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| Red Throat Emperor Photo by CRC Reef. |
The red-throat emperor, Lethrinus miniatus, is a relatively long-lived member of the Lethrinidae family (Emperors). They live to approximately 20 years of age and grow to about 60cm fork length.
Commonly found on mid and outer shelf reefs between Cairns and the Capricorn Bunker group on the Great Barrier Reef, and even further south in Queensland, the red-throat emperor is the second most sought after species in the Great Barrier Reef (GBR) reef line fishery, accounting for up to 1000t of the combined annual commercial and recreational catch.
The current management strategy for red-throat emperor includes a minimum size limit of 35cm for all line fishers and a possession limit of 10 fish per person for recreational and charter fishers. These restrictions are currently uniform throughout the entire Great Barrier Reef and are under review.
Current Effects of Line Fishing Project (ELF) research is aiming to characterise red-throat emperor populations throughout their range in Queensland, from the Swains off Gladstone in the south, to about Cairns in the north. This involves obtaining information on the size and age of individuals in order to determine rates of growth and survival. In addition, information on the sex and reproductive status is providing estimates of maturity and spawning season, as well as valuable data for examining the process of sex change.
ELF scientists also have investigated the genetic makeup of red throat emperor stocks to determine whether there is just one population of red throat emperor on the GBR or different populations in different regions.
Adult red-throat emperor are usually found associated with coral reefs and surrounding shoal areas to depths of over 100m. It is unclear whether adult red-throat emperor move between reefs, however they are often caught in rubble areas between reefs, suggesting at least the potential for such movement.
Unfortunately the juvenile habitat of red-throat emperor has yet to be
identified. Juvenile red-throat emperor have not been observed from any
research in the shallow waters of the Great Barrier Reef or costal areas,
and they do not appear in the bycatch from trawlers.
Therefore, it is thought that the most likely habitat for juveniles is
in deep waters (>40m) adjacent to reefs.
The location of the juvenile habitat remains a high priority for ELF scientists
in future research.
Rates of growth and survival of red-throat emperor have been found to vary in different regions of the Great Barrier Reef. For example, fish in the Mackay region reach a larger maximum size compared with fish in the Townsville region. Further, survival rates in the Townsville region are much higher than in the Mackay region.
Recent genetic research has shown that red-throat emperor populations on the Great Barrier Reef constitute a single homogeneous stock (breeding population), suggesting that the significant regional patterns in growth and survival are not a result of genetically distinct populations. Rather, it appears that the differences in biology might reflect regional differences in the fishs’ environment and/or a response to regional variation in the present or historic fishing pressure.
Red throat emperor are protogynous hermaphrodites, meaning that they change sex from female to male. It is thought that the process of sex change is quite rapid, although, the mechanism prompting sex change is still unclear. Recent research suggests that approximately fifty percent of fish change sex at about 45cm fork length, or approximately 6 years of age.
As the juvenile habitat has not been identified, very few immature fish have been collected, thus precluding the estimation of the size and age at which fish mature
There is limited information available on the spawning behaviour of red-throat emperor. There is anecdotal evidence from the fishing industry of large catches of red-throat emperor from lagoonal areas of the reef around the full moon during the spawning season, It is likely that these catches arise because the fish are aggregating to spawn. At present, however, there are not direct observations of the spawning behaviour of red throat emperor.
The peak spawning season for red-throat emperor on the Great Barrier Reef is between July and October, and is similar throughout the Great Barrier Reef. This is in contrast to many other reef fish species such as coral trout that tend to spawn earlier in the north and later in southern regions.
Red-Throat
Emporer