Factors that influenced nesting beach selection by green turtles (Chelonia mydas) in Vamizi, Mozambique, between 2003 and 2012

Supervisors:Prof. Dr. Rui RebeloProf. Dr. Almeida

Guissamulo

Joana Casimiro Trindade

Conservation Science in Mozambique

Overview

• Circumglobal species, feeding and nesting areas in tropical and subtropical waters

• Endangered (Red List IUCN)

• Big colonies: Costa Rica, Queensland, Ascencion Island and Poilão Island

• Nest site selection

Consequences on the fitness of the hatchlings

Green turtle

Soweto

Munto NkuloPangaio

Farol

Comisse

te

Vamizi IslandStudy site

• 10,5km of nesting beaches• Main nesting beaches:

Comissete e Farol

Group Sections

Comissete 1-41Soweto+Farol 42-73

Pangaio+Munto Nkulo

74-105

Nesting site selectionFactors that influence nesting beach selection*• Elevation above the water mark• Slope• Vegetation cover• Beach width• Silhouette of objects behind the

beach• Rock cover• Granulometry

*(Burger & Montevecchi, 1975; Plummer, 1976; Cox and Marion, 1978; Ehrenfeld, 1979 in Wilson; 1998, Schwarzkopf & Brooks, 1987; Plummer et al., 1994 in Wilson, 1998, Mazaris et al., 2006,

Botha, 2010, Mortimer, 1982, , Karavas et al., 2005, Mortimer, 1990).

• Multiple environmental factors (Mazaris et al., 2006)

Goals

• To understand the nesting process in Vamizi

To identify the factors that influenced nest site selection from 2003 t0 2012

To evaluate if nesting was similar throughout the various nesting beach sections throughout the years

MethodologyData collection

• Registration of nesting actions since 2002

• Profile, beach slope and granulometry

• Proximity to promontaries

• Section

No nest 01 or more nests 1

• Beach characterization• Step height

• Beach width

• Signs of erosion

• % dune

• Height and % of vegetation

• Rock cover

Methodology

Statistic analysis• Are there differences in the

number ofnests per group?

nests per section in each group?

nests per section?

• Which variables are related to the presence of nests?

Nests/section 2006

Nests/section 2005

Results and discussionDistribution of nests throughout the years

• ≠s number of nests/section

abandonment sections 1 to 58 in 2006 and 2007

more frequent use of sections 57 to 105 in 2007 and 2008

• ≠s number of nests/group

• ≠s number of nests/section/group

Comissete

Nests/section 2006

Nests/section 2008

Results and discussionFactors that influenced nest site selection

YearBeach Width

(B)% Dune

(B)Rock Cover

(B)

Proximity to promontori

es(B)

Tree + Bush

Height(B)

% Herbs (B)

Correctly classified

pointsR²

2003 1,060 0,020 -1,142 - - - 73,3% 0,292

2004 1,530 - - - - - 69,5% 0,281

2005 1,389 - - -0,003 - - 74,3% 0,432

2006 1,397 - - - - - 74,3% 0,276

2007 1,733 0,025 -1,014 - -0,212 - 82,9% 0,446

2008 1,499 - - - - - 77,1% 0,455

2011 1,450 0,043 -0,924 - - - 86,7% 0,452

2012 1,863 - - - -0,196 - 76,2% 0,378

Results and discussion• Change in the beach preference

patternIndividual preferencesPositive Indian Ocean Dipole Events

• Individual preferences

Same female doesn’t nest every year (3-4

years)

Females might be influenced by different

factors

Change in the sections that are chosen more or

less often

• Indian Ocean Dipole (IOD)

Impossible to test without tagging each individual

We would expect the pattern to be observed in other years

Change in consecutive years contradicts the fact that females rarily nest in consecutive years

Climate indexes used to explain population dynamics (Limpus & Nicholls, 2000; Chaloupka, 2001; Saba et al., 2007 in Chaloupka

et al., 2007)

Sea turtles are affected by SST and oceanic currents (Poloczanska et al., 2009)

Changes in SST + South Equatorial Current turtle

movements changes in the nest site selection pattern

Capacity to correct drifts in their routes (Benhamou et al., 2011) + there are no direct evidences that the IOD may lead

to a change in nest site selection

Dificult to prove hypothesis

Implications for conservation

Identify priority nesting beaches higher level of protection

Biological and environmental variables linked to higher nest densities and hatching success

(Kolbe & Janzen, 2002)

Spacial analysis of the nesting pattern

Soweto

Munto NkuloPangaio

FarolCom

issete

access to vegetation zone

Appearance of steps

nest construction in erosion/flooding prone areas

• Farol EROSION!!

best conditions: beach width + number of nests

main focus in terms of

protection

Implications for conservation

Obrigada! Asante! Thank you!