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ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

ISRA FACTSHEETS

NEW ZEALAND & PACIFIC ISLANDS REGION

Kāne’ohe Bay ISRA

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Kāne’ohe Bay ISRA

Kāne’ohe Bay

Summary

Kāne’ohe Bay is located on the east coast of O’ahu in the Hawaiian Islands of the United States of America. The area includes a small island and is characterised by its extensive barrier coral reef, mangrove forests, and seagrass beds. The area overlaps with the Hamakua Marsh Complex Ramsar site. Within this area there are: threatened species (e.g., Brown Stingray Bathytoshia lata); reproductive areas (e.g., Scalloped Hammerhead Sphyrna lewini); and feeding areas (Reef Manta Ray Mobula alfredi).

Kāne’ohe Bay

Kāne’ohe Bay

DESCRIPTION OF HABITAT

Kāne’ohe Bay is located on the east coast of O’ahu in the Hawaiian Islands of the United States of America. The bay is bordered by the Ko’olau Mountain Range to the west and the Pacific Ocean to the east and includes Coconut Island, a small island in the southeast part of the bay (Bush 2003). Kāne’ohe Bay is characterised by its extensive barrier coral reef, one of only two in the Hawaiian archipelago, along with over 100 patch reefs that create diverse sheltered, shallow marine habitats (Hunter & Evans 1995). The bay’s bathymetry includes shallow reef areas and deeper channels, with a maximum depth of ~20 m (Dale et al. 2011). The barrier reef runs parallel to the coastline, forming a natural breakwater that protects the bay from ocean swells, contributing to its calm waters (Hunter & Evans 1995). The patch reefs vary in size and structure, supporting both benthic and pelagic species. The bay’s coastline also features mangrove forests and seagrass beds, which serve as important nursery habitats for various marine organisms (Duncan & Holland 2006).

Freshwater inputs from surrounding streams and tidal exchange with the open ocean shape Kāne’ohe Bay’s oceanography (Ringuet & Mackenzie 2005; Tanaka et al 2013). The bay experiences semi-diurnal tides, which influence water circulation and nutrient cycling, supporting the bay’s productivity (Tanaka et al 2013). Periodic plankton blooms, driven by nutrient inputs and upwelling, sustain rich biodiversity within the bay’s waters (Ringuet & Mackenzie 2005). Mixing freshwater with the bay’s saline waters creates a unique planktonic environment, supporting diverse communities of phytoplankton and zooplankton (Ringuet & Mackenzie 2005).

The area overlaps with the Kawainui and Hamakua Marsh Complex Ramsar site (RAMSAR 2024).

This Important Shark and Ray Area is benthic and pelagic and is delineated from inshore and surface waters (0 m) to 20 m based on the bathymetry of the area.

CRITERION A

VULNERABILITY

Three Qualifying Species considered threatened with extinction according to the IUCN Red List of Threatened Species regularly occur in the area. These are the Critically Endangered Scalloped Hammerhead (Rigby et al. 2019); and the Vulnerable Brown Stingray (Jabado et al. 2021) and Reef Manta Ray (Marshall et al. 2022).

CRITERION C

SUB-CRITERION C1 – REPRODUCTIVE AREAS

Kāne’ohe Bay is an important reproductive area for one shark and one ray species.

Based on the ongoing presence of neonates and young-of-the-year (YOY) Scalloped Hammerhead since the 1970s (Clarke 1971), Kāne’ohe Bay has been proposed as a nursery area for the species. Between July–October 1990, six individuals (measuring between 47.8–53.5 cm total length [TL]; converted from fork length based on Holland et al. 1993) were actively tracked (9–72 hours) and showed high residence to the area (Holland et al. 1993). Size-at-birth for this species is between 31–57 cm TL (Ebert et al. 2021), confirming that these individuals were neonates or YOY. Between 1995–1998, 779 individuals (median TL = 55.0 cm, range: 42.2–104.5 cm TL) were sampled with gillnets (2×30 m), and 136 (17.5%) had open umbilical scars (Bush 2003). Further, between 2000–2002 juvenile Scalloped Hammerhead (n = 4,120), including neonates with open umbilical scars and YOY were caught with handlines and tagged in the area (Duncan & Holland 2006). Neonate and YOY were caught between late May and early September, with higher catch rates found in deeper parts of the bay, which had muddy and silt substrates (Duncan & Holland 2006). Presence of these life-stages is higher in the boreal summer and decreases in the winter, which seems to be related to starvation-induced mortality due to high daily food requirements (Lowe 2001, 2002; Bush & Holland 2002; Bush 2003; Duncan & Holland 2006). Based on mark-recapture models, it has been estimated that ~10,000 pups are born each spring in the area (Duncan & Holland 2006) and even if pup mortality is very high (90%), survivors stay in Kāne’ohe Bay for 1-2 years before emigrating (Duncan & Holland 2006). These life-stages are still regularly and predictably observed by scientists and caught by recreational fishers in the area during the summer months (J Hartl pers. obs. 2024).

Between August 2006–December 2010, 544 Brown Stingrays were caught in the area using longlines (Dale 2011). Vertebral samples were collected for 203 of these individuals that measured between 35–133 cm disc width (DW). Of these, 13 measured 35–45 cm DW, and according to growth band readings, were neonates or YOY that were captured in May and June (Dale 2011; Dale et al. 2011). These sizes are similar to the reported size-at-birth for this species (35 cm DW; Last et al. 2016). In addition, 159 were classified as juveniles measuring <95 cm DW (Dale 2011). Stable isotope analysis (bulk and amino acids) and stomach content analysis of 156 juvenile Brown Stingrays revealed long-term foraging fidelity and high residency to the bay for small individuals (35–55 cm DW) with a shift to foraging in offshore areas when reaching sexual maturity (Dale et al. 2011).

CRITERION C

SUB-CRITERION C2 – FEEDING AREAS

Kāne’ohe Bay is an important feeding area for one ray species.

Between 2004–2024, 96 Reef Manta Rays were identified around the island of O’ahu using photographic identification (photo-ID). In total, 456 sightings of these individuals have been confirmed via photo ID, with 80% of sightings recorded since dedicated researcher surveys began in 2021 (n = 366; O’ahu Manta Project unpubl. data 2024).

Between 2021–2024, 83 sightings of Reef Manta Rays were recorded in Kāne’ohe Bay (22.7% of the total sightings around the island; O’ahu Manta Project unpubl. data 2024). During this time, 46 dedicated researcher surveys were conducted, and feeding was observed during 78% of surveys. Observations are mostly of surface feeding, with group size ranging from 1–10 individuals, with an average of 3–4 individuals per sighting. In addition to sightings confirmed via photo-ID, there are numerous anecdotal reports each year of Reef Manta Rays observed feeding in the area, with the species confirmed from a vessel via photographs, but without individual identification (O’ahu Manta Project unpubl. data 2024). For example, during 2022 and 2023, 84 additional sightings were recorded from anecdotal sources in the area.

Using a combination of dedicated research surveys and citizen science contributions, 36 individuals were recorded in the area, highlighting the small resident population (O’ahu Manta Project unpubl. data 2024). No records of inter-island connectivity have been documented, despite collaboration between manta ray research projects using genetics and photo-ID techniques (Deakos et al. 2011, Whitney et al. 2023, C Nevels pers. obs. 2024). Of the 30 individuals identified in the area since dedicated surveys began in 2021, 14 were confirmed as adults and the others of unknown maturity, although notably larger in size than at other aggregation sites in O’ahu. There are also opportunistic reports of courtship behaviour from Kāne’ohe Bay. Other areas around O’ahu have higher frequencies of juveniles observed suggesting there is some degree of habitat segregation between age classes, however, more information is needed to confirm whether this area is also important for reproduction.

Kāne’ohe Bay

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