Communication and outreach efforts are essential for raising awareness about conservation issues among the general public. This paper reviews three in-person approaches (environmental education, outreach events, and field trips), as well as four types of media (print products, news media, visual media, and social media) for communicating about environmental topics, with a focus on highlighting conservation issues in Cambodia. Strengths and weaknesses are considered for each communication tool, along with lessons from a case study example of the Wonders of the Mekong, an interdisciplinary project based in Cambodia that aims to study, protect, and raise awareness about the Mekong River system. We also describe a cross-cutting initiative to share inspiring stories of local conservation practitioners that incorporates both in-person and media-based approaches. In terms of required resources and effort, there is an inherent tradeoff between the depth of in-person engagement and overall reach. While media-based approaches are valuable for reaching large numbers of people with a moderate amount of effort, in-person approaches may create a deeper connection and longer-term impact on an individual level. Ultimately, a diverse communication strategy that utilizes multiple tools to reach different audiences will be most effective. The interdisciplinary Wonders of the Mekong project has successfully communicated the values of the Mekong ecosystem to a broad audience in Cambodia using a variety of strategies, and further evaluation could help illuminate whether and how these communication approaches are shifting attitudes or promoting conservation behaviors.

The Mekong River is one of the most biodiverse, productive rivers in the world, supporting more than 1000 fish species and the livelihoods of tens of millions of people. The spatial dynamics and population status of many Mekong fish species, especially megafishes, are poorly understood. Therefore, this information is rarely incorporated into environmental risk assessments for large infrastructure projects, such as mainstream hydropower developments, which have been accelerating rapidly in the Mekong Basin. In this study, we present initial findings from the ongoing, collaborative, transnational acoustic telemetry monitoring of nearly 300 tagged fishes representing 27 species, which yield important insights into the potential impacts that proposed hydropower dams would have on populations of ecologically and economically important fish species. Included in these data are more than ten months of hydrophone records tracking the location of a 300 kg giant freshwater stingray, Urogymnus polylepis (Bleeker, 1852), currently the world’s largest known freshwater fish, used to detect its migration behavior and distribution patterns. The telemetry data, combined with fisher surveys used to gather local ecological knowledge, provide evidence that the proposed dams would fragment the existing populations of this iconic species as well as those of other fish species that support river food web balance and local food systems. Furthermore, the existence of giant freshwater stringray populations and other unique megafauna reinforces the universal natural heritage value of the stretch of the Mekong River between the Lao People’s Democratic Republic/Cambodia border and the city of Kratie. This stretch of river is located between two proposed megadams, the 900 MW Stung Treng Dam and the 2300 MW Sambor Dam. However, the Cambodian Ministry of Environment has also proposed this area for designation as a UNESCO World Heritage Site (Biosphere Reserve). The documentation of the movement of migratory fishes through this reach of the river using acoustic telemetry, the surprising discovery of the world’s largest freshwater fish, the potential threat posed by dam construction, and the management ramifications of UNESCO World Heritage Site designation underscore the importance of scientific research and community involvement in landscape-scale development decisions. The decisions made today will affect the fate of this global biodiversity hotspot, the world’s most productive inland fisheries, and the livelihoods of millions of people throughout the Lower Mekong Basin.

The Tonle Sap Lake in Cambodia supports several species of threatened megafish and contains one of the largest networks of freshwater fish reserves in the world. Despite these traits, this system remains understudied in terms of its utility for endangered fish conservation and restoration. This study was the first of a series of planned fish releases designed to test the effectiveness of conservation supplementation programs in the Tonle Sap Lake. In March 2022 (during the dry season), 1582 captive-reared fishes, including 1538 striped catfish Pangasianodon hypopthalmus, 42 giant barb Catlocarpio siamensis, and two Mekong giant catfish Pangasianodon gigas, were tagged and released into a 986-hectare fish reserve to assess post-release dispersal and survival. Brightly colored external tags with unique identification numbers were used to facilitate tag returns. A high-profile release event was held to raise awareness about the activity, bringing attention to the importance of fish reserves and endangered species conservation, and disseminating information about the research and tag return and reward program. This, in concert with other efforts, served to be an important education and outreach tool and increased tag return rates. We found that mortality from fishing was rapid and very high. Nineteen percent of released fishes were recaptured in the first 2 days after the fish release, and 46% were recaptured by day 83 after the release, indicating intense fishing pressure on the Tonle Sap Lake fisheries. Eighty percent of recaptured fishes were caught in stationary gill nets, most within 10 km of the release site. Fishing mortality rates were independent of fish size or source (pond-reared or cage-reared). Environmental DNA (eDNA) was found to be capable of detecting each of these species’ presence in the water at the release site and could prove to be a useful tool for endangered species monitoring and restoration. Future research should explore alternative release timing, release location, and other methods of increasing post-release survival. Ultimately, underlying sources of mortality, especially fishing, will need to be addressed for conservation supplementation programs to succeed in the Tonle Sap Lake. Conservation supplementation should not be viewed as a substitute for more fundamental conservation measures, such as maintenance of environmental flows, preservation of ecological connectivity, and science-based fisheries management.

Steelhead (Oncorhynchus mykiss expressing an anadromous life history) in the Sacramento and San Joaquin rivers and their tributaries in California’s Central Valley (CCV) belong to a Distinct Population Segment (DPS) that is listed as threatened under the US Endangered Species Act. Although contemporary management and recovery plans include numerous planned and ongoing efforts seeking to aid in DPS recovery—such as gravel augmentation, manipulation of spring flows, and restoration of rearing and spawning habitat—a paucity of data precludes the possibility of evaluating the effect of these actions on populations of Steelhead in CCV streams. Knowledge gaps relating to historic and current abundance, population-specific ratios of resident and anadromous life-history expression, and the influence of hatchery-reared fish remain largely unaddressed. This is partly a result of aspects of Steelhead biology that make them difficult to monitor, including the multitude of factors that contribute to the expression of anadromy, polymorphic populations, and migration periods that coincide with challenging field conditions. However, these gaps in understanding are also partly the result of an institutional focus on Chinook Salmon (Oncorhynchus tshawytscha) and a pervasive notion that actions benefiting Chinook populations will also benefit Steelhead populations. To evaluate these gaps and to suggest approaches for assessing DPS recovery actions, we review available data and existing monitoring efforts, and consider the actions necessary to inform the development of targeted O. mykiss monitoring programs. Current management and recovery goals focus on abundance estimates of Steelhead only, yet current monitoring is insufficient for reliable estimates. We argue that a reallocation of monitoring resources to better understand the interaction between resident O. mykiss and Steelhead would provide better data to estimate the vital rates needed to evaluate the effects of recovery actions.

Objective: Juvenile salmonids have high mortality during their out-migration into marine environments, and there is disagreement regarding the factors that contribute to low juvenile survival, the relative strength of those factors, and how to develop effective management actions to improve survival. This study provides a planning tool for researchers interested in quantifying component mortality of juvenile salmonids using a multistate mark–recapture model framework for telemetry projects. We discuss approaches to increase study precision and better understand data needs prior to project implementation. Methods: We evaluated the accuracy and precision of multistate mark–recapture models by generating simulated data and model code under six model scenarios of increasing complexity and comparing model estimates, mean relative error, and the CV among these scenarios. Model scenario A.1 considers a passive-only acoustic array (low detection probability) and three observation states (alive, predation, and unknown mortality), with predation identified using predation detection acoustic tags. Model scenario A.2 expands model scenario A.1 to include active tracking (high detection probability). Model scenario A.3 expands model scenario A.2 by increasing predation and unknown mortality estimates. Model scenario B expands model scenario A.2 to model four observation states (alive, fish predation, avian predation, and unknown mortality), where avian predation and fish predation are partitioned using predation detection acoustic tags and combined acoustic–radio tags. Model scenario C.1 expands model scenario A.1 by modeling predation and unknown mortality using biological (fork length) and environmental (temperature) covariates. Model scenario C.2 expands model scenario C.1 via an increased detection probability. Results: Our results suggest that increasing tagging effort may be more effective than increasing detection probability to improve accuracy and precision, in that lower detection probabilities may produce accurate median estimates but have high variability, especially when including model covariates. Additionally, models with low detection probabilities and low sample sizes (n ≤ 100) did not accurately estimate reach-specific unobserved mortality rates, especially when the simulated mortality estimates were increased. In this study, we did not see a plateau in mean relative error or CV estimates as tagging effort increased up to 1,000 individuals; however, between 150 and 500 individuals, most CVs dropped below 10 and the variability surrounding estimates was substantially reduced. Increased simulation processing time above 150 individuals and the cost of acoustic tags for large tagging effort (n ≥ 150) should be considered when budgeting time for project planning and implementation. Conclusions: This study provides realistic model scenarios and code that can be used when designing research projects aimed at identifying component mortality for salmonids or other imperiled juvenile fishes to increase the likelihood of project success while considering the costs of facilitating such research.