|Scientific Name:||Metanephrops challengeri|
|Species Authority:||(Balss, 1914)|
Nephrops challengeri Balss, 1914
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor/s:||Wahle, R., MacDiarmid, A., Butler, M., Cockcroft, A. & Chan, T.Y.|
|Reviewer/s:||Collen, B., Livingstone, S. & Richman, N.|
|Contributor/s:||Batchelor, A., De Silva, R., Dyer, E., Kasthala, G., Lutz, M.L., McGuinness, S., Milligan, H.T., Soulsby, A.-M. & Whitton, F.|
Metanephrops challengeri has been assessed as Least Concern. While this species is harvested in parts of its range, it is not thought that this constitutes a major threat to the global population at the present time owing to recent conservation measures such as the Quote Management System.
|Range Description:||This species is endemic to New Zealand, and is found on the continental shelf around both islands as far east as the Chatham Islands (Holthuis 1991).|
Native:New Zealand (Chatham Is., North Is., South Is.)
|FAO Marine Fishing Areas:||
Pacific – southwest
|Range Map:||Click here to open the map viewer and explore range.|
In the Bay of Plenty, off the coast of New Zealand's North Island, this species made up more than 60% of the invertebrate catch in trawl surveys (Cryer et al. 2002). Estimates of abundance from underwater photography in the same location ranged from 12-28 million animals (including those spotted in burrows and walking), down to 2-11 million (just those animals walking on the sediment, i.e. most susceptible to capture by trawl), although the latter estimate is far less reliable (Cryer et al. 2005). Biomass estimates over the period 1998 to 2003 showed a decline: for all visible scampi, from 988 tonnes to 509 tonnes, and for extrapolations based on burrow openings, ~5,500 tonnes to 3,600 tonnes.
Although little information is available on population structure, preliminary genetic work suggests a high degree of heterogeneity, with up to four genetically distinct sub-populations. Other evidence supports the treatment of these as separate management units (NZ Ministry of Fisheries 2009).
Catch per unit effort (CPUE) has declined since 1995 (Cryer et al. 2005), although with different timing patterns in different Quota Management Areas (QMAs). SCI1 (Auckland East), the oldest fishery, and SCI2 (Central) have both shown declines since peaking in the mid-1990s, and have been relatively stable, although at historically low levels since 2000. SCI3 (South East Coast and Western Chatham Islands), the largest fishery, increased gradually before peaking in 2000 and has declined since to low levels. SCI4A (Chatham Islands East) peaked in 2001 before declining rapidly. SCI6A (Auckland Islands), the second largest fishery, declined rapidly in the early 1990s and has been stable since then. No areas of the fishery show an increasing trend in CPUE, although trends fluctuate. All fishery areas for which data exists have shown substantial declines of between 30 and 80% (M.J. Butler, A.C. Cockcroft, A.B. MacDiarmid and R.A. Wahle pers. comm. 2008).
Stock assessments for this species have been hampered by the lack of a reliable index of abundance (for example, research trawl and commercial CPUE both suffer from temporal changes in catch vulnerability) (Cryer et al. 2005). Assessments of abundance vary according to which estimate is used: if biomass of visible scampi is used, landings represent a significant (12.1 to 27.6%) proportion of total scampi biomass, but if extrapolations from burrow counts are used, fishing only accounts for 2.2-3.6% of the total stock in the Bay of Plenty (Cryer et al. 2005). Those based on visible scampi are likely to be conservative and affected by seasonal and diurnal changes in lobster emergence, while those based on burrow counts assume that burrow occupancy is constant from year to year (which is thus far unknown).
Estimated declines in biomass are consistent with a decline in commercial catch per unit effort (CPUE) since 1996 (Hartill and Cryer 2003); in recent years Total Allowable Catch (TAC) targets have not been met due to fleet economics. CPUE data is available which shows consistent patterns among fishing areas of gradual or rapid increases followed by declines since around 2000 (NZ Ministry of Fisheries 2009). However, these unstandardized analyses are not considered reliable indices of abundance by the Shellfish Fishery Assessment Working Group, and should therefore be interpreted with caution.
|Habitat and Ecology:||This species occurs in mud or sandy mud substrate at depths of 140-640 m (Holthuis 1991). Its size at maturity is 30 mm, which it usually achieves after three to four years, and may live for up to 15 years (Cryer and Oliver 2001). It has a very large egg size associated with low fecundity (about 10-20% of other commercial species, such as Nephrops norvegicus) (MacDiarmid and Sainte-Marie 2006).|
This species is only commercially exploited in a few parts of its range. This is because there are large areas where there is muddy ground broken up with rocky ground and therefore not trawlable. Thus creating natural refugia. Only the emergent fraction is harvested at any one point in time, and only the high density aggregations are exploited. Furthermore, there is a responsive management regime in place, and there are fishery indepenedent surveys coming into place. (A. MacDiarmid pers. comm. 2009) However, according to the New Zealand Ministry of Fisheries "There are no stock assessments or yield estimates for any scampi stock. It is not known if recent catches and current catch limits for any scampi stock are sustainable in the long term..." (NZ Ministry of Fisheries 2009).
Furthermore, trawling can indirectly affect scampi and other species through impacts on seabed habitats; it has been shown to reduce benthic biodiversity (NZ Ministry of Fisheries 2009). Small amounts of scampi may also be taken as bycatch during trawls for other species, although this is not thought to be a major threat.
Trawl fishery access within the range of this species is restricted using a mixture of: vessel retrictions, competitive catch limits, and individually allocated catch limits. Since October 2004, this species was introduced to the Quota Management System (QMS) which directly controls harvest levels for distinct fish stocks in Quota Management Areas (QMA) (M.J. Butler, A.C. Cockcroft, A.B. MacDiarmid and R.A. Wahle pers. comm. 2008).
|Citation:||Wahle, R., MacDiarmid, A., Butler, M., Cockcroft, A. & Chan, T.Y. 2011. Metanephrops challengeri. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 23 May 2013.|
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