Relevant search terms were compiled under three components making up the primary question: subject, intervention, and outcome. Search terms between component categories will be combined using the Boolean operators “AND”, and within categories using the operators “AND” and “OR”. The proximity operator “NEAR” will be used to combine search terms expected to be in relatively close proximity to one another, but may on their own be too broad. Wildcards will be used to expand the search terms. The asterisk (*) represents any number of characters (e.g. fish* returns results including fishery, fisheries, fishes, fishing, fished). The dollar sign ($), in databases where applicable, is a wildcard used to represent zero or one character, and can be used inside or at the end of a word (e.g. harbo$r returns searches for harbour and harbor). Search order precedence for operators is “NEAR” followed by “AND” and “OR”. Parentheses will be used to override the operator precedence, with the expression within parentheses being handled first. The proposed search string appears as:
(stream$ OR river$ OR ditch* OR lake* OR reservoir$ OR pond$ OR canal$ OR channel$ OR wetland$ OR marsh* OR shore* OR harbo$r* OR port)
(dredg* OR excavat* OR dig OR (remov* NEAR/5 (macrophyte$ OR sediment$ OR vegetation)))
((fish* OR habitat$ OR macroinvertebrat* OR invertebrat* OR macrofauna$) AND (abundan* OR biomass OR productiv* OR composition OR densit* OR diversit* OR disturb* OR impact* OR change* OR effect$))
Where a complex search string is not accepted, search terms will be modified with the aid of the database help menu, and will follow the format of the simplified phrase:
(dredg* OR excavat*) AND (impact*) AND (fish* OR habitat). All modified search strings will be recorded.
Only English search terms will be used to conduct all searches. All references returned will be included in the database, including any articles written in other languages, however, they will not be translated and used in the review itself.
Estimating search comprehensiveness
In order to estimate the comprehensiveness of our search strings, we will test the search against a predetermined “test set” of approximately 10 relevant articles. We will also search the bibliographies of the test set articles to ensure that any relevant articles cited are also present in our search results. If any articles are found to be missing from our search, our search string will be amended. The test set of articles is created by obtaining articles from the advisory team, and searching the personal publications of lead investigators in the field for highly relevant articles.
ISI Web of Science Core Collection
WAVES (Fisheries and Oceans Canada)/Federal Science Library)
ProQuest Dissertations and Theses
ProQuest Environmental Sciences and Pollution Management
The first 100 hits (based on relevance) will be examined for inclusion in the review. For citation purposes, as well as for repeatability and transparency, dates of access of online material from search engine searches will be recorded.
The first 50 documents returned from each search will be included in the reference database and be examined for relevance and inclusion in the review. Bibliographies of included material will be searched for any relevant documents to be included in the reference database. Links appearing in relevant documents will be followed to any organisation not originally included in the specialist website search, in order to encompass all available literature. All documents will initially be exported into Mendeley prior to assessment.
Centre for Environment, Fisheries and Aquaculture Science
Central Dredging Association
Commonwealth Scientific and Industrial Research Organization (Australia)
Department for the Environment, Food and Rural Affairs (UK)
Environment Agency (UK)
European Dredging Association
European Environment Agency
Fisheries and Oceans Canada
Food and Agriculture Organization of the United Nations
Great Lakes Fisheries Commission
International Association for Great Lakes Research
International Association of Dredging Companies
Joint Nature Conservation Committee
National Institute of Water and Atmospheric Research (NZ)
National Park Service
Salmon and Trout Conservation UK
United Nations Environment Programme
US Fish and Wildlife Service
US Forest Service
World Wide Fund for Nature
Other literature searches
The reference sections of all articles retained for full article reviewing, as well as any review papers, will be searched by hand for any titles missed in the search strategy, including symposium titles and unpublished literature. These titles will also be included in the database, with reference made to the originating article. Web-based bibliographies will also be checked for missed sources. Both manual searches will check the comprehensiveness of the search strategy. Authors of unpublished literature or unobtainable articles will be contacted to request access to the full article, or when no article is available, access to the data.
Search record database
Publications retrieved from each of the searches (publication databases, search engines, and specialist websites) will be put into separate Mendeley databases. On completion of the initial searches they will be compiled into CADIMA (systematic review software http://www.cadima.info). Duplicates will be identified and merged.
Article screening and study inclusion criteria
Articles will be screened in two stages; screening will take place at the title and abstract, and full text stage. Prior to any screening occurring, two reviewers will check for screening consistency and the repeatability of screening decisions using the greater of either 10% of the articles, or 100 articles. Cohen’s kappa coefficient will be calculated to determine the level of agreement between the 2 reviewers. A kappa score of ≥ 0.6 indicates substantial agreement, and must be achieved before further article review. Discrepancies will be discussed, and if required, the inclusion criteria will be reviewed. Similar consistency checks will take place at all three levels of article screening.
All article screening decisions will be recorded in the database, with justification for all inclusion/exclusion decisions. When there is not enough justification for exclusion, the article will pass to the next stage in the screening process. If the abstract is absent, the article will pass directly to the full-text screening stage. Any article excluded at the full-text stage of the screening process will be included, with reasons for exclusion, with the final review as an appendix.
Temperate freshwater systems, including both lentic and lotic environments. Freshwater bodies can include, but are not limited to, lakes, rivers, streams, reservoirs, ponds, canals, channels, harbours, marches, ports, ditches, and wetlands. To determine if a study falls within the temperate zone, we will use the Köppen–Geiger climate classification , and restrict studies to temperate oceanic climate, hot-summer humid continental climate, and warm-summer humid continental climate zones in both the northern and southern hemispheres.
Relevant types of intervention
Dredging activities to remove either sediment, or vegetation (or both), for purposes including, but not limited to, small dock construction of a size suitable to accommodate pleasure boats, or increasing depth (for recreational boating traffic or canal/agricultural drain maintenance). Dredging activities not included in this review include dredging for pollution control or remediation, large-scale dredging in major rivers and lakes (e.g. St. Lawrence River) for commercial shipping traffic, dredging projects for mining, or channelization projects.
Relevant types of comparator
A control site that is either a site consisting of similar physical habitat features, but not undergoing intervention, within the same water body, or a similar site on an adjacent water body. Before intervention data of the same site.
Relevant types of outcome
A measurable effect (change/no change) in abundance/density/species richness of fish, abundance/density/species richness of benthic macroinvertebrates, habitat features (e.g. depth, vegetation, cover, flow, substrate composition, structure, bank/shore composition).
Relevant types of study design
Study designs considered for inclusion in the review include: studies that compare relevant outcomes before and after intervention (Before/After—BA), studies that compare relevant outcomes between a control site and a site subject to intervention (Control/Impact—CI), studies designed to include both spatial and temporal comparators (Before/After/Control/Impact—BACI). Review papers and policy discussions will be searched for relevant references, but will otherwise not be included in this review.
Potential effect modifiers and reasons for heterogeneity
The following factors may cause variation in measured outcomes, and information on these potential effect modifiers will be extracted and recorded in the MS-Excel spreadsheet when available. Additional effect modifiers may be added during the course of the review. The list of effect modifiers was compiled in consultation with the advisory team.
Study location (coordinates)
Methodology of dredge (e.g. barge/excavator, land based excavator, etc.)
Duration of dredge
Extent of dredging
Time/season of dredging
Time since last dredge (if dredging was for routine maintenance)
Pre/post monitoring effort
Length of monitoring
Frequency of monitoring
Fish species data—life history information including spawning times
Taxonomic level of invertebrates
Study validity assessment
Studies passing the full-text screening stage of the review will be subject to critical appraisal in order to assess the internal and external validity of the study. Articles will be appraised on the a number of selected parameters, which include, but are not limited to, the following:
Study design (BA/CI/BACI)
Temporal extent of study—short-term/long-term
Pre-dredging data—single instance/multiple sampling events
Potential effect modifiers—identified and/or accounted for
Objectives/hypotheses—clarity in relation to methodology
Use of reference/control sites
Adapted from the Cochran Collaboration’s ‘risk of bias’ tool , Bilotta et al.  have outlined criteria for the assessment of internal validity in environmental science. Criteria include assessing for selection bias, performance bias, attrition bias, reporting bias, as well as biases applicable in unique situations. The criteria outlined in Bilotta will be used to assess each article included in the review. A risk assessment of “low risk”, “high risk”, or “unclear risk” will be assigned to the information from each article, and will be used to assess the potential risk of bias of the article. All information, as well as the risk assessment will be recorded in the database.
Data extraction strategy
All data extracted from studies included in the review will be recorded in an MS-Excel spreadsheet. Extracted information will include study characteristics including sample sizes, measured outcome means, measures of variation (standard error, standard deviation), comparators. This information will be used to assess the impact of small-scale dredging activities on aspects of fisheries productivity. When data are presented only in tables and graphs, data will be extracted when possible and the information recorded in the spreadsheet. If information is not easily decipherable, the corresponding author of the article will be contacted to request the information. When only raw data are available, summary statistics will be calculated and recorded. If sufficient data of high enough quality are extracted, a meta-analysis may be performed.
To ensure that data are extracted in a way that is both consistent and repeatable, two reviewers will extract information from the same subset of 10 articles. Extracted information will be compared and any inconsistencies will be discussed. All extracted data entered will be made available as a supporting document with the final review.
Data synthesis and presentation
A narrative synthesis from all studies of sufficient validity included in the review will be generated and will describe the validity of the results, as well as the findings. The synthesis will be presented as visually as possible, with the addition of tables and figures. If sufficient data of similar outcomes is available, meta-analysis may be possible. In such cases, effects sizes will be standardized and weighted appropriately. If data allows, subgroup analysis of different waterbody types (lentic vs lotic) may be possible. Publication bias and sensitivity analysis will be performed when possible. Publication bias will be assessed using the Egger test to produce a funnel plot of the standardised mean difference plotted against the standard error of the standardised mean difference [32, 33]. This review may also identify and highlight major knowledge gaps in the evidence base.