A large fish that is similar to its relative the Hapuka. It can grow to a weight more than 200kg but an average weight is around 20 to 30kg. It is mostly fished for in the deeper waters 200m to 800m. While hardly classed as a sport fish, these large powerful fish are hard to move off the bottom, but often embolise in mid-water and float up the rest of the way.
Groper found in Cook Strait mature over a wide size range, with 50% maturity at 80–85cm for males and 85–90cm for females (Paul, 2002d). Spawning occurs during winter, anecdotally earlier in the north of New Zealand than in the south, but running ripe fish are seldom caught and spawning grounds are unknown. The smallest juveniles are virtually unknown, but are mottled, pelagic and epi-pelagic - perhaps schooling in association with drifting weed.
New Zealand data has indicated that groper may live to be 40 years or more.
Migration patterns are also little known, but are probably related to spawning. Tagging of mostly immature fish in Cook Strait has shown a high level of site fidelity, but about 5% of these fish have moved up to 160km north and south. Other information is largely anecdotal and speculative. It is known that good fishing grounds, particularly pinnacles and reefs or ledges, can be quickly fished out and take some time to recover, suggesting a high level of residency (except, perhaps, for the spawning season). On the other hand, trawlers sometimes catch groper on the flat and clear seafloor, and it is not known whether this represents their normal habitat, whether they are simply dispersing by travelling from one rough ground to another, or whether they are on a purposeful spawning migration.
Groper prey on a wide variety of fish and invertebrates, including red cod, tarakihi, blue cod, hoki and squid. In Cook Strait, they are preyed upon by sperm whales, although probably neither heavily nor selectively.