Broken Water Bay and Sepik River is an important area for undefined aggregations of one ray species.

Fishery observations and local ecological knowledge surveys conducted during three separate surveys (April 2017, September–November 2017, March 2018) indicate that the area is regionally important for various size classes of Narrow Sawfish (Leeney et al. 2018; Grant et al. 2021). Due to the remoteness of the area, no further fishery observation data are available, however, regular catches of Narrow Sawfish across the whole lifetime of fishers in the area were reported (Leeney et al. 2018).

During September–November 2017, catch landing observations of fishers using primarily gillnets of varied mesh sizes to target croakers (Sciaenidae), Barramundi (Lates calcarifer), sharks, and rays were conducted in the area (Grant et al. 2021). Narrow Sawfish (n = 13) were observed from the mouth of both the Sepik and Ramu Rivers measuring 100–300 cm TL (Grant et al. 2021). During this survey, across three days in September, nine Narrow Sawfish measuring 100–223 cm TL were captured, including four individuals caught in a single net (Grant et al. 2021). Size-at-birth for the species is 43–70 cm TL, while maturity is reached at 200–225 cm TL (Last et al. 2016).

Additionally, in April 2017, 46 interviews were conducted from 12 villages along the Sepik, Keram, and Ramu Rivers (flowing into the area) and two additional sites along the coastline within the area where gillnets, longlines, and occasionally spear guns are used during fishing activities (Leeney et al. 2018). Fishers at Kopar Village report that Narrow Sawfish are regularly caught year-round at fishing sites adjacent to the Sepik River mouth, with higher catch rates reported in the drier months (~January–June) (Leeney et al. 2018). During local ecological knowledge interviews, one fisher suggested that 50–60 sawfish could be caught each week if their fishing group set all 15 of their 100–200 m gillnets each day (Leeney et al. 2018). In corroboration of this, in April 2017, five gillnets set in one day resulted in the capture of two Narrow Sawfish measuring 104 and 107 cm TL, indicating that these may be juvenile individuals.

The relatively low contemporary sample size of Narrow Sawfish in scientific studies in the area persists despite being regularly caught in the area, as rostra are infrequently retained (e.g., only five dried rostra from Narrow Sawfish were observed between Kopar and Marangis Village despite high observed catch rates [Leeney et al. 2018; Grant et al. 2021]). Further, the rostra that are retained are likely biased to larger individuals (M Grant pers. obs. 2024).

In a regional context, the Sepik and Ramu Rivers, and the coastal area around and inclusive of Broken Water Bay is the only region on the north coast of mainland Papua New Guinea where sawfish have historically been documented (White et al. 2017). Historic and contemporary data indicate that estuarine/marine waters of both the Sepik and Ramu Rivers support populations of Narrow Sawfish (White et al. 2017; Leeney et al. 2019; Grant et al. 2021). The northern coast of mainland Papua New Guinea has very limited continental shelf habitat and lacks the abundance of large floodplain river systems found in the country’s southern coastline. For this reason, it appears that the Broken Water Bay area, which receives outflow from both the Sepik and Ramu Rivers, supports what are potentially localised populations of this species. It is therefore inferred that the area supports a range of important ecological activities for this species, though further information is required to understand the nature and function of this aggregation.