Environmental drivers of recruitment in a tropical fishery: Monsoonal effects and vulnerability to water abstraction

Fisheries and natural water resources across the world are under increasing pressure from human activity, including fishing and irrigated agriculture. There is an urgent need for information on the climatic/hydrologic drivers of fishery productivity that can be readily applied to management. We use a generalized linear mixed model framework of catch curve regression to resolve the key climatic/hydrological drivers of recruitment in Barramundi Lates calcarifer using biochronological (otolith aging) data collected from four river-estuary systems in the Northern Territory, Australia. These models were then used to generate estimates of the year class strength (YCS) outcomes of different water abstraction scenarios (ranging from 10% to 40% abstraction per season/annum) for two of the rivers in low, moderate, and high discharge years. Barramundi YCS displayed strong interannual variation and was positively correlated with regional monsoon activity in all four rivers. River-specific analyses identified strong relationships between YCS and several river-specific hydrology variables, including wet and dry season discharge and flow duration. Water abstraction scenario models based on YCS-hydrology relationships predicted reductions of >30% in YCS in several cases, suggesting that increased water resource development in the future may pose risks for Barramundi recruitment and fishery productivity. Our study demonstrates the importance of the tropical monsoon as a driver of Barramundi recruitment and the potential for detrimental impacts of increased water abstraction on fishery productivity. The biochronological and statistical approaches we used have the potential to be broadly applied to inform policy and management of water resource and fisheries.

Refuges and ecological traps: Extreme drought threatens persistence of an endangered fish in intermittent streams

Recent droughts raise global concern over potential biodiversity loss and mitigating impacts to vulnerable species has become a management priority. However, drought impacts on populations are difficult to predict, in part, because habitat refuges can buffer organisms from harsh environmental conditions. In a global change context, more extreme droughts may turn previously suitable habitats into ecological traps, where vulnerable species can no longer persist. Here, we explore the impacts of California's recent record-breaking drought on endangered juvenile Coho salmon. We estimated the variability of cumulative salmon survival using mark-recapture of nearly 20,000 tagged fish in intermittent stream pools during a 7-year period encompassing drought and non-drought conditions. We then determined the relative importance of physical habitat, streamflow, precipitation, landscape, and biological characteristics that may limit survival during drought. Our most striking result was an increase in the number of pools with reduced or zero survival during drought years and a coincident increase in spatial variability in survival among study reaches. In nearly half of the stream pools, salmon survival during drought was similar to mean survival of pools assessed during non-drought years, indicating some pools had remarkable resistance (ability to withstand disturbance) to extreme drought. Lower survival was most attributable to longer duration of disconnection between upstream and downstream habitats, a consequence of increasing drought severity. Our results not only suggest that many pools sustain juvenile salmon in non-drought years transition into ecological traps during drought but also highlight that some pools serve as refuges even under extreme drought conditions. Projected increases in drought severity that lead to longer droughts and greater habitat fragmentation could transform an increasing proportion of suitable habitats into ecological traps. Predicting future impacts of drought on Coho salmon and other sensitive species will require identification and protection of drought refuges and management strategies that prevent further habitat fragmentation.

Catchment Level Water Resource Constraints on UK Policies for Low-Carbon Energy System Transitions by 2030

The UK government has proposed different low-carbon energy system options that lead to meeting its greenhouse gas emissions target of 80% reduction on 1990 levels by 2050. While these energy system options meet emission targets at feasible economic cost, water requirement for the deployment of the proposed energy technology mix is not adequately accounted for. This may become critical, as some of the proposed energy technologies are relatively more water-intensive, and could result in significant future water resource constraints. Previous studies have analyzed the potential water resource constraints of future energy systems in the UK at national scale. However, water must be considered as a local resource with significant regional variability. This paper uses a linear spatial-downscaling model to allocate water-intensive energy system infrastructure/technologies at catchment level, and estimates water requirements for the deployment of these technologies for the Committee on Climate Change Carbon Budgets in 2030. The paper concludes that while national-scale analysis shows minimal long-term water related impacts, catchment level appraisal of water resource requirements reveals significant constraints in some locations. This has important implications for regions where the water-energy nexus must be analyzed at appropriate spatial resolution to capture the full water resource impact of national energy policy.