Robust data is critical to ensure sustainability and demonstrate the social and economic benefits of recreational fisheries. Traditional data collection methods can be cost-prohibitive, especially for fisheries operating across large scales, or those requiring real time information. Challenges associated with data collection have been highlighted during COVID-19, where travel restrictions have changed the dynamics of regional tourism and associated recreational fishing. Increased domestic travel is delivering economic benefits to many regional locations, however, there have been concerns about increased effort and the longer-term impact of increased catches on stock sustainability.

Federal and State Governments have implemented a range of policy responses during COVID-19, with support measures and stimulus packages for businesses, including tourism. Many jurisdictions have implemented measures to assist commercial and recreational fishing sectors, while few jurisdictions have implemented changes to recreational fishing regulations. In Western Australia, recreational fishing rules were revised to address sustainability concerns for valuable stocks of demersal finfish. This policy shift was supported by evidence from ongoing monitoring and stakeholder engagement. Further reviews will be conducted following the current state-wide survey (September 2020–August 2021), which will provide estimates of participation, effort, catch and expenditure in regional Western Australia attributed to local and non-local residents and to recreational fishing.

While intensive survey methods are repeated periodically, the adoption of indicators between these intervals can inform ongoing assessments. Social and economic indicators, such as those obtained from administrative data or record of sales, have the potential to provide rapid assessment of changes in participation, fisher demographics and catches. While benchmarking these data against traditional surveys may be required, there is a need to investigate a range of data sources that could measure change and inform rapid assessments.

The proposed work is fundamental for assessment and sustainable, optimal harvest of Australia’s Spanish mackerel resources. This goal requires accurate information on which management decisions can be based. This project therefore seeks to describe the stock structure of a national shared resource, with a view to the development of complementary management approaches.

The NT, WA, Qld, Torres Strait and NSW have separate management regimes for the mackerel fisheries in their waters. However, our lack of information on stock structure means that the appropriate scale of management units is just not known. It is unlikely that it will coincide with current administrative boundaries. Basic questions such as whether management actions in one state will impinge on the fisheries of others cannot yet be answered. With such uncertainty, for example, would declines in one area reflect interception during migration, or over-fishing of spawners in another area? Different responses to such questions may require fundamentally different management approaches. Hence the Northern Australia Fisheries Management meeting of May 1997 recognized that stock definition was required for effective assessment and management of this species.

Most fishery assessments assume a randomly mixed unit stock; an alternative is to explicitly include spatial dynamics. Possibly with the exception of the east coast, there is no real basis for defining Spanish mackerel unit stocks. In none of the Australian fisheries are spatial relationships sufficiently understood to be addressed in assessments. The proposed research is requisite for basic stock assessment, and the first step in developing spatially structured models and management.

Spanish mackerel are also taken across our northern boundaries, in Indonesia, Papua New Guinea, and Pacific Island states. The proposed research is the basic work necessary to develop the methodology and information base for future research into these shared stocks, and for future studies into fine-scale spatial dynamics.

Recently available information suggests the Spanish mackerel fishery is growing rapidly in both commercial and recreational sectors. This underlines the need for this work as a basis for rational management. Commercial catches in WA and NT have increased substantially in recent years, and prices continue to rise. A recent recreational survey in NT revealed that recreational Spanish mackerel catches are of similar order to commercial catches. The species is a favoured target in the rapidly-growing and lucrative fishing tour sector.

The need for good for stock assessment is thus growing. Each state has responded with FRDC- or internally-funded programs. The results of this project could substantially change the directions of these projects, by establishing whether the assessment and management should be on a joint basis across states, or whether they should be on a more regional basis.

We submit this EOI to the priority ‘Biological parameters for stock assessments in South Eastern Australia – a information and capacity uplift’

Empirical observations from around the world have shown that intense fisheries harvest and oceanic warming can both lead to individuals reaching sexual maturity at younger ages and smaller sizes (Waples and Audzijonyte 2016). We know that younger and smaller mothers produce fewer eggs that may be of poorer quality than those from older and larger mothers (Barneche et al. 2018). Further, young mothers often need to build up their energy reserves before spawning each year, meaning that they experience a constrained spawning season. A shorter spawning window reduces the likelihood that their offspring will encounter an environment favourable for growth and survival (Wright and Gibb 2005). Harvest-induced declines in age and size at maturity have, for example, been implicated as one of the main drivers underpinning the collapse of Canadian Atlantic cod stocks (Hutchings and Rangeley 2011).

Environmental stress can also lead to poorer conditioned fish that lack the resources to spawn at all. The prevalence of ‘skip spawning’, as it is known, is hard to ascertain in wild populations but could be as high as 30% of the sexually mature biomass in some years (Rideout and Tomkiewicz 2011). Earlier maturity and skip spawning both have the potential to significantly impact on the biomass of sexually mature individuals in a stock and overall levels of recruitment success. Failure to properly account for these reproductive phenomena can lead to significant under- or over-estimation of SSB, which in turn leads to ineffective management advice that may heighten the risk of stock decline, unnecessarily limit catches, or impede stock recovery.

The rapid warming of southeast Australian waters has already been implicated in driving significant increases in the juvenile growth rates of harvested species, including tiger flathead, redfish and jackass morwong (Thresher et al. 2007, Morrongiello and Thresher 2015). It is plausible that these growth changes (predicted by eco-physiological theory, Atkinson 1994) are linked to commensurate, yet unknown, declines in age and size at maturity. Further, warmer waters may be stressing spawning adults (Portner and Farrell 2008), leading to an increased prevalence of skip spawning in southeast Australian fishes. Importantly, in recent times the biomass of several SESSF species has failed to recover despite significant management intervention. There is a real and pressing need to update the maturity parameters used in assessment models to reduce uncertainty in stock projections.

Our two-part project will refine and validate novel otolith-based methods to estimate an individual’s age at maturity and spawning dynamics from information naturally recorded in its otolith, and then apply this to existing otolith collections. AFMA already invests significant resources into the routine collection of otoliths for ageing purposes. In Part One of our project, we propose to value-add to these existing monitoring programs by developing new maturity and spawning assays that can be readily integrated into stock assessments to reduce model uncertainty and improve harvest strategies (FRDC strategic outcome 2 & 4), in turn bolstering community trust in projections (FRDC strategic outcome 5). In Part Two of our project, we will develop unprecedented insight into the reproductive history of SESSF stocks by recreating time series of maturity using archived otoliths that are currently sitting idle in storage.

Postgraduate students and early career researchers will play a central role in the development and delivery of our project. This experience will help provide a clear pathway for graduates into fisheries science. Our project will bolster the capacity and capability of fish ageing laboratories across Australia to deliver improved monitoring services to fisheries managers (FRDC enabling strategy IV).

More generally, we believe that our novel maturity and spawning assays have the potential to impact on fisheries assessment in other jurisdictions across the world that experience the same time and cost impediments we face here in Australia. Perhaps most excitingly, our assays have the potential to provide much needed maturity information to data poor and emerging fisheries across the Info-Pacific region using information in already collected otoliths.

References
Atkinson, D. 1994. Temperature and organism size: a biological law for ectotherms? Advances in ecological research 25:1-58.
Barneche, D. R., D. R. Robertson, C. R. White, and D. J. Marshall. 2018. Fish reproductive-energy output increases disproportionately with body size. Science 360:642-645.
Hutchings, J. A., and R. W. Rangeley. 2011. Correlates of recovery for Canadian Atlantic cod (Gadus morhua). Canadian Journal of Zoology 89:386-400.
Morrongiello, J. R., and R. E. Thresher. 2015. A statistical framework to explore ontogenetic growth variation among individuals and populations: a marine fish example. Ecological Monographs 85:93-115.
Portner, H. O., and A. P. Farrell. 2008. Physiology and climate change. Science 322:690-692.
Rideout, R. M., and J. Tomkiewicz. 2011. Skipped spawning in fishes: more common than you might think. Marine and Coastal Fisheries 3:176-189.
Thresher, R. E., J. A. Koslow, A. K. Morison, and D. C. Smith. 2007. Depth-mediated reversal of the effects of climate change on long-term growth rates of exploited marine fish. Proc. Natl. Acad. Sci. U.S.A. 104:7461-7465.
Waples, R. S., and A. Audzijonyte. 2016. Fishery-induced evolution provides insights into adaptive responses of marine species to climate change. Front. Ecol. Environ. 14:217-224.
Wright, P. J., and F. M. Gibb. 2005. Selection for birth date in North Sea haddock and its relation to maternal age. Journal of Animal Ecology 74:303-312.