Acute thermal tolerance of tropical estuarine fish occupying a man-made tidal lake, and increased exposure risk with climate change

Understanding acute hyperthermic exposure risk to animals, including fish in tropical estuaries, is increasingly necessary under future climate change. To examine this hypothesis, fish (upper water column species - glassfish, Ambassis vachellii; river mullet, Chelon subviridis; diamond scale mullet, Ellochelon vaigiensis; and ponyfish, Leiognathus equulus; and lower water bottom dwelling species – whiting Sillago analis) were caught in an artificial tidal lake in tropical north Queensland (Australia), and transported to a laboratory tank to acclimate (3wks). After acclimation, fish (between 10 and 17 individuals each time) were transferred to a temperature ramping experimental tank, where a thermoline increased (2.5 °C/hr; which is the average summer water temperature increasing rate measured in the urban lakes) tank water temperature to establish threshold points where each fish species lost equilibrium (defined here as Acute Effect Temperature; AET). The coolest AET among all species was 33.1 °C (S. analis), while the highest was 39.9 °C (A. vachellii). High frequency loggers were deployed (November and March representing Austral summer) in the same urban lake where fish were sourced, to measure continuous (20min) surface (0.15 m) and bottom (0.1 m) temperature to derive thermal frequency curves to examine how often lake temperatures exceed AET thresholds. For most fish species examined, water temperature that could be lethal were exceeded at the surface, but rarely, if ever, at the bottom waters suggesting deep, cooler, water provides thermal refugia for fish. An energy-balance model was used to estimate daily mean lake water temperature with good accuracy (±1 °C; R² = 0.91, modelled vs lake measured temperature). The model was used to predict climate change effects on lake water temperature, and the exceedance of thermal threshold change. A 2.3 °C climate warming (based on 2100 local climate prediction) raised lake water temperature by 1.3 °C. However, small as this increase might seem, it led to a doubling of time that water temperatures were in excess of AET thresholds at the surface, but also the bottom waters that presently provide thermal refugia for fish

Effects of forest width on fish use of fringing mangroves in a highly urbanised tropical estuary

The size and shape of a habitat patch can influence patterns of species utilisation. The present study examined how the width of fringing mangrove habitats affects the composition and use patterns of the fish assemblage using mangrove edge habitats on the flooding tide. Underwater cameras surveyed fish approaching mangrove habitats, ranging from a thin fringe 5 m wide to forests over 75 m wide, in a highly modified tropical estuary. The fish assemblage composition was similar across all mangrove widths, although the temporal patterns of use varied among mangrove widths for some species. The mean maximum number of individuals in the field of view was similar among mangrove widths, but fish were visible for a significantly greater proportion of time in videos from narrow (,20 m) than wide ($20 m) mangrove stands (15 v. 3% respectively). At least some fish were visible in the field of view in narrow mangrove fringes throughout the first hour of the flood tide, whereas in wide mangroves areas the presence of fish declined over time. The findings suggest that estuarine fish are using mangrove edge habitat regardless of width, making narrow mangroves viable habitats for estuarine fish

Estimating the value of tropical coastal wetland habitats to fisheries: caveats and assumptions

Habitat valuation can provide an objective basis for the prioritisation of conservation and restoration actions. The attribution of fisheries production to particular habitat units is an important measure of value, but is difficult to estimate. Using the case study of habitat use by juvenile banana prawns in a tropical estuary, we assessed the potential to produce valid value estimates at two spatio-conceptual scales: estuary reach and whole estuary. Additionally, we also explore the potential to produce meaningful value estimates at the scale of whole estuary contribution to the offshore fisheries stock. A diversity of potential and actual sources of error and logical problems means that quantification at any scale is at best of uncertain validity and produces estimates that are likely to produce unreliable results if treated as quantitative inputs to production models. Estimates for the whole estuary were the most viable, although still requiring substantial assumptions that may or may not be reasonable in particular situations. Estimates for individual habitats required the unreasonable assumption of limited prawn movement, while estimates of contribution of an estuary to the fishery required difficult-to-obtain and usually unavailable information. Because low occupancy habitats can have trophic value, we also used stable isotope analysis to assess the importance of mangroves and saltmarshes to prawn nutrition. No particular habitat was of critical trophic importance, again suggesting that the habitat-production link is most usefully assessed at the whole-of-estuary scale. While valuable and required to support targeted ecosystem management and protection and restoration efforts, valid estimates of the contribution of particular units to fisheries are likely to be unachievable in many situations

Tracking the long-term vegetation and soil characteristics of restored mangroves: a case study from Guyana's coast

The global urgency to halt and reverse mangrove loss has led to the implementation of numerous initiatives to protect and restore mangroves and recover critical ecological functions and services. Restoration success is assessed by estimating mangrove survival, while diversity, vegetation structure, and soil characteristics are often overlooked with no long-term monitoring. Here, we investigated long-term changes in vegetation and soil characteristics of Avicennia germinans-dominated stands planted along Guyana's coast between 5 and 11 years old. A chronosequence approach was used to examine changes in vegetation and soil parameters in restored mangrove stands of different ages compared to natural stands of the same ages. Tree height, diameter, and aboveground biomass were inconsistent between restored and natural mangrove stands. Redundancy analysis (RDA) revealed that the soil properties were the important factors influencing both the restored and natural mangrove communities. There were no clear trajectories between the vegetation and soil characteristics with age, possibly due to site-specific and hydrodynamic environmental factors, such as tidal dynamics, riverine inputs, and climatic variations. While there were some equivalent vegetation and soil characteristics at the end of the first decade after restoration, the restored mangroves may require a longer timespan (approximately 25 years) than the period overserved in our study to be entirely identical to the natural mangroves. This case study from Guyana provides valuable insights into the ecological processes driving mangrove recovery dynamics, growth patterns, and restoration effectiveness and offers reliable data needed to inform future restoration projects

Underwater Fish Detection with Weak Multi-Domain Supervision

Given a sufficiently large training dataset, it is relatively easy to train a modern convolution neural network (CNN) as a required image classifier. However, for the task of fish classification and/or fish detection, if a CNN was trained to detect or classify particular fish species in particular background habitats, the same CNN exhibits much lower accuracy when applied to new/unseen fish species and/or fish habitats. Therefore, in practice, the CNN needs to be continuously fine-tuned to improve its classification accuracy to handle new project-specific fish species or habitats. In this work we present a labelling-efficient method of training a CNN-based fish-detector (the Xception CNN was used as the base) on relatively small numbers (4,000) of project-domain underwater fish/no-fish images from 20 different habitats. Additionally, 17,000 of known negative (that is, missing fish) general-domain (VOC2012) above-water images were used. Two publicly available fish-domain datasets supplied additional 27,000 of above-water and underwater positive/fish images. By using this multi-domain collection of images, the trained Xception-based binary (fish/not-fish) classifier achieved 0.17% false-positives and 0.61% false-negatives on the project's 20,000 negative and 16,000 positive holdout test images, respectively. The area under the ROC curve (AUC) was 99.94%.Comment: Published in the 2019 International Joint Conference on Neural Networks (IJCNN-2019), Budapest, Hungary, July 14-19, 2019, https://www.ijcnn.org/ , https://ieeexplore.ieee.org/document/885190

Urban-industrial seascapes can be abundant and dynamic fish habitat

Urban-industrial seascapes are prevalent around the world, yet we lack a basic understanding of how the mosaic of different habitats in these areas are used by mobile marine fauna, including features such as industrial ports and marinas. Urbanised areas have been alternately characterised in scientific literature as degraded, depauperate, or in some cases diverse and abundant. To advance our spatial and temporal understanding of the community of mobile marine fauna in these areas, we used repeated sonar image sampling over large swathes of two urban-industrial seascapes, combined with underwater video. 2,341 sonar segments were captured across Mackay Harbour and the Pioneer River estuary (North Queensland, Australia). We used this information to generate a preliminary understanding of the ecology of these locations. We found that overall, urban-industrial seascapes can contain counts of mobile marine fauna similar to natural areas, and that these seascapes are characterised by dynamic diel shifts in the spatial arrangement of mobile marine fauna in the water column. At night, large fish are prevalent in the water column, while during the day, assemblages are dominated by small fish. Within these urban-industrial seascapes, deeper areas containing heavy infrastructure such as ports can harbour large densities of fish, including heavily targeted fisheries species. These areas deserve recognition as marine habitat, are of consequence to fisheries, and have the potential to influence surrounding ecosystems. Important research questions remain regarding their impact on food webs and animal movement at larger scales

Social capital plays a central role in transitions to sportfishing tourism in small-scale fishing communities in Papua New Guinea

Growing concerns about pressures of global change on small-scale fishing communities have resulted in a proliferation of livelihood diversification initiatives linked to tourism. Where the focus is often on the role of financial, physical, and human capital in influencing the uptake of new opportunities, we argue for more consideration of the role of social capital. We implemented 157 household-level surveys in small-scale fishing communities in Papua New Guinea and modelled the influence of social and other capital assets on people’s perceptions of how easy it would be to become involved in sportfishing tourism. Social capital had a stronger influence relative to other forms of capital, with perceptions of reciprocity and satisfaction with leadership being the most influential aspects. Based on these results, we stress the importance of developing strategies aimed at understanding, building, and maintaining social capital and related social dynamics when implementing livelihood diversification initiatives

Promoting resilience in regional Australian industries: a case study of the North Queensland commercial fishing industry

Background: Promoting the sustainability of key existing industries is crucial to the continued development of regional Australia. In doing so, it is important to consider the role of industry workers responsible for engaging with and adhering to sustainability guidelines and practices within these key industries. This is particularly important for industries such as commercial fishing due to the ongoing challenges they face. For example, challenges such as increasing operating costs, complex regulatory systems and the impacts of extreme weather, contribute to downsizing of the industry. Method: The findings from the case study discussed have been drawn from an ongoing PhD project investigating the role of commercial fishers in the sustainability of the North Queensland commercial fishing industry. Results: Interviews with commercial fishers highlight the perceived lack of genuine involvement of commercial fishers in the development and implementation of industry regulations. From these interviews it was identified that commercial fishers did not feel included in the process of regulation development and implementation or that if they were involved, their input was not genuinely incorporated. Perceived lack of consultation has implications for how regulations are received, adhered to and endorsed by stakeholders. Discussion: Based upon the findings of this case study, it is suggested that stakeholders be genuinely involved in the development and implementation of regulations. Genuine consultation processes may enhance the sustainability of key industries such as commercial fishing. For example, it is expected that those who engage in the development and implementation process are more likely to adhere to and engage in sustainability measures and practices leading to improved resilience of the industry

What Darwin could not see: island formation and historical sea levels shape genetic divergence and island biogeography in a coastal marine species

Oceanic islands play a central role in the study of evolution and island biogeography. The Galapagos Islands are one of the most studied oceanic archipelagos but research has almost exclusively focused on terrestrial organisms compared to marine species. Here we used the Galapagos bullhead shark (Heterodontus quoyi) and single nucleotide polymorphisms (SNPs) to examine evolutionary processes and their consequences for genetic divergence and island biogeography in a shallow-water marine species without larval dispersal. The sequential separation of individual islands from a central island cluster gradually established different ocean depths between islands that pose barriers to dispersal in H. quoyi. Isolation by resistance analysis suggested that ocean bathymetry and historical sea level fluctuations modified genetic connectivity. These processes resulted in at least three genetic clusters that exhibit low genetic diversity and effective population sizes that scale with island size and the level of geographic isolation. Our results exemplify that island formation and climatic cycles shape genetic divergence and biogeography of coastal marine organisms with limited dispersal comparable to terrestrial taxa. Because similar scenarios exist in oceanic islands around the globe our research provides a new perspective on marine evolution and biogeography with implications for the conservation of island biodiversity

Limits of tilapia aquaculture for rural livelihoods in the Solomon Islands

Increasing pressure on coastal fisheries poses serious threats to local livelihoods and the food security of Pacific Islanders. In response, governments and development agencies have explored tilapia pond aquaculture as an alternative fish production source. Yet, evidence to date on the impact of tilapia aquaculture on rural livelihoods has been inconclusive. Drawing on the sustainable livelihood framework, we analysed the contribution of Mozambique tilapia (Oreochromis mossambicus) aquaculture to the livelihood assets and outcomes of 40 rural farmers in Solomon Islands. First, results showed that 53% of tilapia farmers were satisfied with tilapia aquaculture’s contribution to their human and social assets, while only 28% and 13% were satisfied with its contribution to their physical and financial assets, respectively. Tilapia aquaculture’s contribution to farmers’ natural assets was also limited. Second, and most importantly, there was an insignificant contribution of tilapia aquaculture to food and income security. Our results demonstrate that tilapia farmers rarely consumed tilapia, with only two of the 40 households having consumed tilapia in the seven days prior the interview. Moreover, only eight tilapia farmers sold their tilapia, which contributed 0.002–0.5% of their total weekly revenue. We argue the limited contribution of tilapia aquaculture to food and income stems from the low productivity of the available tilapia species and the low local demand for tilapia at rural markets. Given the current context of declining coastal fisheries and food insecurity concerns in rural Pacific Islands, it is unlikely that the current form of Mozambique tilapia aquaculture will be able to achieve its objective of addressing food and income security as a complement to coastal fisheries