Fisheries recruitment is generally variable and seldom related to spawning stock size, except in the case of salmonid fishes. Environmental variability has a large effect on recruitment that can be stronger than the effect of stock size. It is difficult to understand whether fishing pressure is affecting stock sizes unless we have some understanding of how the environment affects the populations of exploited species. While the environment is known to significantly affect recruitment, the relationship is complex and multivariate. To gain insight into the relationship, we need to assemble a range of environmental variables for appropriate statistical analyses. These data are often scattered, and have varying spatial and temporal resolutions and quality. An important step along the way to elucidating relationships between environment and recruitment is to compile the datasets into a form that can be spatially matched, appropriately averaged and statistically scaled to extract the environmental signal from the background noise that could otherwise obscure a relationship with recruitment.

If environmental indices are related to fisheries recruitment of specific species (e.g. marine scale fish, rock lobsters and prawns) then management can use the indices (1) to understand the physical processes that account for variability in recruitment and fishery productivity, (2) possibly predict recruitment a year or two in advance, and (3) to speculate about the effects of global warming on our fisheries.

Pearce et al. (FRDC 94/032) compiled time series of environmental variables in Western Australia, and found that variations in the strength and path of the Leeuwin Current affected mainly the larval stages of commercial species. The magnitude and sign (positive or negative) of the effect differed by species. We will build on this study, incorporating some of their recommendations, to gain insight into the processes affecting recruitment.

In NSW, inherent variation among the characteristics of different estuarine fisheries has resulted in a range of physical modifications designed to improve the selectivity of conventional gears. While some of these designs have been effective in reducing the bycatches of unwanted species by up to 95%, rates of reduction more commonly range between 30 and 70%. Such reductions have obvious benefits for the stocks of bycatch species. considering the magnitudes of bycatches in many estuarine fisheries, and especially those targeting prawns (i.e. often 1000s of fish per haul), it is apparent that despite the use of modified gears, in nearly all cases there still remains some capture and mortality of unwanted individuals.

To augment the post-release survival of unwanted bycatch throughout nearly all of NSW estuarine fisheries (including those involving static gears, where no BRDs have been developed), ancillary options within the second category of input controls (listed above in B2) need to be investigated. The sorts of modifications that warrant examination include, defined soak times for gears, devices to limit predation on discarded bycatch, netting materials in codends that reduce damage to bycatch, the use of gloves to handle bycatch, and the utility of separating target and bycaught species in water after capture.

The majority of these operational and/or post-capture handling procedures have NOT been examined, but have the potential to significantly reduce the remaining impacts of commercial fishing gears on non-target species and sizes in NSW’s estuaries. This is one of the main research priorities detailed in the Fishery Management Strategy for the NSW Estuary General Fishery and comprises a key category within the 2004-2007 Strategic Research Plan for Fisheries, Aquaculture and Aquatic Conservation in NSW. Quantification of the utility of this category of input controls would also have benefit and application throughout all other coastal fisheries in Australia.

The research will form the basis of a PhD candidature. This approach is justified because (i) the work is new and there is sufficient intellectual content to support a PhD student, (ii) there is a paucity of researchers with higher degrees working in the applied fields of gear technology and bycatch mitigation in Australia and (iii) previous, similarly-structured FRDC projects (e.g. 93/180 and 2001/031) have resulted in successful PhD candidatures by project staff. Specifying a PhD candidature formalizes what would already occur if funding was sought for a Fisheries Technician, but at approx. 1/3 the cost, while attracting a substantial in-kind contribution from affiliated institutions (the National Marine Science Centre and University of New England).

Available evidence suggests that most fish species harvested by the NSW demersal trap and recreational fisheries are taken at sizes that are too small to optimise yield and/or economic return. This is because most species taken in both of these fisheries either have MLL’s that are too small or do not have MLL's at all. There have only been stock assessments done on snapper (FRDC project No. 93/074) and silver trevally (FRDC project No. 97/125) in the trap fishery. Both studies showed that they were growth overfished and the results have been used to increase the MLL for snapper and to impose a MLL for silver trevally across all fisheries. Many other species taken by fish traps are in decline and it is highly likely that they are also growth overfished. Unfortunately, very little is known about the biology or life-history of these other species. Recreational fishers are significant harvesters of all species taken in the NSW demersal trap fishery and it is important that any MLL’s designed to reduce overfishing are applied across all fisheries.

NSW Fisheries does not currently have a policy for setting MLL's at particular sizes and the process developed during this study may form the basis for such a policy. It is important to consider several issues when setting appropriate harvest sizes and these include: (i) the size at sexual maturity; (ii) the size that will optimise yield; (iii) market requirements; (iv) an economic assessment, and (iv) public perception.

The information on biology, stock-assessment and protocols for setting appropriate harvest sizes developed during this project will directly address several key areas of importance recognized by the FRDC. The planned outcomes will lead to fisheries management being based more on the precautionary principle, will maximise the economic and social returns from harvesting these species while also providing for effective management of recreational fishing. These areas are considered to be high priorities by the NSW FRAB and by Recfish Australia in their National Research and Development plan for the recreational sector.

The recently-completed National Recreational and Indigenous Fishing Survey (NRIFS) estimated that more than 11 million bream and pink snapper (comprising over 10% of the total released catch) were caught and released from recreational hook-and-line fisheries during 2000/01 (Henry and Lyle 2003). These rates of discarding are of considerable concern, because they have the potential to represent high levels of previously unaccounted fishing mortalities.

In order for Australia’s commercial and recreational hook-and-line fisheries to be considered ecologically sustainable, their fishing operations should minimize the mortality of discarded fish. The release of large numbers of fish from commercial and recreational fisheries whose fate is currently unknown is, therefore, of major concern to all stakeholders in these fisheries. The review by McLeay et al. (2002) prioritised breams and snappers as two species potentially susceptible to high levels of mortality after release from hoon-and-line fisheries in Australian. Further, hook damage and handling (e.g. exposure to air, physical damage, etc ) were identified as factors that probably contribute the most towards these mortalities.

The regulation of fishing mortality in all Australian hook-and-line fisheries is mostly based on legal lengths and daily bag limits on the assumption that the majority of discarded fish survive. The almost complete absence of information on survival rates for the majority of species precludes any validation of the benefits of current management options or the effects of proposed changes. For example, in Victoria during the late 1990’s, the minimum legal length (MLL) for black bream was increased to conserve fish stocks in the Gippsland Lakes. While this has resulted in larger fish being retained by anglers, recent creel surveys in the Gippsland Lakes showed that up to 80% of the black bream catch is below legal size and therefore discarded (Conron and Bills, 2000). If the PRS of these discarded bream is low, then the increased MLL will achieve little in terms of conserving stocks. Similarly, Victorian fisheries managers will be reviewing the MLL for pink snapper which, at 27 cm total length (TL), is low compared to other States and which per-recruit analyses suggest is less than optimal for maximising yield (Coutin, 1997). Knowledge of the PRS rates of pink snapper is critical for evaluating the benefits of any change to the current MLL.

There is a perception among all stakeholders (including recreational and commercial fishers, tourism organisations, conservationists and Fisheries Managers) and evidence from related studies (McLeay et al., 2002) that many fish released after capture by current hook-and-line methods may die. Despite these widespread concerns, there are very few scientific data available on the actual PRS rates for line-caught fish in sheltered temperate ecosystems in Australia. There is a clear need to do this research for the key species identified, and to assess the significance of any mortalities on their populations. If the levels of PRS are of concern then there is a consequent need to (i) identify the deleterious hooking, handling and release procedures, (ii) examine ways to improve PRS, and (iii) incorporate realistic estimates of PRS into fishery and stock assessments.

The FRDC-funded review of this issue in Australia highlighted the need to coordinate research projects and to develop a standardised system for classifying stress, condition and injury and the stressors applied during catch-and-release procedures. By expanding and refining the field based experiment undertaken as part the pilot project funded by the Victorian FRAC, this proposed project would be taking an important step towards addressing these needs. It would also allow recommendations for the appropriate types of hooks and handling protocols to be used and ensure the protection of large numbers of discarded fish caught in sheltered temperate ecosystems. Further, as a demonstration of how these sorts of field-based, fishing-impact studies should be designed, analysed and interpreted, the proposed project will help develop standardized methodologies for estimating PRS and evaluating its impact on fish stocks.