Otters in the City!

A recent survey finds almost 200 indicators of otter activity across Dublin

While otters have long been observed in Dublin, a new study commissioned by Dublin City Council under the Dublin City Biodiversity Action Plan (2015-2020) provides key information on how otters are using the city’s waterways. The study was carried out over a 2 year period and discovered 196 signs of this elusive mammal.

The Dublin Otter Survey was carried out by Triturus Environmental Ltd over the past two years (2018-2019). The study area included the coastline of Dublin Bay to the M50, covering 84 kilometres of fourteen watercourses, including rivers (Mayne, Santry, Naniken, Tolka, Liffey, Camac,  Poddle, Dodder, Owendoher, Little Dargle and Slang) and streams (Whitechurch, Wyckham, River and Elm Park).

It provided new location records and these results have significantly expanded what we know about the otter populations of Dublin City.The survey also supports the objectives of the Biodiversity Action Plans of the other Dublin local authorities and the Dublin Bay UNESCO Biosphere. The Otter is a protected species throughout the European Union under the EU Habitats Directive (92/43/EEC) and Ireland is required to monitor and conserve otter populations.

Otter are shy animals that mainly come out at night and can be difficult to find. However, their presence can be revealed by a range of field signs including spraint (droppings), latrines (regular spraint sites), slides (worn areas where otters enter the water), couches (resting areas) and holts (burrows). More otter signs suggest a more active otter population in a river corridor and more intense marking. The ecologists discovered 196 signs of otter, including 25 holts. The most heavily marked rivers by otter included the Dodder and Tolka, while some of the smaller, more heavily modified rivers such as the Naniken (St. Anne’s Park) had no otter signs recorded.

The Dublin Otter Survey was innovative because it used new methods: 1) a novel total corridor otter survey methodology (TCOS), which looks at entire reaches of river not just localised strategic point surveys such as bridges; and 2) a new index to calculate relative levels of human disturbance to otter habitat (the Human Disturbance Index (HDI)) was developed. The distribution of otter signs was examined in relation to natural and disturbed areas of urban river habitat. These methods helped to identify the most valuable otter habitat, which can then be prioritised for conservation and future management efforts.

Although it is commonly believed that otters avoid disturbance from humans, the co-authors of the report, Bill Brazier and Ross Macklin, pointed out that the evidence in Dublin City shows that “it isn’t quite that clear-cut. We did find that the less-disturbed areas of the city’s rivers and streams featured more otter activity in general. Having said that, provided there is some substantial buffer, such as mature treelines or inaccessible areas bounded by high walls, between the river channel and human disturbance, otters can be found in surprisingly urbanised areas”.

The Dublin Otter Survey shows that the rivers of Dublin “Remain highly important passageways for wildlife and also important breeding areas for otter, given they are some of the last remaining secluded habitats in cities that are becoming increasingly fragmented”. In this respect, the study identified the most critical sections of riverine habitat which should be conserved. “Such conservation efforts will ensure that one of the most charismatic species representing urban biodiversity - the otter - can continue to survive in densely populated areas such as Dublin”, the authors concluded.

This study expands on earlier surveys of the Dodder and Liffey which were carried out by volunteers and coordinated by the Irish Wildlife Trust in 2012-2013 for Dublin City Council and also research by a UCD student on the Dodder. Commenting on the results of the new study, Maryann Harris, Senior Executive Parks and Landscape Officer said “the number of holts and extent of otter activity was a surprise to us particularly in highly urbanised areas. It highlights the need to conserve undisturbed sections of rivers for otters to breed and reinforces Dublin City Council’s ambition for the re-naturalisation of river corridors. Otter are sensitive to encroachment by development and this study will better inform the management and conservation requirements for otter in the City”.

To view the survey go to