What are the impacts of small-scale dredging activities on inland fisheries productivity? A systematic review protocol

Review topic identification and stakeholder input

Recent changes to the Canadian Fisheries Act switched the focus of promoting sustainable fisheries in Canada from an approach of managing the habitats sustaining fish populations, to one that manages the ongoing productivity of fishes related to commercial, recreational, or aboriginal (CRA) fisheries [23]. For the purpose of this review, we will follow the definition of fisheries productivity laid out it Randall et al. [24] as “the sustained yield of all component populations and species and their habitat which support and contribute to a fishery”. Very few projects require assessment at the scale of an entire fishery [24], so assessments of smaller projects focus on surrogates for effects on productivity [25]. The Fisheries Protection Program has established a number of conceptual pathways of effects (PoE) for development projects with the potential to affect fisheries productivity. These PoE describe development projects in terms of the cause and effects relationships known to exist, and the mechanisms through which the stressors lead to effects. Each cause and effect relationship is represented by a line, termed a pathway, leading from the activity to the potential stressor and then to the ultimate effect on fish and fish habitat. For example, dredging may result in a change in aquatic macrophytes (vegetation) and this may ultimately affect fish populations through a change in food resources (Fig. 1). It should be noted that pathways are highly generalized, and in the assessment of projects, the impacts and predicted changes in fisheries productivity need to be carefully and expertly considered prior to the project start [25].

In order to streamline the assessment of projects, the Fisheries Protection Program of Fisheries and Oceans Canada is implementing tools to aid in the self-assessment of smaller projects, as well as adapting existing resources for the decision-making process involving larger projects [23]. Accordingly, the review of the impacts of small-scale dredging activities on inland fisheries productivity has been explicitly proposed by the Canadian stakeholder, the Fisheries Protection Program of Fisheries and Oceans Canada (DFO).

This review will use the conceptual framework of the PoE for dredging activities to establish suitable surrogates of fisheries productivity. Dredging activities are common in freshwater environments, and occur in all types of waterbodies; sediments and aquatic vegetation are dredged, both for capital works in lakes and large rivers (e.g. the creation of new harbours), as routine fluvial maintenance (e.g. maintenance of shipping channel depth), or pollution control and remediation of contaminated sediments [19, 26–28].

However, of interest within this review are the dredging activities that may fall within the scope of self-assessment or the assessment of smaller-scale projects that fall under the jurisdiction of the Fisheries Protection Program (e.g. dredging for dock building, pleasure boat access to deep water, agricultural drain maintenance, maintenance of boating channels, etc.), but that may result in broader cumulative effects. Major, large-scale construction projects on industrialized or urban waterfronts, extensive dredging for commercial shipping, or projects involving pollution control or remediation fall outside of this current review.

An advisory team was made up during the formulation of the initial question, and is comprised of topic experts and staff from Fisheries and Oceans Canada. The advisory team guided the focus of the review, and was also consulted on the creation of search terms, development of screening inclusion criteria, and the list of specialist websites.

Primary question

How does small-scale dredging, both macrophyte and/or substrate removal, impact correlates of fisheries productivity?

Components of the primary question

Searches

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.

Potential effect modifiers and reasons for heterogeneity

Study validity assessment

Adapted from the Cochran Collaboration’s ‘risk of bias’ tool [30], Bilotta et al. [31] 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.