Rick D Stuart-Smith, Daniela Ceccarelli, Graham J Edgar, Antonia T Cooper. Report to Parks Australia, Department of the Environment, 2017.

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• 2016 Biodiversity Surveys of the Cod Grounds and Pimpernel Rocks Commonwealth Marine Reserves

Executive summary

The Cod Grounds Commonwealth Marine Reserve (CMR) is located in Commonwealth waters approximately four nautical miles off the coast of New South Wales, encompassing three underwater pinnacles rising to ~18 m depth from a seabed 40 m deep.

This CMR is highly protected by a Marine National Park Zone (IUCN II).

The Solitary Islands are protected within NSW State waters within the boundaries of the Solitary Islands Marine Park, with areas further than 3 nautical miles from the islands protected by the Solitary Islands Commonwealth Marine Reserve.

Most of this CMR is classified as Multiple Use or Special Purpose Zone (IUCN VI), but Pimpernel Rock is highly protected by a Marine National Park Zone (IUCN II).

Pimpernel Rock is a submerged pinnacle that rises from the ocean floor to within 10 m of the surface.

It is an extremely significant feature of the Solitary Islands CMR, as it attracts large pelagic fishes, marine mammals, grey nurse sharks Carcharias taurus, black cod Epinephelus daemelii, and marine turtles.

Both the Cod Grounds and Pimpernel Rock CMRs are primarily recognised for providing key habitat for grey nurse sharks and black cod, which are protected under both NSW State and Commonwealth legislation.

This report describes patterns of reef biodiversity in the Cod Grounds and Pimpernel Rock CMRs and at a number of external reference sites.

It follows the 2009 baseline survey on the condition and biodiversity values of the Cod Grounds CMR.

The surveys of the Cod Grounds and Solitary Islands revealed:

• a dominance of temperate species in deeper areas, with more subtropical species in the shallows
• distinct depth stratification
• very high fish biomass, including exploited fish species
• a high abundance of grey nurse sharks during recent surveys of the CGCMR.

Depth stratification was found across all surveyed communities, including fishes, invertebrates and benthos.

Previous studies, including the Cod Grounds baseline survey, have also noted depth structuring along narrow bands, driven to some degree by the distribution and abundance of grazing sea urchins.

Spatial differences were also apparent between the Cod Grounds, Pimpernel Rock and the Solitary Islands sites. The Solitary Islands sites chosen as reference sites for the CMR (Pimpernel Rock) were as similar as possible in wave exposure and underlying habitat structure, however, they were much shallower than the Cod Grounds and Pimpernel Rock sites.

The fish community at the Solitary Islands reference sites were more similar to those found in subtropical and tropical waters further north than to the largely temperate species found at depth in the CMRs.

Ultimately, given the strong effects of depth on reef communities in this region, deeper sites would be ideal to provide reference sites for Pimpernel Rock. However, the pinnacles of Pimpernel Rock and the Cod Grounds are geomorphologically unique, also making it difficult to find appropriate reference sites outside the CMR, and meaning that trends through time within these CMRs will need to be carefully interpreted in light of broader regional change.

Pimpernel Rock and some of the Cod Grounds sites had very high biomass of fishes; in a number of cases this was driven by very large schools of planktivores, and in some cases also high abundances of carnivores and sharks.

In the Cod Grounds, the highest biomass values were recorded at the reference sites in 2009, but in the CMR sites in 2016.

Although possible, it is unlikely that successful protection of the CMR has displaced fishing effort to areas outside the CMR, because analysis of large and exploited fish species indicated that both had marginally higher biomass in the CMR than at reference sites, but not significantly so.

The high abundance of the grey nurse sharks, especially during the 2016 surveys, suggests that the east coast population is benefiting from national regulations for no-take protection.