Shark Gillnet and Shark Hook sectors
Chapter 12: Shark Gillnet and Shark Hook sectors
J Woodhams, T Emery and R Curtotti
|Fishing mortality||Biomass||Fishing mortality||Biomass|
|Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Recent catches are unlikely to drive the stock into an overfished state. Recent CPUE is relatively stable and above the limit reference point, indicating stability in biomass and fishing mortality.|
|Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Recent catches are below RBC. Estimates of pup production are close to, or above, the target reference point.|
(Pristiophorus cirratus, P. nudipinnis)
|Not subject to overfishing||Not overfished||Not subject to overfishing||Not overfished||Recent catch is below RBC; recent CPUE is above the target reference point.|
|Uncertain||Overfished||Uncertain||Overfished||Uncertain if fishing mortality in 2019–20 will allow recovery within the specified time frame. Biomass is likely to remain below 20% of unexploited levels.|
|Economic status||NER for the Gillnet, Hook and Trap Sector were $3.4 million in 2016–17. Preliminary estimates indicate that NER were likely negative for 2017–18 and positive $5.6 million in 2018–19. Although gummy shark biomass is not constraining NER, the management of non-target species and marine mammal interactions has likely contributed to low NER in recent years.|
a NER refer to the entire Gillnet, Hook and Trap Sector; therefore, this figure includes scalefish. Shark species account for around 65% of total Gillnet, Hook and Trap Sector gross value of production.
Notes: CPUE Catch-per-unit-effort. NER Net economic returns. RBC Recommended biological catch.
12.1 Description of the fishery
The Shark Gillnet and Shark Hook sectors (SGSHS) of the Southern and Eastern Scalefish and Shark Fishery (SESSF) extend south from the New South Wales – Victoria border, around Tasmania, and west to the South Australia – Western Australia border. Most fishing occurs in waters adjacent to the coastline and throughout Bass Strait (Figure 12.1).
Fishing methods and key species
The SGSHS uses demersal gillnet and longline to target gummy shark (Mustelus antarcticus). School shark (Galeorhinus galeus), elephantfish (Callorhinchus milii) and sawsharks (Pristiophorus cirratus and P. nudipinnis) are byproducts of fishing for gummy sharks. School shark was historically the primary target species in the fishery, but biomass was reduced below the limit reference point around 1990. Although overfished, school shark is the second most economically important species in the fishery.
Other important byproduct species (by weight) are snapper (Chrysophrys auratus), whiskery shark (Furgaleus macki), broadnose sevengill shark (Notorynchus cepedianus), bronze whaler (Carcharhinus brachyurus), draughtboard shark (Cephaloscyllium laticeps) and blue morwong (Nemadactylus valenciennesi).
The fishery is managed using a combination of input controls (gear restrictions and closed areas) and output controls (individual transferable quotas and limits on the proportion of school shark to gummy shark catch). The 4 principle commercial stocks taken in the SGSHS are managed under the SESSF harvest strategy framework (AFMA 2019). The harvest strategy is summarised in Chapter 8. School shark is subject to an incidental catch limit, and other measures to reduce targeting and catch. Spatial closures are implemented across the fishery to protect school shark breeding populations, pupping and nursery areas, and school and gummy shark habitat, and to promote the recovery of upper-slope dogfish stocks.
Gear and area closures have been implemented (primarily off South Australia) to reduce the risk of interactions with Australian sea lions and dolphins. These have changed the fishing areas and targeting behaviour of fishers, influenced the take of target species, and consequently affected catch-per-unit-effort (CPUE). These and other key wildlife bycatch issues are discussed further in Chapter 8.
From 1 July 2015, electronic monitoring (e-monitoring) has been mandatory for all full-time vessels in the SGSHS. The management aim is to review at least 10% of all recorded hauls to verify the accuracy of logbooks. In addition, gillnet boats operating off South Australia’s Australian Sea Lion Management Zones are subject to 100% review of video footage to monitor interactions with protected species. The deployment of physical observers ceased with the commencement of e-monitoring. This meant that some important data from the fishery were not collected. Physical observers were deployed again from September 2017 to July 2018. The Australian Fisheries Management Authority (AFMA) subsequently implemented a crew-collected data program in October 2018, to collect biological data needed to support stock assessments. AFMA is also investigating the use of e-monitoring to collect data previously collected by observers (for example, fish lengths).
Before spatial closures, which have been progressively implemented since 2003, effort in the SGSHS was spread across the waters of South Australia and eastern Victoria. However, the spatial closures outlined above have resulted in gillnet effort being concentrated off Victoria more recently (Figure 12.1). Effort in the gillnet sector peaked in 1987 at 99,000 km of gillnet hauled but has decreased to around one-third of this level in recent years (31,208 km of gillnet hauled in 2019–20). Hook effort has been variable in recent years, increasing from 2.17 million hooks in the 2018–19 season to 2.76 million hooks in the 2019–20 season.
Fishing for sharks in the waters off southern Australia began in the 1920s, using longlines. During the 1970s and 1980s, the sector mainly targeted school shark (Figure 12.2). Adoption of monofilament gillnets and concern about mercury content in large school sharks, coupled with declining school shark catches, resulted in gummy shark becoming the principal target species from around 1986 (Figures 12.2 and 12.3). This transition occurred in the early 1970s in Bass Strait, and later in the waters off South Australia and Tasmania. Additional information on catch and catch history is provided below for each of the key stocks.
Note: CTS Commonwealth Trawl Sector
Source: AFMA catch disposal records
Gavin Kewan, AFMA
|Fishery statistics a||2018–19 fishing season||2019–20 fishing season|
(t) (GHTS, CTS + GABTS))
(t) (GHTS, CTS + GABTS)
(<$0.10 million, <$0.10 million)
($19.59 million, $1.35 million)
($0.28 million, $0.31 million)
|School shark||215 b||196
($1.73 million, $0.31 million)
($21.66 million, $2.01 million)
|Effort||Gillnet: 32,008 km of net hauled
Hook: 2,165,571 hooks set
|Gillnet: 31,208 km of net hauled
Hook: 2,759,233 hooks set
|Fishing permits c||Gillnet: 61
|Active vessels||Gillnet: 41
|Observer coverage d||Gillnet: 10%
|Fishing methods||Demersal gillnet, demersal longline, dropline, mechanised handline, auto-longline|
|Primary landing ports||Adelaide, Port Lincoln, Robe (South Australia); Devonport, Hobart (Tasmania); Lakes Entrance, San Remo, Port Welshpool (Victoria)|
|Management methods||Input controls: gear restrictions, closed areas
Output controls: ITQs, school shark/gummy shark catch ratio restriction, size limits, trip limits
|Primary markets||Domestic: Melbourne, Adelaide and Sydney—fresh and frozen|
|Management plan||Southern and Eastern Scalefish and Shark Fishery Management Plan 2003|
a Fishery statistics are provided by fishing season, unless otherwise indicated. Fishing season is 1 May to 30 April. Value statistics are by financial year and were not available for the 2019–20 financial year at the time of publication. Components of catch may not sum to totals due to rounding. b Incidental catch allowance. c In the GHTS, additional permit types limit gear use and access to state waters. d Numbers of hooks observed relate only to the Shark Hook Sector. Since 1 July 2015, e-monitoring has been mandatory for all full-time vessels in the SGSHS. Video footage of at least 10% of all recorded hauls is reviewed to verify the accuracy of logbooks. In addition, gillnet boats operating off South Australia’s Australian Sea
Lion Management Zones are subject to 100% review of video footage for interactions with protected species.
Notes: CTS Commonwealth Trawl Sector.GABTS Great Australian Bight Trawl Sector. GHTS Gillnet, Hook and Trap Sector. GVP Gross value of production. ITQ Individual transferable quota. TAC Total allowable catch (for the entire SESSF).
12.2 Biological status
Elephantfish (Callorhinchus milii)
Line drawing: Karina Hansen
Stock structure of elephantfish is not known, and populations are considered to constitute a single stock for management purposes.
Elephantfish is a small component (~2%) of landed catch of the 4 stocks assessed in this chapter. Catch of elephantfish in the SGSHS increased during the 1970s and peaked at almost 120 t in 1985 (for catch since 1997, see Figure 12.4a). Catch has since declined, and has been relatively stable at around 40–60 t in recent years. Combined landings from the Gillnet, Hook and Trap Sector (GHTS), Commonwealth Trawl Sector (CTS) and Great Australian Bight Trawl Sector (GABTS) in 2019–20 was 47 t (Figure 12.4b; Table 12.2).
Discards of elephantfish reported in logbooks in 2019–20 were 24.4 t (20.3 t in 2018–19 and 16.5 t in 2017–18). The life-state information for this discarded catch is mostly recorded as ‘unknown’ or with no detail provided. More generally, post-release survival of discarded live elephantfish is uncertain. It is unknown if all discarded catch is reflected in logbooks. Burch, Althaus & Thomson (2019) estimated a total catch in 2018 at 182.5 t, comprising 129.4 t of discards and 53 t of commercial catch (SESSF 50.6 t and state catch 2.4 t).1
Recreational catch of elephantfish is unknown for all states but has been considered insignificant in New South Wales and Tasmania (Woodhams et al. 2018a). In Victoria, historical recreational catches have been significant, with up to 45 t caught in Western Port in March to May 2008. Catch rates and popularity of this fishery have declined more recently (Conron 2016), which presents an uncertainty in assessing the stock.
Elephantfish has been managed as a tier 4 stock under the SESSF harvest strategy framework since 2009. The tier 4 harvest strategy framework uses standardised CPUE as an index of abundance for the stock and proxy for biomass. However, the stock has been increasingly difficult to assess using this method, and as a result the harvest control rules that are typically applied to this method have not been applied in recent years. In 2018, the Shark Resource Assessment Group (SharkRAG) recommended rolling over the total allowable catch (TAC) from the previous year for the 2019–20 season.
At its January 2020 meeting, SharkRAG discussed the low reliability of generating a recommended biological catch (RBC) through applying the tier 4 harvest control rule, and agreed to recommend rolling over the TAC from the previous season (114 t) to the 2020–21 fishing season (and the subsequent 2 seasons; 2021–22 and 2022–23). In making its recommendation, the RAG noted the low risk rating of the stock from the recent draft ecological risk assessment (ERA) (AFMA 2020). However, the RAG also expressed concerns about its ability to provide robust recommendations on the RBC for the stock due to limited reliable information.
The CPUE standardisations applied to the stock in 2018 show a variable catch rate, with a slight decreasing trend in recent years (Sporcic & Haddon 2018). The recent average CPUE was above the target reference point for both series.
Stock status determination
Although it has not been possible to output a reliable RBC through a harvest control rule for this stock for the last couple of seasons, recent CPUE is above the target reference point, and reported catches have been relatively stable and below previous (and accepted) RBCs. Further, the stock is not actively targeted in the fishery and has been classified as low risk through the draft ERA. The above information indicates that recent catches from the fishery are unlikely to result in the stock becoming overfished. On this basis, the stock is classified as not overfished and not subject to overfishing.
Gummy shark (Mustelus antarcticus)
Line drawing: Karina Hansen
The most recent research on stock structure for gummy shark indicates that there are most likely 2 stocks in Australian waters: 1 in southern Australia, extending from Bunbury in Western Australia to Jervis Bay in New South Wales, and another in eastern Australia, extending from Newcastle to the Clarence River in New South Wales (White & Last 2008). The southern Australian biological stock is split into 4 populations for modelling purposes: the continental shelf of Bass Strait, Tasmania, South Australia and Western Australia. The first 3 are assessed together by the Commonwealth (Punt, Thomson & Sporcic 2016) and are reported here. The fourth is assessed and reported separately by Western Australia (Braccini, McAuley & Rowland 2013).
Catch of gummy shark in the SGSHS increased after 1970, initially as byproduct in the school shark fishery, and then increasingly as a target as school shark catches decreased from 1986 (Figure 12.5a). Catch in the SGSHS reached a peak of around 2,300 t in 1993. Catch has been around 2,200 t in recent years (Figure 12.5a). The 2019–20 season was the fourth year of a multiyear TAC for the stock. The initial TAC for 2019–20 was 1,785 t, but the actual TAC was 1,897 t with the carryover of undercaught quota (undercatch provisions) from the previous season (Figure 12.5b). Combined landings for the GHTS, CTS and GABTS in 2019–20 was 1,781 t, which is approximately 81% of the total catch across the 4 stocks assessed in this chapter.
Discards of gummy shark reported in logbooks in 2019–20 were 11.7 t (13.8 t in 2018–19 and 11.1 t in 2017–18). Multiple life states were recorded by fishers for discards, with most (13.6 t) recorded as ‘unknown’ or with no detail provided. The post-release survival of discarded live gummy shark is uncertain. Burch, Althaus & Thomson (2019) estimated a total catch in 2018 of 1,865.6 t, comprising 73.6 t of discards and 1,791.9 t of commercial catch (SESSF 1,672.6 t and state catch 119.3 t).2
Recent state recreational catch is uncertain. For example, 37 t was reported in South Australia in 2013–14 and 934 fish were reported caught in Western Australia in 2015–16 (Woodhams et al. 2018b).
The stock assessment for gummy shark has not been updated since 2016; however, an updated assessment is expected in 2020. The most recent integrated stock assessment model used data to the end of 2015 (Punt, Thomson & Sporcic 2016). Updated inputs to the assessment included catch data from 2013 to 2015, revisions to earlier catch and length-frequency data, new age-frequency data, and updated CPUE indices. Some changes to the model structure were also made: catches by the different gear types are now assumed to occur simultaneously rather than sequentially; the ‘hook fleet’ has been separated into trawl, deep and shallow fleets; and allowances have been made for age-reading errors. As in previous assessments, the 2016 assessment uses estimated pup production as a proxy for biomass because of the expected close relationship between pup production and female spawning biomass. This is because most of the data come from the gillnet sector, which catches a narrow size range of fish and does not catch adults.
Bass Strait, South Australian and Tasmanian regions were treated as separate populations in the model, with no movement of animals between these populations and no density-dependent effects of 1 population on another. The models share some model-estimated parameter values, especially Tasmania, where the data are unable to support full parameter estimation. The model also assumes commonality in biological parameters, including age–length and length–weight relationships, fecundity, gear selectivity, and overall availability as a function of age.
The gillnet closures off South Australia have influenced catch and CPUE of gummy shark in this area. When the previous 2014 assessment was run, there was concern that the CPUE data in the South Australian region were less reliable as an index of abundance in recent years (Thomson & Sporcic 2014). Consequently, data after 2009 were not included in the 2014 or 2016 assessments.
The model estimated relative pup production and RBCs (according to the harvest control rule) for each population. The RBCs were then summed to give a stock-level RBC for the fishery (1,961 t). In addition, different gear types are known to catch different size ranges of sharks (selectivities), which affect the RBC calculation. Consequently, a range of RBCs were calculated, based on different catch proportions taken by line and gillnet, which were assessed against their effect on pup production at a regional level (Punt, Thomson & Sporcic 2016).
The base-case assessment estimated 2016 pup production as a proportion of the unfished level of pup production (P0; 1927) to be above 48% of virgin pup production (0.48P0) for all 3 populations modelled: 0.53P0 for Bass Strait (Figure 12.6a), 0.63P0 for South Australia (Figure 12.6b) and 0.75P0 for Tasmania (Figure 12.6c). These are all slightly lower than those estimated by the 2014 assessment (Thomson & Sporcic 2014).
FIGURE 12.6 Estimated pup production as a proportion of unfished level of pup production for gummy shark in (a) Bass Strait, (b) South Australia and (c) Tasmania, 1927 to 2016
Source: Punt, Thomson & Sporcic 2016
Stock status determination
The 2016 stock assessment estimated pup production in the most recent year (2015) to be above the target for each of the 3 populations modelled. Total catch has been less than the RBC since it was calculated (including in 2019–20) and so is unlikely to have driven the stock into an overfished state. On this basis, gummy shark in the SGSHS is classified as not subject to overfishing and not overfished.
Sawshark (Pristiophorus cirratus, P. nudipinnis)
Line drawing: FAO
Three species of sawshark (common sawshark—P. cirratus, southern sawshark—P. nudipinnis and eastern sawshark—P. peroniensis) are caught in southern Australian waters. Little is known about the stock structure or movements of sawshark. Two species dominate reported sawshark catches in this sector: common sawshark and southern sawshark. For assessment purposes, all sawsharks found south of the Victoria – New South Wales border are assumed to be common or southern sawshark, and those found north of that border are assumed to be eastern sawshark (AFMA 2014d). Around 90% of the total sawshark catch from southern Australia is taken from Bass Strait (AFMA 2011a). All sawshark catch in the SESSF is managed under a single TAC, and status is reported for a single multispecies stock.
Catch of sawshark in the SGSHS increased in the early 1970s to around 200 t by 1974, and then fluctuated between about 170 and 350 t per year until the early 2000s (Figure 12.7a). Combined landings for the GHTS, CTS and GABTS in 2019–20 was 189 t (Figure 12.7b; Table 12.2), which is approximately 9% of the total catch across the 4 stocks assessed in this chapter.
Discards of sawshark reported in logbooks in 2019–20 were 2.8 t (2.8 t in 2018–19 and 0.4 t in 2017–18). The life state for all discarded catch was recorded in logbooks as ‘unknown’. The post-release survival of discarded live sawshark is uncertain. It is unknown if all discarded catch is reflected in logbooks.
Burch, Althaus & Thomson (2019) estimated a total catch in 2018 of 223.5 t, comprising 26.5 t of discards and 197 t of commercial catch (SESSF 188 t and state catch 8.9 t).3 State recreational catches are unknown but considered low (Woodhams et al. 2018c).
Sawshark has been managed as a tier 4 stock under the SESSF harvest strategy framework since 2009. Potential avoidance of this species by operators using gillnets suggests that the corresponding standardised CPUE may not adequately reflect stock abundance. As a result, SharkRAG recommended using standardised trawl CPUE as an index of abundance (AFMA 2015c) when applying the tier 4 harvest control rule.
Haddon and Sporcic (2018) estimated an RBC (using SESSF trawl data to 2017) of 519 t in 2017, which was converted to the first year of a 3-year TAC of 430 t for the 2018–19 fishing season.
In 2014, SharkRAG recommended a decrease in the biomass target reference point (BTARG) for sawshark from 48% to 40% of unfished biomass to reflect the byproduct nature of the stock (AFMA 2014b). The recent average CPUE for sawshark was estimated to be above the target reference point (Figure 12.8).
Stock status determination
Commercial catch in the SGSHS in 2019–20 (189 t) was below the RBC and the TAC. The addition of available discard estimates will not increase the total catch to a point where it exceeds the RBC. On this basis, the stock is assessed as not subject to overfishing.
The recent average CPUE for sawshark was estimated to be above the target reference point. On this basis, the stock is assessed as not overfished.
School shark (Galeorhinus galeus)
Line drawing: Karina Hansen
School shark has a broad distribution throughout temperate waters of the eastern North Atlantic, western South Atlantic, and north-eastern and south-eastern Pacific oceans; and temperate waters off South Africa, New Zealand and southern Australia. There is some uncertainty about the stock structure for school shark; however, a recent genetic study found no genetic differences between Australia and New Zealand (Hernández et al. 2015). School shark is managed as a single stock in the SESSF.
Catch of school shark in the SGSHS peaked at more than 2,500 t in 1970 and then declined rapidly to around 700 t in 1973. Catch in the sector again increased to around 2,000 t in 1986, before declining steadily through the late 1980s and 1990s, stabilising at around 200 t per year from 2000 onwards (Figure 12.9a). In 2009, the species was listed as conservation-dependent under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and since then has been subject to measures to reduce catch. These measures include the implementation of a catch ratio of 20% school shark to gummy shark—whereby a quota holder must hold 5 times more gummy shark quota than their school shark catch (2011–12 season)—and the requirement that all live-caught school shark be released (2014–15 season).
Combined landings for the GHTS, CTS and GABTS in 2019–20 was 184 t (Figure 12.9b), which is approximately 8% of the total catch across the 4 stocks assessed in this chapter. Discards of school shark reported from logbooks in 2019–20 were 13.4 t (10.9 t in 2018–19 and 7.7 t in 2017–18), with 8.4 t having a recorded life status of ‘unknown’. Of the 2.1 t with some information to indicate an ‘alive’ status upon release, 670 kg was reported as ‘alive and vigorous’, the balance being either ‘alive’, ‘alive, just’ or ‘alive sluggish’. The post-release survival of sharks alive upon release in this sector is likely to be variable and influenced by a number of factors. However, this element of fishing mortality is uncertain. Until such time as this uncertainty is rectified, the post-release survival of ‘alive’ sharks will be assumed to be zero when determining status.
Burch, Althaus & Thomson (2019) estimated a total catch in 2018 of 209.7 t, comprising approximately 177.1 t of commercial catch in the SESSF, 29.4 t of state catch and 3.3 t of discards.4 The discard estimate was carried over from 2016. Since recent estimates of state recreational catches are not available, total mortality in state fisheries is uncertain.
Assessments for school shark indicate that the stock has been overfished since approximately 1990, and the stock has been classified as such since ABARES began status reporting in 1992. The most recent full assessment was undertaken in 2009 using data to 2008 (Thomson & Punt 2009). At that time, the base-case model estimated biomass to be at 0.12B0. The catch data from 1998 to 2008 used in the assessment comprised low (per vessel) catch levels, and the CPUE derived was considered unlikely to accurately reflect the underlying stock dynamics.
In 2012, the 2009 assessment was re-run with additional catch data for 2009 to 2012 (Thomson 2012), specifically to estimate recovery time frames for the stock under a range of future incidental catch levels and to investigate the impact of a proposed auto-longline shark fishery in South Australia. Under a zero-catch scenario, the stock was projected to rebuild to 0.2B0 within 23 years. At a constant catch of 250 t, the stock was projected to rebuild to 0.2B0 in 80 years, and a constant catch of 275 t was projected to collapse the stock. These projections were based on assumptions that the gear selectivity, and spatial and temporal distribution of catches remain similar to those in 2011. Uncertainties around these median projections were not provided by the assessment. The school shark rebuilding strategy was revised in 2015 using the outputs of these analyses. It specifies a maximum catch of 225 t, which would allow recovery to the 0.2B0 limit reference point in the specified recovery time frame (in this case, set at 3 times the estimated generation time or 66 years) (AFMA 2015b).
In 2018, a close-kin mark–recapture study and a population dynamics model that makes use of those data (termed a ‘close-kin model’ [CKM]) provided an estimate of current absolute abundance and recent population trend (2000 to 2017) from a single region and population (that is, assuming 1 mixed stock) (Thomson et al. 2019). In contrast to previous assessments, the CKM does not provide an estimate of biomass depletion compared with unfished biomass.
The abundance of school shark (in numbers) estimated by the CKM (c. 50,000 adults; Thomson et al. 2019) was lower than the 2012 assessment model projections (c. 250,000 adults; Thomson 2012).
Thomson et al. (2019) undertook projections based on 4 constant exploitation scenarios (zero, 2016 rate, 2017 rate and the mean exploitation rate for 2013 to 2017). All 4 exploitation rates resulted in a long-term upward trend in population size. SharkRAG agreed to use the mean exploitation rate for 2013 to 2017 to recommend the incidental catch allowance for the stock. This exploitation rate provided for a consistent recovery, as opposed to the 2017 fishing mortality rate, which appeared to lead to an initial reduction in stock size (for the first 2 years) before recovery (AFMA 2018).
The median trend for the stock response to the 2013 to 2017 exploitation rate was upwards; however, the confidence interval was wide enough to allow a downward trend, and Thomson et al. (2019) note that there was no guarantee of the sustainability of these catches. Thomson et al. (2019) note that the collection of close-kin samples for an additional 4 years is expected to greatly reduce these confidence intervals. The 2013 to 2017 exploitation rate resulted in total mortality recommendations of 256 t in 2019–20, 263 t in 2020–21 and 270 t in 2021–22.
The CKM considers the period 2000 to 2017, since this was the period over which the juveniles sampled would have been born. The approach is unable to evaluate biomass relative to an unfished state, as required under the School Shark Rebuilding Strategy (AFMA 2015b). Additionally, Thomson et al. (2019) propose that there are likely to be a number of school shark stocks (that is, units that are reproductively isolated, at least to some degree, and that show differing, but almost certainly overlapping, spatial distribution), some of which are severely depleted. As such, there remains a significant uncertainty associated with assessing the status of the school shark stock as it is currently defined (that is, a single SESSF stock).
In December 2018, SharkRAG supported continued close-kin sampling (for 3 years) and use of the CKM for estimating abundance of school shark. The RAG also discussed the difficulties associated with updating the old school shark assessment with the recent close-kin information and agreed not to pursue such an assessment. SharkRAG also discussed the need for updating the School Shark Rebuilding Strategy (AFMA 2015b), due to be undertaken in 2020.
Stock status determination
Combining Commonwealth commercial catch (184 t) with the estimate of discards from logbooks in 2019–20 (13.4 t, assuming 100% mortality) and the most recent estimate of state catches (29.4 t) provides an estimated total mortality in 2019–20 of 226.8 t. This is above the incidental catch allowance in the rebuilding strategy (215 t), and slightly above the maximum level reported to allow recovery in the time frame specified in the rebuilding strategy (225 t). However, this level of catch is below the highest level (250 t) forecast to allow for recovery in the 2012 modelling, assuming gear selectivity, and spatial and temporal distribution of catches remain similar to those in 2011. This total (226.8 t) is also below the level of catch estimated through the CKM work to allow for rebuilding, noting the uncertainty associated with these trends and the uncertainty in stock structure.
Other indications that the school shark stock may have stabilised and may even be recovering include an increasing preliminary index of school shark abundance based on trawl CPUE (Sporcic & Haddon 2018), surveys by the Institute for Marine and Antarctic Studies showing higher numbers of pups from school shark pupping areas off Tasmania (McAllister et al. 2015) and anecdotal reports from industry.
Given the above information, the fishing mortality of the stock remains classified as uncertain.
Since the recent CKM work does not provide an estimate of biomass depletion compared with unfished biomass, biomass status in 2019–20 is determined based on the most recent estimate of population depletion. The last full stock assessment in 2009 (Thomson & Punt 2009), which used data up to 2008, estimated the biomass at 0.12B0. Projections of this model in 2012 indicated that recovery to 0.2B0 would take 23 years under a zero-catch scenario (Thomson 2012). Catches have not been zero in the intervening period. On this basis, the stock is unlikely to have recovered to above 0.2B0 and as such remains classified as overfished.
12.3 Economic status
Key economic trends
The real gross value of production (GVP) in the SGSHS for the 4 shark species taken in the GHTS declined from a peak of $28.2 million in 2008–09 to $17.21 million in 2013–14 and then recovered to $23.66 million by 2018–19 (Figure 12.10). This recent recovery is primarily the result of higher volumes of gummy shark catch. Gummy shark accounts for the majority of GVP in the SGSHS (89% in 2018–19).
The 4 shark species that make up the SGSHS—gummy shark, school shark, sawshark and elephantfish—accounted for around 74% of the GHTS GVP in 2018–19, with scalefish species making up the remainder. Therefore, overall economic performance in the GHTS may contribute to an understanding of the economic status of the SGSHS.
Survey-based estimates of revenue, costs and net economic returns (NER) in the GHTS are available for 2016–17, and preliminary estimates are available for 2017–18 and 2018–19 (Figures 12.11 and 12.12). In 2017–18, non–survey based estimates indicate that NER became negative, −$3.4 million, potentially a result of lower catch volume of gummy shark and higher unit fuel prices. In 2018–19, non–survey based estimates show a strong recovery, with NER estimated to reach $5.6 million, largely driven by a significant increase in fishing revenue from higher catch volumes and lower overall fishing costs.
A profit decomposition of the gillnet sector of the GHTS (Skirtun & Vieira 2012) showed that the key driver of profitability in the sector from 2006–07 to 2008–09 was productivity growth. This was linked to the Securing our Fishing Future structural adjustment package (completed in 2006–07), which is considered to have removed the least efficient vessels from the sector (Vieira et al. 2010). The decline in NER in recent years can be partly linked to falls in the price of fish in the fishery, making the role of productivity in driving NER improvement less clear. Productivity followed an increasing trend between 2009–10 and 2013–14, and may have provided some support to a declining trend in NER (Mobsby forthcoming). Productivity was more variable from 2014–15 to 2016–17, and coincided with a period of improvement in NER for the fishery, indicating that fisher terms of trade may have been a more important factor driving NER improvement in this period (Mobsby forthcoming).
Significant spatial closures implemented in recent years have resulted in fishing intensity relocating to other areas. Particularly affected were operators who had the full extent of their usual fishing grounds closed, and those who had to switch to the use of hooks rather than gillnets in areas where gillnet closures are in place. Some South Australian gillnet fishers also operate in the South Australian Rock Lobster Fishery, which is considered to be profitable (Econsearch 2014) and could have supported some SGSHS operators affected by the closures. These changes would have reduced the profitability of gillnet operations in South Australia, contributing to the negative NER in the GHTS following the closures.
Performance against economic objective
A comparison of the biomass levels of key species with harvest strategy targets gives additional information on the economic status of the SGSHS. Gummy shark is the primary driver of economic performance in the SGSHS, accounting for 89% of SGSHS GVP in 2018–19. The target reference point for gummy shark is the biomass that corresponds to maximum economic yield (BMEY) proxy of 0.48P0 (48% of virgin pup production). The results of the 2016 stock assessment indicate that the biomass of gummy shark stocks is likely to be above the target reference point. If the proxy accurately reflects BMEY for this species, the results indicate that biomass is not currently constraining NER and that there may be potential for expansion in the sector.
School shark is the second most valuable species in the sector, accounting for 9% of SGSHS GVP in 2018–19, despite being caught under an incidental catch allowance. School shark biomass remains below the limit reference point, and stock rebuilding measures are likely to be affecting sector profitability. The school shark to gummy shark quota restriction implemented in 2011–12 may have reduced gummy shark catch and therefore current GVP (AFMA 2014c). Efforts to rebuild the school shark stock towards target levels should lead to increases in NER.
The challenge of reducing marine mammal interactions may affect the degree to which economic performance can be improved in the short term. Recent closures to mitigate interactions are likely to have contributed to the observed negative NER for the GHTS from 2009–10 to 2014–15, and may be related to increased gummy shark quota latency during this period. In 2015–16 to 2016–17, NER were positive and linked to productivity growth, indicating that the industry is actively adjusting to new operating conditions.
12.4 Environmental status
The SESSF is accredited against parts 13 and 13A of the EPBC Act until 12 February 2022. Conditions associated with the accreditation relate to the impact of fishing on bycatch species, particularly Australian sea lions (Neophoca cinerea), dolphins, seals and seabirds. Further recommendations associated with the accreditation relate to requirements for ERA, and monitoring of bycatch and discarding.
A level 2 ERA of 329 species resulted in 21 assessed as being at high risk (16 chondrichthyans and 5 marine mammals; Walker et al. 2007). A level 3 sustainability assessment of fishing effects assessment was completed for all 195 chondrichthyan and teleost species identified in the shark gillnet fishery, regardless of their level 2 productivity susceptibility analysis (PSA) risk score. The assessment found 7 species (all chondrichthyan) to be at high risk (Zhou, Fuller & Daley 2012). One species (common sawshark) was removed during the residual risk analysis (AFMA 2014a). The remaining 6 species considered to be at high risk are all sharks: bronze whaler, white shark (Carcharodon carcharias), whiskery shark, smooth hammerhead shark (Sphyrna zygaena), school shark and broadnose sevengill shark. A 2010 residual risk assessment of PSA results for non-teleost and non-chondrichthyan species identified 5 marine mammal species as high risk (AFMA 2010). A subsequent residual risk analysis removed 2 species (as a result of no interactions being recorded in the fishery) and included 1 further species (as a result of higher than expected interactions), resulting in 4 marine mammal species considered to be at high risk in the fishery: Australian fur seal (Arctocephalus pusillus doriferus), Australian sea lion, New Zealand fur seal (A. forsteri) and common dolphin (Delphinus delphis) (AFMA 2012). The results of the ERAs have been consolidated to form a priority list in an ERA strategy for the SESSF (AFMA 2015a). A revised ERA for the SGSHS is still in draft and expected to be finalised in late 2020.
In accordance with accreditation under the EPBC Act (see Chapter 1, ‘Protected species interactions’) AFMA publishes and reports quarterly on interactions with protected species on behalf of Commonwealth fishing operators to the Department of Agriculture, Water and the Environment (DAWE), and these are summarised below.
Reports for the GHTS in the 2019 calendar year indicate 278 interactions: 103 with mammals, 37 with seabirds, 136 with sharks and 2 with little penguins—Eudyptula minor (both dead). The mammal interactions comprised 35 interactions with dolphins (all dead), 2 with sea lions (1 alive; 1 dead), 2 with killer whales (both alive), 21 with New Zealand fur seals (all dead), 21 with Australian fur seals (6 alive; 15 dead) and 22 with seals (unclassified; 32 alive and 20 dead). The seabirds caught included albatrosses, petrels, prions and shearwaters; 16 were alive and 21 were dead.
Logbooks reported that 92 shortfin mako sharks—Isurus oxyrinchus (2 alive; 82 dead; 8 in unknown condition), 16 longfin mako sharks—I. paucus (8 alive; 8 dead), 12 porbeagle sharks—Lamna nasus (3 alive, 9 dead) and 16 white sharks (12 alive; 4 dead) were caught during 2019. Measures to reduce interactions with Australian sea lions and dolphins are discussed in Chapter 8.
These reported interactions with protected species form a part of the ongoing monitoring by DAWE of the performance of fisheries within their accreditation under the EPBC Act.
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