Developing and validating novel methods to estimate age- and size-at-maturity in South Eastern Australian fisheries

Project number: 2022-047
Project Status:
Current
Budget expenditure: $348,420.00
Principal Investigator: John R. Morrongiello
Organisation: University of Melbourne
Project start/end date: 29 Oct 2023 - 27 Sep 2026
Contact:
FRDC
TAGS
Rac Cmwth
Fisheries Management
Ageing

Need

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.

Objectives

1. Refinement and validation of three methods to estimate the maturity and spawning history of SESSF species, using information naturally archived in fish otoliths
2. Identification of an accurate and cost-effective method to estimate fish age at maturity and spawning history from their otoliths
3. Recreation of the maturity and spawning history of a SESSF species using one of our three novel assays
4. Quantification of how rapid ocean warming and harvest have affected the expression of age at maturity and the propensity of a SESSF species to skip spawn

Related research

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Environment
Industry

Characterising the impacts of warm water and other stressors on the boom-and-bust cycle of the Commercial Scallop

Project number: 2022-044
Project Status:
Current
Budget expenditure: $373,032.00
Principal Investigator: Ryan Day
Organisation: Institute for Marine and Antarctic Studies (IMAS) Hobart
Project start/end date: 30 Jun 2023 - 29 Jun 2026
Contact:
FRDC
TAGS
Rac Tas
Fishing Gear
Fisheries Management
Climate Change
Climate Adaptation
SPECIES
Commercial Scallop

Need

The commercial scallop (Pecten fumatus) fisheries in south-eastern Australia have long been characterised as boom-and-bust (Tracey & Lyle 2010). While historic overfishing has contributed to this (Young 1989), unpredictable cycles of alternating abundance and large-scale die-off characterise the species, particularly in the eastern portion of the region. For instance, there have been five sudden die-offs on the eastern side of the Tasmanian fishery (TSF) and Commonwealth fishery (BSCZSF) combined since 2005. Whereas, since most recently being fished in 2014, the scallop beds in the King Island region of the BSCZSF have been harvested each year due to predictable and constant recruitment and scallop conditioning.
The relative difference in predictability between the regions likely lie with the changing nature of the EAC on the east coast bringing warm, nutrient-poor water to the east coast and the Leeuwin current bringing cold nutrient-rich water to the west coast, with these differences likely to be further exacerbated due to climate change. A case in point is the Tasmanian fishery, which after being closed for five years due to the stocks being depleted, opened in 2021 off Babel Island (east) only to find the bed had died-off only a few months post-preseason surveying. A sudden influx of warm water was likely the cause of the die-off, with beds in the eastern portion of both the BSCZSF and the Victorian scallop fishery (OSF) simultaneously suffering a significant loss of condition but not death (Semmens unpublished). In 2022, again a major die-off has impacted the TSF, with beds at White Rock (east) found to be dying off upon opening in late June. The unpredictability of these die-offs confounds management decisions, as a lack of understanding into the drivers of die-offs means that even if beds with commercially significant biomass are surveyed and opened, they may be lost before fishing begins. There is a clear need to understand these die-offs, determine if they can be predicted and adapt management such that it can be reactive and is tailored to the region in which the bed occurs (e.g., east vs west). Fitting management strategies to the fishing region also makes sense biologically, with the east and west portions of the species’ distribution displaying different life history features (e.g., spawning and settlement times, growth rates, etc; Semmens et al. 2019) and this may be a contributing factor to die-offs.
This project will use a collaborative industry/management/research approach to investigate the factors causing mass die-off of scallop beds, characterising the impacts of stressors including fishery practices, such as the use of tumblers, survey method (e.g., dredge vs video) and environmental factors, such as location of beds, sea temperatures (considering both absolute temperature and rate of change) and food availability, and assessing them in a framework that fits management practices to the relative risk of loss of fishable stock. Developing an understanding of the factors driving mortalities will also enable evaluation of existing data capture capabilities to identify whether potentially harmful conditions can be identified before beds are lost. Where deficiencies are identified, new data collection techniques will be evaluated, including video surveying of closed regions (both permanent, e.g., MPAs, and fishery closures) to allow more flexibility in decision making around when an area should be fished. The outcome of this research will provide the evidence needed to develop a decision-making framework that will enhance the rapid response capabilities of management of scallop fisheries in the future, but also ensure that they fit the changing environment and region within which the stocks sit, improving the sustainability of this vulnerable industry.

Objectives

1. Identify intrinsic stressors (e.g., surveying techniques (e.g., video vs dredge) and timing, location (e.g., east vs west) and timing of fishing, the use of tumblers, size limits of scallops, etc.) and extrinsic stressors (e.g., temperature, food availability, etc.) commonly faced within the Pecten fumatus fishery that have the capacity to negatively impact scallop condition and cause mortality
2. Experimentally evaluate the effects of intrinsic, extrinsic and synergistic stressors on scallop physiology, condition, and mortality
3. Opportunistically video survey and collect scallops for sampling from scallop beds exposed to adverse conditions and/or experiencing die-offs to corroborate experimental results against real-world results
4. Develop recommendations to monitor for, and respond to, environmental conditions that may drive scallop bed die-offs
5. Work with industry and management to co-design decision frameworks for the sustainable management of Commercial scallop fisheries, including designing regional-specific approaches to optimising fishing opportunity and maximising continuity of stock, including obtaining video survey data from closed areas that may support recruitment