Contribution of three rivers to floodplain and coastal productivity in the Gulf of Carpentaria: Finfish catch and growth

Barramundi were used as an indicator species for the effects of river flows on estuaries because they use a variety of aquatic habitats (marine to freshwater) and are an iconic fisheries species of significance in northern Australia. The Fisheries Queensland commercial catch logbook and monitoring data for length, age and reproductive data provide a long-term data series of this estuarine-dependent species in the Gulf of Carpentaria (GoC)

Modelling environmental changes and effects on wild-caught species in Queensland. Environmental drivers.

We report on the findings of a collaborative research project that was designed to identify and measure the effects of environmental drivers on the abundance and population dynamics of key Queensland fishery species. The project was co-funded by the Commonwealth Government’s Fisheries Research and Development Corporation (FRDC) and carried out by a multi-disciplinary team of scientists from the University of Queensland (UQ), the Queensland Department of Agriculture and Fisheries (DAF) and the Australian Institute of Marine Science (AIMS). The research team applied modern statistical, data science and modelling techniques in combination with biological insights into the life cycles of the three target species. Background With increasing evidence that environmental conditions in the marine environment are changing rapidly, it is becoming ever more important to understand how these changes may impact on the population dynamics and abundance of important fish stocks. Understanding the influence of environmental conditions can provide greater certainty that the risk of overfishing (under adverse environmental conditions) or under harvesting (under favourable conditions) are accounted for by resource managers. This project aimed to identify the environmental factors which may be influencing the recruitment, catchability or productivity of Snapper, Pearl Perch, and Spanner Crab stocks in Queensland. Results from this work will support sustainable management of Queensland’s fisheries by directly informing the assessment and management of these key species within Queensland waters

River flows affect the growth of a tropical finfish in the wet-dry rivers of northern Australia, with implications for water resource development

Freshwater is a critical input to estuaries but is under increasing demand to support upstream human activities. In this study, otolith biochronology was used to quantify the relationship between river discharge and juvenile growth rates of barramundi (Lates calcarifer) in three regions of the Gulf of Carpentaria in northern Australia. In all regions, river discharge had a strong positive effect on juvenile growth rates. Models were also developed which incorporated the Southern Oscillation Index (SOI) and the Madden–Julian Oscillation (MJO). SOI values corresponding to La Niña events had strong positive consequences for juvenile barramundi growth rates in all regions, and the intensity of positive wet season MJO pulses had a strong positive effect on growth rates in the perennially flowing river, but not the intermittently flowing rivers. The consequences of three hypothetical water development scenarios were estimated for the perennial river. The model predicted a 12%, 8% and 1% reduction in annual barramundi growth rates under proposed scenarios for 18%, 8%, and 3% reduction in river discharge, respectively. Fish growth is a robust, quantitative metric that can be monitored pre and post water resource development to identify the least impactful development scenario and monitor its compliance and success through time

Rapid decline and decadal-scale recovery of corals and Chaetodon butterflyfish on Philippine coral reefs

Environmental disturbances to benthic habitat on coral reefs can affect fish assemblages, with dietary specialists like corallivorous Chaetodon butterflyfishes particularly sensitive to declines in hard coral cover. However, declines in density of corallivorous Chaetodon due to declines in hard coral cover are usually documented for individual environmental disturbances, often with limited quantification of post-disturbance recovery. Here, we documented effects of hard coral loss and recovery on the Chaetodon assemblage for 31 years at four sites in the Philippines. In this long-term “natural experiment”, we documented five environmental disturbance events (two typhoons, two mass coral bleaching events, and one period of destructive fishing) that reduced live branching hard coral cover on average by 61% and density of corallivorous butterflyfish by 47%, with an average duration of decline of 2 years. On average, these disturbance events resulted in an 8% annual decrease in absolute coral cover. We also monitored five periods of hard coral and butterflyfish recovery, with an average 202% increase in branching hard coral cover over 11 years, and a 196% increase in density of corallivorous butterflyfish over 12 years. On average, these recovery periods had a 2.4% annual rate of increase in absolute coral cover. The density of butterflyfish was not significantly affected by marine reserve protection, and thus, changes in butterflyfish density were most likely driven by change in benthic habitat. Assemblage structure of Chaetodon at each site was distinct and remained remarkably consistent for 31 years, despite substantial declines and recovery of coral cover. The difference in the rates of decline and recovery of butterflyfish raises concerns for the persistence of this iconic taxon in the face of increasing frequency and intensity of environmental disturbances to coral reefs

Rapid decline and decadal-scale recovery of corals and Chaetodon butterflyfish on Philippine coral reefs

Environmental disturbances to benthic habitat on coral reefs can affect fish assemblages, with dietary specialists like corallivorous Chaetodon butterflyfishes particularly sensitive to declines in hard coral cover. However, declines in density of corallivorous Chaetodon due to declines in hard coral cover are usually documented for individual environmental disturbances, often with limited quantification of post-disturbance recovery. Here, we documented effects of hard coral loss and recovery on the Chaetodon assemblage for 31 years at four sites in the Philippines. In this long-term "natural experiment", we documented five environmental disturbance events (two typhoons, two mass coral bleaching events, and one period of destructive fishing) that reduced live branching hard coral cover on average by 61% and density of corallivorous butterflyfish by 47%, with an average duration of decline of 2 years. On average, these disturbance events resulted in an 8% annual decrease in absolute coral cover. We also monitored five periods of hard coral and butterflyfish recovery, with an average 202% increase in branching hard coral cover over 11 years, and a 196% increase in density of corallivorous butterflyfish over 12 years. On average, these recovery periods had a 2.4% annual rate of increase in absolute coral cover. The density of butterflyfish was not significantly affected by marine reserve protection, and thus, changes in butterflyfish density were most likely driven by change in benthic habitat. Assemblage structure of Chaetodon at each site was distinct and remained remarkably consistent for 31 years, despite substantial declines and recovery of coral cover. The difference in the rates of decline and recovery of butterflyfish raises concerns for the persistence of this iconic taxon in the face of increasing frequency and intensity of environmental disturbances to coral reefs

18 years of otolith increment widths of barramundi (Lates calcarifer) in three catchments in the Gulf of Carpentaria

Measurements of the otolith increment widths of barramundi in three regions in the Gulf of Carpentaria. Measurements were taken during the course of NESP Northern Australia Environmental Resources Hub projects 1.3.1 and 1.4. Otoliths were predominantly sourced from Fisheries Queensland’s historical otolith collection, supplemented with samples collected during FRDC project 2007/002. The comma separated values (csv) file contains the following fields: - Region from which the fish was collected- Unique reference ID for each fish - The age at capture of each fish, used as a covariate in growth models - The year class of each fish - The year of growth represented by the increment being measured (range: 1997 to 2014) - The otolith increment being measured (one, two, or three in most instances, unless the fish was less than 3 years old) - The measured width of the increment, in mm

Pelagic larval duration and settlement size of a reef fish are spatially consistent, but post-settlement growth varies at the reef scale

Recent research has demonstrated that, despite a pelagic larval stage, many coral reef fishes disperse over relatively small distances, leading to well-connected populations on scales of 0–30 km. Although variation in key biological characteristics has been explored on the scale of 100–1000 s of km, it has rarely been explored at the scale relevant to actual larval dispersal and population connectivity on ecological timescales. In this study, we surveyed the habitat and collected specimens (n = 447) of juvenile butterflyfish, Chaetodon vagabundus, at nine sites along an 80-km stretch of coastline in the central Philippines to identify variation in key life history parameters at a spatial scale relevant to population connectivity. Mean pelagic larval duration (PLD) was 24.03 d (SE = 0.16 d), and settlement size was estimated to be 20.54 mm total length (TL; SE = 0.61 mm). Both traits were spatially consistent, although this PLD is considerably shorter than that reported elsewhere. In contrast, post-settlement daily growth rates, calculated from otolith increment widths from 1 to 50 d post-settlement, varied strongly across the study region. Elevated growth rates were associated with rocky habitats that this species is known to recruit to, but were strongly negatively correlated with macroalgal cover and exhibited negative density dependence with conspecific juveniles. Larger animals had lower early (first 50 d post-settlement) growth rates than smaller animals, even after accounting for seasonal variation in growth rates. Both VBGF and Gompertz models provided good fits to post-settlement size-at-age data (n = 447 fish), but the VBGF's estimate of asymptotic length (L ∞ = 168 mm) was more consistent with field observations of maximum fish length. Our findings indicate that larval characteristics are consistent at the spatial scale at which populations are likely well connected, but that site-level biological differences develop post-settlement, most likely as a result of key differences in quality of recruitment habitat

Primacy of bottom-up effects on a butterflyfish assemblage

The question of whether biological systems are maintained by top-down versus bottom-up drivers is a recurring one in ecology. It is a particularly important question to address in the management of coral reefs, which are at risk from a variety of anthropogenic stressors. Here, we explicitly test whether the abundance of different feeding guilds of coral-associated Chaetodon butterflyfishes are controlled by top-down or bottom-up drivers, and we assess the relative influence of all statistically significant drivers. We find that the abundance and species richness of Chaetodon butterflyfishes are predominately determined by bottom-up drivers. The abundance of corallivores is primarily driven by availability of branching and tabular live corals, whereas the abundance of generalists is most strongly influenced by a negative association with macroalgal cover. We also find evidence of weak top-down control on the abundance of corallivorous butterflyfish by gape-limited mesopredators, but no such effects on generalist butterflyfish. Our findings indicate that conservation of coral reefs for Chaetodon butterflyfishes must include management at a larger spatial scale in order to reduce the effect of coral reef stressors such as declining water quality and climate change, but should also include implementation of fisheries management tools in order to increase local herbivory