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Anthropogenic alterations to river flow could have repercussions for flow-dependent species downstream but few studies account for these dynamic relationships or quantify impacts of altered river flow. Scylla serrata— a widely distributed portunid crab—was used as an example of a flow-dependent species to model impacts of altered flow on species abundance and catch. Crab population dynamics were modelled across a large semi-enclosed tropical sea in northern Australia. Environmental drivers, primarily river flow, but also temperature and the Southern Oscillation Index were linked to crab dynamics to explain variability in historical catches. Catch and abundance could then be predicted under altered flow scenarios. River flow significantly improved the ability to explain historical catches for some regions but not all, and the strength of this relationship varied across catchments. Altered flows had negligible effects for perennial rivers but for ephemeral and temporally variable rivers, predicted decreases in abundance and catch ranged from 36 to 46% on average. Our modelling approach showcases a way to dynamically and rigorously quantify impacts of altered river flow on a key species with potential to help inform natural resource management, including policy decisions on the timing, quantity, and method of water removed from rivers. [ABSTRACT FROM AUTHOR]

Short‐lived, fast‐growing species that contribute greatly to global capture fisheries are sensitive to fluctuations in the environment. Uncertainties in exact stock–environment relationships have meant that environmental variability and extremes have been difficult to integrate directly into fisheries management. We applied a management strategy evaluation approach for one of Australia's large prawn stocks to test the robustness of harvest control rules to environmental variability. The model ensemble included coupled environmental‐population models and an alternative catchability scenario fitted to historical catch per unit effort data. We compared the efficacy of alternative management actions to conserve marine resources under a variable environment while accounting for fisher livelihoods. Model fits to catch per unit effort were reasonably good and similar across operating models (OMs). For models that were coupled to the environment, environmental parameters for El Niño years were estimated with good associated precision, and OM3 had a lower AIC score (77.61) than the base model (OM1, 80.39), whereas OM2 (AIC 82.41) had a similar AIC score, suggesting the OMs were all plausible model alternatives. Our model testing resulted in a plausible subset of management options, and stakeholders selected a permanent closure of the first fishing season based on overall performance of this option; ability to reduce the risk of fishery closure and stock collapse; robustness to uncertainties; and ease of implementation. Our simulation approach enabled the selection of an optimal yet pragmatic solution for addressing economic and conservation objectives under a variable environment with extreme events. Article Impact statement: Simulation testing shows a seasonal closure protects fisher livelihoods and the stock in years with extreme environmental conditions. [ABSTRACT FROM AUTHOR]

Formal harvest strategies (HS) confer increased certainty for stakeholders in decision-making processes because they include pre-agreed, transparent rules that can be simulation tested prior to implementation. An important trade-off for small, low-value fisheries relates to balancing the value of the fishery with the costs of data collection, analysis and completing a stock assessment. Harvest strategies also need to effectively balance risks to the fish stock with the objective of maximising yield or economic returns from a fishery. As part of this balancing act, short-lived highly-variable stocks present some unique challenges that need to be accounted for in a HS. We describe the process used to revise the HS for Australia's redleg banana prawn fishery (Penaeus indicus) to address these challenges. The fishery is managed using input controls and recently implemented a seasonal closure (based on management strategy evaluation testing) to improve the robustness of the HS to extreme environmental variability while providing ecological and economic benefits. An additional positive trade-off was that this conservative measure simplified the HS and added a risk buffer to counter uncertainties due to relying solely on catch-per-unit-effort (CPUE) data as an index of relative abundance. The stock assessment model and associated hockey-stick control rule were modified to account for the high natural variability of the stock by stipulating that closure of the fishery in any given year is only deemed necessary if the limit reference point is breached in two consecutive years prior. In years with low fishing effort (whether due to ecological or economic factors), it may not be necessary to conduct a stock assessment or there may not be sufficient data to inform a reliable assessment. We analysed fishery data to inform selection of a data-sufficient cut-off threshold that triggers whether or not a stock assessment is required in any particular year. We also considered potential risks to the fishery of not doing an assessment as well as the impact of this decision rule on the performance of future stock assessments. Finally, we summarise some general lessons around pragmatic design of a HS for a small, highly variable fishery needing to balance risk to the stock with optimising catches and reducing management costs. • Risk-catch-cost frontiers are important considerations in fisheries management. • Pragmatic simple harvest strategies are needed for small data-poor fisheries. • A data-sufficient cut-off number can be used to trigger a stock assessment. • Precautionary risk buffers can reduce management costs. • Short-lived highly variable fisheries benefit from tailored harvest strategies. [ABSTRACT FROM AUTHOR]

Fishery-independent scientific surveys are highly valuable for monitoring lobsters and other fisheries. Yet, there are relatively few long-term monitoring surveys to support the provision of management advice. A number of challenges can prevent the continuity of long-term monitoring series. This paper uses the 35-year continuous annual dive surveys for Australia's Torres Strait tropical rock lobster (TRL) to overview strengths and limitations of a long-term scientific survey, as well as lessons learnt from having overcome a range of challenges. Fishery-independent surveys are more reliable than fishery-dependent data and are more robust to external shocks such as market drivers and fuel prices. The primary purpose of the surveys is to provide a reliable index of stock abundance together with data to inform on size and age structure, plus model parameters and reference points. Here, we also highlight additional survey benefits including: yielding positive gains relative to cost, facilitating an adaptive management approach that serves as an early warning system, reducing and resolving inter-sector conflicts, reduced frequency of stock assessments, providing data from associated habitat monitoring, improved stakeholder buy-in, utility for development of Operating Models for Management Strategy Evaluation, contribution to achieving certification, contributing to biodiversity agreements and consistent cross-jurisdictional monitoring. We analyse lessons learnt from challenges such as changes in resource management, budget cuts, increased health and safety requirements, maintenance of capability and staff capacity, stakeholder buy-in, need to validate survey results, a pandemic and changing climate. Our experiences highlight why long-term scientific surveys are considered the gold standard for fisheries monitoring and we provide insights for building and maintaining key marine monitoring series. [Display omitted] • Fishery-independent surveys are valuable but challenging to maintain long-term. • Challenges include costs, capacity, management changes, COVID19, climate change. • Survey data robust to extreme events and external system shocks. • Benefits include reliability, positive benefit:cost, habitat data, science buy-in. • Long-term scientific surveys considered the gold standard for fisheries monitoring. [ABSTRACT FROM AUTHOR]