There’s something rather fishy going on at Conservation Evidence…
This blog post was written by Dr Ann Thornton and Dr Vanessa Cutts, Research Associates in the Conservation Evidence team, University of Cambridge, UK
A new synopsis on fish conservation
One of the many things I (Ann) enjoy about working at Conservation Evidence is the opportunity to delve into subject areas outside my research field. So it was with the newly published Fish Conservation in Inland Habitats synopsis – you could say I started out feeling a bit like a fish out of water! That said, it’s always exciting to learn more about species or habitats that are less familiar. The basic principles and format for summarizing studies mean that it doesn’t matter if this isn’t your primary research area, just as long as you follow the rules and identify the action and the outcome for fishes (I was lead author on the Coral Conservation synopsis in 2024). Sure, there is terminology that is unfamiliar. Redds, for example, are fish nests; electrofishing is where fish are stunned, counted, then wake up none the worse for their experience. The synopsis authors are not left floundering though as we form an Advisory Board of global experts for each synopsis that we rely on to oversee and advise on the synopsis content.
Our first conundrum was the scope of the synopsis. We couldn’t simply call this the Freshwater Fish synopsis as this would exclude all those species that spend some time in saltier environments (e.g. salmonids, lampreys, shad etc.) but we needed to exclude species living entirely in estuarine or marine habitats. Hence deciding upon Inland Habitats as the scope.
Those of you familiar with the synopses produced by Conservation Evidence may be a little surprised that there are, apparently, fewer actions and studies than you might expect included in the Fish Conservation synopsis (although ‘selected actions’ in the title gives a clue). When we came to look at compiling this synopsis, it soon became apparent that with 4,140 studies included in our search of titles and abstracts, there were far too many to summarize given the time, and funding, available. At this point, we called upon the expertise of our Advisory Board to ask them to prioritize actions for evidence collation. The answer? A resounding vote for actions relating to habitat restoration and creation.
This is hardly surprising given that between 1930 and 1980 more than 8,500 km of rivers in the UK alone were modified for the purposes of flood control, land drainage, and navigation (Pretty et al. 2003). Modifications included channelising and clearing in-channel and bankside obstructions. These modifications led to rivers becoming straight channels with no variation in depth or flow velocity resulting in a loss of habitat variation and, consequently, a reduction in freshwater fish diversity.
Lakes, reservoirs and ponds have also been subject to modification through urban and residential development resulting in shoreline armouring with concrete, removal of woody debris, and clearance of riparian vegetation leading to a reduction in habitat complexity. Nearshore habitats, with natural variation in structure and depth, are vital for freshwater fishes as they provide shelter from predation, and a diversity of habitats for feeding and nesting (Tabor et al. 2022).
The aim of the actions within the published Habitat Restoration and Creation chapter is to mitigate these threats by restoring habitat heterogeneity or creating new habitat to support freshwater fishes (defined in the synopsis as fish that spend some, or all, of their lifecycle in freshwater). We have summarized 284 studies of the effectiveness of 39 actions (35 of which have evidence) that aim to restore or create habitat for freshwater fishes.
The actions with the highest number of summaries were: Add woody debris (33 studies); Install engineered woody structures (e.g. log-jams) (25 studies); Create artificial habitat structures (18 studies); and Add boulders (15 studies). Some of the actions were surprising such as adding salmonid carcasses to a nutrient-limited river. Salmonid (or other diadromous species) carcasses are used as these replicate or support the ‘natural’ process for delivery of essential nutrients derived from the marine environment. These nutrients would normally be released as fish return from the sea to the river to spawn, die and subsequently decompose.
Studies that test the effect of a single action usually produce more compelling results. In contrast, testing a number of actions simultaneously without separating the results can often mask the effectiveness (or otherwise) of actions. Interestingly, the action with the highest number of studies, (Add woody debris) is one of the simpler actions to carry out. Perhaps that’s why?
Most actions looked at outcomes for salmonid species with the highest number of appearances by brook trout Salmo trutta (in 57 summaries), followed by steelhead/rainbow trout Oncorhynchus mykiss (32 summaries), and Chinook salmon Oncorhynchus tshawytscha (24 summaries). That was one of the many things I learned – steelhead and rainbow trout are the same species, but steelhead migrate to the ocean and return to spawn whereas rainbow trout remain in freshwater throughout their life. Common names for fishes led to some raised eyebrows: we have been introduced to the northern hog sucker, black redhorse, and, my favourite, dolly varden.
What are we going to do with this information? The first job is to assess the evidence, and we are working our way through the synopsis, applying a ‘score’ to each summary. This score reflects the benefits vs harms of the action, as well as assessing the reliability (i.e. study design) and relevance (i.e. any assumptions made) of each study. Scores will be calculated across each action and reported on the Conservation Evidence website very soon.
We are also developing a suite of evidence-based guidance documents to accompany and support the synopsis.
From synopsis to practical guidance
Using the evidence gathered in the synopsis, we are now turning our attention to practical guidance. We are writing collated guidance for groups of related conservation actions, organized into multiple chapters. Each chapter is designed to be a stand-alone piece of guidance, but the chapters also work together as a more complete resource for habitat restoration and creation actions for fish in inland habitats. This means you can dip into whichever action is most relevant to you without having to read the whole document. We took a similar approach in our previous guidance on ‘Restoration, creation and management of salt marshes and tidal flats: a collation of evidence-based guidance’. We create guidance following the co-produced principles for evidence-based guidance, meaning everything we recommend is transparently grounded in either published evidence or expert opinion.
So how will the guidance for fish conservation differ from the synopsis? While the synopsis focuses on which actions work (or don’t work), the guidance shifts the lens to how those actions were implemented. What did people actually do, and what did or didn’t work as a result? In other words, it’s about the practical side of conservation. However, this is easier said than done. Scientific papers are often light on implementation detail, which makes it hard to give truly actionable advice based on the literature alone. That’s why we work closely with an advisory board of practitioners and experts, whose real-world experience helps fill in the gaps.
We expect the guidance to be completed within the coming months so watch this space!
References
Pretty J.L., Harrison S.S.C, Shepherd D. J., Smith C., Hildrew A.G. & Hey R.D. (2003) River rehabilitation and fish populations: assessing the benefit of instream structures. Journal of Applied Ecology, 40, 251–265. https://doi.org/10.1046/j.1365-2664.2003.00808.x
Tabor R.A., Liermann M.C., Gearns H.A., Moore Z.J., Lynch K.D., Kurko K., Crittenden J. & Shoemaker M.E. (2022) Effectiveness monitoring of juvenile chinook salmon restoration projects in South Lake Washington, Washington State. Lake and Reservoir Management, 38, 180–196. https://doi.org/10.1080/10402381.2022.2027054
