Otter surveys and working windows on a watercourse

Otters are a European protected species, and the protection that matters most on a riparian construction site is the one covering resting places. Under the Conservation of Habitats and Species Regulations 2017 it is an offence to damage or destroy a breeding site or resting place of an otter, and that protection applies whether or not the animal is there at the time. So a holt on the bank within your working corridor is a constraint on day one, not something to check the night before the excavator arrives.

What the protection covers

Three categories of offence arise in practice. Deliberate capture, injury or killing. Deliberate disturbance, which includes disturbance likely to affect the ability of a group to survive, breed, rear young or, for a species that hibernates or migrates, to do so. And damage or destruction of a breeding site or resting place.

That third offence has no deliberateness requirement in the same way, which is why it drives site programming. Machinery tracking over a bank, piling vibration close to a holt, or removal of scrub over a couch can all fall within it.

Otters are also listed under the Wildlife and Countryside Act 1981, which adds protection against intentional or reckless disturbance while an animal occupies a place of shelter. For a developer the practical position is that both regimes have to be satisfied.

Survey extent along the channel

Otter survey is a field-sign exercise, and the field signs are distinctive enough that an experienced surveyor can cover a substantial length of bank in a day. What is surveyed is the channel and both banks, upstream and downstream of the works, commonly to 250 metres in each direction and further where the scheme is large, where the channel is a known commuting route, or where the works involve diversion or impoundment.

The signs looked for are spraint on prominent rocks, ledges and under bridges, anal jelly, five-toed footprints in soft sediment, slides on steep banks, feeding remains, paths through bankside vegetation, and the resting places themselves.

Timing is less restrictive than for many species, because surveys can be carried out year-round. Low water and low vegetation make signs easier to find, so late winter and early spring are efficient. But a single visit records a moment. Where the evidence will support a licence application, repeat visits across the year give a picture of how the site is used and are worth the fee. A Protected Species Survey and any mitigation licence require a suitably licensed ecologist, and the survey design is their call rather than the design team's.

Holts, couches and natal sites

The three types of resting place have different consequences.

A holt is an underground shelter, often in a bank cavity, under tree roots or in a rock pile. A couch is an above-ground resting place in dense vegetation, reeds or scrub, which is easily missed because it looks like nothing much. A natal holt is where cubs are born and reared, and it is the most sensitive feature you can find on a riparian site.

Where a natal holt is present, expect buffers measured in hundreds of metres and a working restriction that may run for months, because otters breed at any time of year rather than within a defined season. Buffers around other resting places are usually measured in tens of metres and are agreed case by case. Both figures are for the ecologist and the regulator to set on the evidence, not for a method statement to assume.

When a licence is needed

Where an offence cannot be avoided by design or by timing, a mitigation licence from Natural England is required before the works proceed. The test the licensing authority applies has three limbs: the works must be for a purpose the regulations recognise, there must be no satisfactory alternative, and the action must not be detrimental to the maintenance of the population at favourable conservation status.

Two practical consequences follow. Licence applications are evidenced by survey, so a scheme with one visit and a thin report will not get one. And the planning authority is expected to consider the likelihood of a licence being granted before it grants permission, which is why the ecology work has to be done before the application rather than deferred to a condition.

Where the works are minor and the resting place can be avoided with a buffer and supervision, no licence is needed. That is the outcome to design for.

Working windows and night time restrictions

Otters are largely nocturnal, so the single most effective mitigation on most sites is a prohibition on working after dusk and a requirement that any site lighting is directed away from the channel with cut-off luminaires.

In-channel works carry a second set of constraints that have nothing to do with otters. Fisheries interests generally restrict works during salmonid spawning in the late autumn and winter and during coarse fish spawning in spring and early summer, which on many rivers leaves a working window in late summer. Add a requirement for a flood risk activity permit where the works fall within the regulated distance of a main river, and the programme narrows further.

Those windows interact badly. An ecological restriction that pushes work later and a fisheries restriction that pushes it earlier can close the year entirely, which is the point at which the scheme gets redesigned rather than rescheduled. The same squeeze appears on terrestrial sites, and our note on reptile surveys and the temperature window shows how narrow a survey season can get.

Mitigation that works

• Retain a vegetated buffer along both banks, wider than the minimum, and fence it before any plant arrives.
• Keep the channel passable throughout the works, because otters use watercourses as commuting routes and a blocked culvert pushes animals onto roads.
• Provide mammal ledges or dry culvert shelves where a crossing is being rebuilt.
• Where a resting place has to be lost, provide an artificial holt in a suitable location well before the works, so it is available rather than notional.
• Cover or ramp any open excavation overnight so animals can escape.
• Appoint a named ecological clerk of works with authority to stop work.

Artificial holts are worth a caution. They are accepted mitigation, but uptake is not guaranteed and a licence will not be granted on the basis that one has been built. Treat it as part of a package rather than as the answer.

Conditions on a riparian scheme

Expect conditions requiring a construction environmental management plan with the ecological measures embedded, a lighting scheme designed to avoid spill onto the channel, a pre-commencement update survey where the permission is more than a year old, and delivery of the buffer planting and its long-term management.

Where the scheme also triggers biodiversity net gain, the riparian habitat is assessed through the watercourse element of the statutory metric, separately from the area habitats, and the two should not be conflated. A Preliminary Ecological Appraisal is normally the document that scopes both, and the wider question of how effects are characterised runs through our note on significance of effects in an ecological impact assessment.

Protected species surveys and mitigation licences require a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and a PlanScope draft is a starting point for that professional rather than a substitute for their work. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.