AMAZING SEA CREATURES PINK DOLPHINS

trends and habitat preferences of Pink and Grey Dolphins in the

Peruvian Amazon

The pink

river dolphin

(

Inia

geoffrensis

)

and

the grey

dolphin

(

Sotalia fluviatilis

)

are endemic

to the Amazon River

system,

and

an important part of the aqua

tic environment. As such,

their population trends and habitat use are being used to monitor the overall conservation

status of the aquatic system.

D

olphins range widely throughout the rivers, lakes and channels of the Amazon River basin,

and are

renowned

for their mobility. Thus, if either human induced changes (such as

pollution or overfishing) or natural changes (such as effects of climate change)

occur in the

aquatic system dolphins

are

likely

to

move out of the

a

ffected areas. They would therefore

rap

idly indicate a change in the system, unlike other species that would go through

demographic changes that would take much longer to observe.

In addition, dolphins are not

hunted or killed by

the indigenous people of the area

.

Throughout the Amazon basin,

and

especially in the Peruvian Amazon,

the folklore surrounding the river dolphins protects them

from being hunted by the local people, who retain enormous respect for the species.

T

he

relative ease with which

dolphins

can be

counted

allows for

the

long

term monitoring of

the

se species

over time

. Combined with

the

ir

mobility and the

cultural taboos against

killing

these creatures

,

this makes

dolphins

ideal indicator species for monitoring the health of

river ecosystem

.

Research is being conducted at the

Samiria River research sites in the Pacaya

-

Samiria

National Reserve on the population trends and habitat use of the

se

two

dolphin

s

pecies

. The

research aims to monitor the dolphins at several river sites and understand the ecology and

habitat use of the s

pecies. The grey dolphin is primarily found in the river environments,

whereas the more ancient pink river dolphin is better adapted to the flooded forests and

ranges frequently in the lakes and channels. Behavioural studies have shown that the pink

river

dolphins use the lakes as nurseries for their young, whilst the grey dolphin raises their

young in the main rivers. The two species also have very different feeding behaviour, with

the grey dolphin often feeding in communal pods that ambush fish along rive

r banks.

In

contrast, pink d

olphins are more solitary hunter

s who dive and stun fish with blasts of sonar,

and forage amongst the submerged vegetation.

As a result of seasonal variation in rainfall in the Andean headwaters, the rivers

of the

Amazon basi

n are subject to large fluctuations in water levels throughout the year

that flood

the surrounding forest

.

The Pacaya Samiria National Reserve is no exception, with as little as

2

% of land in the reserve above water at the height of the flooded season.

T

he ecology of

both the aquatic and terrestrial wildlife revolves around these seasonal changes.

The

forests

of the National R

eserve

flood as

the waters rise

between December and June,

reducing the

land available for terrestrial mammals but vastly increas

ing the aquatic habitat

available to fish, which move into the forest to feed on the abundant vegetation and to

breed.

Dolphins in turn are affected by the seasonal inundation of water

,

since their prey is

more sparsely distributed throughout the large ex

panses of the flooded forests

.

Between

July and November the water recedes, condensing populations of fish into the reduced

rivers, lakes and channels and driving some

fish to

migrate to the larger rivers.

The dolphins

have an abundance of prey during th

is time, and may even follow the fish migrations down

the rivers and channels.

In recent years

these normal seasonal change

s have become

more intense. Both

the wildlife

and local people

are affected by these extreme events, which are tentatively being

at

tributed to climate change.

The flooded fores

ts are particularly important for

understanding the impacts of climate change in the Amazon, since the aquatic and

terrestrial interface

between high and low water seasons makes this habitat sensitive to

greate

r seasonal variations.

In 2009 the water levels of the Samiria and other Amazon rivers

reached unprecedented heights, flooding huge area

s

of Amazonian forests, yet i

n 2010 the

water levels

were at a historic low

,

resu

lting in extreme dry conditions

.

I

n 2

011

and in 2012

the

rivers

again reached

record highs

, whilst in 201

3

the water levels

during the flooded

season

were not as extreme but

took far l

onger to recede.

The r

esearch

being conducted

on dolphin populations

can therefore

also

be used to

understa

nd how the ever increasing climatic changes are impacting their ecol

ogy, behaviour

and populations, and the wider effects of these climatic events on the aquatic ecosystem.

Methods

Aquatic Surveys

Aquatic

line

-

transect

surveys will be used to census d

olphins. 5 km aquatic transects will be

marked out, trave

l

ling upstream on the main river, travel

l

ing downstream on the main river

and in nearby channels

and

lakes. Each transect will be marked using the aid of a GPS (Global

Positioning System). At least t

wo dolphin transects will be carried out per day, weather

permitting. Transects usually take three hours to complete depending on the speed

at which

the river is flowing, but start and finish times will also be recorded.

An auxiliary boat will be used to c

arry out the census. Any dolphins seen coming to the

surface for air, swimming with their h

eads above water, sunbathing or

swimming just below

the surface of the water will be recorded. With the aid of the GPS the exact distance along

the

transect will be

recorded, while the animal’s position on the river and the time at which

it was seen will also be noted. The dolphin species will be determined

, and the group size

and observations on

the behaviour will be recorded, including feeding, resting, moving, or

p

laying.

This method of fixed

-

width sampling means

the average

abundance of each dolphin species

in the different macro habitats

can be calculated as follows:

Where A = abundance

N = number of individuals

L = distance travelled along river

The statistic

al analyses will involve comparisons between the

average abundance and group

sizes of

grey and pink river d

olphins, their use of macr

o habitats (river, lake or channels),

their use of micro habitats (position in the river, lake or channels), and their beha

viour.

Comparisons will also be made in relation to the time of day, age classes, and macro

habitats. In addition, data from previous years will be analysed to compare changes in

dolphin densities, habitat use and age class composition over time.

Suggested

reading

Aliaga

-

Rossel, E.

(2002). Distribution and abundance of the river dolphin (

Inia geoffrensis

) in

the Tijamuchi River, Beni, Bolivia.

Aquatic Mammals

, Vol. 28, pp. 312

-

323

A =

N

L

Davidson, E. A., de Araujo, A. C., Artaxo, P., Balch, J. K., Brown, I. F.,

Bustamante, M. M. C.,

Coe, M. T., DeFries, R. S., Keller, M., Longo, M., Munger, J. W., Schroeder, W., Soares, B. S.,

Souza, C. M. and Wofsy, S. C. (2012). The Amazon Basin in transition.

Nature

, Vol. 481, pp.

321

-

328

Gomez

-

Salazar, C., Trujilo, F., Po

rtocarrero

-

Aya, M. and Whitehead, H. (2012). Population,

density estimates and conservation of river dolphins (

Inia

and

Sotalia

) in the Amazon and

Orinoco river basins.

Marine Mammal Science

, Vol. 28, pp. 124

-

153

Gomez

-

Salazar, C., Coll, M. and Whitehea

d, H. (2012). River dolphins as indicators of

ecosystem degradation in large tropical rivers.

Ecological Indicators

, Vol. 23, pp. 19

–

26

Martin, A. R. and da Silva, V. V. F. (2004). River dolphins and flooded forest: seasonal habit

use and sexual segreg

ation of

boto

(

Inia geoffrensis

) in an extreme cetacean environment.

The Zoological Society of London, Vol. 263, pp. 295

-

305

Martin, A. R.,

da Silva, V. V. F.

and Salmon, D. L. (2004). Riverine habitat preferences of

botos (

Inia geoffrensis

) and tucuxis

(

Sotalia fluviatilis

) in the central Amazon.

Marine

Mammal Science

, Vol. 20, pp. 189

-

200

Vidal, O. Barlow, J., Hurtado, L., Torre, J., Cendon, P. and Ojeda, Z. (1997). Distribution and

abundance of the Amazon river dolphin (

Inia geoffrensis

) and tucuxi

(

Sotalia fluviatilis

) in the

upper Amazon River.

Marine Mammal Science

, Vol. 13, pp. 427

-

445.