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.