White Banana Prawn Fenneropenaeus merguiensis

Justin Roach^a, James Woodhams^a, Mervi Kangas^b and Brad Zeller^c

Table 1: Stock status determination for White Banana Prawn

Jurisdiction	Commonwealth	Queensland	Western Australia
Stock	NPF	East coast (ECOTF, RIBTF)	NBPMF	KPMF
Stock status
Stock status	Sustainable	Sustainable	Sustainable	Sustainable
Indicators	Catch, CPUE, trigger limits, escapement strategy	Catch, CPUE, stock assessments	Catch, catch projections

CPUE = catch per unit effort; ECOTF= East Coast Otter Trawl Fishery (Queensland); KPMF= Kimberley Prawn Managed Fishery (Western Australia); NBPMF= Nickol Bay Prawn Managed Fishery (Western Australia); NPF= Northern Prawn Fishery (Commonwealth); RIBTF= River and Inshore Beam Trawl Fishery (Queensland)

Stock Structure

The biological stock structure of White Banana Prawn is uncertain. There is some evidence that there may be separate biological stocks of White Banana Prawn in the Northern Prawn Fishery (Commonwealth); however, the boundaries of these biological stocks are unknown¹. Additionally, biological stocks within Western Australia and Queensland are unlikely to be completely independent, although it does appear that biological stocks separated by large distances are more independent than adjacent biological stocks². In the absence of clear information on biological stock structure, status is reported at the management unit level.

Stock Status

Northern Prawn Fishery (Commonwealth) management unit

Recruitment of White Banana Prawns in the Northern Prawn Fishery (Commonwealth) is thought to be largely determined by rainfall³. As a result, a reliable stock–recruitment relationship has not been established. No formal stock assessment exists for this stock. However, a model that predicts catch, using rainfall data, is currently being developed by CSIRO (the Commonwealth Scientific and Industrial Research Organisation).

The harvest strategy for White Banana Prawns in the Northern Prawn Fishery (Commonwealth) is designed to allow for sufficient escapement to ensure adequate spawning biomass (based on historical data). This is achieved through season length and catch-rate thresholds⁴. The harvest strategy is designed to perform under conditions of substantial variation in biomass that are thought to be largely independent of fishing.

In 2010, the season ran for approximately 10 weeks (the minimum season length is 6 weeks), with total reported commercial landings of 5642 tonnes (t). This catch is similar to that of the previous two seasons and is approximately 25 per cent above the average catch of the preceding 10 years (2000–09). The commercial catch in 2011 was higher, at 7141 t. These catch levels are indicative of a larger than average biomass, assuming that fishing power has remained relatively constant. Although fishing mortality is thought to be high for White Banana Prawns in some years⁵, the species is thought to be resilient to fishing pressure. Effort expended on White Banana Prawns in the Northern Prawn Fishery (Commonwealth) in 2010 (3146 vessel days) was around 82 per cent of the average effort over the preceding 10 years.

The recent historically high commercial catch of White Banana Prawns and a longer than minimum season length (supported by high catch rates) indicate that the management unit is unlikely to be recruitment overfished. The comparatively low effort indicates that fishing mortality is unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the Northern Prawn Fishery (Commonwealth) management unit is classified as a sustainable stock.

East coast (Queensland) White Banana Prawn management unit

The White Banana Prawn fishery is characterised by highly variable commercial catches, which are believed to be strongly affected by environmental factors such as rainfall, salinity, river flow and temperature^2–3. The most recent quantitative assessment of the Queensland White Banana Prawn stock² estimated that annual maximum sustainable yield (MSY) in 2004 was 802 t, with a 90 per cent confidence interval of 453–1031 t. In 2004, the reported total catch was 928 t, which exceeded MSY. However, it appears that recruitment in 2004 was high, and hence the available biomass was also high—biomass did not fall below 50–70 per cent of unfished biomass. It is important to note that MSY is the long-term average catch required to maximise yield from a fishery. High annual commercial catches that exceed MSY from time to time do not necessarily equate to overfishing; in 2004, they reflected the high recruitment and subsequently high available biomass in that year. The fishery's average catch over the past 10 years was 580 t, which is below MSY but within the 90 per cent confidence interval for MSY. In 2009 and 2010, the commercial harvest (908 t and 851 t, respectively) was above MSY but within the 90 per cent confidence interval.

The assessment² also found that, although biomass fell below 40 per cent of the unfished level in some of the substocks in some years, these substocks recovered without management intervention within 1–2 years. The management unit is not considered to be recruitment overfished, and the current level of fishing pressure is unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the east coast (Queensland) White Banana Prawn management unit is classified as a sustainable stock.

Nickol Bay Prawn Managed Fishery (Western Australia) management unit

Historical commercial catch levels from 1989 to 1998 have been used as the basis for calculating target catch ranges. The target catch range is 40–220 t⁶. Annual commercial catch projections for the fishing season are based on summer rainfall (between December and March). The commercial catch projection for the 2010 fishing season was 30–60 t. Total commercial catch for 2010 was 40 t, which is within the target catch range and projected catch range. Because of the low catch prediction, only three boats fished in 2010, for a low total effort of 69 vessel days. The management unit is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the Nickol Bay Prawn Managed Fishery (Western Australia) management unit is classified as a sustainable stock.

Kimberley Prawn Managed Fishery (Western Australia) management unit

Historical commercial catch levels from 1989 to 1998 have been used as the basis for calculating target catch ranges. The range in the Kimberley Prawn Managed Fishery (Western Australia) is 200–450 t⁶. Annual commercial catch projections for the fishing season are based on January and February rainfall levels in Kalumburu and Derby, and the spawning stock being adequate. The commercial catch projection for the 2010 fishing season was 230–350 t. Total commercial catch for 2010 was 241 t, which is within the target catch range and projected catch range. The management unit operates under an upper limit effort cap of 1500 vessel days (based on historical effort levels), and only 365 vessel days were fished in 2010. The management unit is not considered to be recruitment overfished, and the current level of fishing mortality is unlikely to cause the management unit to become recruitment overfished.

On the basis of the evidence provided above, the Kimberley Prawn Managed Fishery (Western Australia) management unit is classified as a sustainable stock.

Table 2: White Banana Prawn biology^1–2,6

Longevity and maximum size	1–2 years; >24 cm TL
Maturity (50%)	~6 months; 12–15 cm CL

CL = carapace length; TL = total length

Figure 1: Distribution of reported commercial catch of White Banana Prawn in Australian waters, 2010 (calendar year)

Main features and statistics for White Banana Prawn stocks/fisheries in Australia in 2010

Fishing is primarily undertaken using demersal prawn otter trawl gear. Spotter planes may be used to direct trawlers to prawn aggregations.
Management measures used are predominantly input controls, including vessel and gear restrictions, temporal and spatial closures, variable season lengths, effort allocation, and mandatory use of bycatch reduction and turtle excluder devices. Catch and catch-rate trigger limits are in place in the Northern Prawn Fishery (Commonwealth). The Northern Prawn Fishery is in the process of moving to output controls, in the form of total allowable catches and individual transferable quotas.
Numbers of vessels that caught White Banana Prawns commercially in 2010 were 50 in the Northern Prawn Fishery (Commonwealth), 227 in the East Coast Otter Trawl and River and Inshore Beam fisheries (Queensland), 3 in the Nickol Bay Prawn Managed Fishery (Western Australia) and 13 in the Kimberley Prawn Managed Fishery (Western Australia).
The total amount of White Banana Prawns caught commercially in 2010 was 6202 t, comprising 5070 t in the Northern Prawn Fishery (Commonwealth), 851 t in the East Coast Otter Trawl and River and Inshore Beam fisheries (Queensland), 241 t in the Kimberley Prawn Managed Fishery (Western Australia) and 40 t in the Nickol Bay Prawn Managed Fishery (Western Australia). The most recent estimate of recreational catch in Queensland suggests that catch of White Banana Prawns in 2010 was in the range of 45–70 t⁷. Indigenous catch of White Banana Prawns in Queensland is unknown. Recreational and Indigenous catch is unknown in the fisheries managed by the Commonwealth and Western Australia⁸.

Figure 2: Commercial catch of White Banana Prawns in Australian waters, 2000–10 (calendar year)

Catch Explanation

The Northern Prawn Fishery (Commonwealth) catch in 2000 was almost the lowest on record, despite good rainfall before the season in the Gulf of Carpentaria, whereas the catch in 2001 (7245 t) was considerably higher than expected. Between 2003 and 2007, catches declined, possibly as a result of fewer vessels operating in the fishery (decreasing from 114 in 2001 to 55 in 2007), and structural adjustment, which resulted in a 45 per cent reduction in the number of statutory fishing rights during 2006. Poor rainfall is also believed to have affected catches. Better catches have been seen in the 2008–10 seasons, with 5070 t of White Banana Prawns landed in 2010⁹. In Queensland, catch levels varied widely from 1991 to 2010, ranging from 344 to 1080 t. The factors underlying this variability are uncertain, but may include effort switching between White Banana Prawns and other prawn species.

Effects of fishing on the marine environment

There is typically a high proportion of bycatch relative to retained product in tropical prawn trawl fisheries. However, since White Banana Prawn is an aggregating species, bycatch can be minimised. The ratio of bycatch to catch for White Banana Prawns in the Northern Prawn Fishery (Commonwealth) is much lower than for Tiger Prawns in the same fishery. Post-release survival of these species is variable¹⁰.
To address impacts of trawling on the environment, the Northern Prawn Fishery (Commonwealth) conducts ecological risk assessments. A scientific and crew-based observer program is also implemented in the fishery to monitor the level of bycatch.
The use of turtle excluder devices and bycatch reduction devices is compulsory in all fisheries targeting White Banana Prawns. Use of turtle excluder devices in the Northern Prawn Fishery (Commonwealth) reduced turtle bycatch from an estimated 5700 individuals per year (before 2001) to approximately 30 per year (after 2001)¹². The introduction of turtle excluder devices in the Western Australia prawn trawl fisheries in 2003 reduced turtle bycatch by at least 95 per cent¹³. Turtle excluder devices have reduced annual sea turtle interactions to an intermediate–low risk in the East Coast Otter Trawl Fishery (Queensland)¹¹.
The Northern Prawn Fishery (Commonwealth) was certified as a sustainable and well-managed fishery by the Marine Stewardship Council in November 2012.

Environmental effects on White Banana Prawn

The abundance of prawns can be highly variable and influenced by environmental factors such as water temperatures, cyclones and broadscale oceanographic features³. For example, in Western Australia, cyclones can have either a positive or a negative impact on prawn biomass and availability. Early-season (December–January) cyclones can increase mortality of small prawns through the scouring of nursery areas, which destroys seagrass and algal habitat. Conversely, mortality can decrease when water becomes turbid because prawn mortality through predation is reduced⁶.
River flow as a result of rainfall is highly correlated with offshore commercial catches of banana prawns in the south-eastern Gulf of Carpentaria³. It has been suggested that increased river flow has different effects on different stages of the White Banana Prawn life cycle: high flows can increase emigration of juveniles from estuaries; increased flows can prevent immigration, settlement and survival of post-larvae; and rainfall run-off may increase the overall productivity, through the contribution of increased nutrient input to increased growth and survival rates².

^aAustralian Bureau of Agricultural and Resource Economics and Sciences
^b Department of Fisheries, Western Australia
^c Department of Agriculture, Fisheries and Forestry, Queensland