Assessing changes in threatened black rockcod Epinephelus daemelii abundance and length over the past 15 years in New South Wales, Australia.

Abstract

Ideally, protection of a threatened fish will lead to their recovery in abundance, distribution, and size structure within the population, to a point where they are no longer considered threatened. Monitoring abundance and size is crucial to evaluate this, although low numbers associated with being threatened can strongly constrain the methods used. To assess if population recovery is occurring for the black rockcod Epinephelus daemelii, a large subtropical grouper endemic to shallow reefs in the southwest Pacific, surveys were undertaken across northern New South Wales and Lord Howe Island using roving diver timed counts and diver stereo-video measurements to assess relative abundance and length. Surveys in 2023 were compared with initial baseline data captured in 2009-2011 using the same methods. Relative abundance of E. daemelii at long-term monitoring sites has remained relatively constant or declined since 2010 rather than increasing. Comparisons between 84 broadscale sites in 2009-2011 versus 2023 (117 vs. 69 observed E. daemelii) indicate a recent decline in abundance. Although protected from fishing and spearfishing for over 40 years, the relative abundance of E. daemelii does not appear to be increasing over the past 15 years since monitoring commenced. This is a concerning trend that does not indicate recovery, although an increase in the proportion of mature females in the population from 2010 to 2023 is positive. As E. daemelii is slow growing, long lived, late to mature and still susceptible to incidental capture mortality, more active management may be needed to help assist with the slow recovery of this threatened species.