Presence and distribution of mother-calf pair humpback whales in Central American Breeding grounds are influenced by temperature

Abstract

The North-East Pacific humpback whale population migrates to warm breeding grounds to give birth and reproduce. Although a lot of research effort has been put in place to understand general humpback whale migration behavior, little is known on the distribution of Mother-calf (MC) pairs in breeding grounds. The objective is to understand MC spatio-temporal distribution during wintering months in Central America. Data was gathered on temperature, distribution, group composition and behavior between January and April on four different sites in Central America: Padre Ramos (PR) and San Juan del Sur (SJDS), Nicaragua (2016-2018) and Drake Bay (DB) and Golfo Dulce (GD), Costa Rica (2001-2017).

Preliminary observations on group composition reveals that MC pairs represents 43% in of the groups PR (n=15), 7% (n=9) in SJDS, 58% in DB (n=67) and 48% in GD (n=7). MC pairs displayed a higher percentage of Travelling (78%) in SJDS compared to PR (46.7%), DB (50%) and GD (57.1%). Higher proportions of MC were observed in February North (PR) and South (DB) of SJDS (upwelling site). MC were present close to the coast (0.8-4.8km) in shallow waters (0-80m) in all study sites, excluding these parameters as explaining the remarkable difference in MC presence between sites. Measured Sea Surface Temperatures in Nicaragua (range 17-31°C) were lower than the breeding range temperature (21.1-28.3°C) suggested by Rasmussen et al (2007), which might be unfavorable conditions for calf development.

Our results suggest that MC pairs likely searches for warmer waters to nurse their calves to avoid the cold upwelling waters of the South-West Coast of Nicaragua. These results can have important implications for future management strategies of the endangered Central America Subpopulation. Surveys should be conducted in other Central-American countries to accurately determine mother-calf humpback whale seasonal occurrence and behavior in the whole breeding area, including Guatemala and Panama.

Full text

PRESENCIA Y DISTRIBUCIÓN DE LAS MADRES CON SU CRÍA DE LAS BALLENAS
JOROBADA DEL PACIFICO NORTE-OESTE EN LAS ZONAS DE REPRODUCCIÓN
DE CENTROAMÉRICA
Photo: G. Barathieu
Joëlle De Weerdt, E. Pouplard, L. Oviedo
SOLAMAC 2018

▪Migration of Humpbacks from cold feeding grounds to warm breeding grounds
▪Distinct Population Segment Central America = Endangered (411-600 individuals) according
to NOAA Bettridge et al 2015
▪Lack of detailed informations about the patterns of use of habitat in Central America
INTRODUCTION

▪Breeding ground defined between 21.1°C –28.3°C Rasmussen et al 2007
INTRODUCTION

But: Are there areas they prefer to use or to avoid within breeding grounds?
Low predation risk
Corkeron & Connor, 1999
1
Warm &
Protected areas
Clapham, 2000
2
INTRODUCTION
Increase chance of survival of humpback whale calves

How does
humpback whale
mother-calf pairs
distribute within
the Central
American breeding
ground ?
Photo G. Barathieu
RESEARCH QUESTION

January –April
2016-2018
Two Study sites
+-900h of boat survey
Approx. 250 km apart
Distribution, group
composition, behaviour,
SST
MC = All groups
including calf (MC, MCE,
MC2E, MC>2E)
MATERIAL & METHOD

RESULTS
•Mean monthly SST was significantly lower at SJDS (24.88 °C ± 3.59 °C)
compared to PR (27.68 °C ± 1.14 °C) (Wilcoxon signed-rank test: V= 1, P<
0.05)
•Less variability in 2017 compared to 2018

Costa Rican Dome
- Spatio-temporal variation
- Upwelling system
- Presence coincides with occurrence timing of MC pair in breeding grounds
RESULTS

General behaviour proportion for MC in
PR
TR R M
% PR % SJDS
T46.7 78
R46.7 11
M6.7 -
UK -11
PR
SJDS ?
What about Costa Rica
RESULTS
Is the CRD acting as a natural barrier for MC pairs?

Costa Rica
•Opportunistic sightings
•From 2003-…
•Define behaviours
MATERIAL & METHOD

Bathymetric map
Sightings Nicaragua + CR
Preliminary observations on group composition reveals that MC pairs represents:
•43% in PR (n=15)
•7% in SJDS (n=9)
•58% in DB (n=67)
•48% in GD (n=7)
…of the groups
MC pairs displayed a higher percentage of Travelling (78%) in SJDS compared to P
R (46.7%), DB (50%) and GD (57.1%) -> p-value ?
HOW MUCH % SIGHTED VS DEPTH ? / DISTANCE TO COAST
-> Similar depths (MAP)
-> concentrate near the coast (CALCULATE ?)
RESULTS

0
5
10
15
20
25
30
35
40
January February March April Nov Dec
GD
DB
SJDS
PR
Definition of breeding ground
•Peak of MC
observation in
February (PR vs
SJDS)
<-> coincides with
other breeding
grounds
•SST are lower in
February &
March than
defined for
breeding ground
by Rasmussen et
al 2007

Conclusions & perspectives
•MC pairs likely searches for warmer waters within breeding grounds
to nurse their calves & avoid the cold upwelling waters of the
South-West Coast of Nicaragua
•Alternative hypothesis: avoid feeding adults in the area &
aggressive behavior (De Weerdt & Ramos in review)
•Include other Central-American countries (seasonal occurrence &
behavior) including Guatemala, El Salvador, Honduras, Oaxaca
(Mexico) & Panama + recent sighting data of Mother-calf pairs of
Costa Rica (2019)
•Environmental and spatial modelling to have a better
understanding of habitat use patterns
•Include dorsal fin bending of calves for approx. age estimate

Acknowledgements
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ELI-Scientific
Eric Angel Ramos
&
Research assistants
2016 -2018