Otters and holts: survey, protection and works near water

Otters are a European protected species, and the offence that catches development is damage to a breeding site or resting place rather than harm to the animal itself. You do not have to see an otter to commit it. A holt under a bank of tree roots, a couch in bramble on a river margin, or a drainage culvert used as a lie-up are all resting places, and they are protected whether or not an otter is present on the day the excavator arrives. That is why riparian works need a survey before the programme is fixed, not after.

The legal protection and the offences that apply

Otters are listed under the Conservation of Habitats and Species Regulations 2017 and Schedule 5 of the Wildlife and Countryside Act 1981. Between them the offences cover deliberate capture, killing, injury and disturbance, and damage to or destruction of a breeding site or resting place.

Two features matter on site. The resting place offence does not require intent in the same way as the disturbance offences, so a contractor who fills a culvert without knowing it is used commits the offence. And disturbance extends to acts likely to impair an otter's ability to survive, breed, rear young or to affect the local distribution of the species, which brings noise, light and vibration into the assessment rather than only physical works.

Otters breed at any time of year in Britain. There is no closed season that makes works safe, which separates otters from the seasonal survey regimes that govern bats and newts.

Survey method: spraints, couches and holts

Field signs carry the survey. Spraints are the most reliable, deposited on prominent features such as boulders, ledges, fallen trunks and the dry shelves under bridges, and they smell distinctly different from mink scats. Anal jelly, footprints in soft silt showing five toes, slides on steep banks, and paths through vegetation build the picture.

The distinction that matters for the assessment is between a holt, an underground or enclosed structure used for shelter and breeding, and a couch, an above-ground lie-up in dense vegetation. Both are resting places. Holts are frequently in root plates of bankside trees, in cavities behind revetments, in old land drains and in rock piles.

A surveyor should walk the watercourse both upstream and downstream of the works, with the distance justified by the site rather than taken from a rule of thumb, and should record culverts, bridges, tributaries and ditches as well as the main channel. A Preliminary Ecological Appraisal normally scopes this, and where signs are found a targeted survey follows.

Timing and the limits of field sign surveys

Signs can be recorded in any month, so survey timing is about conditions rather than season. High flows wash spraints away, dense summer growth hides couches, and a single visit after a spate can produce a false negative on a watercourse that is used regularly.

Repeat visits are the usual answer, spaced to cover different flow conditions. Camera traps help where a specific structure needs to be confirmed as in use, though they need care in public places and they miss animals that pass outside the detection zone.

What a survey cannot do is prove absence. Otters range over long distances along river systems, and a holt unused in March may be occupied in September. Assessments should be written on that basis, with the precautionary measures that follow.

Working distances, lighting and the construction method

The practical controls are set by the ecologist and written into a method statement. Buffers around a confirmed holt scale with the works: modest for hand tools and short duration activity, substantially larger for percussive piling, blasting or sustained heavy plant. Check the current Natural England advice for the distances applied to each category of work.

The recurring problems on riparian sites are these.

• Night working and floodlighting on the bank, which deters otters from using a corridor even when nothing is physically damaged.
• Open trenches and unfenced excavations, which trap otters overnight unless ramps are installed or the trench is capped.
• Pipes and culverts left open, which are used as resting places and then blocked.
• Loss of dry passage under a bridge when a channel is widened or a headwall rebuilt.
• Vegetation clearance on the bank top, which removes couch habitat well away from the water's edge.

Retaining or building a dry mammal ledge through a culvert or under a bridge is the single most useful design measure on most schemes, and it is far more easily secured at design stage than retrofitted.

Licensing where a holt cannot be avoided

Where works will damage or destroy a resting place, or cause disturbance that cannot be designed out, a European protected species mitigation licence from Natural England is required. The licence is assessed against three tests: that the works are for a purpose of overriding public interest or another permitted purpose, that there is no satisfactory alternative, and that the favourable conservation status of the species is maintained.

Licences are applied for after planning permission, which is why the planning application has to contain enough survey and mitigation detail for the authority to be satisfied the tests can be met. A Protected Species Survey and any licence application require a suitably licensed ecologist, and a draft report is a starting point for that person rather than a substitute.

Mitigation normally includes an artificial holt built in advance, in a location chosen with the ecologist, plus the timing and supervision controls in the method statement. Artificial holts need to be built and settled before the original is lost, and they need protecting from later site works.

Conditions, supervision and what goes in the submission

Councils secure otter measures by condition, usually requiring an ecological method statement and works in accordance with it. Ask for the condition wording to name the mitigation document by title and date, because a generic condition creates arguments later.

1. Submit survey results with dates, conditions, the extent walked and the signs recorded.
2. Set out avoidance measures in the design, including mammal ledges and lighting restrictions.
3. Provide an outline method statement covering trenches, pipes, working hours and buffers.
4. State whether a licence is likely to be needed and when it will be applied for.
5. Name the ecological clerk of works and the supervision regime for sensitive operations.

Works in, over or near a main river usually also need a flood risk activity permit from the Environment Agency, and the permit programme runs alongside the licence rather than replacing it. Both take time. Neither is a formality.

An illustrative example: a footbridge replacement on a small river, with a spraint on the abutment ledge and no holt found, still needs the ledge rebuilding into the new structure, a lighting scheme that keeps the bank dark, and a pre-works check by the ecologist on the morning the old abutment comes out. None of that is expensive. All of it is easier to design in than to add once the steelwork is ordered.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

PlanScope drafts ecology documents and labels those where a licensed ecologist is legally required, otter work among them. Enter your postcode on PlanScope to see which reports your site needs.

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