2017a, 2017b, 2017c).

Pagan Island

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