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Kristi Fazioli1, Vanessa Mintzer2,3, George Guillen1
1 Environmental Institute of Houston, University of [email protected]; [email protected]
2 The Galveston Bay Foundation3School of Natural Resources and Environment, University of Florida
INTRODUCTIONFrom the 1980’s to early 2000’s, studies of bottlenose dolphins in Galveston Bay (GB) found:• High concentrations of dolphins near the entrance to GB• A decrease in abundance moving north into the Bay and little or no activity in upper GB 1,2,3
Observational surveys conducted between August 2013 and January 2017 resulted in the identification of 586 individual dolphins, suggesting a recent increase in dolphin activity in upper GB.
Galveston Bay (GB) is a 1600km2 anthropogenically altered shallow bay system. Growth and industrialization from the 1950’s – 70’s contributed to massive fish kills, a 95% decline in submerged aquatic vegetation and
an EPA listing on the 10 most polluted waterways. Management activities have improved water quality and health; however, concerns over pathogenic bacteria and chlorinated organic compounds persist.4
Jan-
17
Dec- 1
6
Nov- 16
Oc t- 16
Sep- 1
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16
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Apr-16
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Aug- 15
250
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50
Month
Cum
ulat
ive
Indi
vidu
als
Dis
cove
red
Cumulative Individual Discovery Curve
29.46
19.64
9.82
0.00
Individual Dolphins
Eucl
idea
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ista
nce
Dendrogram of Dolphin Groups Ward Linkage, Euclidean Distance
Group 12Group
Group 3
Objective: to explore the site fidelity of bottlenose dolphins to upper GB and identify groups within the population, if any, with varying affinity to upper GB.
L e a r n m o r e a b o u t t h e G a l v e s t o n B a y D o l p h i n R e s e a r c h a n d C o n s e r v a t i o n P r o g r a m a t w w w. g a l v b a y. o r g / d o l p h i n
Literature Cited1 Moreno, M.P.T., Environmental Predictors of Bottlenose Dolphin Distribution and Core Feeding Densities in Galveston Bay, Texas. 2005, Texas A&M
University. Ph.D. Dissertation.2 Henningsen, T. (1991) The distribution and ecology of bottlenose dolphin (Tursiops truncatus ) in Galveston, Texas. Thesis from the Faculty of Mathematics
and Natural Sciences of the University of Kiel , 79 pages3 Blaylock, R. A. and W. Hoggard (1994) Preliminary estimates of bottlenose dolphin abundance in southern US Atlantic and Gulf of Mexico continental shelf
waters. NOAA Tech. Memo. NMFS-SEFSC 356(10)4 TCEQ (2011) The State of the Bay: A Characterization of the Galveston Bay Ecosystem, Third Edition. 356pp5 Urian, K. et al. (2015) Recommendations for photo-identification methods used in capture-recapture models with cetaceans. Mar Mam Sci, 31: 298–3216 Rosel, P. et al. (2011) Photo-identification Capture-Mark-Recapture Techniques for Estimating Abundance of Bay, Sound and Estuary Populations of
Bottlenose Dolphins along the U.S. East Coast and Gulf of Mexico: A Workshop Report. NOAA Technical Memorandum NMFS-SEFSC-621. 30 p.7 Zanardo, N., Parra, G. J. and Möller, L. M. (2016), Site fidelity, residency, and abundance of bottlenose dolphins (Tursiops sp.) in Adelaide's coastal waters,
South Australia. Mar Mam Sci, 32: 1381–1401.
RESULTS AND CONCLUSIONS• Dolphins utilize upper GB (Fig. 1,2), a region
previously thought to have little or no dolphin activity. This could be an indication of water quality improvements.
No. of Dolphin Sightings in upper Galveston Bay
# of Sightings1 2 3 4 5 7 8 9 10
# of
Indi
vidu
als
0102030405060
110
120
130
140
Group 1 Group 2 Group 3
Many thanks to the staff and students at UHCL-EIH for field and data support.We also greatly appreciate the support of the following organizations:
All work conducted under NMFS Permit# 18881
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0.6
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0.0
Groups
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elity
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95% Confidence Interval Plot of Mean Site Fidelity Index
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0.45
0.40
0.35
0.30
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0.15
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onal
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htin
g R
ate
95% Confidence Interval Plot of Mean Seasonal Sighting Rate
321
0.200
0.175
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0.125
0.100
0.075
0.050
Group
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thly
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ate
95% Confidence Interval Plot of Mean Monthly Sighting Rate
1,291 dolphins sighted in 162 groups during the study period
232 individuals included in the site fidelity analysis
• The cluster analysis identified at least three distinct groups of dolphins showing varying degrees of site fidelity (Fig. 2, 3, 4). While the number of year-round residents appears to be small (<%5), the number of seasonal (warm) residents make up at least a quarter of the marked population included in this analysis.
• The influx of dolphins during the warm months is supported by several trends: transient dolphins were primarily recorded during summer months, the greatest period of discovery is the summer (Fig. 1), and dolphin densities are higher in the warm months.
• Based on observations outside the study area but within GB, we expect that many transients of our study area spend most of their time in other areas within the Bay system (i.e., high level of site fidelity to GB as a whole, seasonal movement and
individual regional preferences within). • With the continued expansion of industry and human
activity in GB, research efforts should continue toward a better understanding this potentially vulnerable
population.53%
14%
33%
Site FidelityGroup 1 - apparent one-time visitors to the study area (i.e.,
transients; n=124)
Group 2 - individuals that were only seen during one set of consecutive months or seasons (i.e., temporary
residents; n=32)Group 3 - individuals observed
year-round or in multiple non-consecutive months or seasons
(i.e. year-around residents and seasonal residents; n=76)
METHODS• Monthly boat-based photo-identification surveys were
conducted between August 2015 and January 2017 238hrs and 3441km of total survey effort
• Individual dolphins were identified using the natural marks on their dorsal fins, following photo-analysis ‘best practices’5,6. Fins with low distinctiveness or poor photo quality were excluded, as were all calves.
• Site fidelity the “tendency of individuals to remain, or return to, and reuse the study area”7
• Calculated three site fidelity parameters 7 : 1) monthly sighting rate2) seasonal sighting rate seasons: late warm
(Aug-Oct), early cold (Nov-Jan), late cold (Feb-Apr), early warm (May-Jul)
• Incorporated the three parameters into an agglomerative hierarchical cluster (AHC) analysis to identify groups of individuals with similar degrees of site fidelity
3) site fidelity index: ratio of the number of recaptures of an individual and the number of total surveys from the individual’s first capture to its last
Prepared for the 22nd Biennial Conference on the Biology of Marine Mammals, October 2017
Figure 1. Discovery curve of the cumulative number of bottlenose dolphins identified in upper Galveston Bay, TX between August 2015 and January 2017.
Figure 2. Number of sightings for individual bottlenose dolphins in upper GB from Aug 2015 to Jan 2017. Three groups are displayed based on the results of the AHC analysis using site fidelity metrics.
Figure 3. Dendrogram of the AHC analyses used to separate groups of bottlenose dolphins in upper Galveston Bay, TX based on three measures of site fidelity.
Figures 4a-c. Confidence interval plots of the means of the three measures incorporated in the site fidelity analysis. Three groups are displayed based on the results of the AHC analysis.
