|Scientific Name:||Choerodon rubescens (Günther, 1862)|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Fairclough, D. & Cornish, A. (Grouper & Wrasse Specialist Group)|
|Reviewer(s):||Sadovy, Y. & Russell, B. (Grouper & Wrasse Red List Authority)|
Choerodon rubescens is a sought after species for its high quality white flesh by both commercial and recreational fishers in Western Australia (Crowe et al. 1999, Last et al. 1999, Sumner and Williamson 1999, Sumner et al. 2002). Commercial wetline catches, from the main region in which this species is fished, i.e., the Houtman-Abrolhos Islands, a group of islands and reefs ca 70 km offshore at ca 28º45'S, 113º45'E (hereafter referred to as the Abrolhos Islands), remained stable during the 1990s (average ca. 31.5 tons per year)(Crowe et al. 1999). Penn et al. (2003) stated that fishing effort for C. rubescens increased to its highest recorded levels in 2001/02, an increase of 16% from the previous year. However, the catch only increased 2% and thus Penn et al. (2003) suggested that the fishery at the Abrolhos Islands may be showing signs of over-exploitation. Levels of impact on this species are likely to be lower outside of the Abrolhos Islands region, since commercial fishers outside that area target other species primarily (Penn et al. 2003). Total annual commercial catches of C. rubescens using all fishing methods (wetline, gill net, long-line) in Western Australia from 1991/92 to 1997/98 ranged between ca. 40 and 53 t (Crowe et al. 1999).
There are no long term data on recreational catches. A survey by Sumner and Williamson (1999) demonstrated that ca. 23 t of C. rubescens were taken in a one year period (September 1996 to August 1997) on the west coast of Australia between Augusta (34º19'S, 115º9'E) and Kalbarri (27º42'S, 114º9'E). A substantial proportion of this came from Jurien Bay (30º18'S, 115º2'E). While more regular monitoring of recreational catches is required in areas where there is higher fishing pressure (Harrison 2001, Sumner et al. 2002), e.g., Jurien Bay and Shark Bay, many areas of the west coast are remote and are less likely to be targeted by recreational fishers.
New fishing regulations, which came into effect on the 1st July 2003, reduced the catch limit for recreational fishers to four C. rubescens per day (Department of Fisheries Western Australia 2003a, b). Further reductions have been proposed along with an increase in the minimum legal size for capture from 40 cm to 45 cm (Harrison 2001). A closed season has been introduced during the spawning period of C. rubescens, preventing the take of this species in the fish habitat protection area at the Abrolhos Islands (Department of Fisheries Western Australia 2003a). A marine park was declared at Jurien Bay in August 2003 by the Western Australian Department of Conservation and Land Management, which contains several no take and restricted activities zones (Anonymous 2003). The above measures will assist in the maintenance of population levels in areas where C. rubescens is more heavily targeted. Furthermore, continued monitoring of catches, examination of the effects of protected areas at the Abrolhos Islands on numbers and size structure of C. rubescens using visual surveys, and enforcement of existing legislation should ensure that any change in stock levels are recognised (Chubb et al. 2002, Pogonoski et al. 2002).
Choerodon rubescens does not appear to be overexploited currently, based on commercial catch data for the Abrolhos Islands, where the majority of the catch comes from. However, there are several reasons to indicate this species could be vulnerable to overexploitation in the future and as such, should be re-assessed at regular intervals.
1). The species has a relatively small global distribution.
2). It occurs in coastal waters, and is sought after by recreational fishers for its fighting qualities, size and high quality flesh and it attracts high prices for commercial fishers.
3). It is one of the largest wrasses (reaching 70 cm and 7 kg), it matures on average at approximately 3 years and 29 cm, is long-lived, reaching at least 22 years, and is a protogynous hermaphrodite (Fairclough in prep.).
4). While sex ratios of adult fish are biased towards females, ratios in commercial catches, i.e., of fish above the minimum size limit of 40 cm, are approximately 1:1, suggesting that many males are being removed from the population (at least in the Abrolhos Islands). This may be the cause of a smaller size at sex change in this region, when compared to Shark Bay (further north), since the removal of large males in hermaphroditic species can cause this undesirable effect on sex change, as has been demonstrated for the Venus Tuskfish Choerodon venustus (Platten et al. 2002).
5). Minimum size limits and catch limits regulate the recreational fishery for this species, however, the number of recreational fishers in Western Australia is continually increasing. Furthermore, reports of increased effort by commercial fishers with little increase in catch from the Abrolhos Islands fishery, may imply overexploitation of this species in that region (Penn et al. 2003).
This species is classified as Least Concern, since it does not meet the threatened criteria of "An observed, estimated, inferred, projected or suspected population size reduction of 30% over any 10 year or three generation period, whichever is longer (up to a maximum of 100 years in the future), where the time period must include both the past and the future, and where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on either A1 (c) a decline in area of occupancy, extent of occurrence and/or quality of habitat or A1 (d) actual or potential levels of exploitation" (VU A4c or d). Also, there is some management action in place. However, this species must be monitored and reassessed regularly due to the potential threats of increased fishing effort and the likelihood that this large size species may be particularly susceptible to fishing pressure, especially if target for export.
|Range Description:||Choerodon rubescens is found on coastal and offshore reefs on the continental shelf of Western Australia and is suggested to be most abundant at the Abrolhos Islands (ca. 28.5ºS, 113.5ºE), which is approximately in the centre of this species’ distribution (Walker 1983, Hutchins and Swainston 1986, Allen 1999, Hutchins 2001). These islands are situated approximately 70 km offshore from Geraldton, on the west coast of Australia. It is likely to be similarly abundant at sites further north, e.g., along the Zuytdorp Cliffs and the western sides of large islands at the western border of Shark Bay, i.e., Dirk Hartog, Bernier and Dorre Islands (ca. 26ºS, 113.5ºE), although most of these areas are fairly inaccessible, except by boat (Hutchins 1990, Hutchins et al. 1995, Fairclough in prep.). It is also found at Coral Bay at the southern end of Ningaloo Reef (Hutchins and Swainston 1986). Choerodon rubescens is captured by commercial and recreational fishers further south from Geraldton, e.g., Jurien Bay and Perth, where there are more coastal and offshore limestone reefs and islands (Hutchins 1979, Crowe et al. 1999, Sumner and Williamson 1999).|
Native:Australia (Western Australia)
|FAO Marine Fishing Areas:|
Indian Ocean – eastern
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Choerodon rubescens is abundant in the centre of its distribution at the Abrolhos Islands (Walker 1983, Hutchins 2001). Average mean densities in waters close to the islands recorded during visual census work by Nardi (1999) ranged between 3 and 9 fish/250 m². The Abrolhos Islands support the largest commercial fishery for this species, however, commercial fishers tend to fish in deeper waters away from the actual islands (Webster et al. 2002). Wetline catches in this region average 31.5 tons per year and have been consistent for approximately 10 years, however, Penn et al. (2003) suggested that the population at the Abrolhos Islands may be showing signs of over-exploitation, due to increasing fishing effort by wetliners with little increase in total catch.
Hutchins (2001) observed C. rubescens frequently at sites surveyed between Jurien Bay and the northern limit of this species distribution at Coral Bay. But this species was occasionally to rarely observed at sites surveyed to the south of Jurien Bay. Visual census surveys in South Passage, at the southern end of Dirk Hartog Island, Shark Bay (ca. 26ºS, 113.5ºE), and on the east and west coasts of Bernier and Dorre Islands, suggest that C. rubescens is abundant in these areas (Hutchins 1990, Hutchins et al. 1995, Fairclough in prep.). Since much of the coastline within this species distribution consists of limestone reefs, on which C. rubescens is found, the distribution of this species is likely to be fairly continuous at least between Jurien and Coral Bay (Hutchins 2001, Hutchins et al. 1995).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Choerodon rubescens is a demersal species found commonly on bare rocky (predominantly limestone) reefs, coral reefs, and rocky reefs with associated coral, algae or seagrass (Hutchins and Swainston 1986, Allen 1999, Fairclough in prep.). It is common in shallow waters (< 20 m) and known to be collected in substantial numbers by commercial fishers in deeper waters (up to 100 m) around the Abrolhos Islands (Fairclough, in prep., S. McCaskie, pers. comm.).
Small juveniles (< ca. 150 mm) are common in shallow weedy rock habitats and generally move onto more open habitats after the first 1–2 years of life, where they mature after 3 or more years (Fairclough, in prep.). Choerodon rubescens grows to approximately 70 cm in length and has been aged at up to 22 years (Hutchins and Swainston 1986, Nardi 1999, Fairclough, in prep.). Fish at the minimum legal length for capture of 40 cm range from 4 to 14 years of age (Nardi 1999, Fairclough, in prep.).
Choerodon rubescens is a protogynous hermaphrodite and is an indeterminate multiple spawner. It spawns between August and January, however, spawning fish are most abundant between September and November, i.e., spring (Nardi 1999, Fairclough, in prep.). Small male gonads indicate that male fish would spawn with only one to a few females at once and Nardi (1999) observed males herding females during the spawning season, suggesting that they maintain harems at this time. Sex ratios of adult fish, i.e., above the size at which 50% of females reach sexual maturity (ca. 290 mm), are biased towards females, i.e., ca. 10 females :1 male (Fairclough, in prep.). Nardi (1999) suggests that C. rubescens aggregates to spawn in shallow waters at the Abrolhos Islands, due to increased counts of this species during visual surveys during its spawning season.
Current research in Shark Bay and the Abrolhos Islands demonstrates that the size at sexual maturity of females is similar in both regions, but fish are older at this size in the Abrolhos Islands, related to slower growth in this region (Fairclough, in prep.). The sizes at which 50% of individuals change sex in Shark Bay and the Abrolhos Islands are substantially different and may be related to the differences in growth at different latitudes and/or fishing pressure influencing the social structure (Fairclough, in prep.). The ratio of females to males of C. rubescens in commercial catches from the Abrolhos Islands is approximately 1:1. The high fishing pressure and consistent capture of larger, often male, Venus Tuskfish Choerodon venustus, at some locations in Queensland resulted in a decrease in the size at sex change for this species at those sites (Platten et all. 2002).
An increase in commercial and/or recreational fishing pressure is the main threat to this species, with the largest catches coming from around the Abrolhos Islands, and other areas of importance being Jurien Bay and Shark Bay (Sumner and Williamson 1999, Penn et al. 2003, Sumner et al. 2002). Although commercial wetline catches have remained consistent during the 1990s in the Abrolhos Islands, where 50% of the commercial wetline catch is derived from (Crowe et al. 1999), a 16% increase in effort in 2001/02 compared to the previous year, but with little increase in catches (2%), suggested that stocks in that region were showing signs of over-explotation (Penn et al. 2003).
The lower length at which 50% of females change sex in the Abrolhos Islands (479 mm) versus Shark Bay (545 mm), may indicate that fishing pressure is having an impact on social structure in the former region, as was demonstrated for Choerodon venustus in Queensland (Platten et al. 2002). High fishing pressure resulted in a decrease in the length at sex change for the latter species.
In the Abrolhos Islands, ratios of females to males in catches of fish that were above the length at 50% sexual maturity and were caught by recreational rod and line fishing are approximately 10:1, whilst for fish collected by commercial fishers, the sex ratios are close to 1:1 (Fairclough in prep.). This implies that there are greater numbers of females in the adult population, as is common for protogynous hermaphrodites, but that commercial fishers are taking approximately equal numbers of females and males. If the minimum legal size limit is increased to 45 cm, the proportion of males in commercial catches may increase. This may have an undesirable impact on the size at sex change in the Abrolhos Islands, as occurred for C. venustus and may eventually have an impact on assemblages elsewhere on the west coast of Australia, if fishing pressure is high enough.
The Abrolhos Islands represents a unique environment, being the southernmost coral reefs in the Indian Ocean and containing 211 species of hermatypic and ahermatypic corals (Hatcher 1991, Nardi 1998). Anthropogenic threats to habitats at the Abrolhos Islands, such as coral areas, that are occupied by C. rubescens, are well documented, and include activities such as diving and recreational boating. These impacts are considered to be minimal (Webster et al. 2002). However, they do require further quantification and the development of suitable management plans (Webster et al. 2002).
The minimum legal size limit for retention (commercial and recreational) of C. rubescens in Western Australia is 40 cm, which is above the length at sexual maturity of ca. 290 mm (Department of Fisheries Western Australia 2003a, b; Fairclough, in prep.). Catch limits of four fish per person per day for recreational fishers came into effect on 1st July 2003, however there have been recommendations that this be further reduced to two and the minimum size limit be increased to 45 cm (Department of Fisheries Western Australia 2003a, b; Harrison 2001). These limits are based on the type of life history that a particular species has. Thus, tuskfish are included in the category of "highest risk" (Harrison 2001). Species in this category are generalized as having the following characteristics: they are long-lived, slow-growing, they mature at four years plus, form semi-resident populations, are vulnerable to localised depletion due to their life history, or are of low abundance or highly targeted (Harrison 2001).
Sanctuary zones at the Abrolhos Islands include four no take "Reef Observation Areas" (ROA), which were introduced in the mid-1990s (Nardi 1998). These ROAs have apparently had little impact on the size or abundance of C. rubescens (K. Nardi, Department of Fisheries, Western Australia, pers. comm.). Monitoring of future catches and the impact of protected areas on fish numbers has been highlighted as a priority for research (Webster et al. 2002). A closed fishing season for C. rubescens was introduced for the "Fish Habitat Protection Area", that surrounds the Abrolhos Islands, from 1 November to 31 January, which encompasses a substantial proportion of the spawning period of theis species (Department of Fisheries Western Australia 2003a).
There is a no take sanctuary zone in South Passage (southern end of Dirk Hartog Island), Shark Bay, and eight no take sanctuary zones within the Ningaloo Reef Marine Park (Anonymous 1996, Anonymous 2004a). Spearfishing of tuskfish is prohibited throughout the Ningaloo marine park (Anonymous 2004a). A no take sanctuary zone was also introduced at Mary Anne Island in the western gulf of Shark Bay for C. rubescens, however this may be due to a misidentification of the Choerodon species, since C. rubescens does not occur within the more southern regions of the gulfs of Shark Bay (Anonymous 1996, Fairclough in prep.). Choerodon rubescens is found only occasionally at Rottnest Island, near Perth (Hutchins 1979, 2001). Spearfishing is prohibited within 200 metres from shore and netting is prohibited within 500 metres from shore around Rottnest Island (Anonymous 2004b).
A marine park was declared at Jurien Bay in August 2003, which contains several no take sanctuary zones and areas which restrict commercial or recreational fishing activities, and in which C. rubescens is likely to occur (Anonymous 2003).
|Citation:||Fairclough, D. & Cornish, A. (Grouper & Wrasse Specialist Group). 2004. Choerodon rubescens. The IUCN Red List of Threatened Species 2004: e.T44671A10933976.Downloaded on 24 February 2018.|