8.4 Information and Monitoring
8.4.1 Range of Information
season management arrangements for the following year. Catch rates below the target level (in the threshold range) trigger a review of management arrangements for the next season, which may subsequently result in management action if sustainability is considered to be at risk. Catch rates below the limit will trigger a review of the fleet’s spatial fishing patterns and catch rates to investigate why stock abundance is low. This will either result in more severe management action to protect the stock, or a change in monitoring if it is considered to be inaccurate.
8.3.2 Accounting for Uncertainty
Harvest control rules in place for the SBPMF are highly precautionary and as such are designed to account for a wide range of uncertainties. In addition to control rules that operate on an annual basis, there are many well-defined in-season control rules. These ensure a rapid response to evidence of stock depletion and are appropriate given the biological characteristics of the target species. Also important are the existence of control rules associated with both the opening and closing of the main fishing grounds. For example, catch rates from the recruitment surveys must demonstrate that the stock is above target levels before fishing can commence within the areas east of the CPL in a given season. Control rules also govern the total number of fishing nights within the season, restricting the total level of exploitation that can occur given the fishery is a limited entry fishery and effort is partly constrained by a maximum fleet headrope allocation (as a standardised fleet).
8.3.3 Evaluation
Evidence indicates that the current harvest control rules are appropriate and effective in achieving target exploitation levels. With the exception of 2012, catch rates of brown tiger prawns from the spawning stock surveys, a key annual performance indicator, have fluctuated around the target level and above the limit level since 2002 (see Section 6.1.1 for a review of the cause of the low brown tiger prawn spawning stock index for 2012 and what the outcomes were). Catch rates of western king prawns from the spawning stock surveys have fluctuated around the target level in all years since 2002. In summary, there is strong evidence that the harvest control rules for both species are working effectively for achieving acceptable exploitation levels.
8.4 Information and Monitoring
prawns, these fishery-dependent data alone were no longer considered adequate as the single source of information for monitoring these stocks.
Fishery-independent recruitment and spawning stock surveys have been undertaken annually since 2000 to determine the brown tiger and western king prawn recruitment and spawning stock levels. These measures of prawn abundance are used to assess the performance of the fishery each year and ensure that there is a sufficient level of escapement of prawns to sustain a sufficient level of breeding stock.
In addition to an abundance of biological information available from studies of the brown tiger and western king prawn stocks in Shark Bay (see Section 2), several FRDC-funded projects have examined various aspects of this fishery over the past decade. These have included:
• A study of the effectiveness of bycatch reduction devices in trawl nets was completed in 2002 (Kangas & Thomson 2004; Broadhurst et al. 2007).
• A biodiversity project comparing faunal assemblages in trawled and untrawled areas within Shark Bay was completed in 2007 (Kangas et al. 2007; Kangas & Morrison 2013).
• A collaborative study with researchers at Edith Cowan University analysed prawn logbook data using geostatistics to provide a better understanding of stock and fleet dynamics and to assess the appropriateness of the North CPL was completed in 2008 (Mueller et al. 2008, 2012).
• A project undertaken in collaboration with researchers at the University of Western Australia focused on minimising gear conflict and resource sharing issues in Shark Bay, and which included oceanographic modelling of prawn and scallop larval movement within the embayment (Kangas et al. 2012).
Data on environmental variables (e.g. Leeuwin Current strength, rainfall and temperature) that have shown to be important drivers of recruitment of prawns are also collected in Shark Bay annually.
Table 8.3. Summary of monitoring of brown tiger and western king prawns in the SBPMF
Data type Fishery- dependent or independent
Analyses and
purpose Areas of data
collection Frequency of
collection History of collection
Daily logbooks Dependent Catch and effort trends, calculation of commercial catch rates and area trawled
Detailed, by shot latitude and longitude
Daily (shot-by-shot since 1998)
Since 1962 Compulsory since 2008
Processor
unloads Dependent Validation of
logbook catches Shark Bay Monthly Since 1960s VMS Dependent Verification of boat
locations for logbook analysis
Shark Bay Every fishing
season Since 2000
Recruitment
surveys Independent Catch rates provide indices of
recruitment strength for tiger and king prawns and is used to predict catches for season Size composition data are used to inform the rolling opening/closures of different fishery areas during season
Eastern Shark
Bay March and
April Since 2000
Spawning stock
surveys Independent Catch rates provide indices of spawning stock abundance, which is used to determine the SRR for both species Provides
information on sex ratios and the reproductive stage of female prawns
North CPL, South CPL and Denham Sound
June, August and September
Since 2002
Biological
information Dependent and
independent Patterns of growth and reproduction, stock structure
Shark Bay Occasional Since 1970s