A synthesis of the existing scientific data on the coral reefs in the southern Gulf of Carpentaria

Overview

Marine Protected Areas (MPAs) are globally recognised as valuable tools for marine conservation and resource management, and scientific studies have shown that they provide a range of ecological, economic and social benefits. As coral reefs and other marine ecosystems face escalating threats, including climate change, overfishing, and habitat degradation, there is an increasing need for establishing more MPAs to increase levels of protection. The Australian government is one of over 190 nations that have committed to the “30 by 30” initiative, which aims to protect at least 30% of terrestrial, freshwater, coastal, and marine areas by 2030.

The Gulf of Carpentaria Marine Park (GOCMP) was established in 2018 and is one in a comprehensive network of 60 offshore MPAs around Australia. It consists of a National Park Zone (or green zone) where no extractive activities are permitted, and two Special Purpose (Trawl) Zones (or blue zones) where recreational fishing is permitted, and commercial trawling and fishing are permitted with prior authorisation.

Most of the scientific research on coral reefs in Australia has been focused on the Great Barrier Reef, and more recently on Ningaloo Reef in western Australia, and there has been very little research on coral reefs in the Gulf of Carpentaria (GOC). This report presents the findings of a desktop study which aimed to summarise, synthesise and analyse the available scientific information in the southern GOC, within and around the GOCMP, in order to inform the 2028 management plan review of the GOCMP. The reefs in this region are deeply known and important to Indigenous communities in the Wellesley Islands, south of the GOCMP. Anecdotally, western researchers have previously visited Sea Country, including reefs, and failed to report their findings back to the Traditional custodians, so this report, and an accompanying summary sheet, aim to rectify this by returning the findings from all known western scientific research to the local community. While this western science data is extremely limited compared to the Indigenous knowledge of the area, it is hoped that it will help to inform and empower Traditional custodians when making decisions on future management and research priorities.

The scientific research examined included bathymetric mapping of the reefs in this region. Between 2003 and 2005, multibeam sonar surveys conducted by Geoscience Australia identified and mapped seven submerged reefs in the southern GOC, four of which are in the GOCMP. These reefs have minimum depths of 18–20 m and vary in size and structure. There are large, submerged shoals or patch reefs, and submerged pinnacles with steep sides either rising from the seafloor or from a large platform made up of other smaller bommies and pinnacles.

Three biological studies on coral reefs were also examined in this region. The first two, one in 1997–1998 and the other in 2002, conducted visual observations and collections of coral reef fishes around the Wellesley Islands and produced species lists and estimates of relative abundance. The third was a series of surveys of benthic organisms and habitats, fish and mobile invertebrates carried out by the Reef Life Survey (RLS) program in 2010 and 2015 as part of a larger survey of the reefs in the North Commonwealth Marine Reserves Network. These surveys included five offshore sites within the blue zones of the GOCMP, three of which have been mapped by Geoscience Australia, as well as an additional three offshore sites outside the GOCMP, and six nearshore, fringing reef sites around Mornington Island. Coral cover ranged from 10 to 40%, with considerable variation among sites. There were no differences in coral cover between offshore and nearshore reefs or between reefs within the GOCMP and those outside the park.

The density, biomass and species richness of reef fishes were higher at offshore reefs compared to nearshore reefs, but there were no differences between reefs within and outside the GOCMP. Species composition of reef fish communities differed between offshore and nearshore reefs. Of the three offshore reefs outside the GOCMP, one had a fish species composition similar to the five reefs inside the park, while the other two differed. When compared with RLS data from other sites around the GOC, reefs in the southern GOC had similar ranges for coral cover and fish metrics to reefs elsewhere in the GOC. Species composition of fish communities in the southern GOC was distinct from those at other RLS sites at similar latitudes in the Great Barrier Reef and Western Australia, and comprised a combination of widespread Indo-Pacific species, species found mainly in northern Australia and species found mainly in the GOC and northwestern Australia.

Apparent fishing effort data for the southern GOC in the last 10 years extracted from Global Fishing Watch indicates that fishing activity within the Special Purpose (Trawl) Zones of the GOCMP has been relatively low compared to areas closer to the coast. Although there was some apparent fishing activity in the Green Zone of the GOCMP, this was very low, ranging from 0 to 26 hours per year. However, this data is based on Automatic Identification System (AIS) data and should be treated as a conservative estimate, given that AIS is compulsory only for larger vessels and is less likely to be carried or consistently transmitted by small-scale, domestic, or nearshore fishing vessels.

Our findings highlight that there are unique coral reef systems in the southern GOC with relatively high coral cover on some reefs and differences in the fish communities between deep offshore reefs and shallower nearshore reefs. The fish communities are also unique and composed of a mixture of species found on the GBR and in northwestern Australia.

The following knowledge/research gaps were identified:

• No mapped reefs or complete surveys of the full extent of reef development in the region.
• No scientific studies on reefs within the National Park Zone of the GOCMP provide comprehensive assessments of the abundance and biodiversity of the coral reef flora and fauna.
• No regular, repeated ecological monitoring surveys on the reefs in and around the GOCMP.
• No systematic evaluation of an MPA network designed to maximise protection of the majority of coral reef species in the region.