What are the effects of flow-regime changes on fish productivity in temperate regions? A systematic map

Abstract

Background: There is growing evidence of the potential negative consequences of altered flow regimes, in terms of magnitude, frequency, timing, duration or season pattern, on fluvial ecosystems and the fisheries they support. The scientific and policy communities have acknowledged the need for a better understanding of the effects of flow alteration on fish productivity. We conducted a systematic map to provide an overview of the existing literature base on the effects of flow-regime changes on direct outcomes of freshwater or estuarine fish productivity in temperate regions to inform stakeholders and policy makers. Methods: To identify relevant articles for inclusion in this systematic map, we searched six bibliographic databases, 29 organizational websites, one search engine, and 297 reviews, and solicited grey literature through relevant sources. We screened articles at title and abstract, then by full-text using predefined inclusion criteria. Included studies were coded for key variables of interest, along with a very basic critical appraisal for internal validity (i.e., susceptibility to bias). The quantity and characteristics of the available evidence, knowledge gaps and subtopics with sufficient coverage for full systematic reviewing are reported in a narrative synthesis. The distribution and frequency of examined effects of flow-regime changes on fish productivity outcomes are presented in visual heatmaps. Review findings: A total of 1368 studies from 1199 articles were included in the systematic map database and used to identify a number of interesting themes in the evidence base: (1) large evidence bases were found in temperate regions of United States of America (USA), Canada, and Australia; (2) most studies either used a temporal or spatial trend design i.e., lacking a 'true' before intervention time period, or no intervention control sites; (3) the most studied causes of altered flow regime were natural (e.g., floods, droughts, climate change), hydroelectric facilities (hydro), and dams with no hydro; and (4) there were clear clusters of studies evaluating effects of changes in magnitude and surrogate measures (e.g., velocity, water depth) on fish productivity outcomes, in particular abundance and diversity metrics. A number of potential knowledge gaps were identified: including geographic (Northern Africa, and possibly parts of Asia), causes of altered flow regime (restoration, land-use change, and water abstraction/extraction/diversion), interventions (flow duration, frequency, rate of change, or timing), outcomes (population viability) and specific intervention/cause/outcome groups (e.g., changes in flow magnitude due to hydro or natural causes and fish survival,

What evidence exists on the impacts of flow variability on fish and macroinvertebrates of temperate floodplain rivers in Central and Western Europe? A systematic map protocol

“…Despite some overlap with the existing evidence syntheses, especially Piniewski et al [13] and Rytwinski et al [6], the proposed systematic map will be a valuable contribution to the subject. The work by Piniewski et al [13] focused on the responses of biota (fish and macroinvertebrates) to floods and droughts in Europe, but-unlike the proposed systematic map-it did not take into account non-extreme flow variability, and did not follow the CEE guidelines.…”

“…The preliminary search string tested in Web of Science Core Collection reached approximately 42,000 results. When tested for the same time frame (1900-2017) and biota (fish, with macroinvertebrate terms removed), the search string yielded 29,000 results compared to around 10,500 found in Web of Science Core Collection by Rytwinski et al [6]. The addition of new inclusion criteria together with development of a more robust search string will hopefully allow for the identification of new pieces of evidence.…”

“…Flow regime may change due to numerous factors. In this map, the relevant causes of change will include (1) anthropogenic causes: dams, reservoirs, hydroelectric facilities, locks, levees, water abstraction, water diversion, land-use changes, road culverts; (2) natural causes: floods, droughts, seasonal changes [6]; or (3) climate change. These three groups do not only vary in the mechanism of change, but also imply further differences.…”

“…Despite rapid proliferation of studies on flow-ecology relationships over the last two decades, few attempts have been made so far to synthesise the existing evidence in a systematic way [5,6,13,[18][19][20]. Only two most recent ones: the systematic map by Rytwinski et al [6] and the forthcoming systematic review proposed by Harper et al [18], followed the guidelines established by the Collaboration for Environmental Evidence [21]. Poff and Zimmerman [5] and Webb et al [20] devoted their systematic reviews of ecological responses to flow alterations at the global scale.…”

“…The systematic map by Rytwinski et al [6] about the impact of flow regime changes on fish in temperate regions included both anthropogenic and natural causes of flow alteration, accounting for a substantial overlap with the proposed map. However, despite the similarities in scope, the two systematic maps differ in several ways.…”