None of the jurisdictions currently have a harvest strategy informed by modelled biomass with associated performance measures, reference points for those measures, and explicit decision rules prescribing management responses. Victoria did have such performance measures prescribed in its 2002 fishery management plan4 , and these are still used in assessing two of its three stock management units.
All states rely on empirical performance measures, specifically catch, catch per unit effort (CPUE)—as kilograms (kg) of abalone meat harvested per hour—and commercial catch size structure. The annual catch in Blacklip Abalone fisheries is generally equivalent to the total allowable commercial catch (TACC), with negligible overcatch or undercatch of the TACC. In some jurisdictions, additional fishery-independent data are available from underwater research surveys; in Victoria this is extensive, encompassing 204 fixed monitoring stations spanning 23 years, and supports model-based analyses, but it is more limited in other states.
Undertaking assessment of abalone stock status is complicated by several factors, including:
- the high number of biological stocks
- changes to management unit boundaries and size limits
- absence of, and difficulty in determining, an empirical performance measure and reference point below which the fishery would be defined as recruitment overfished
- changes in fishing power, which impede comparisons of current and historical CPUE
- the multitude of factors that affect the effort component of CPUE
- the degree to which CPUE reflects abalone abundance.
This means that the assessments of Blacklip Abalone in this chapter were necessarily based on a weight-of-evidence approach, which involved careful cross-jurisdictional consideration and interpretation of information for each management unit.
The harvest strategy in the Management plan for the South Australian commercial abalone fishery5 includes a catch-weighted determination of stock status for the fishing zone. However, the harvest strategy does not identify a performance indicator and reference point below which the fishery would be defined as overfished. In addition, several weaknesses in the harvest strategy result in more optimistic assessments of stock status than those from more traditional weight-of-evidence methods6–8. Consequently, in this assessment, commercial catch rates (CPUE) are used as the index of relative Blacklip Abalone abundance. This measure can, however, provide a more optimistic index of relative abundance than measures from fishery-independent surveys, because catch rates in dive fisheries can be hyperstable9,10. Decreases in CPUE in abalone fisheries are considered to be a reliable indicator of decline in abalone abundance during periods when management arrangements remain unchanged, but can underestimate the magnitude of the reduction11.
Data sources available in Victoria for this assessment included fishery-dependent data (commercial catch and effort, and shell length frequency reported by divers) and fishery-independent data (abundance of adults, sub-adults and juveniles, together with shell size frequency across all size classes, acquired during population surveys). In the Victorian Central and Eastern Zone management units, assessments were primarily based on outputs from a population dynamics model, and reference points for mature biomass prescribed for quota setting in the 2002 Victorian Abalone Fishery management plan4. This information was supplemented by trends in CPUE and abundance, which were analysed using two different statistical models. In the Western Zone Fishery, the effects of disease during 2006 to 2008 have precluded the ongoing use of the population dynamics model; however, trends in CPUE, and trends in the abundance of sub-adult and adult size categories were used.
In Tasmania, stock status and TACC is determined by annual fishery assessment and a multi-workshop process (four workshops annually). Annual assessments of the Tasmanian fishery zones rely heavily on fishery-dependent data11. There are no direct or derived estimates of biomass or fishing mortality, or agreed reference points or limits. Geometric mean CPUE and CPUE frequency distribution are key performance measures. Catch, catch rates, commercial catch size structure and diver observations are reviewed to form an expert opinion based on the weight of evidence. Each TACC is set at a level considered sustainable. The Tasmanian Abalone Fishery Management Plan Policy requires size limits to be established that allow two breeding seasons post-reproductive maturity. Research programs to obtain empirical data encompassing the variability in growth rates and size at reproductive maturity have been in progress since 1997, resulting in a range of legal minimum length (LML) regulations spanning 110 mm to 140 mm11.
South Australian Western Zone Fishery management unit
The CPUE for Blacklip Abalone in the western zone management unit of South Australia increased steadily from 17.1 kg/hour in 1979 to more than 25.6 kg/hour in 2003, the highest level on record. Subsequently, CPUE has decreased each year. In 2013, CPUE was 20.8 kg/hour, 18 per cent below that in 2003, and the lowest since 1996. This evidence indicates, that although the biomass of this stock is not likely to be recruitment overfished, the current level of fishing pressure is likely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
South Australian Central Zone Fishery management unit
In the central zone management unit of South Australia, CPUE for Blacklip Abalone increased rapidly from 18.9 kg/hour in 1979 to 26.5 kg/hour in 1989, the highest level on record. From 1990 to 2003, CPUE was relatively stable, but variable among years. Since 2003, CPUE has decreased rapidly. In 2012 and 2013, CPUE was 18.5 and 19.2 kg/hour, respectively, the lowest since 1985. This evidence indicates that, although the biomass of this stock is not likely to be recruitment overfished, the current level of fishing pressure is likely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
South Australian Southern Zone Fishery management unit
The CPUE for Blacklip Abalone in the southern zone management unit of South Australia increased from 64 kg/hour in 1979–80 to more than 107 kg/hour in 2010–11, the highest level on record. Although CPUE has subsequently declined, in 2012–13 it was 94.6 kg/hour, remaining among the highest values on record. The above evidence indicates that the biomass of this stock is unlikely to be recruitment overfished and that the current level of fishing pressure is unlikely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a sustainable stock.
Victorian Western Zone Fishery management unit
The CPUE trend for the Victorian Western Zone management unit as a whole has shown a significant decline during the period 2001 to 2013. Two change points in the trend can be identified: one in 2007 and another in 2011. The former coincides with a disease outbreak12, when the rate of reduction in CPUE steepened significantly. The latter coincides with a shift in effort. Although the catch of 49 tonnes (t) for the 2012–13 quota year was only 15 per cent of the 280 t allocation for 2001–0213 the average CPUE of 54 kg/hour during 2013 was within the lower range of values observed before the impact of disease. Both these measures point to a significant decline in stock.
Trends in total abundance estimated from fishery-independent surveys indicate a high probability (greater than or equal to 0.8) that abundance on most reefs in the management unit has been depleting at an annual rate of 3–15 per cent since 200014,15. A declining trend in the abundance of sub-adults, at a rate of 10 per cent each year, was evident from 2001 to 2009, after which there was no significant change. This placed the number of future recruits to the stock in 2013 at 71 per cent below the average for 2001 to 2005. The trend in adult abalone increased by 17 per cent annually during 2002 and 2003, after which it declined at an annual rate of 12 per cent until 2008. There was a marginally significant annual increase among the mature stock of 4 per cent from 2008 to 2013. This placed the number of future mature-sized abalone in the stock in 2013 at 31 per cent below the average for 2001 to 2005.
Decreases in the proportion of sub-adult abalone, below the LML, threaten the resilience of the stock. Negative trends in most indicators are evident on reefs that remained disease free, as well as on those that were affected by disease. Recovery cannot occur through growth alone, and will not occur during the next few years unless there is a consistent increase in the abundance of juvenile and sub-adult abalone. The above evidence indicates that the stock is likely to be recruitment overfished.
In response to concern about the level of fishing pressure, the TACC of 280 t (which had prevailed for 15 years) was reduced by 21 per cent by 2006. At the same time, size limits were increased voluntarily to protect breeding potential. Fishing pressure was adjusted following the disease outbreak in 2006. By 2008, the disease had abated, and fishing progressively resumed on disease-affected reefs from 2009, with a more conservative size limit of 135 mm. In the past couple of years, the catch on disease-free reefs was reduced to zero because of concerns that they had become depleted. Consequently, effort is more focused and, with increases in TACC (by 17 per cent in 2013), represents a risk of serial depletion9,10. The stock remains depleted and has yet to show a measurable recovery at the scale of the management unit. While the current level of fishing pressure may allow the stock to recover from its recruitment overfished state, and there is some increase in spawning biomass, there is no statistically demonstrable increase in numbers of juveniles and sub-adults.
On the basis of the evidence provided above, the management unit is classified as an overfished stock.
Victorian Central Zone Fishery management unit
Between 2007 and 2009, populations in the Victorian central zone management unit were reduced substantially by disease in the region west of Cape Otway. Population dynamics modelling has shown that, for the remainder of this management unit, when compared with the reference biomass of 90 per cent of the biomass in 200014, it was 80 per cent likely that biomass in 2013 had decreased by 16 per cent at Cape Otway, 26 per cent along the coastline encompassing the Mornington Peninsula and Phillip Island, and 10 per cent at those areas at Wilsons Promontory open to fishing15,16. In other words, the most recent assessment for this management unit estimates that the mature biomass is 74–90 per cent of the reference biomass (2000)14 . This is at or below what has been considered to be the minimum allowable biological limit for the stock before it would be considered to be recruitment overfished17.
The CPUE across the management unit declined significantly, by 33 per cent, from 2001 to 2013. The average CPUE for 2013 was 59 kg/hour, which is within the lower range of values reported between 2001 and 2005. In addition, the catch for the 2012–13 quota year was 44 per cent of the 700 t allocation for 2001–02. Both these measures point to a significant decline in stock.
Abundance of sub-adult-sized abalone declined at a rate of 16 per cent per year until 2004, followed by an annual decline of 8 per cent until 2013. This placed the number of sub-adults that will become future recruits to the stock in 2013 at 71 per cent below the average for 2001 to 2005. The abundance of larger, more mature adult abalone declined at 6 per cent per year during the decade from 2003 to 2013. This placed the number of adult abalone in the stock during 2013 at 55 per cent below the average for 2001 to 2005.
The TACC has been progressively reduced over the past 10 years from 616 t to 308 t during the 2012–13 fishing season. Despite this TACC reduction, significant declines in abundance have persisted throughout the zone, with the exception of some reefs located adjacent to the Mornington Peninsula back-beaches between Port Phillip Heads and Cape Schanck15.
Collectively, the modelled biomass, trends in abundance, and CPUE provide evidence that the central zone is recruitment overfished. Management measures are in place, but are unlikely to change the overall status of this stock in the short term. It is uncertain whether the current level of fishing pressure will allow the stock to recover from its recruitment overfished state, and measurable improvements in biomass are yet to be detected.
On the basis of the evidence provided above, the management unit is classified as an overfished stock.
Victorian Eastern Zone Fishery management unit
Biomass has been estimated by population dynamics modelling for the majority (75 per cent) of the Victorian eastern zone management unit. Biomass was either below the trigger reference point16 (Airport Management Area) or marginally above, but nevertheless trending downwards, over the period 2008 to 2013 (Point Hicks to Little Rame).
Analysis of CPUE trends showed that there was a significant but gradual increase of 10 per cent until 2005, followed by a stable pattern that was neither significantly increasing nor decreasing. CPUE tends to be unresponsive to depletion in exploitable biomass until levels of stock become sufficiently low that divers are no longer able to compensate for the decrease by increasing their fishing power or concentrating their fishing effort on the areas that have yet to become depleted9,10.
Trends in abundance estimated from fishery-independent surveys have also been modelled for most of the commercially productive reefs. For most areas within the management unit, it was found that abundance across all size classes has been decreasing annually at a rate of 3–9 per cent16. Sub-adult abalone abundance declined at 19 per cent annually from 2001 and 2004, after which there was no significant change. This placed the number of future recruits to the stock in 2013 at 50 per cent below the average for 2001 to 2005. In contrast, adult abalone increased at an annual rate of 15 per cent between 2001 and 2003, and then declined at 9 per cent annually until 2009, after which there was no significant change. This placed the number of adult-sized abalone in the stock in 2013 at 49 per cent below the average for 2001 to 2005.
The TACCs have been progressively reduced during the past 5 years, from 490 t to 433 t, in response to an ongoing decline in available biomass. Only some of this decline is due to overharvesting; range expansion of the Black Sea Urchin (Centrostephanus rodgersii) has led to the formation of extensive barrens—habitat that will not support abalone.
Collectively, the evidence suggests that the abalone biomass within this management unit is depleting. Management measures are in place, but these have not yet resulted in measurable improvements. Although the biomass of this stock is not likely to be recruitment overfished at present, the above evidence indicates that the current level of fishing pressure is likely to cause the stock to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
Tasmanian Western Zone Fishery management unit
The Tasmanian western zone management unit has an LML of 140 mm. The Tasmanian Western Zone Fishery was split into the western and central western zones in 2007, with subsequent boundary changes in 2013. The TACC in this management unit was reduced in 2013 to 1001 t, associated with the zonal restructure and a downturn in CPUE11. The TACC reduction reflects a management action to redistribute effort from the south to the underutilised north of the western zone. Spatial catch caps are set annually for four broad geographic regions within this zone, to prevent excess catch being harvested as a result of economic pressures. CPUE has declined gradually, from record highs in excess of 150 kg/hour in 2000 to less than 100 kg/hour in 2013. Accumulation of stock biomass following a period of underexploitation in the 1990s led to the high catch rates in the early 2000s. The continuous decline in CPUE over the past 14 years reflects the historically high TACCs set over the past decade. While the CPUE in 2013 is high relative to other management areas, it is continuing to decline, despite TACC reductions, and the rate of decline is increasing.
The above evidence indicates that, although the biomass in this management unit is not likely to be recruitment overfished, the stocks are likely to become recruitment overfished at the current level of fishing mortality.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
Tasmanian Central - western Zone Fishery management unit
The Tasmanian central western zone management unit has an LML of 132 mm. The Tasmanian Western Zone Fishery was split into the western and central western zones in 2007. The boundary between the western zone and the central western zone was moved northwards in 201311. This part of the west coast was underexploited in the mid-2000s, and spatial management measures were used to shift effort into this region. CPUE has oscillated over the past 15 years, but has declined over the past 5 years, suggesting that the biomass has decreased rapidly. Accordingly, the TACC in this management unit was reduced in 2013 to 105.1 t. CPUE has declined gradually, from around 140 kg/hour in 2008 to less than 80 kg/hour in 2013. CPUE continued to decline in 2013 despite a TACC reduction, and the rate of decline since 2010 has been sharp.
The above evidence indicates that, although the biomass in this management unit is not likely to be recruitment overfished, the stocks in the management unit are likely to become recruitment overfished at the current level of fishing mortality.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
Tasmanian Northern Zone Fishery management unit
The Tasmanian northern zone management unit and the Tasmanian Bass Strait fishery management unit were separated in 2003. Three different LMLs (120 mm, 127 mm and 132 mm) were in place during the reference year, reflecting the variation in growth rates within this zone. Catch and catch rates have varied between 2000 and 2013 as a function of changing market preference and adaptive management (that is, effort redistribution and change in LML). The TACC for the northern zone reached a peak of 402.5 t in 2011. Geometric mean CPUE varies across different geographic regions within the northern zone, but has fallen for the zone overall over the past 3 years, despite TACC reductions in 2012 and 201311.
The above evidence indicates that, although the biomass in this management unit is not likely to be recruitment overfished, the stocks in the management unit are likely to become recruitment overfished at the current level of fishing mortality.
On the basis of the evidence provided above, the management unit is classified as a transitional–depleting stock.
Tasmanian Bass Strait Zone Fishery management unit
The Tasmanian northern zone fishery was split into two zones in 2003, creating the Tasmanian northern zone fishery management unit and the Tasmanian Bass Strait fishery management unit11. Two different LMLs (110 mm and 114 mm) were in place during the reference year, reflecting the variation in growth rates within this zone. Since the creation of this zone, catch and CPUE have been stable, except for 2007, when the fishery was closed because of concerns about the possible risk of transferring abalone viral ganglioneuritis (AVG) from Victoria to Tasmania. The TACC for the Bass Strait zone remains at 70 t, and the geometric mean CPUE has been stable at around 65 kg/hour11.
The above evidence indicates that stocks in the Tasmanian Bass Strait zone are unlikely to be recruitment overfished and that the current level of fishing mortality is unlikely to cause these stocks to become recruitment overfished.
On the basis of the evidence provided above, the management unit is classified as a sustainable stock.
Tasmanian Eastern Zone Fishery management unit
The Tasmanian eastern zone fishery management unit has an LML of 138 mm. Relative stock biomass in this fishery (estimated using CPUE as a proxy) has oscillated substantially since 1995, with evidence of an approximate 8‑year cycle11. Based on declining CPUE between 2000 and 2003, the TACC was reduced from 1190 t to 857 t in 2002, and to 770 t in 2004. Subsequent increases in CPUE and increasing median length of the commercial catch led to increases in the TACC of 5 per cent in 2008, 2009 and 2010, resulting in a TACC of 896 t by 2010. Rapid declines in CPUE in late 2010 resulted in a reduced TACC of 721 t for 2011. Further rapid decline in 2011 resulted in an additional TACC reduction to 549.5 t for 2012. In 2013, minor reductions in the TACC to 528.5 t were made to address local concerns in one subregion. In 2013, a slight increase in zonal geometric mean CPUE was observed, suggesting that the TACC reductions over the previous 3 years had achieved the objective of reducing exploitation to a level at which biomass could rebuild. However, the historically low CPUE and catch observed in 2012 suggest that biomass in this fishery is at its lowest point to date.
The above evidence indicates that biomass of the Tasmanian eastern zone fishery management unit is recruitment overfished. However, the current level of fishing pressure should allow the management unit to recover from its recruitment overfished state, and measurable improvements in biomass were detected in 2013.
On the basis of the evidence provided above, the management unit is classified as a transitional–recovering stock.
New South Wales management unit
The New South Wales Abalone Fishery is managed as a single management unit with a single TACC, set by an independent Total Allowable Catch Committee. Recent annual assessments have relied heavily on fishery-dependent data, including catch, CPUE and mean weight of abalone, summarised at a range of spatial scales. At present, there are no direct or derived estimates of biomass or fishing mortality.
Blacklip Abalone stocks have historically suffered from overfishing associated with serial depletion. Mortality events in the late 1990s and early 2000s, associated with infection by the Perkinsus parasite, further contributed to depletion of stocks from Jervis Bay to the north18. Catch rates fluctuated in the 1990s and early 2000s, with the lowest catch rate on record in 2005. The mean weight of catches at this time was close to the weight of abalone at the LML. The abundance of legal-sized abalone detected during a fishery-independent survey was low. These indicators are consistent with a stock that was, at this time, fished-down hard against the LML, was experiencing very high fishing mortality, had lost most of its age structure and resilience, and had significantly reduced breeding potential19.
Substantial reductions in the TACC, from 333 t during the 1990s through several stepwise decreases to 75 t in 2009–10, were intended to limit further depletion of the stock and facilitate stock recovery. The LML was increased from 115 mm to 117 mm across the fishery in 2008 and, subsequently, to 123 mm south of Wonboyn Lake. Consequently, since 2005, there has been a strong recovery in CPUE and mean weight of abalone in the catches in many, but not all, areas of the fishery. Improvements in these indicators have generally been greatest on the far south coast of New South Wales. Although stock rebuilding is continuing overall, it is spatially patchy. Low catches and modest increases in CPUE in the northern spatial components of the fishery suggest a slower recovery of stocks in these areas. Moreover, rebuilding is uncertain in areas of the fishery that were severely depleted by 2005 and that have not recently been fished19.
The above evidence indicates that the biomass of this stock was recruitment overfished during the 1990s and early 2000s, and that some spatial components of the fishery have not demonstrably recovered from this state. However, for the period 2006 to 2013, the indicators described above suggest a recovering stock.
Despite substantial increases in catch rates since 2005, the current TACC of 125 t is still relatively low compared with historical catches, to facilitate further rebuilding of stock. This evidence indicates that the current level of fishing pressure should allow the stock to recover from its recruitment overfished state.
On the basis of the evidence provided above, the biological stock is classified as a transitional–recovering stock.