# The Use of Spraints for Surveying Otter Lutra lutra Populations: An Evaluation

> Can otter droppings tell you where otters live and how well they are doing? Responding to a study that doubted it, two otter researchers tested the standard spraint survey with data from Wales, Spain, Greece, North Africa and beyond. They found the method maps otters reliably, gives a broad guide to population health, and shows that bankside cover matters, as long as surveys avoid floods and allow for the season.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1987-mason-macdonald-use-spraints-surveying-otter/

## Citation and access

- **Authors:** C. F. Mason and S. M. Macdonald
- **Year published:** 1987
- **Journal or source:** Biological Conservation
- **Full citation:** Mason, C. F. and Macdonald, S. M. 1987. The use of spraints for surveying otter Lutra lutra populations: an evaluation. Biological Conservation 41(3): 167–177.
- **DOI:** 10.1016/0006-3207(87)90100-5
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.1016/0006-3207(87)90100-5

## Tags

- **Species:** Mammals > Eurasian otter
- **Region:** Africa > Algeria; Europe > Greece; Europe > Italy; Africa > Morocco; Europe > Portugal; Europe > Spain; Africa > Tunisia; Europe > United Kingdom
- **Tracking:** Scat; Sign surveys; Tracking; Tracks; Tracks and signs identification
- **Behaviour and ecology:** Behaviour; Communication; Habitat selection
- **Methods and technology:** Analysis of variance (ANOVA); Distribution mapping; Linear regression; Literature review
- **Data type:** Existing data; New field data; Review
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology; Wildlife tracking
- **Year published:** 1987

## Detailed keywords

- **Species:** Studied: Eurasian otter (Lutra lutra), through their spraints (droppings). Discussed from other studies: North American river otter (Lutra canadensis, radio-tracked in Idaho, USA) and a tame captive otter in an enclosure. Plants named as cover linked to sprainting: ash (Fraxinus excelsior), sycamore (Acer pseudoplatanus), Rhododendron thickets, Rubus (brambles), Salix (willow) scrub and Phragmites (reeds).
- **Location and habitat:** Rivers, streams and canals. Distribution surveys in Wales, north-east Greece and Andalucia (south-west Spain), and across the Mediterranean region: Portugal, Greece (Thrace, the western Peloponnese and central Greece, in the catchments of the Sperchios and Pinios rivers), Italy, Spain, Tunisia, Morocco and Algeria. Intensive surveys in north-east Greece, central Wales and south-western Spain. Cited studies from the River Teme (West Midlands, England), north-east Scotland and the River Dee, west Wales, the River Wye (Wales), Perthshire (Scotland), East Anglia (England), Shropshire (England), Idaho (USA), and the Shetland coast (Scotland), where the study they respond to was done.
- **Topics:** spraint (otter dropping) surveys; the standard 600 m otter survey; survey length and detection of positive sites; otter distribution; spraint density as an index of population status; seasonal cycles in sprainting; effect of floods and spates on surveys; spraints as signals (scent marking); spraint density and habitat (bankside cover, holts, trees and scrub); weathering and disappearance of spraints; criticism of the method by Kruuk et al. (1986) on Shetland and the authors’ reply; otter conservation.
- **Statistics or models:** linear regression of cumulative positive sites against distance searched (Wales: y = 93 + 0.09x, r = 0.97; Mediterranean: y = 148 + 0.23x, r = 0.99); Spearman rank correlation (rs = 0.84, P < 0.01, spraint density against percentage of positive sites in ten surveys; rs = 0.63, P < 0.01, the authors’ reanalysis of Kruuk et al.’s observation time against recorded activity); analysis of variance (F = 4.95, P < 0.01) and t-tests comparing three regions of Greece.
- **Data type:** New field data and existing data: the authors’ own surveys, recording all otter signs in 100 m stretches over 1000 m at each site (north-east Greece 1983; Andalucia and Wales 1986; 92 km in total); 329 sites in a survey of Wales (Andrews and Crawford 1986); 712 sites in Mediterranean surveys (1982 to 1985); seven extensive and three intensive surveys for the spraint density comparison. Also a review of nine published habitat studies and three radio-telemetry studies. Inconsistencies noted: the text cites Jefferies (1986) four times, but the reference list gives Jefferies (1966) for that paper, which is likely a typo. Figure 1 is described as “data derived from a survey of Wales, n = 146” while the text gives 329 sites; 146 appears to be the number of positive sites (44% of 329), and Figure 2 likewise gives n = 313 for 44% of 712 sites. The caption for Figure 1 says “within the first 100m” while the text says 74% of positive sites were confirmed within the first 200 m.

## Synopsis

### 1. What they did

For about ten years, otters had been surveyed in many countries by searching up to 600 m of riverbank for their signs, mostly spraints (droppings), and stopping as soon as a sign was found. Otters seem to use spraints to signal to each other and often leave them in conspicuous places, which makes them easy to find. A 1986 study of daytime-active, coastal otters on Shetland (Kruuk et al.) found no link between spraints and the time otters spent on stretches of shore, and questioned the method.

The authors set out to test the method with their own survey data, asking three questions:

- Distribution. Does the standard 600 m search reliably show where otters are? They recorded all signs in 100 m stretches over 1000 m at sites in north-east Greece, Andalucia (Spain) and Wales (92 km in total), and plotted when sites were first confirmed in a Welsh survey of 329 sites and Mediterranean surveys of 712 sites.

- Population status. Does the number of spraints per 200 m match the share of positive sites, across ten surveys in Portugal, Greece, Italy, Spain, Tunisia, Morocco, Algeria and Wales? And does it differ between regions of Greece thought to hold thriving or declining otter populations?

- Habitat. Does spraint density reflect the habitat otters use? They reviewed nine studies of spraints and habitat, three radio-telemetry studies and one experiment with a captive otter.

They also re-examined the design of the Shetland study.

### 2. What they found

Distribution

- Where 1000 m was searched, 73% of sites were positive within the first 600 m. The extra 400 m added only 6% more. 79% of positive sites were confirmed within the first 200 m.

- In Wales, 44% of 329 sites were positive, 74% of them within 200 m. Extending the search to 1000 m was predicted to add 11.7% more positive sites.

- In the Mediterranean, 44% of 712 sites were positive, 69% of them within 200 m. Extending to 1000 m was predicted to add 7.5%.

- Negative sites were not scattered at random. In Greece (a thriving population) they clustered in distinct sub-catchments; in Italy (otters close to extinction) the positive sites clustered. A survey of 1300 Italian sites by another researcher found a very similar picture to the authors’ 188 sites (6.2% and 8.5% positive).

Population status

- Across ten surveys, spraint density rose with the percentage of positive sites (a significant correlation). The main outlier was central Wales, surveyed in September when marking is at its lowest and straight after unseasonal heavy rain and flooding.

- In Greece, central Greece had far fewer spraints per 200 m (2.69) than Thrace (10.04) or the western Peloponnese (9.90), matching its lower share of positive sites (56.4% against 92.3% and 85.0%). Thrace and the Peloponnese did not differ.

Habitat

- All nine studies that looked for it found more spraints where there was more cover: woodland and trees along the bank (especially ash and sycamore), scrub, brambles, willow, reeds and potential holts (resting sites).

- Radio-telemetry supported this. In Perthshire, otters fed a radioactive marker left labelled spraints concentrated at their centres of activity, and used ash and sycamore roots as holts. Released otters in East Anglia spent 53% of their time in woodland. In Idaho, river otters hardly used stretches with plenty of food if there was too little cover.

- A captive otter entered and left the water mostly by bankside bushes, and moved their entry points when the bushes were moved.

- Cover is not everything: one stretch of bare grazed pasture in Wales was heavily sprainted, especially in winter. It faces the meeting of two major tributaries with the main river, and the marking may have social importance at this “crossroads”.

The Shetland study

- The Shetland otters were daytime-active, at high density on the coast, unlike nocturnal river otters at lower density along a line of river. That study did find more spraints near holts.

- Observations were irregular, and time spent watching blocks of coast varied more than fifteen-fold. No otters were seen in the three least-watched blocks, although spraints were found there. Recorded activity correlated with observation time, suggesting observers watched longest where they expected otters.

- Spraints were collected only three times (May, July, September), but spraints weather away in about four weeks on Shetland, and half of marked spraints disappeared within three weeks in Shropshire. Many spraints linked to observed activity would have been missed.

### 3. What they concluded

- Spraint surveys using the standard method give a reliable picture of where otters are. A whole catchment is very unlikely to be wrongly recorded as having no otters.

- Used with care, and with large enough samples, spraint density gives a broad indication of the status of an otter population. It is more valuable as part of repeated monitoring than as a single survey.

- The link between spraint density and cover is real, so spraint surveys can identify habitat features important for otter conservation.

- The Shetland study’s conclusions may reflect its design. Proving there is no link would need radio-tagged otters producing labelled spraints.

- Most surveys were a first step towards conservation, meant to find where otters are widespread and raise local awareness, not to find every otter population. Local otter groups in Iberia, Italy and Greece suggest this aim is being met.

### 4. How tracking was or was not used

The whole method is a sign survey: observers search riverbanks for otter spraints, and occasionally footprints, and count spraints per 200 m. Sites count as positive when any sign is found. The paper does not describe how spraints were identified or how fresh and old spraints were told apart.

### 5. Tracker or observer certification

Not reported. The surveys were done by the authors and others (one author examined the 329 Welsh sites); no qualification or test of the observers’ skill is described.

### 6. Other technologies, skills or innovations

- Cumulative detection curves (sites confirmed against distance searched) to judge how long a survey stretch needs to be.

- Radio-telemetry and spraints labelled with a radioactive marker (from a cited study) to link spraints to where otters actually spent their time.

### 7. Implications for conservation (from the paper)

- Spraint surveys can map otter distribution well enough to guide conservation at the scale of catchments.

- Spraint density linked with bankside cover identifies habitat features worth protecting for otters.

- Surveys straight after unseasonal floods should be avoided where possible, and the season of sprainting should be kept in mind.

- Repeated monitoring of contrasting sites with the same methods could refine estimates of population status.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- How useful a sign is depends on how long it lasts and when animals leave it. Weathering, seasonal marking and floods all change spraint counts, so the timing of a survey matters as much as the effort.

- The critique of the Shetland study shows that sign counts and direct observation can disagree simply because they cover different time windows or uneven effort.

## Cite this summary

Lawrence, K. 2026. Summary of: The Use of Spraints for Surveying Otter Lutra lutra Populations: An Evaluation (Mason and Macdonald, 1987). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1987-mason-macdonald-use-spraints-surveying-otter/