Index Home Join IPCC

River Otter, Sea Otter or Bog Otter?

The Irish for otter is 'dobharchú' or 'madra uisce, which translates respectively as dark hound or water dog or more poetically the hound of the flowing water.

Because of its aquatic life style we usually associate the otter with a variety of watery places but not readily with bog. Otters are found in streams, rivers, marshes, lakes, estuaries, lagoons and on the coast. There are no sea otters in Ireland, nor is there such a thing as a bog otter. We only have the river otter in Ireland (Lutra lutra), which exploits a range wetlands.

Otter, pen and ink drawings by Sabine Springer	Above: front pawprint of an otter. Life size 6-6.5cm.

I have always been an enthusiastic otter spotter and three years ago I became aware of the very obvious signs of otters in environments, where I did not expect to find them. Otters are notoriously elusive and because there is not much human-sized but plenty of otter-sized cover in bogs it is very difficult to observe them. Even so, there is still the excitement of finding signs, following otter tracks and being aware of the presence of an animal in the wild which in many countries is no longer possible. The most obvious otter signs are spraint heaps - grassy mounds with spraints (or droppings) which are often bright green because of the nutrient enrichment and thus very obvious in bog vegetation. These mounds are sited at stream confluences, where a stream enters the sea or where otters cross waterways. Often one can find them on large, prominent boulders where the otter enters the water. Spraints are usually black and tarry when fresh, with a pleasant musky odour and spiked with fish bones, feathers and beetle wings. Quite often one will be led to the sprainting site simply by following well worn tracks along streams. Another tell tale sign for otter usage are entrances into the water at regular intervals along the track. If otters wander from lake to lake they do so in a direct line, the shortest way possible. If otters cross areas of soft bog, one will be able to see their foot prints. Sometimes at bog banks scratch marks can be seen, (whose purpose is one of the many otter secrets), as well as slides leading into the water or down a peat bank. If I had to choose between the explanation for these slides as energy saving behaviour or fun, I would prefer the idea of otters having endless fun. Because scavengers such as Gulls and Crows are not as common ) in the bog as in other places, one occasionally finds food remains of otter meals like fish heads, or closer to the coast, crabs with the typical otter indenture at the back of the carapace.

Since 2000, I have studied otters in Iar-Chonnachta as part of a larger otter survey of Galway Bay and its hinterland. Some of the questions that really interest me about otters are their food and their travels between the coast and the lakes in the bog.

Scratch marks on a turf bank in the bog caused by Otters. Photos: Sabine Springer	Otter slide through a peat bank into a stream. Photos: Sabine Springer

The first baseline study of the distribution of otters in Ireland, was undertaken in 1981-82. This found otters to be widespread but probably not numerous in Iar-Chonnachta except on the coast. Iar-Chonnachta is a wide, open area of bogland and rock west of Lough Corrib and north of Galway Bay. About 17 rivers and streams enter the sea along the coastline draining the lake studded bogland plateau 200-300m above sea level. Otters use rivers and tiny streams to move between upland areas in the bog and the coast. The objective of my study was to revisit sites recorded in the 1981-82 survey to assess the habitat and any changes in otter populations based on their spraint occurrences. I found almost no changes in otter population numbers and density in Iar Connacht over the last 20 years.

Otters in bog areas feed largely on freshwater fish, but also on inshore marine fish, as well as a variety of small animals, particularly frogs. Fish are generally not plentiful in upland streams, except when the trout come upstream to spawn in winter. Some lakes have good stocks of brown trout and other fish species. Another mainstay of the otters' diet, the European eel, is widespread in most Conamara rivers. Frogs are common in a wide range of habitats from mountain lakes down to the sea. On the coast otters catch rocklings, wrasses, gobies, blennies, butterfish, sea scorpions, flatfish and crabs. Looking at otter spraints, I recorded an obvious change in otter diet from the coastal zone, following the streams to the lakes in the bog. All coastal sites surveyed were on river inlets and all spraints contained remains of marine fish. No frog or bird remains were found in spraints in this zone. The average spraint number was 8 spraints per site. From 2-5km up and away form the coast, into the bog, only 2 spraints out of an average of 7.3 contained marine fish, the rest contained freshwater fish species. All spraints in this zone contained frog bones and some had beetle wings. Further upstream again (6-15km from the coast), only fresh water fish bones were found in spraints including the Stickleback. Half of the spraints contained frog bones and others contained feathers and bird remains. The average spraint number per site was 4.3.

Otter spraint heaps stand out in the bog because of the nutrient enrichment they cause. Photos: Sabine Springer	Crab for dinner? - Crab shells with the characteristic incisor indentation at the back of the shells caused by hungry otters. Photo: Sabine Springer

These results show how the otters exploit different food sources in a complex of habitats including seashore, river, lake and bog. The increased number of spraints nearer the coast suggests that food is more plentiful by the sea compared to the bog. To exploit these resources, otters travel considerable distances between feeding and resting sites. Holts have been found close to upland lakes, and although food is scarce the otters are quite undisturbed. On bogland bordering the coast, connected to the sea by streams, the otter seems to have found a habitat that supplies plenty of food, a source of freshwater used to maintain the thermoinsulation properties of its fur and safe and relatively undisturbed sites for resting and raising cubs. For future conservation, it will be important to keep the otters' water routes between the shore and bog habitats open and to make every effort to minimise road deaths caused when roads cross otter tracks. - Sabine Springer