Stable carbon isotope ratios (13C) were measured in annual layers of otoliths of Atlantic cod (Gadus morhua) from the northeastern Scotian Shelf, Atlantic Canada. Layers deposited during the first 4-6 years of otolith growth increased in 13C from minimum values between -5‰ and -2.5‰ to a maximum near 0‰. This pattern of increase was independent of the years in which the fish was collected. Layers formed after reaching the maximum 13C value displayed decreasing or nearly constant isotopic ratios. Early rise in 13C may be a combined result of (i) decrease in the fraction of metabolic oxidized carbon in the fishes' blood as they mature, relative to the proportion of seawater-derived carbon, and (ii) dietary shift to higher trophic-level foods with higher 13C values. Age of maximum in 13C may be indicative of age of maturity of cod. The maximum 13C value attained by otoliths decreased steadily between 1983 and 1993, while cod stocks in Atlantic Canada were declining. Drop in age of attainment of maximum 13C between 1984 and 1985 coincides with changes in population dynamics of the 4Vs stock. This decrease, as well as the post maximum decrease in 13C values of the mature cod otoliths may represent movement of the fish to deeper waters of the shelf, where 13C of dissolved inorganic carbon is lower.

In aquatic systems, biological invasions can result in adverse ecological effects. Management techniques available for non-native fish removal programs (including eradication and population size control) vary widely, but include chemicals, harvest regimes, physical removal, or biological control. For management agencies, deciding on what non-native fish removal program to use has been challenging because there is little reliable information about the relative effectiveness of these measures in controlling or eradicating non-native fish. We conducted a systematic review, including a critical appraisal of study validity, to assess the effectiveness of different non-native fish removal methods and to identify the factors that influence the overall success rate of each type of method. We found 95 relevant studies, generating 158 data sets. The evidence base was dominated by poorly documented studies with inadequate experimental designs (76% of removal projects). When the management goal was non-native fish eradication, chemical treatments were relatively successful (antimycin 89%; rotenone 75%) compared with other interventions. Electrofishing and passive removal measure studies indicated successful eradication was possible (58% each) but required intensive effort and multiple treatments over a number of years. Of these studies with sufficient information, electrofishing had the highest success for population size control (56% of data sets). Overall, inadequate data quality and completeness severely limited our ability to make strong conclusions about the relationships between non-native fish abundance and different methods of eradication and population control and the factors influencing the overall success rate of each method. Our review highlights that there is considerable scope for improving our evaluations of non-native fish removal methods. It is recommended that programs should have explicitly stated objectives, better data reporting, and study designs that (when possible and appropriate) incorporate replicated and controlled investigations with rigorous, long-term quantitative monitoring. Future research on the effectiveness of non-native fish removal methods should focus on: (i) the efficacy of existing or potentially new removal measures in larger, more complex environments; (ii) a broader range of removal measures in general; and (iii) phenotypic characteristics of individual fish within a population that fail to be eradicated or controlled.

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Environmental decision-makers and practitioners need and deserve high quality environmental evidence for effective decision-making. We collate and share a suite of best practices for applied environmental researchers to support their capacity to inform such decision-making processes. This raises a number of important questions: What does “relevant” and informative evidence look like? How do we know when evidence has been applied? We assembled an experienced team of knowledge generators and users in Canada to identify insights that have emerged from their work and that could serve as guideposts for others who seek to apply environmental research to policy challenges. By reflecting on successes and failures, we define “success” in applied environmental science as respectfully conducted, partner-relevant research that is accessible, understandable, and shared, and that can create opportunities for change (e.g., in policy, behaviour, management). Next, we generated a list of best practices for delivering “successful” applied environmental research. Our guidance emphasizes the importance of engaging early and often, in a respectful manner, with partners, generating high-quality, relevant research (which requires flexibility), having a plan for communicating and sharing outputs, and being transparent about uncertainties and limitations. Other important considerations include acknowledging partners for involvement and training early career researchers in applied partnership research. Finally, we generated a list of specific, measurable indicators for evaluating success including: quality and quantity of scientific outputs, the relationship with the partner(s), relevance and connectedness of the research, accessibility and availability of outputs to users, provision of outputs that are digestible and usable by different audiences, training and capacity building, and ultimate outcomes (e.g., including social, environmental, and economic outcomes, as well as partner satisfaction). We encourage those embarking on applied environmental research to consider embracing the strategies, to continuously reflect on progress toward shared research goals, and to be flexible. Doing so will increase the likelihood of delivering research that is “successful” and in doing so contribute to overcoming and addressing environmental issues and problems.