Scientific summary of otter research and recollections 8 years on

For those of you interested in the nuts and bolts of the otter research and river dynamics …read on!

A. GENERAL

The study area was parts of 4 rivers in the lower agricultural and wooded valley emanating from the high forested land around the Arenal Volcano and Monteverde cloud forest. The rivers were the Peñas Blancas, Chachagua, Chachaguita and Burro.  Most of the sub roads are stone tracks and the area is well farmed with bungalows or small fincas..farms ..along the tracks with cattle pasture and partly open sided wooden metal byres with a dairy parlour and small fields of banana, yucca, papaya or harvestable timber saplings etc.  Although tractors were seen, it seems much of the work was by hand with mainly men bent double digging up crops, pushing a small rotovator or carrying bananas over their shoulder and 2 oxen came past pulling a cart.  The bananas are protected from insects and birds by blue plastic bags as well as men spraying them with I guess some sort of fungicide or pesticide.

The upper reaches are too difficult and dangerous to survey due I believe to the typography and speed of the water. One of the reasons we were always accompanied by a local biologist was that sudden and dangerous cloud bursts bring a rush of water sweeping down and people do drown.  I asked if otters use the upper reaches of such rivers, apparantely not, but am unsure if this is because no one has looked, they are too steep and hard to survey or there are very few fish as prey.  I would have thought there would be at least small fish as in our upland  streams plus frogs etc.  Does this neo tropcial otter species eat such prey to exist in the uplands?

ICE the national communications and electric company were not required to carry out an environmental assessment prior to the current construction of hydro electric dams in Peñas Blancas.  However, I think the law has been changed and this is now needed for other similar proposals.  ICE employ agricultural, socio economists and biologists etc.  Their 2 biologists with whom we did the field work and electro fishing have data for several years on fish populations.  They are also responsible for the running of a fish experimental station where we helped count (in spanish..up to a thousand .. I did learn numbers!), measure and weigh the length of young fish. This seems to be done every week to provide data as to the growth rates of various species etc.

The construction of the hydro electric dams has carved roads and huge holes into the steeply forested river valley.  As seen on an earlier trip, such structures and consequent water deluges are vulnerable in an active earthquake region. The dams have considerably disturbed the flow characteristics of the river as well as probably invertebrate, fish and presumably mammal populations such as otter. I don´t think there are any fish passes and I guess otters have to go up and around the huge dam walls.  It seems that most days ICE have big machinery at work on the gravel sand plain at the entrance to the dammed lake, excavating away deposited material.

2. RIVER AND OTTER DATA

Part of each river, say 8km, was mapped into 300m segments with x number chosen randomly for surveying. Within each such 300m segment, there were 6 x 50m sub segments and 4 of these were chosen randomly. In each such sub-segment, the following characteristics of river typography and potential otter habitat features were recorded;

a) percentage of river types such as pool, glide, riffle, rapid and cascade in the main river channel.   Sometimes there was a secondary channel on the other side of a midriver gravel bed or island and this channel was not assessed.

b) potential otter holt features:

excavacion entre las raices de arboles…holes between tree roots

debajo de arboles muertos…under dead trees

cuevas en rocas….holes in rocks

matorrales…scrub ..

excavaciones en paredes….holes in banks or walls

otro…other

c) At zero, 100, 200 and 300m Ancho and Profundidad …the width and average depth…were measured.

d) At a randomly chosen spot, choose a 10m by 10m imaginary plot on both banks …derecha and izquierdo… running from the water edge inland and estimate:

i) percentage size and type of typical rock such as bedrock, boulders (small or large)  cobbles (coarse or fine), gravel and sand and vegetation

ii) percentage canopy cover of Dosel.. .trees ie taller than 5m, Sotobosque..scrub ie between 0.5 and 5m tall and Suelo…ground cover less than 0.5m high. Plus either measure with a tape measure or guess the Distancia a Cobertura de Escape…distance for an otter to escape from the water´s edge to cover.

e) For each otter spraint found, I believe Rocio recorded type of water eg pool, rapid…, substrate such as a large rock which was very typical, location in the river such as midriver or the edge and GPS data.

3. ELECTRO FISHING

On some river segments through electro fishing with the ICE biologists, we carried out say 5 catches, in different types of the river such as across a rapid between rocks. Data was recorded as to species, weight, sex, length.

4. SPRAINT COLLECTION

Approximately 150 spraints have been collected from the initial field visit and one subsquent visit to those sub-segments which had a positive earlier presence.

5. SPRAINT ASSESSMENT

The spraints were washed by soaking in a bucket overnight in water and washing powder. They were then rinsed through a small sieve under finger pressure from a fast flowing tap until they looked clean and left to dry in the sun.  These were stored separately in plastic bags.

The lab work was to remove any dead insects and then sort the often very fine material ie tiny bits of crab shell or fish scale into crab or fish. This was hard work on my eyes especially as the work days are usually from about 7am to 5 or 6pm. It was bad eye strain with contact lenses as I ended up with some bad headaches and seeing double crab pieces! Glasses are better for such work.

At first I had no tweezers, so I used a pencil or someone´s toothbrush left in the lab! Then I got a lamp which helped too. Some Bob Marley music and hey, its OK! Involvement by assistants finished at this stage and R continued the studies with identification of the different prey species.