An ensonified bubble curtain blocks 4 species of invasive carp in a laboratory flume but also deters other fish, while sound alone is less effective overall and does not target carp

Four species of invasive carp from Asia are advancing up the Mississippi River through its locks and dams and threatening to damage to its ecosystems. It has been hypothesized that sensory stimuli could be projected into locks to block the movement of these carp. Sound has garnered attention because carp are hearing specialists, so they might be targetable. A recent study demonstrated that when a broadband cyclic sound was projected into an air curtain to create an ensonified bubble curtain (EBC), it was especially effective at blocking bighead and common carp and less effective at blocking a native species that lacked hearing specializations, while sound alone was generally less effective. However, whether an EBC might be similarly and uniquely effective at blocking all species of carp, and what its effects might be on other fishes in general, has not yet been addressed. To answer these questions, this study examined the responses of 10 species of fishes including 4 carps, 2 native hearing specialists, and 4 native non-specialists in a darkened laboratory flume while either a cyclic sound was played on its own or projected into an air curtain. The EBC blocked all 4 carps 9297% of the time without habituation, but 5 native fish were also partially blocked. In contrast, sound alone only blocked 2 carps and affected the other fishes in ways not related to their hearing abilities. An EBC appears well suited to blocking carp invasions, especially if native fish movement is a secondary concern.

A map of South Africa’s perennial rivers. Non-perenn

<p>Maps can be many things: colourful, or dull; complex, or very simple; helpful, or very difficult to read. They also have the potential to support the public’s knowledge of environmental and social issues, and to lay out paths towards behavioural changes and conservation consciousness.</p> <p>This potential is already being explored in some parts of the world. For example, the <a href="https://greatlakesconnectivity.org/fishApp">FishWerks App</a> uses maps to highlight the barriers to fish movement in the Great Lakes region of the United States. Based on the ongoing work with <a href="https://theconversation.com/what-we-learned-when-our-map-of-southern-africas-rivers-went-viral-110735">a map of southern African rivers</a> that went viral two years ago, the same potential exists to drive conservation awareness and action in the southern African region.</p>

A map of South Africa’s perennial rivers. Non-perenn

<p>Maps can be many things: colourful, or dull; complex, or very simple; helpful, or very difficult to read. They also have the potential to support the public’s knowledge of environmental and social issues, and to lay out paths towards behavioural changes and conservation consciousness.</p> <p>This potential is already being explored in some parts of the world. For example, the <a href="https://greatlakesconnectivity.org/fishApp">FishWerks App</a> uses maps to highlight the barriers to fish movement in the Great Lakes region of the United States. Based on the ongoing work with <a href="https://theconversation.com/what-we-learned-when-our-map-of-southern-africas-rivers-went-viral-110735">a map of southern African rivers</a> that went viral two years ago, the same potential exists to drive conservation awareness and action in the southern African region.</p>

Risks to Fish Populations in Dryland Rivers From the Combined Threats of Drought and Instream Barriers

In dryland rivers, flow intermittency means fish populations are often subjected to drought disturbance. The viability of these fish populations depends on the availability of waterhole refuges for individuals to survive drought (resistance) and the ability of surviving fish to repopulate the rivers by recruitment and dispersal once flow returns (resilience). In this study we combined remote-sensed mapping of the locations of waterholes that lasted through an extreme drought in the northern Murray Darling Basin, Australia, with an assessment of the impacts of in-stream barriers on limiting the opportunities for fish to move and repopulate after drought. We found that at the peak of this 2018–2020 drought, the worst on record for some rivers and the most spatially synchronous recorded across the region, waterholes were few and generally small – representing only 11% of the total river channel network. All the fish in the region that survived the drought were concentrated into this limited waterhole refuge habitat. Even small instream structures, such as minor weirs, caused large reductions in the opportunities for fish to move between river segments when there is flow. Almost all the 104 instream structures assessed reduced long-term fish movement opportunities, measured as days with discharge greater than calculated barrier drown out thresholds, by more than 70% and up to 100%, when compared to opportunities for movement if the barrier was not present. This large impact from small instream barriers is a consequence of flow intermittency and is likely to reduce fish population resilience and impact the capacity of fish populations to recover after drought. Combining information on the risks posed by limited refuge habitat availability during drought and from reduced movement opportunity following drought allowed us to identify river segments where these combined threats are the greatest risk to viability of local fish populations. Considering the spatial arrangements of these risks provides a means to systematically prioritize mitigation measures such as weir removal to improve fish movement opportunities and local management of key waterholes to increase drought resistance. The approach used here provides a guide for assessing and prioritizing the management of fish population viability risks from drought and fragmentation by barriers in any non-perennial river setting.

The Influence of Stream Barriers and The Hypothetical Origin of Highlands Fishes.

Instream barriers such as waterfalls and man-made dams may result in distinct fish assemblages on both sides of the barriers. To determine the influence of these barriers on fish assemblages, a study was conducted in Sungai Enam that have substantial barriers including an 18-m high waterfall with 6.1% slope. Fish were captured using a backpack electrofishing gear together with scoop nets. Thirteen fish species from six families were recorded along this stream, but only Poropuntius smedleyi (Cyprinidae) can be found along the stream and the reach above the waterfall. Studies on a second site, Sungai Kooi, that has a 65m high and 90° slope waterfall, revealed eight fish species from three families, but only P. smedleyi and Devario regina (Cyprinidae) occurred above the waterfall. The number of species in both streams increases from upstream to downstream. A chi-square test revealed that the total number of species among reaches in Sungai Enam differed significantly. Fish species found above the waterfall are known to have no special adaptations to climb or jump over the barriers. Therefore, to explain their existence above the substantial waterfalls especially in Sungai Kooi, we proposed three hypotheses: (1) the world was once flooded and there was no limitation to fish distribution, (2) fish species assemblages were separated by land uplifting, and (3) there are other stream branches enabling fish movement into respective streams. Further studies are required to confirm these hypotheses.

ECOLOGIA DO MOVIMENTO EM PEIXES DE RIACHO

Movement is a key factor in spatial dynamics and the size of fish populations. It is one of the main mechanisms for maintaining viable populations and also accounts for the dispersion, colonization and performance of individuals life stages. The currently refuted restricted movement paradigm predicted that freshwater fish would not move. However, studies show that in addition to moving on a short and large scale, the movement patterns of these fish have, in general, reproductive, food, search for shelter, colonization or exploitation motivation. Studies on the movement of Neotropical fish are concentrated on the large migrators from large basins, such as Amazonas and Paraná. For streams, where small species predominate, little is known about the movement and its motivations. In this review, we show that studies on the movement of fish in neotropical streams are still very scarce. We propose a protocol for obtaining data and analytical tools for determining fish movement in streams. We highlight three tools for that: (i) analysis of the spatio-temporal structure of the size of the fish, (ii) mark-recapture experiments and (iii) molecular analyzes. We conclude that, given the limitation of each analysis, the use of the three tools must be carried out jointly.

THE USE OF ACOUSTIC TELEMETRY TO MONITOR FISH SPECIES IN MARINE PROTECTED AREAS: A SYSTEMATIC REVIEW WITH NOTES ON BRAZILIAN PERSPECTIVES

Inferring pathways used by organisms within ecosystems is essential to the design, management and evaluation of Marine Protected Areas (MPAs). This study aimed to present a systematic review on the literature regarding the use of acoustic telemetry to monitor marine fish movement and its application on MPAs. Searches were conducted on electronic databases. The first studies using telemetry on marine fish date back to the 60’s, while application on MPAs only appeared 30 years later. However, over the last decade, studies in MPAs accounted for 20% of the overall acoustic telemetry publications on marine fish species. Recent technological development has had an important impact on those results. The number of studies inside MPAs followed the number of general studies and coverage areas of MPAs declared around the world, although frequency of studies did not match MPA coverage in some countries. Developed countries scored more studies, probably due to the relative high cost of acoustic telemetry. Studies in Brazilian MPAs are scarce, with only one study available on elasmobranchs. Brazil has recently increased its MPA coverage to 26%, so it is expected to increase the need for MPA effectiveness studies. Brazilian participation on global tracking networks may help filling this gap. Keywords: PRISMA statement, fish movement, remote monitoring, MPA effectiveness, tracking networks

High turbidity levels alter coral reef fish movement in a foraging task

Sensory systems allow animals to detect and respond to stimuli in their environment and underlie all behaviour. However, human induced pollution is increasingly interfering with the functioning of these systems. Increased suspended sediment, or turbidity, in aquatic habitats reduces the reactive distance to visual signals and may therefore alter movement behaviour. Using a foraging task in which fish (Rhinecanthus aculeatus) had to find six food sites in an aquarium, we tested the impact of high turbidity (40–68 NTU; 154 mg/L) on foraging efficiency using a detailed and novel analysis of individual movements. High turbidity led to a significant decrease in task efficacy as fish took longer to begin searching and find food, and they travelled further whilst searching. Trajectory analyses revealed that routes were less efficient and that fish in high turbidity conditions were more likely to cover the same ground and search at a slower speed. These results were observed despite the experimental protocol allowing for the use of alternate sensory systems (e.g. olfaction, lateral line). Given that movement underlies fundamental behaviours including foraging, mating, and predator avoidance, a reduction in movement efficiency is likely to have a significant impact on the health and population dynamics of visually-guided fish species.