Potential_effects_of_a_major_hurricane_o

MARINE MAMMAL SCIENCE, 26(3): 707–715 (July 2010)
C 2010 by the Society for Marine Mammalogy
DOI: 10.1111/j.1748-7692.2010.00371.x
Potential effects of a major hurricane on Atlantic bottlenose dolphin
(Tursiops truncatus) reproduction in the Mississippi Sound
LANCE J. MILLER
Department of Psychology,
University of Southern Mississippi,
118 College Drive #5025, Hattiesburg, Mississippi 39406, U.S.A.
and
San Diego Zoo’s Institute for Conservation Research,
15600 San Pasqual Valley Road,
Escondido, California 92027, U.S.A.
E-mail: lmiller@sandiegozoo.org
ANGELA D. MACKEY
TIM HOFFLAND
MOBY SOLANGI
Institute for Marine Mammal Studies,
P. O. Box 207, Gulfport, Mississippi 39502, U.S.A.
STAN A. KUCZAJ II
The effects of natural disasters on wildlife populations are poorly understood.
This is due to the difficulty in predicting the timing, intensity and location of such
rare events. Because of this, when natural disasters occur in locations with long-
term monitoring of wildlife populations, it is important to examine and document
these events to gain a better understanding of how they affect wildlife. In August
2005 Hurricane Katrina devastated many coastal communities throughout Louisiana,
Mississippi, and Alabama.
In the state of Mississippi alone, it was reported that 87% of commercial fishing
vessels were damaged or destroyed (Posadas 2006). The observed loss in fishing vessels
coincided with a decrease in commercial fishery landings at the Gulfport-Biloxi
Harbors from 16.3 million pounds (7.4 million kg) in 2004 to 8.5 and 9.6 million
pounds (3.9 and 4.4 million kg) in 2005 and 2006, respectively.1
Additionally, there
was a 41% decrease in hook and line commercial fishing licenses between 2005 and
2006 and a 50% decrease in finfish net fishing licenses between those same years
1
Commercial fishery landings for Gulfport–Biloxi, Mississippi. Available at http://www.st.nmfs.
noaa.gov/st1/commercial/landings/lport_hist.html.
707

708 MARINE MAMMAL SCIENCE, VOL. 26, NO. 3, 2010
(National Marine Fisheries Service 2007). Residential saltwater fishing licenses also
saw a decrease during this time period with a 40% decrease from 2005 to 2006
(National Marine Fisheries Service 2007). This reduction in recreational saltwater
fishing licenses mirrored the number of recreational boat trips and fish landings.
On average, it was reported that between 2000 and 2005 there were 1,110,101
private recreational fishing trips per year, which decreased to 766,254 trips in 2006
(National Marine Fisheries Service 2007). Fish landings from private recreational
fishing averaged 2,689,201 lbs/yr (1,219,801 kg/yr) between 2000 and 2005 and
decreased to 1,568,986 lbs (711,680 kg) in 2006 (National Marine Fisheries Service
2007). With the decrease in commercial and recreational vessel traffic, and a potential
increase in fish abundance as a result of the decrease in fishing activity, it was possible
that these effects could in turn affect reproductive rates for bottlenose dolphins
within the Mississippi Sound.
In addition to changes in human disturbance, loss of calves as a result of the
storm could increase the number of reproductively active adult females the following
breeding season. Female bottlenose dolphins become fertile within two months to one
year following the loss of a calf (Mann et al. 2000). Thus, any adult females that lost
calves during Hurricane Katrina should have been fertile during the next breeding
season. If a significant number of calves perished during the storm, the percentage
of reproductively active females within the population should have increased for the
next breeding season.
The purpose of the current report is to document the possible effect of increased
reproduction for Atlantic bottlenose dolphins as a result of Hurricane Katrina. Data
were utilized from ongoing opportunistic surveys conducted in the Mississippi Sound
near Cat and Ship islands (see Fig. 1) as well as stranding data for Atlantic bottlenose
dolphins provided by the Southeast Region Marine Mammal Stranding Network.
The time frame examined was from December 2004 through November 2007.
All research was conducted from either a 7 m vessel with a 225 hp Ram injection
outboard motor, a 10 m vessel powered by a 135 hp outboard motor, or an inflatable
catamaran with twin 150 hp motors. Surveys originated from Gulfport, Mississippi,
and research effort alternated between the two islands. After surveying an entire
island for dolphins, any additional time was spent at the other island. All surveys
began at approximately 08:30 and continued until approximately 14:00. During the
study period there were a total of 598 encounters with groups of Atlantic bottlenose
dolphins. Table 1 provides a summary of the research efforts over the 3 yr period.
Encounters with dolphin groups lasted an average of 26 min with a range of
15–105 min. A group was defined as two or more dolphins within 100 m of one
another exhibiting similar behavior (Wells et al. 1987, Shane 1990). Individual fins
were photographed using a Canon EOS 10D digital camera with a Canon EF 100–
400 mm f/4.5–5.6L IS USM telephoto zoom lens for photo-identification purposes.
Photographers were instructed to take as many pictures of all individuals within
an encounter as possible. Environmental, acoustic, and behavioral data were also
collected, but were not analyzed for this paper.
Photographs from all encounters were initially scanned for the presence of any
Atlantic bottlenose dolphin that could have been a calf. Images of the same

NOTES 709
Figure 1. Map of the study area in the Mississippi Sound.
individuals based on dorsal ﬁns from the adult females presumed to be the mother
were removed from further analysis. These images were then rated by three inde-
pendent observers to determine the likelihood, on a scale of 1–10 (10 being most
likely), that the individual or individuals within each photograph were a calf less
than 1 yr of age. Raters were instructed to use the deﬁnition of any animal less then
approximately half the length of an adult or 1.5 m (Constantine 2001, Bearzi 2005)
Table 1. Summary of survey effort during the study period.
Distance Duration Number Number
Year Season (km) (hh:mm) of groups of photos
2005 Winter 602.91 39:37 25 610
Spring 923.63 56:56 43 1,130
Summer 492.34 39:22 28 2,474
Fall 384.43 25:50 24 950
2006 Winter 853.93 39:09 32 567
Spring 446.47 30:33 38 1,268
Summer 644.73 47:44 55 4,014
Fall 475.77 34:20 33 1,554
2007 Winter 639.70 35:24 37 836
Spring 516.29 34:09 37 1,099
Summer 477.98 27:41 33 2,538
Fall 542.85 33:47 36 2,376

to help with consistency in rating. The scores of all three raters were then compared
and any individual dolphin with a median score of ≥7 was selected as a calf less than
1 yr of age. Using the median ensured that at least two of the three observers had a
score of ≥7. Of the images selected all three of the observers had a score >7 on 48%
of the images. There were no significant differences between years for percentage of
photographs all three observers scored 7 or higher (␹2
= 1.73, df = 2, P = 0.42).
The total number of calves per encounter was tallied and rates were calculated
based on number of calves per kilometer traveled by the research vessel. Additionally,
rates were calculated for the number of calves per group of dolphins encountered
and percentage of calves vs. noncalves. The number of noncalves was calculated by
removing duplicate photos of each individual from each encounter and totaling the
number of noncalves present. Data were divided into the following seasons based on
sea surface temperature: winter (December–February), spring (March–May), summer
(June–August), and fall (September–November). This allowed for visual inspection
of calf encounter rates between the years. Each year of consecutive data started in
December and went through the following November (e.g. December 2004 through
November 2005). A repeated measures analysis of variance (ANOVA) was used
to examine significant differences between years based on the monthly rates of
calves per kilometer surveyed, calves per groups of dolphins, and survey effort.
Measures for survey effort included distance surveyed, trip duration, number of
groups encountered, and number of photographs. A Tukey’s post hoc test for individual
comparisons was used to follow up all significant results. Chi-square analysis was
used to look for significant differences between calf and noncalf by year. Follow-up
analyses included examining the percent deviations from expected frequencies and
creating standardized residuals to examine significant differences between the years.
Alpha level was set at 0.05 for all statistical tests.
In addition to the data collected as described above, stranding data for Atlantic bot-
tlenose dolphins were provided by the Southeast Region Marine Mammal Stranding
Network. The stranding data included all live and dead strandings within Alabama,
Mississippi, Louisiana, and Texas. Information provided for each stranding included
the date, location, body length of the dolphin and initial condition of the animal
(alive, fresh dead, moderate decomposition, advanced decomposition, or skeletal).
Data were only used for dolphins that were juveniles or younger (dolphins <228 cm)
to examine the same time periods as for calf encounter rates. All coastal counties
within Alabama, Mississippi, and Louisiana and the counties of Texas closest to
Louisiana (Galveston, Harris, Jefferson, and Chamers) were used in the analysis. The
length of 228 cm was determined based on previous studies examining the length
of each age class (Read et al. 1993, Fernandez and Hohn 1998, Mattson et al. 2006)
and animals of this size were most likely still socially/physically dependent on their
mother. A one-sample t-test was used to analyze calf stranding rates during the fall
of 2005.
A repeated measures analysis of variance revealed no significant differences in
survey effort across the years (distance surveyed, F2,22 = 0.150, P = 0.862; trip
duration, F2,22 = 0.482, P = 0.624; number of groups encountered, F2,22 = 0.678,
P = 0.518; number of photographs, F2,22 = 0.519, P = 0.602). Examining the calf

NOTES 711
Table 2. Tukey’s follow-up statistics on calf encounter rates.
Mean
Variable Year (i) Year ( j) difference (i − j) SE
Calves/kilometer 2005 2006 0.001 0.002
2007 −0.011∗
0.004
2006 2007 −0.012∗
0.005
Calves/groups 2005 2006 0.026 0.027
2007 −0.179∗
0.059
2006 2007 −0.205∗
0.070
∗
P < 0.05.
encounter rates, there was a significant increase in 2007 (Table 2) for both calves per
km surveyed (F2,18 = 6.076, P < 0.05) and calves per number of groups encountered
(F2,18 = 8.162, P < 0.01). Additionally, chi-square analysis revealed a significant
difference between years in percentage of calves to noncalves (␹2
= 36.11, df = 3,
P < 0.01). Follow-up analysis revealed a significantly higher percentage of calves in
2007 (z = 4.7, P < 0.01). Figures 2 and 3 illustrate the calf encounter rates and
percentage of calves to noncalves in relation to Hurricane Katrina. A one-sample t-
test examining stranding rates revealed significantly more live strandings of dolphins
less than 228 cm during the fall of 2005 (t10 = −22.892, P < 0.01). Additionally,
the proportion of calves stranded to calves encountered per kilometer during the
spring of 2007 was 0.02 compared to 0.11 in 2006 and 0.14 in 2005. Figure 4
illustrates calf standings by season in relation to Hurricane Katrina.
These results show a significant increase in calf encounter rates and percentage of
calves to noncalves approximately 2 yr following Hurricane Katrina, which suggests
that the Atlantic bottlenose dolphins within the Mississippi Sound experienced an
increase in reproduction during this time. While there are many possible reasons for
this increase, it could result from the combination of an increase in fish abundance,
Figure 2. Encounter rates of Atlantic bottlenose dolphin calves per km traveled by the
research vessel and number of groups.

Figure 3. Percentage of Atlantic bottlenose dolphin calves to noncalves during the study
period.
a decrease in recreational/commercial boats, and an increase in number of reproduc-
tively active females following the storm. In the following discussion, we highlight
the potential impacts of each of these factors.
Commercial fisheries landings and recreational fisheries landings decreased by 48%
and 42%, respectively between 2005 and 2006 for Gulfport and Biloxi harbors.1
This
decrease in recreational and commercial fishing, similar to the effects of creating a
marine reserve, could have resulted in increased prey availability for dolphins within
the area. Although data are lacking on the preferred food items of dolphins within
the Mississippi Sound, 62% of the species of fish found in the stomach contents of
bottlenose dolphins in Sarasota Bay (Barros and Wells 1998) are also found within
the Mississippi Sound (Benson 1982). Additionally, of the prey species found within
the study area, 75% are used or target species for commercial fishing and 63% for
recreational or sport fishing (Benson 1982). Decreasing the impact on such prey
Figure 4. Total and live stranding rates of Atlantic bottlenose dolphins with a straight
length of ≤266 cm in Alabama, Mississippi, Louisiana, and northeast Texas.

NOTES 713
species could increase abundance in a short time frame as has been demonstrated by
the creation of marine sanctuaries or marine reserves. Halpern and Warner (2002)
reported an increase in fish populations within 1–3 yr following the establishment
of marine reserves. Increased prey availability decreases nutritional stress on females
during lactation (Mann et al. 2000), which may lead to increased reproductive success.
A comparison of the proportion of stranded individuals to calves encountered from
2007 to the two previous years revealed a decrease in proportion of animals stranding.
There was also a significant increase in percentage of calves to noncalves 2 yr following
the storm. This suggests that the calves born 2 yr following the storm were surviving
at higher rates which could potentially be attributed to increased prey availability.
In the presence of boats, short-term changes in behavior have been observed for
Atlantic bottlenose dolphins. Increases in group synchrony (Hastie et al. 2003),
group cohesion (Ribeiro et al. 2005), and dive duration (Lusseau 2003) all suggest
that dolphins actively avoid boat interactions. Additionally, Miller et al. (2008) found
a decrease in time spent foraging immediately following the presence of a high-speed
personal watercraft. Published reports for this area of the Gulf of Mexico indicate
that between 2000 and 2005 there was an average of 1,110,101 private recreational
fishing trips per year, which decreased to 766,254 trips in 2006 (National Marine
Fisheries Service 2007). While no data are available, it is likely that recreational
nonfishing boaters were also lower in number as a result of the storm. With a
reduction in overall boat presence, dolphins would be able to spend more time
foraging instead of traveling or diving to avoid boats. Combined with potentially
more plentiful resources, an increase in opportunities to forage without expending
energy avoiding boat interactions could also decrease nutritional stress on females
with offspring leading to higher rates of reproduction.
Research on bottlenose dolphin reproduction has shown that when an adult female
loses her calf, she can be reproductively active the following breeding season (Mann
et al. 2000). If a large number of calves perished as a result of Hurricane Katrina,
this would allow for a greater percentage of females in the population to become
reproductively active the following year. An examination of the stranding data
around the time of the hurricane compared to the same seasons in other years
revealed a slight increase in total numbers of juvenile or younger strandings, as well
as live strandings of these same age classes throughout the Gulf States affected by
Hurricane Katrina. Additionally, there was a decrease in the percentage of calves to
noncalves immediately following the storm. Due to the impact of the storm on local
communities, it is likely these estimates of calves affected by the storm were low and
the true number of calves lost was much greater. An increase in reproductively active
females due to loss of calves could be an important factor leading to the increase in
observed calves 2 yr after Hurricane Katrina.
Although the exact reason or reasons for the observed increase in calf encounter
rates is unknown, it is possible the increase could have resulted from the com-
bination of an increased number of reproductively active females and a reduction
in anthropogenic factors leading to a decrease in disturbance and an increase in
prey availability. Alternatively, it is possible that the hurricane changed the habitat
in a significant manner within the Mississippi Sound which caused the observed

increase in calf sightings around the islands. Unfortunately with the current data
set, we were unable to track individual reproductive success for females within the
Mississippi Sound which would have provided greater evidence for the possibility of
increased reproductive success. Future research with long-term data sets and smaller
populations of dolphins, where tracking individual female’s reproductive success
is possible, might add greater insight into this complex situation. Examining the
effects of human activities on the reproductive success of bottlenose dolphins by
examining yearly boat densities, amount of fish caught or harvested, and calf survival
rates could provide these answers. This could also provide greater insight on the
long-term effects of fishing and boat interactions on Atlantic bottlenose dolphins.
ACKNOWLEDGMENTS
The authors thank students, interns, and volunteers at the Marine Mammal Behavior
and Cognition Lab at the University of Southern Mississippi and personnel at the Institute
for Marine Mammal Studies for their assistance in data collection. We would also like to
thank the Southeast US Marine Mammal Stranding Network for providing additional data
for this project. This project was supported in part by the Dolphin Communication Fund
at the University of Southern Mississippi and by grants awarded to Stan Kuczaj from the
Department of Commerce and the Institute of Marine Mammal Studies. All research efforts
were conducted under permit #1041-1701 through the National Marine Fisheries Service.
LITERATURE CITED
Barros, N. B., and R. S. Wells. 1998. Prey and feeding patterns of resident bottlenose dolphins
(Tursiops truncatus) in Sarasota Bay, Florida. Journal of Mammalogy 79:1045–1059.
Bearzi, G. 2005. Aspects of the ecology and behaviour of bottlenose dolphins (Tursiops trun-
catus) in Santa Monica Bay, California. Journal of Cetacean Research Management 7:
75–83.
Benson, N. G. 1982. Life history requirements of selected fin fish and shell fish in Mississippi
Sound and adjacent areas. FWS/OBS-81/51, US Fish and Wildlife Service, Washington,
DC.
Constantine, R. 2001. Increased avoidance by wild bottlenose dolphins (Tursiops truncatus)
due to long term exposure to swim-with-dolphin tourism. Marine Mammal Science
17:689–701.
Fernandez, S., and A. Hohn. 1998. Age, growth, and calving season of bottlenose dolphins,
Tursiops truncatus, off coastal Texas. Fishery Bulletin 96:357–365.
Halpern, B. S., and R. R. Warner. 2002. Marine reserves have rapid and lasting effects.
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breathing synchrony in response to boat traffic. Marine Mammal Science 19:74–84.
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22:654–666.

NOTES 715
Miller, L. J., M. Solangi and S. A. Kuczaj. 2008. Immediate response of Atlantic bottlenose
dolphins to high-speed personal watercraft in the Mississippi Sound. Journal of the
Marine Biological Association of the United Kingdom 88:1139–1143.
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National Oceanic and Atmospheric Administration, Silver Spring, MD. 133 pp.
Posadas, B. 2006. Economic assessment of the impacts of Hurricanes Katrina and Rita on the
Mississippi commercial fishing fleet. National Marine Fisheries Service, Silver Spring,
MD. 9 pp.
Read, A., R. Wells, A. Hohn and M. Scott. 1993. Patterns of growth in wild bottlenose
dolphins, Tursiops truncatus. Journal of the Zoological Society of London 231:107–123.
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31:234–242.
Shane, S. H. 1990. Comparison of bottlenose dolphin behavior in Texas and Florida, with a
critique of methods for studying dolphin behavior. Pages 541–558 in S. Leatherwood
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Wells, R. S., M. D. Scott and A. B. Irvine. 1987. The social structure of free-ranging
bottlenose dolphins. Pages 247–305 in H. H. Genoways, ed. Current mammalogy.
Volume 1. Plenum Press, New York, NY.
Received: 17 March 2009
Accepted: 23 November 2009

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