Humpback Whales (Megaptera novaeangliae) Cluster by Geological Features off Puerto Rico, USA
1,2Mithriel M. MacKay Ph.D., 1Cathy E. Bacon MSc., 2Bernd Würsig Ph.D., 3Jason D. Selwyn MSc.
1Marine and Coastal Ecology Research Center, Field Station at San German, Puerto Rico, USA; 2Marine Mammal Behavioral Ecology Group, Marine Biology Department, Texas A&M University at Galveston, Galveston, Texas, USA; Department of Life Sciences, 3Texas University- Corpus Christi, Texas, USA
ABSTRACT
North Atlantic humpback whales (Megaptera novaeangliae) (NAHW) migrate to the West Indies to areas where recreational and commercial activities overlap. It is important to predict where whales aggregate, especially as NAHW are presently considered for delisting as endangered by the U.S. National Marine Fisheries Service, and increased interactions between humans and whales are anticipated as numbers increase. Seasonal occurrence patterns were examined off Puerto Rico's west coast to describe where whales aggregate. Between 2011 and 2014, 165 days of 240.9 hours (h) vessel, 13.0 h aerial, and 303.6 h land observations were conducted. We documented 331 individuals among 197groups: 91 (46.2%) singletons, 67 (34%) dyads, 17 (8.6%) mother-calf pairs (M-C), 8 (4.1%) in surface active groups (SAG), 8 (4.1%) mother-calf-escort groups (M-C-E), and 6 (3.1%) whales in mixed-species associations, dispersed among four discrete geological features. A multinomial logistic regression was used to analyze the relationship between geological features (depth, Euclidean distance to ledge, and seafloor slope) and group type. The model revealed that singletons occurred further from a ledge (p=0.002, log.odds +0.229), and singing males were strongly associated with a ledge (p < 0.001, log.odds -1.339). There were strong trends for dyads (p=0.074, log.odds +0.212) and SAG (p=0.084, log.odds +0.496) to occur in deeper water. Preliminary data suggest that M-C pairs aggregated in nearshore (mean distance from shore = 2.42km + 2.99 SD, n= 16) km shallow water (model p = 0.006, log.odds -0.670 for depth) unless accompanied by an escort (M-C-E mean distance from shore = 16.40km+5.99SD, n=8) (Mann-Whitney U=2.000; p = 0.0003). Slope did not improve the model. Predicting where NAHW cluster on winter grounds may enable managers to suggest/enforce minimization of interactions between humans and NAHW.
Results
Introduction
Methods
Pilot study in 2011
Shore based methods from cliffs: scan sampling and theodolite tracking
Vessel surveys: 32ft panga boat, 4-6hr/day (1-3 days/week), 2012-2014
Aerial surveys: Cessna Skyhawk II, reconnaissance
Behavioral observations, passive acoustic monitoring, digital photographs, video
Spatial distribution of NAHW off western Puerto Rico
Examined coastlines, seamounts , ridges, shelves, and ledges in Mona Passage
Physical features may provide an acoustic advantage to singing males.
Conclusions
Acknowledgements
The authors wish to extend gratitude for funding to The Marine and Coastal Ecology Research Center, Texas A&M University at Galveston, Erma Lee and Luke Mooney Foundation. The Caribbean Coral Reef Institute, Caribbean Fishery Management Council, Southeast Area Monitoring and Assessment Program for the Caribbean, University of Puerto Rico Department of Marine Science. We also wish to thank Captain Michael Lopez, Captain Jeffery Albrecht, and the many research assistants and interns who dedicated effort to this study. We extend special thanks to Dr. Jooke Robbins, Dr. David Mattila, and Dr. Phillip Clapham for their guidance.
Data collected under National Marine Fisheries permit #15682
References
MacKay, M. M. 2015. Occurrence patterns and social behaviors of humpback whales (Megaptera novaeangliae) wintering off Puerto Rico, USA (Doctoral dissertation), Texas A&M University Galveston, Galveston, Texas
MacKay, M.M., B. Würsig, C.E. Bacon, and J.D. Selwyn. Humpback Whale (Megaptera novaeangliae)
"Hotspots" potentially defined by bathymetric features off Western Puerto Rico, USA. Submitted September 2015 to Canadian Journal of Zoology.
NAWH numbers varied between years
Aggregations of humpback whales are a heterogeneous representation of age, class, and sex
Whales found predictably in 4 locations marked by geographic features
Euclidean distance and depth are significant as predictors for finding NAHW group association types with geological features
website: www.Marine-Eco.org
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Year
Number of Individuals*
Number of Groups
Number of Mother-Calf Groups
Number of Mother-Calf-Escort Groups
Number of Breeding Groups
Total Number of Individuals in Breeding Groups
Number of Singletons
Number of Pairs+
Number of Mixed-Species Groups
Total Number of Humpback Whales in Mixed-Species Groups
2011
63
36
8
0
3
9
12
13
0
0
2012
19
12
4
0
0
0
5
3
0
0
2013
145
78
1
2
5
22
28
38
4
11
2014
104
71
4
6
0
0
46
13
2
6
Total
331
197
17
8
8
31
91
67
6
17
Percent of Total Individuals
10.3
7.3
9.4
27.5
40.5
6
5.1
Percent of Total Groups
8.6
4.1
4.06
46.2
34.0
3.05
*Individual counts are exclusively humpback whale +Excludes mother-calf pairs
"Perspective" View of the Bathymetry of the Mona Passage, looking eastward toward Puerto Rico. Depths indicated by color, from red (shallowest) to purple (deepest); black indicates sea floor not mapped during this study. Small islands are outlined in white."1
Null Hypotheses:
1) NAHW occurrence patterns are not seasonal and predictable during winter in Mona Passage with breeding groups and non-breeding groups equally represented
2) Groups (M-C, M-C-E, singers, SAG, dyads) are not associated with bathymetric features.
Alternative hypotheses (based on studies conducted on other winter habitats in the North Atlantic and Hawai'i):
1) NAHW migrate to Mona Passage each winter, with the number of group associations favoring non-breeding groups (M-C pairs)
2) Groups are likely to be found associated with bathymetric features
Summary of seasonal occurrence of NAHW by groups during 2011-2014 surveys.
View of the Dominican Republic and Puerto Rico, including the areas where humpback whales aggregate in winter.
Kernel Density Estimates by Group Type of North Atlantic humpback whales in Mona Passage. Dark areas indicate whales were aggregated in four "hotspots" associated with 4 distinct bathymetric features between 2011 and 2014.
Distribution of 197 groups of North Atlantic humpback whales between 2011 and 2014 in Mona Passage with an overlay of bathymetry
Multinomial Logistic Regression Models : test whether bathymetric features (depth, Euclidean distance from the shelf edge and slope of the seafloor) could be used as predictors for finding NAHW group association types with bathymetric features revealed
The best AIC model includes distance and depth, not slope
M-C pairs in shallower water
Dyads and SAG in deeper water
Singletons away from shelf edges
Singing males very close to the shelf edge
M-C pairs near shore, unless accompanied by an escort
Sightings Per Kilometer Surveyed : a summation of sightings divided by the summation of distances surveyed (sightings/km). One block = 5 km2
Four clusters of NAHW sightings can be identified.
Scattergrams Representing the Multinomial Linear Regression Models for humpback whale group association types with depth and Euclidean distance from a ledge.
Y axis: log of the absolute value of depth where water becomes shallow as points move to the top of the scatterplot.
X axis: Euclidean distance raised to the ¼ power where the strongest association with a ledge occurs at zero.
The sum of all group models = 1.
Boat survey tracks in Mona Passage between 2012 and 2014
Future Research
Examine the possibility of an acoustic advantage for singers off ledges
Attempt to determine the age (calf/juvenile/adult) of singers in Mona Passage
Expand the survey area off Puerto Rico
Individuals lunging during energetic competition in a surface active group
Corresponding author:
[email protected]
MC = mother-calf; MCE = mother-calf-escort
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