Assessing changes in black rockcod abundance and size

In 1983 the black rockcod was listed as Vulnerable in NSW waters. In 2012 it was also listed as Vulnerable in commonwealth waters. These protections mean that black rockcod must not be being taken from the wild and it is illegal to possess or harm them. They are still caught by fishers, however, and although they must be immediately released they are likely to die from barotrauma (decompression caused by the rapid ascent on a fishing line).

Long-term monitoring of black rockcod is a high priority identified by the species’ recovery plan and the NSW Fisheries Scientific Committee. This is essential to assessing the effectiveness of conservation and management actions being implemented to protect the species.

In 2009–2011 NSW Marine Park researchers conducted the first broadscale (baseline) black rockcod survey at 83 sites off northern NSW (Port Stephens to Cook Island) and at Lord Howe Island. They have conducted smaller surveys at 19 key monitoring sites every four to five years. The broadscale survey was repeated for the first time in 2023 as part of this hub project. In 2024, this project also repeated the smaller-scale survey at key monitoring sites. 

The surveys found that despite 40 years of protection, black rockcod are still declining across their range. The 2023 survey recorded a 40% decline in black rockcod numbers since the previous survey 15 years ago. Positive findings were the observation of more black rockcod in ‘no-take’ sanctuary zones, and an increase in the number of individuals old enough to breed. These results suggest that more active management may be needed to assist the ongoing recovery of this species.

Approach and findings

The black rockcod survey involves researchers in scuba gear swimming along each site for up to 45 minutes searching for and photographing any individual black rockcod. For each sighting, the depth range and habitat type is recorded, and the length of the fish is visually estimated. Where possible, the fish is also filmed using a camera stereo system. 

The 2009–2011 broadscale survey recorded 117 individuals, at 34 of the 83 survey sites. The 2023 survey recorded 66 individuals at 27 of the 83 sites. This equates to a 42% reduction in the relative abundance of black rock cod at these sites, and an 8% reduction in the proportion of sites at which black rock cod were observed (41% of sites reduced to 32%).

When compared with observations by spearfishers and captures of black rockcod from the 1950s and 1960s, the 2023 and 2024 surveys indicate the species is a long way off recovering to abundances of more than 50 years ago. The declines are most evident at sites in the Port Stephens-Great Lakes Marine Park, Fish Rock at South-West Rocks and the Lord Howe Island Marine Park. Oral history records and historical photographs from Lord Howe Island also suggest black rockcod were considerably more abundant there in the mid-1900s.

Some positive signs

One positive finding from the 2023 broadscale survey is that the mean length of black rockcod had significantly increased since 2009–2011. The length class with the most individuals in 2009–11 was 60 to 70 cm, which are sub-adult. In 2023, the length class with most individuals was 90–100 cm, a length class of large mature females that would soon be transitioning to males.

The relative abundance counts in the 2024 survey of key monitoring sites also had some positive signs. The highest total count at Lord Howe Island was recorded in 2024, after the lowest in 2019. This is a good indication that black rockcod populations at these sites could be stable, but there is no indication they are recovering.

The 2009–11 and 2023 broadscale surveys found significantly greater numbers of black rockcod in ‘no-take’ sanctuary zones than in fished areas. This may be influenced by some sanctuary zones being situated on good black rockcod habitat. At Lord Howe Island, however, the best habitat surveyed (which also had the largest individuals) was in fished areas of the Admiralty Group of islets, so this is not a consistent bias.

The Solitary Islands Marine Park is a stronghold for black rockcod, with the largest and most stable abundances in the past 15 years recorded there. Sites such as the northern end of South Solitary Island, Anemone Bay (North Solitary Island), and Fish Soup (North-West Rock) are in no-take sanctuary zones that provide high levels of protection. These no-take areas prevent all forms of fishing,. The incidental capture and subsequent injuries or mortality from hooking injuries therefore is reduced, increasing the chance of survival in these locations.

Future prospects

There is no indication that black rockcod are becoming more widespread on rocky reefs in northern NSW and Lord Howe Island. This is concerning as after 40 years of protection. As the black rockcod is slow growing, long-lived, late to mature and still in low abundances across NSW, the recovery of this species will take time, even if all the threats from incidental fishing pressure were eliminated. They are unlikely to recover to the level of an ‘unthreatened’ population in the decadal-scale future.

One positive is that our findings suggest the size structure of black rockcod has increased since 2009–2011 at broadscale and key survey sites. The presence of more mature large females is positive for the reproductive potential of overall population. Protection from fishing in key locations is likely to be important for the recovery and long-term survival of this species. Given this species is known to display strong site fidelity, the continued protection of sites where black rockcod occur, through the continued implementation of no-take sanctuary zones or other fishing restrictions, will ultimately be of benefit.

Project recommendations

Management actions: The ongoing review of NSW marine park management plans provides an opportunity to consider how marine parks might assist with the recovery of this and other threatened species. Continued and increased spatial protection from incidental fishing and an educational campaign on species identification and how to release incidentally caught black rockcod would be of use to reduce fishing-related mortalities.

Future monitoring: Further monitoring of the 12 key NSW monitoring sites in 2028 and 2029 (at a minimum) is essential to help evaluate the upward trend in black rockcod abundance observed in 2023 and 2024.

Threatened species status evaluation: Given a 15-year dataset now exists for black rockcod populations, a reassessment of its threatened species status in NSW should be undertaken. Data collected in this research can be used by the NSW Fisheries Scientific committee to evaluate which IUCN Red list threatened species category applies (Critically Endangered, Endangered or Vulnerable).

Indigenous engagement: capacity building, training and employment

The project team collaborated with several Indigenous organisations and built on existing partnerships established with the NSW Government. Sea-time experience and on-water training provided to four Gumbaynggirr and one Yaegl coxswain trainees. Bundjalung Arakwaal rangers gained experience on survey vessels in Cape Byron Marine Park.

This capacity building was supported through NSW Marine Estate Management Strategy and coordinated through the Coffs Harbour and District Local Aboriginal Land Council (Garby Elders rangers program) and the Yaegl Local Aboriginal Land Council. Hours of work undertaken by the trainee coxswains were paid for through the NSW Marine Estate Management Strategy. Opportunities were taken to build shared understanding about reciprocal benefits of the project, and to communicate the research findings.

Outcomes

This project together with the overall black rockcod monitoring program conducted by NSW DPI – Fisheries Research provides a 15-year time series (2009–2024) indicating whether black rockcod are increasing in abundance, getting larger, and/or becoming more widespread. These indicators can be used to assess the effectiveness of management actions being implemented in NSW.

Commonwealth and state marine park managers and threatened species managers have an improved evidence base for assessing the success of species recovery actions. This includes ensuring the effective protection of black rockcod in marine parks through sanctuary zones, management of hook and line fishing, and reassessments of population status and conservation listings.

Black rockcod will benefit through threatened species recovery planning and actions informed by this research. Marine user groups such as divers. fishers and Indigenous groups will benefit from the communication of these research findings.

The Community Group Green Heroes, with strong Bunjalung ties, have conservation objectives and strong Sea Country connection to Jungarra Gnarrian/Cook Island and are helping to assess black rockcod and sea turtles at this special place to them. More frequent community monitoring at Jungarra Gnarrian provides an extra temporal layer of insight that can be incorporated into the overall NSW DPI black rockcod monitoring program.

Project location

Survey sites will be in northern NSW, Solitary Islands Marine Park, Port Stephens-Great Lakes Marine Park and Lord Howe Island Marine Park.