Investigating Potential Hurricane and Red Tide Related Impacts on Bottlenose Dolphin

Final Technical Report

Project Number: PWD 2006-3

MML Technical Report #: 1231

Investigator(s): Kim Bassos-Hull (PI), Randall Wells (Co-PI),

Mote Marine Laboratory 1600 Ken Thompson Parkway Sarasota, FL 34236 Phone: 941-388-4441 ext. 215 Email: [email protected]

Project Title: INVESTIGATING POTENTIAL HURRICANE AND RED TIDE RELATED IMPACTS ON BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) ABUNDANCE, REPRODUCTIVE RATES, DISTRIBUTION, AND SITE FIDELITY IN CHARLOTTE HARBOR AND PINE ISLAND SOUND, FLORIDA

Submitted To: Harbor Branch Oceanographic Institution Protect Wild Dolphins Program Attn: CFO, Protect Wild Dolphins Award 5600 U.S. #1 North Fort Pierce, Florida 34946

Date: 31 October 2007

1 INTRODUCTION

Little information is available on the effects on cetaceans of catastrophic changes to their ecosystems. Along the west coast of Florida, such changes can result from sources such as hurricanes, or harmful algal blooms (HABs) from the red tide organism, Karenia brevis. Immediate concerns for coastal cetaceans in the path of a hurricane might include direct physical impacts such as high winds, waves, tidal surge, flying objects, and sinking objects. Short-term changes in their environment within weeks after the storm might include hypoxia and salinity changes, contaminant input (sewage, fuels, pesticides, fertilizers, industrial chemicals), mangrove damage, and seagrass loss. In the short-term, red tides can cause direct cetacean mortality from exposure to brevetoxins, and can lead to diminished prey availability. In both cases, these short-term dramatic changes have the potential to further influence changes in the food web from benthic infauna to fish to larger predators. The unpredictability of storm occurrence, course and strength make it difficult to do directed studies of hurricane impacts on animals and their habitats. Some research projects have been in the position of having studies underway when a tropical system impacted their study area, allowing them to measure direct behavioral responses of their study animals to the storm. For example, juvenile blacktip sharks (Carcharhinus limbatus) moved from shallow nursery habitat to deeper water, probably triggered by a drop in barometric pressure, before Tropical Storm Gabrielle (Heupel et al. 2003). Opportunistic observation and sampling have provided what little information is available about short-and/or long-term effects of hurricane on populations and habitats. In 1992, flooding from Hurricane Andrew caused high levels of sea turtle mortality and nest loss in southeast Florida (Milton et al. 1994). Massive fish kills occurred in Everglades National Park following Hurricane Andrew, possibly from depleted oxygen levels (Tilmant et al. 1994). Hurricane Fran in 1996 caused severe dissolved oxygen deficits and high contaminant loadings near Cape Fear, North Carolina, resulting in massive fish kills (Burkholder 2004) and decline in total benthic abundances (Mallin et al. 1999 and 2002). Three sequential hurricanes (Dennis, Floyd, and Irene) impacted Pamlico Sound, North Carolina in 1999, resulting in strong vertical stratification of the water column, bottom water hypoxia, a sustained increase in algal biomass, displacement of many marine organisms, and a rise in fish disease (Paerl et al. 2001). Hurricanes have caused significant decline in coral cover followed by depletion of fish (Rogers and Beets 2001, Gardner et al. 2005). To date, effects of hurricanes on top-level predators in coastal ecosystems have received little attention. A few cetacean strandings immediately following hurricanes have been reported. Five pygmy killer whales (Feresa attenuata) stranded in the British Virgin Islands in 1995 after Hurricane Marilyn (Mignucci-Giannoni et al. 1999). The whales had chronically-compromised respiratory systems and scientists suspected that the hurricane’s waves caused the whales to become disoriented. Caldwell and Caldwell (1969) reported a stranding of a dolphin (Stenella sp.) on the west coast of Florida near Tampa Bay immediately following Hurricane Gladys in 1968. Dramatic changes in the habitat quality and abundance of food and prey may have a delayed effect on some primarily herbivorous marine mammal populations, such as sirenians. For example, eight months after a cyclone hit Hervey Bay, Queensland, Australia in 1992 the population of dugongs (Dugong dugon) had declined to approximately 71, down from a previous estimate of 1,753 (Preen and Marsh 1995). In this case there was a 1,000 sq. km loss of seagrass and many of the dugong carcasses found six to eight months after the cyclone were severely emaciated. Langtimm and Beck (2003) reported lower survival rates of adult Florida manatees 2 (Trichechus manatus latirostris) in the panhandle and north Gulf Coast during the 1980s and 1990s during years when there were intense hurricanes or storms. An opportunity to examine the impacts of a major hurricane on bottlenose dolphins (Tursiops truncatus) occurred with the passage of Hurricane Charley, a Category 4 storm, on 13 August 2004, through Charlotte Harbor and Pine Island Sound on the west coast of Florida. Sustained winds were recorded at 67 m s-1 and a 2 m storm surge created a breach in the barrier island, North Captiva (Sallenger et al. 2006). Severe defoliation of mangrove and riparian vegetation occurred along Hurricane Charley’s track. Within one week of the storm’s passage, dissolved oxygen was at the lowest levels ever recorded at several monitoring stations and absent from surface waters in upper Charlotte Harbor (Tomasko et al. 2006). Estuarine fish abundance in these areas declined dramatically during this short time but was found to recover within a month after the hypoxic conditions subsided, demonstrating short term acute effects but long- term resilience (Stevens et al. 2006). Some fish species were opportunistically monitored acoustically during the passage of Hurricane Charley. Sand seatrout (Cynosium arenarius) sound production showed no detectable decrease in either the intensity or duration of the chorus immediately following the passage of Hurricane Charley (Locasio and Mann 2005). Four different acoustically-tagged shark species that had been continuously present within an acoustic array in Pine Island Sound left the estuary in the morning just before the arrival of Hurricane Charley and then returned within the next few days (Heupel et al. 2004). While hurricanes can have dramatic ecological impacts on coastal estuaries, red tide can also cause ecological disturbance in these estuaries. Severe red tides at fish kill levels can cause major depletions in fish stocks, affecting dolphin prey availability. This effect was directly measured in Sarasota Bay, the next estuary to the north of Charlotte Harbor during 2005 (Gannon et al. 2006). During 2004 and 2005, a severe red tide bloom affected much of the west coast of Florida, and resulted in the declaration of a Marine Mammal Unusual Mortality Event by the National Marine Fisheries Service (NMFS). While it is known that red tides can kill large numbers of dolphins (e.g., Flewelling et al. 2005), estimates of population-level impacts have not been possible to date. The Sarasota Dolphin Research Program (SDRP) has been studying the dolphin population in Charlotte Harbor and Pine Island Sound since 1982. Abundance estimates were obtained for the NMFS for Charlotte Harbor (including Lemon Bay) during 1990-1994 (Wells et al. 1996a) and for Pine Island Sound during 1996 (Wells et al. 1997). Between September 2001 and February 2004 we conducted summer and winter boat-based surveys in order to update abundance estimates for the entire Charlotte Harbor/Pine Island Sound region (Bassos-Hull et al. 2005). After Hurricane Charley passed through this study area in August 2004 and was followed by a severe red tide, we were in the opportunistic position with funding from the HBOI “Protect Wild Dolphins” program to conduct another survey in September 2006. This allowed us to examine potential impacts of hurricanes and/or severe red tides on abundance, distribution, reproductive rates, and site fidelity of bottlenose dolphins in this estuary.

METHODS

Study Area

The Charlotte Harbor and Pine Island Sound study area includes the enclosed bay waters eastward of the chain of barrier islands from the north end of Lemon Bay southward to San Carlos Bay as well as the shallow Gulf coastal waters around the passes immediately between the barrier islands (Figure 1). The southern boundary of the study area extends across Sanibel 3 Causeway Bridge and the mouth of the Caloosahatchee Bridge. To the northeast, the study area extends to the Rt. 41 bridge over the Peace River in Punta Gorda, and the El Jobean bridge over the Myakka River. The study area is approximately 750 km2 and composed of a variety of habitats and conditions, including highly productive seagrass meadows and mangrove shorelines, deep passes between barrier islands, dredged channels, river mouths, and open bays. We divided the study area into regions for assessment of survey effort, site fidelity, and distribution following the segmentation scheme used in our 1990-94 and 1996 Charlotte Harbor and Pine Island Sound surveys (Wells et al. 1996a, Wells et al. 1997) (Figure 1). The northernmost section, Region 1 (~28 km2), includes Lemon Bay, a shallow bay with a narrow dredged Intracoastal Waterway (ICW) channel and Stump Pass, a variably navigable inlet from the Gulf of Mexico. Water depths range from less than 1 m nearshore to 6 m in the Pass, but generally waters were 2 m or less. Coastal development, primarily residential, was greater in this region than in all others. Region 2 (~55 km2) includes Gasparilla Sound, Placida Harbor, Gasparilla Pass, and Bull and Turtle Bays. Waters were generally less than 2 m deep, except for the dredged ICW channel and a basin in Gasparilla Sound, where depths ranged up to 3 m, and Gasparilla Pass, where depths reached 7 m. Bull and Turtle Bays are very shallow, undeveloped, mangrove-fringed bays with extensive coverage by seagrass meadows. Between these bays and Charlotte Harbor to the south is a wide band of shallow waters, less than 2 m deep. Coastal development is intermediate between Region 1 and the remaining regions. The next section to the south, Region 3 (~161 km2), includes a large inlet, Boca Grande Pass, and the open waters of Charlotte Harbor proper, along with the shallow southeastern coastal waters. Boca Grande Pass is the primary connection between Charlotte Harbor and the Gulf of Mexico, with depths of up to 24 m. Charlotte Harbor is about 3 m to 7 m deep through its east-west axis, with fringing shallows of less than 2 m. Region 4 (~207 km2) is the continuation of Charlotte Harbor to the north and east, to the mouths of the Peace and Myakka Rivers. The open waters of the north-south axis of Charlotte Harbor are generally 3 m to 7 m deep, with fringing shallows of less than 2 m depth. Freshwater inflow from the rivers varies seasonally, but continues year-round. Little development is evident except at the mouths of the rivers, especially the town of Punta Gorda on the Peace River. Region 5 (~105 km2) includes the shallow waters to the south of Charlotte Harbor through northern Pine Island Sound. This region includes numerous sandy shoals and small mangrove islands, with channels through some of the shoals and seagrass meadows. Depths average less than 2 m in most areas, ranging up to 3 m to 4 m in the channels. Low levels of residential development occur on some of the islands. Region 6 (~114 km2) is composed of Pine Island Sound south of Captiva Pass, including those waters between North Captiva Island, Captiva Island, and northern Sanibel Island on the west, and Pine Island on the east, including shallow open bay, seagrass meadows, fringing mangrove forests, numerous small mangrove islands, and the dredged ICW. Redfish Pass, a small inlet between Captiva and Sanibel Islands, communicates with the Gulf. Region 7 (~75 km2) includes the southernmost and easternmost waters of the study area, north and east of southern Sanibel Island, and between Pine Island and the mainland, as far north as the Matlacha Bridge, and including the mouth of the Caloosahatchee River. To the south, this region includes northern San Carlos Bay.

4 Field Effort and Survey Methodology

The survey approach used for this project is based on previous low-level monitoring studies using small boats to conduct photographic identification (photo-ID) surveys (Scott et al. 1990, Wells and Scott 1990, Würsig and Jefferson 1990). This technique has proven effective in long-term studies of population-rate parameters in the contiguous waters of Sarasota Bay, immediately to the north (Wells and Scott 1990), Tampa Bay (Wells et al. 1996b), and from our earlier surveys in the Charlotte Harbor and Pine Island Sound areas (Wells et al. 1996a, Wells et al. 1997). Additional studies have shown long-term residency for this region (Irvine and Wells 1972, Wells 1986, Shane 1987, 1990a,b). During 2001 - 2006, surveys were conducted from 6-7 m outboard-powered boats under three types of effort: transect surveys (T), opportunistic surveys (O), and biopsy darting (B). Charlotte Harbor and Pine Island Sound were divided into three zones, Charlotte Harbor North (CHN), Charlotte Harbor Middle (CHM), and Charlotte Harbor South (CHS) and each of these zones was divided by transects (Figure 2). During seven field seasons (September/October 2001, January/February 2002, September 2002, February 2003, September 2003, February 2004, and September 2006) we attempted to complete each set of transects two times, weather permitting, under a randomization scheme without replacement in a Beaufort Sea State of 2 or less. During these multi-week surveys, three boats were used on each survey day when the weather was favorable (one boat covering CHN transects, one CHM, and one CHS). Each boat was equipped with a VHF radio, depth sounder, compass, thermometer, refractometer, and a hand-held GPS unit, additionally in 2006 one boat each day was equipped with a YSI meter to measure dissolved oxygen, temperature, and salinity. Survey crews included a minimum of three people per boat and observer positions were rotated approximately every 60 minutes. Opportunistic transects were also done in sheltered areas if weather did not permit the open bay cross-harbor transects. Biopsy darting for genetic and contaminant sampling was conducted in association with photo-ID during some days within the multi-week seasons. A detailed time-effort log was kept that included type of effort, transect number, location, and speed. While searching for dolphin groups, the boats operated at the slowest possible speed that would still allow the vessel to plane, typically 30-35 km/hr, depending on the vessel. When groups were encountered, the boats slowed to match the speed of the dolphins and moved parallel to the groups to obtain photographs. Every dolphin group encountered along a survey route was approached for photographs. We remained with each dolphin group until we were satisfied that we photographed the dorsal fin of each member of the group, or until conditions precluded complete coverage of the group. During 2001 and 2002 we used Nikon film camera systems with zoom-telephoto lenses (up to 300 mm), motor drives, data backs and Kodachrome 64 color slide film. In February 2003 we experimented with the use of Nikon D100 digital camera systems with 80-300 mm zoom- telephoto lenses complementary to the Nikon film camera systems on some surveys. During September 2003 we moved fully to digital camera systems. A suite of data including date, time, location, activities, headings, and environmental conditions (tidal state, depth, surface salinity, surface temperature, Beaufort state, cloud cover and glare) was recorded for each sighting. We recorded minimum, maximum, and best point estimates of numbers of total dolphins, calves (dolphins < about 80-85% adult size, typically swimming alongside an adult, a subset of the total number of dolphins), and young-of-the-year (as a subset of the number of calves). Red tide water samples were collected concurrently with our surveys on 16 and 17 September 2006 throughout the Charlotte Harbor study area. Our program did not collect red 5 tide samples concurrently with our surveys during the earlier field seasons but we were able to access past records of red tide cell counts within the Charlotte Harbor area from Mote’s Phytoplankton Ecology Program.

Analysis of Photographs

Each dorsal fin in a photograph was graded by two independent graders relative to photographic quality and dorsal fin distinctiveness (Urian et al.1999, Read et al. 2003). Slide photographs were examined using a high power (15x) loupe eyepiece while digital photos were downloaded, labeled, cropped in ACDSee and/or Adobe Photoshop, and viewed on a computer screen. Photograph quality rank was based on focus clarity, contrast, angle, portion of fin showing, and percent of photograph frame filled (Q1= Excellent Quality; Q2=Average Quality; Q3=Poor Quality). Dorsal fin distinctiveness was ranked on the strength of fin markings: (D1=Dolphins with major fin markings, very distinctive fins with features evident in distant or poor quality photographs; D2= Dolphins with minor fin markings, fins with difficult to distinguish features in distant or poor photograph; D3= Dolphins with clean or non-distinctive fins). In every sighting where each individual could be accounted for (Photo Grade 1) by distinctive markings on their fins (D1 or D2), by scars, rakes, fin shape on cleaner fins, or the presence of unmarked calves in predictable association with identifiable adults (D3), the ratio of D1+D2 dolphins to D1+D2+D3 dolphins was calculated to be used in abundance estimation procedures described later. The best photograph of each individual with a D1 or D2 fin within each sighting was compared to our established SDRP Photo-Identification Catalog which includes individuals from Tampa Bay, Sarasota Bay, Charlotte Harbor and near-shore Gulf of Mexico coastal waters. The SDRP catalog is based on exclusive categories that classify individuals with similar features together. The 12 categories of the catalog are based on: (1) the division of the trailing edge of the dorsal fin into thirds and distinctive features located in each third; (2) distinctive features on the leading edge of the fin; (3) distinctive features at the tip of the fin and fins missing part of the top; (4) distinctive features on the anterior portion of the peduncle and (5) evidence of permanent scarring or pigmentation patterns on the fin or body. The most prominent feature of the selected fin is identified and the category that best describes that feature is searched for a potential match. When a match is made with a fin in the catalog, all photos are labeled with the dolphin's unique 4-character code. When a match is not found in the first category searched, all other possible categories are searched to account for dolphins that have multiple identifying characteristics or the possibility of a changed fin. The entire catalog is searched by two staff members before a new animal is added to the catalog with a new 4-character code. Currently there are 3,499 marked individuals in the Sarasota Dolphin Research Program catalog. All sighting and environmental data including identified individuals were entered into an Access database. In addition date, sighting number, location code, transect number, individual identification with 4- character code and quality and distinctiveness grades are entered into a Microsoft Excel spreadsheet for ease of use with Program MARK (White and Burnham 1999).

Estimation Procedures: Abundance

We approached our abundance estimation procedures based on similar recent studies done with coastal and estuarine bottlenose dolphins (Williams et al. 1993, Wilson et al. 1999, Read et al. 2003, and Chilvers et al. 2003). Like these studies, in order to use the closed mark- recapture models (Seber 1982), we assumed: (1) a demographically and geographically closed 6 population, (2) homogeneity of capture probabilities, (3) marks are recognized on recapture, (4) marks are not lost during study period. These were reasonable assumptions for our study area as documented by our previous mark-recapture studies in this area (see Wells et al. 1996a, Wells et al. 1997). For all abundance calculations we used only individual identifications with D1 or D2 distinctiveness and photo qualities of Q1 or Q2. For the simplest abundance calculation we used a Chapman modification of the Lincoln- Petersen model (Chapman 1951, Thompson et al. 1998) where the mark period (n1) was considered the first “equal effort” half of the survey period and the recapture (n2) was the second “equal effort” half. Each (n) refers to the number of individuals photographically captured in each set and (m2) refers to the number of individuals that were counted in both the mark and recapture period. The abundance estimate (Nc), variance (var Nc), and standard error (SE) were calculated as described in Chapman (1951):

Nc = ((n1+1)(n2+1)/(m2+1))-1

2 var Nc = (n1+1)(n2+1)(n1-m2)(n2-m2)/(m2+1) (m2+2)

0.5 SE = (var Nc)

More complex closed population models are available in Program MARK (Rexstad and Burnham 1992, White and Burnham 1999) that allow some variation in heterogeneity in capture probability of individuals, survey effort, and time. We used three different closed mark-recapture models: M0, the null model; Chao Mt, allows capture probability to vary by time; and Chao Mth, allows capture probability to vary by time and by animal due to heterogeneity (Chao et al. 1992, Otis et al. 1978). Both the Lincoln-Petersen model and MARK Program models only give a population estimate (Nc) of the marked (D1 and D2) animals in the population. They do not account for the unmarked, or D3, segment of the population. In order to account for the unmarked animals, the Nc is scaled up by the proportion of D3 animals present in the population using the delta method (Williams et al. 1993; Wilson et al. 1999). We estimated this mark-proportion rate for each field season using only “Photo Grade 1” sightings, where every individual was accounted for, and averaged across each field season. We also used the mark-proportion rate to estimate the minimum population size by dividing it into the catalog size for each field season.

Estimation procedures: Natality and Female Status

Examination of reproductive rates is one way to measure possible impacts from ecological disturbances such as hurricanes or red tides. A spring through early fall peak in calving with occasional births occurring at any time during the year has been reported for Sarasota Bay (Wells et al. 1987) and for the west coast of Florida in general (Urian et al. 1996). Therefore, we used only summer field seasons, three pre-Hurricane Charley (2001, 2002, 2003) and one post-Hurricane Charley (2006), to measure natality in the study area. Natality was calculated as the proportion of dolphins in each sighting considered to have been born within the calendar year. Though the total number of calves was recorded for each group sighted, only the subset of calves considered to be young-of-the-year (YOYs) was considered to be relevant to the measurement of natality (Wells and Scott 1990). The average proportion of YOYs in each sighting was calculated for each year.

7 We also were able to track calf production for several marked females in the study area. Our criteria for considering an individual marked dolphin a female is presence of a calf with her in at least three sightings.

Distribution

All survey tracks and dolphin sightings were downloaded from the handheld GPS to Arcview GIS 3.3 program and converted to shapefiles for plotting. We plotted only sightings from transects to compare across field seasons with approximately equal effort. We looked at dolphin density by region by comparing the number of unique individuals seen (D1+D2 dolphins with Q1 or Q2 photos) on transect-only surveys across seasons. This was normalized by dividing the number of unique identifications by region by the area of the region in square kilometers.

Site Fidelity

One measure of the effects of Hurricane Charley would be changes in the home ranges of identifiable dolphins with substantial sighting histories. In order to examine long-term, seasonal, and pre- and post-Hurricane Charley site fidelity of individuals we used all photos (Q1-Q3) of marked (D1 or D2) individuals. The span of years over which an individual was seen was calculated using only sightings within the study area, using data from opportunistic sightings in the 1980’s and survey and opportunistic sighting data from the 1990’s through May 2007.

RESULTS

Survey Effort

Survey effort for 2001 through 2007 is summarized in Table 1, including systematic and opportunistic surveys. The HBOI/PWD award specifically supported two sets of transect surveys in September 2006, post-Hurricane Charley, to make comparisons with our existing pre- Hurricane Charley surveys. HBOI/PWD-funded survey effort and dolphin sightings during 5-22 September 2006 are presented in Figure 3. Two sets of transects were completed in each field season with the exception of summer 2001 due to bad weather that impeded completion of surveys. Seasonal variations in surface salinities and water temperatures were found in summer compared to winter field seasons. Salinity stratification throughout the Harbor was most pronounced in Region 4 and occurs when large volumes of fresh water approach 15,000 cubic feet per second combined flows over a seven day period from the Peace and Myakka Rivers during the summer rainy season. This large fresh water input into the upper Harbor often set up large surface to bottom salinity differences which led to hypoxic events. Hypoxia was recorded in each of our summer field seasons with bottom dissolved oxygen values in the upper half of Region 4 reported at 0.01-2.17 mg/l. The area at the mouth of the Caloosahatchee River and the southern portion of Matlacha Pass (southeast part of Region 7) also showed low surface salinity values in summer, although no extreme hypoxic conditions were noted. This area has large tidal volume exchange with the Gulf of Mexico through San Carlos Pass.

Dolphin Abundance

Abundance estimates of dolphins in the Charlotte Harbor Study area using the mark- proportion method ranged from a low of 361 in summer 2001 to a high of 498 in summer 2002 (Table 2). The summer 2006 post-Hurricane Charley estimate using this method was 469, an intermediate value. Since the mark-proportion method uses the catalog size for the survey period (number of D1 and D2 dolphins with Q1 or Q2 photos), mark-proportion estimates are sensitive to level of field effort, and should be considered minimum estimates, requiring complete photographic coverage of all marked dolphins in the area for greatest accuracy. Over the six years of surveys, the decline of annual additions to the catalog (Figure 6) indicated that the survey design was successful in identifying most of the marked animals over time, but it is unclear if the survey effort within each survey session was sufficient to capture all available marked animals. For additional perspective, we used several other standard mark-recapture models to estimate the number of marked (D1+D2) individuals in the population (Table 2, Figure 4). Once these marked estimates were generated we scaled our estimates to account for the unmarked, D3, component of the population. These scaled estimates were at their lowest levels in summer 2001 and their highest levels in winter 2002 and 2003. Summer 2006 estimates were similar to the closest two previous field seasons (winter 2004 and summer 2003) in the Mth model and Lincoln-Petersen model estimates but showed wider variation between the Mo and Mt model estimates.

Natality and Female Status

The mean proportion of young-of-the-year per sighting for each summer field season ranged from 0.020 to 0.042, with an intermediate value for 2006 (Table 3). These values were within the range reported from our 1990-1994 and 1996 summer surveys in the region (Wells et al. 1996a, Wells et al. 1997). If these rates are applied to the population size estimates derived by the mark-proportion method (Table 2), then estimates of 7, 18, 20, and 20 young-of-the-year are derived for the entire study area for 2001, 2002, 2003, and 2006 respectively. Since 2001 we identified 108 individuals with calves that met our female criteria. Sixty seven of these females were seen with the same calf at least three times allowing us to give the calf a code (three sightings of a calf is our minimum criteria to give the calf a code and add it to our master code list). Sixty-one females were observed with a YOY between 2001 and 2006 (Table 1). Ten females were observed with a two different YOYs between 2001-2006. For these ten females their calving interval ranged from two years (2 animals), to three years (5 animals), to four years (3 animals). The numbers young-of-the-year calves observed with marked females each year were consistent with the estimated numbers based on calculations above (Table 3).

Red Tide Effects

Between 2001 and 2007, red tide was present in the Charlotte Harbor study area at fish kill levels (>100,000 cells/liter) during some of our field seasons. During September 2001 there were very high levels detected in the study area with some locations over 1,000,000 cells per liter. Red tide was detected within Charlotte Harbor during January 2002, but below fish kill 9 levels. Samples were collected just prior to (August 2002) and just after (October 2002) our September 2002 surveys and showed no red tide cells present. By January 2003 low levels (under 38,000 cells/liter) were detected just prior to the start of our February 2003 surveys. There were no samples collected during or close to September 2003 to report values. In January 2004 there was no red tide within Charlotte Harbor just prior to the start of our February 2004 surveys. By July of 2006 there were over 125,000,000 cells/liter in the Caloosahatchee River but none reported in Charlotte Harbor. However, by September 2006, samples we obtained in Charlotte Harbor during our surveys showed high concentrations between 100,000-300,000 cells/liter in the western half and pass areas of the Harbor. We observed many of dead fish in Gasparilla Pass, Boca Grande Pass, and Captiva Pass. Dolphins in the Charlotte Harbor/Pine Island Sound region are exposed to red tides, on occasion leading to mortalities. Thirteen carcasses collected in Charlotte and Lee counties during red tide events during 1991-1996 were tested for the presence of red tide toxin (brevetoxin). In three of these cases brevetoxin concentrations were sufficiently high for red tide intoxication to be considered the cause of death (Fauquier et al. 2007). Three additional carcasses were examined from 2006-2007, and one of these was considered to have died from brevetoxin. Carcass recovery in this large and sometimes remote area is likely incomplete, so it is not possible to translate these data into population-level effects.

Distribution

A rough estimate of dolphin density per region (# of unique ID’s per square kilometer) is summarized in Figure 5. The density is slightly lower in all four summer seasons compared to the three winter seasons in Region 4. Region 3 shows a strong spike in 2006. Region 6 has the highest densities in summer seasons with the exception of 1 and 3 in 2006 and 3 in 2002.

Site Fidelity

Photographs of distinctive individuals taken between 2001 and 2007 built upon an existing catalog initiated in 1982 and supplemented by other large field efforts (August 1990- 1994 north half Charlotte Harbor and August 1996 south half Charlotte Harbor including Pine Island Sound) and opportunistic effort through 2000 (Figure 6). The discovery curve of new individuals increased and then leveled with each large field effort within Charlotte Harbor separated by location or time (Figure 6). Between 2001 and 2006, we added 487 new individuals to the Charlotte Harbor study area catalog. The proportion of new identifications to the yearly catalog size declined from 38% in 2001, to 27% in 2002, to 22% in 2003, to 12% in 2004, to 8% in 2006 indicating a high degree of re-sights and a relatively closed population. Since 1982, 1,154 distinctive individuals have been recorded from within the Charlotte Harbor study area. Over this period of time, 269 dolphins were re-sighted 10 or more times (Figure 7). Long-term site-fidelity in Charlotte Harbor appears common with 289 individuals seen over a span of ten years or more and 475 individuals seen over a span of 5 years or more (Figure 8). The 2001-2004 winter surveys allowed us to examine seasonal site-fidelity for the first time and 60% of the distinctive dolphins seen in a summer field season were also seen in a winter field season (Figure 9). During Hurricane Charley, the eye-wall passed through Regions 3, 4, and 5. The eastern half of Region 2 and these areas sustained the most habitat damage. We examined how this might impact an individual dolphin’s site fidelity by determining if a dolphin was re-sighted in the same Region pre-and-post-Hurricane Charley (Figure 10). A large percentage, 94% (193 10 individuals), were re-sighted within the same region. Figures 11a-11o include representative examples of several individuals that were re-sighted within the same Region and show long-term site fidelity.

DISCUSSION

Opportunities to measure the impacts of large-scale natural catastrophic events on marine mammal populations are rare. Understanding how a resident population of dolphins responds to a major ecological disturbance within their habitat is an important piece of information for wildlife managers to assess population trends and survival. While evolutionarily animals may have adapted to respond to natural ecological changes that might occur with red tides or hurricane impacts, recent anthropogenic effects such as over fishing, contaminant input, coastal habitat destruction and loss, increase in marine debris leading to entanglement, and increase in boat traffic have the possibility of over-stressing a population’s ability to adapt. SDRP was in the unique position to evaluate potential impacts from these types of catastrophic natural events, because of an existing baseline of data on dolphin abundance, reproductive rates, distribution, and site fidelity collected in this region during intensive seasonal surveys over several years immediately prior to a major hurricane and subsequent red tide event, as well as longer-term data on dolphin residency collected over the past 25 years. While Hurricane Charley devastated the shoreline, terrestrial flora, and man-made structures along its path through Charlotte Harbor, two years after the hurricane and one year after a subsequent red tide event we found no indications of long-term impacts on the dolphin population of Charlotte Harbor. Dolphin abundance in 2006 was within, or less than 10% greater than, the range of abundance estimates from previous years, by all measures. Although each estimation method produced different absolute estimates of abundance, the pattern was consistent across all models used. The occurrence of 2006 estimates greater than in previous years argues against any adverse impacts on dolphin survival and/or reproduction. Similarly, reproductive rates two years after the storm, based on proportion of young-of-the-year, were within the previously-documented range for Charlotte Harbor. Of the 206 identifiable dolphins seen 10 or more times, 94% were found in the same region of Charlotte Harbor two years after the storm as they were prior to the storm. The general distributional patterns as well as specific ranging patterns of identifiable individual dolphins with long-term sighting histories in the area were unchanged from those documented prior to the storm and red tide. The apparent resilience of the dolphins of Charlotte Harbor to some potentially catastrophic natural events is noteworthy. This resilience occurs in contrast to recent large-scale mortalities of bottlenose dolphins in the Gulf of Mexico and elsewhere during Unusual Mortality Events (UMEs). While the causes of a number of these UMEs remain unknown, several have resulted from Harmful Algal Blooms, including the Florida red tide organism (Spradlin et al. 2005). Red tides can have variable impacts on dolphin populations, beyond mortality from red tide intoxication. In Sarasota Bay, Florida, immediately to the north of the study area, a severe red tide in 2005 caused dramatic declines in dolphin prey (Gannon et al. 2006), but brevetoxin did not kill any resident dolphins directly. Latent impacts of the red tide are thought to include the deaths in 2006 of 2% of the long- term resident dolphins of Sarasota Bay from ingestion of recreational fishing gear (Wells et al. 2006). Increased interactions between anglers and dolphins in the Charlotte Harbor area have been noted in recent years. Mortality rates on the order of 2% might not have been detectable through our abundance estimation approach. Such a rate of additional loss, maintained over 11 years, would not be sustainable. Longer-term monitoring will be required to determine if smaller scale, cumulative changes to the population might be occurring. Although no clear long-term significant impacts from the hurricane and red tide were found, smaller scale responses to red tide may have been observed. In 2006, an unusual large clustering of group sightings was noted in the middle of Region 3. Red tide was recorded at fish kill levels around the passes of Regions 1, 2, 3, and 5 during our surveys and the upper Harbor, region 4, was hypoxic. It can be hypothesized that the dolphins’ prey may have been concentrating in the middle Harbor between the red tide to the west and hypoxia to the northeast and the dolphins were taking advantage of a concentrated prey source. The HBOI/PWD-funded surveys provided an opportunity to obtain updated abundance estimates for the National Marine Fisheries Service (NMFS) for three stocks of bottlenose dolphins. Current NMFS estimates for all 33 Gulf of Mexico bay, sound and estuary stocks are more than eight years old and are considered to be out of date for management purposes (Waring et al. 2007). Updated abundance estimates are required for determination of levels of sustainable levels of anthropogenic “takes” or removals from the area, and for trend analyses for detection of population declines. The HBOI/PWD-funded surveys also provided important data for evaluation of dolphin distribution patterns in the greater Charlotte Harbor area. The consistent, rigorous 2006 survey design will facilitate direct integration with data from previous surveys, allowing the investigation of the roles of a suite of environmental parameters on dolphin habitat use.

Significance of Project Our project provides the first systematic data examining the potential impacts from an intense hurricane and/or severe red tide on a resident population of bottlenose dolphins. By every measure, two years after a Category 4 hurricane, the dolphins of Charlotte Harbor did not appear to have been adversely impacted by the storm and subsequent red tide. Abundance estimates, reproductive rates, distributional patterns, and individual ranges after the storm were consistent with those documented prior to the storm. The level of resilience documented for the Charlotte Harbor dolphins provides important perspective for evaluating the threats to dolphin populations from a variety of natural and anthropogenic sources.

ACKNOWLEDGEMENTS

This project was funded in part by a grant awarded from HARBOR BRANCH Oceanographic Institution, Inc. from proceeds collected from the sale of Protect Wild Dolphins License Plate as authorized by Florida Statute 320.08058(20). Additional support for previous and supplemental surveys as well as analyses of the 2006 data were provided by Mote Scientific Foundation, the Chicago Zoological Society, Mote Marine Laboratory, the National Marine Fisheries Service, Dolphin Biology Research Institute, and Earthwatch Institute. This project involved many years of dedicated field work and laboratory analyses and would not have been possible without the help of many SDRP program staff and numerous interns and volunteers. These include: SDRP staff (past and present): Robin Perrtree, Chris Shepard, Stephanie Schilling, Aaron Barleycorn, Jason Allen, Brian Balmer, Sandra Camilleri, Bill Carr, Kara Moore, Stephanie and Doug Nowacek, Sue Hofmann, Anna Sellas, Todd Speakman, Spencer Fire, Gene Stover, and numerous interns and volunteers : Jenn Thera, 12 Kristina Alexander, Ginny Fuhs, Ronni DeCamp, Kate Cobb, Lauren Giese, Lorry Stover, Gill Braulik, Albert Reichert, Patti Haase, Maureen Powell, Monika Merriman, Mindy Schneider, Shelby Moneysmith, Petra Schneider, Maija Gadient, Salome Dussan, Marlena Adema, Carrie Wall, Kristi Fazioli, Stuart and Rita Stauss, Mike and Patricia Armstrong, Kari Higgs, Nélio Barros, Brendan Hurley, Sandy Wiggins, Sandy Beksic, Jane Bauer, Marissa Kakoyiannis, Eleanor Stone, Sarah Layton, Kara Antinarelli, Donna Krabill, Gretchen Hurst, Debbie Fauquier, Jim Grimes, Randy Wayne White, Todd McConchie, Ernie Estevez, Heidi Petersen, Kate Grellier, Traci Hedgepath, Diana Gietl, Courtney Smith, Lauren Gaster, Kevin Lavelle, Jocelyn Greene, Chloe Tatum, Alison Campbell, Lindsey Dryden, Andrea Guerrini, Jessica Atwell, Carly Gaebe, Kristen Clark, Zuzana Slovakova, Marsha Thompson, Allie Sherman, Jenna Voss, Rubai and Elisabeth Fahrni Mansur, Laura Markley, Goldie Phillips, Katie McHugh, Vanessa Greenwood, Erika Fredericksen, Leah Card, Sarah Alessi, Justine Bartow-Funk, Christina Toms, Bill Kayser, Elly Roland, Caroline Baumgartner, Carpi Echezarreta, Ibiza Martinez-Serrano, Shimpei Yamamoto, and Todd Musgrove. We would especially like to thank Robin Perrtree and Janet Gannon for their help with database updates and GIS analyses. Robin, along with Chris Shepard and Stephanie Schilling, endured many long hours of photo-id for this project. Stephanie Nowacek helped with grading a large portion of the photographs. We also thank Bill Pine for his input on the abundance estimation techniques and Program Mark. We greatly appreciate the generosity of Don and Dorothy Gulnac for opening their home to us as a field station on Demere Key after Hurricane Charley destroyed our previous field station on Pine Island. Research during the HBOI/PWD-funded surveys of 2006 was conducted under NMFS Scientific Research Permit No. 522-1785, issued to Wells, and valid through May 2010.

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17 Table 1. Charlotte Harbor survey effort by month (*indicates multi-week field seasons used for abundance estimation). Effort types are (T) transect surveys, (O) opportunistic surveys, and (B) surveys during which biopsy darting occurred.

Charlotte Harbor Survey Effort by Month

#dolphins Month # Boat Days Effort Type(s) #sightings approached # photographs Feb 2001 5 B 29 175 717 *Sep-Oct 2001 40 T+O+B 279 1380 4409 *Jan-Feb 2002 25 T+O 159 700 2406 May 2002 4 O 46 175 941 Jul 2002 2 T 21 166 583 *Sep 2002 29 T+O+B 208 1044 3526 *Feb 2003 41 T+O+B 231 924 3994 May 2003 5 O 40 202 1365 Jun 2003 3 O 14 101 477 *Sep 2003 44 T+O+B 272 1278 7406 *Feb-Mar 2004 33 T+O+B 226 956 5496 Apr 2004 2 O 3 23 127 May 2004 15 O 63 318 1913 Jun 2004 6 O 10 46 185 Aug 2004 5 T+O 43 220 849 Sep 2004 6 O 61 288 1772 May 2005 2 O 25 104 726 Aug 2005 1 O 2 25 98 May 2006 1 O 2 12 49 Jun 2006 1 O 1 8 67 *Sep 2006 46 T+O 246 1222 10318 Oct 2006 2 O 2 12 66 Feb 2007 1 O 2 3 18 Mar 2007 1 O 5 16 95 May 2007 1 O 3 16 61

18 Table 2. Abundance estimate summary. N = estimate of marked animals in the population, p = probability of recapture, SE = standard error, CV = coefficient of variation.

Summer Winter Summer Winter Summer Winter Summer Field Season 2001 2002 2002 2003 2003 2004 2006 Mark/Proportion Rate 0.69 0.62 0.65 0.71 0.75 0.78 0.70 Minimum Catalog Size 249 222 324 280 326 345 328 Mark/Proportion N 361 358 498 394 435 442 469

Lincoln-Petersen Model N (of marked animals) 435 484 593 532 655 696 609 p 0.21 0.14 0.22 0.20 0.23 0.24 0.22 SE 39.80 61.30 49.30 51.70 66.60 63.00 44.70 CV 0.09 0.13 0.08 0.10 0.10 0.09 0.07 N Scaled by Mark/Proportion Rate 630 780 912 750 873 892 870

Model M0 N (of marked animals) 454 600 609 571 585 616 673 SE 38.0 82.4 47.4 54.6 44.4 43.4 49.9 CV 0.08 0.14 0.08 0.10 0.08 0.07 0.1 p1 0.21 0.14 0.22 0.20 0.23 0.24 0.22 p2 0.21 0.14 0.22 0.20 0.23 0.24 0.22 p3 0.21 0.14 0.22 0.20 0.23 0.24 0.22 N Scaled by Mark/Proportion Rate 658 968 937 804 780 790 961

Model Mt N (of marked animals) 435 613 599 611 595 618 662 SE 39.0 93.3 60.0 70.0 52.1 49.0 53.1 CV 0.09 0.15 0.10 0.11 0.09 0.08 0.08 p1 0.21 0.14 0.18 0.12 0.18 0.18 0.21 p2 0.18 0.17 0.30 0.23 0.20 0.26 0.21 p3 0.35 0.11 0.19 0.19 0.30 0.28 0.26 N Scaled by Mark/Proportion Rate 630 989 922 861 793 792 946

Model Mth N (of marked animals) 499 748 660 841 742 712 686 SE 84.0 189.7 99.1 183.9 126.0 106.6 94.0 CV 0.17 0.25 0.15 0.22 0.17 0.15 0.14 p1 0.18 0.11 0.17 0.09 0.14 0.15 0.21 p2 0.15 0.14 0.28 0.17 0.16 0.22 0.20 p3 0.31 0.09 0.18 0.14 0.24 0.25 0.25 N Scaled by Mark/Proportion Rate 723 1206 1015 1185 989 913 980 19 Table 3. Estimated number of young-of-the-year (YOYs) calculated using the mark-proportion summer population estimates and compared to the number of identified females confirmed with a YOY for each summer field season.

2001 2002 2003 2006 Average

Mean Young-of-the-Year Proportion 0.020 0.037 0.047 0.042 0.037 Standard Deviation (SD) 0.0690 0.0970 0.1090 0.1030 Calculated No. of Young-of-the-Year in Population 7 18 20 20 16 Upper 95& CL (+ 2 SD) 8 21 24 24 Lower 95& CL (- 2 SD) 6 15 16 16

Number of Grade 1 Sightings Used for Mean 54 96 85 113 Mark-Proportion Population Size Estimate (N) 361 498 435 469

Number of Marked Females confirmed with YOY 1 13 21 22

20 Figure 1. Study area showing region boundaries, passes, barrier islands, rivers, bodies of water, and 2 meter depth contours throughout the area.

Figure 2. Study area showing cross-harbor (solid blue lines) and contour transects (dashed blue lines).

22 Figure 3. Summary of survey effort and dolphin sightings during 5-22 September 2006, differentiating between dolphin sightings on transect versus opportunistic effort.

23 1600 Mark/ Proportion N Lincoln Petersen N 1400 M0 Mt Mth 1200

1000

800

# of Dolphins 600

400

200

02 001 2 20 ter 2004 inter n mmer 2003 ummer W Winter 2003 u Wi ummer 2006 S Summer 2002 S S

Figure 4. Mark-proportion and mark-recapture population estimates (±1 SE). The last three models (Null M0, Chao Mt, and Chao Mth) were generated in Program MARK. Only D1 and D2 dolphins that had Q1 or Q2 photographs were used in these analyses.

24 0.9

0.8

0.7 Summer 2001 Summer 2002 Summer 2003 0.6 Summer 2006 Winter 2002 Winter 2003 0.5 Winter 2004

0.4

0.3 # Unique ID's per square km square per ID's Unique #

0.2

0.1

0 1234567 Region

Figure 5. Number of unique individuals per square kilometer within Regions 1-7. Only animals seen on transect effort were used for effort equal across seasons and regions.

25 1200 New Individuals Resights Catalog Size

1000

800

600

Number of Animals of Number 400

200

0 1982198419901991199219931994199519961997199819992001200220032004200520062007 Year

Figure 6. Number of individuals sighted during all photo-identification efforts and discovery curve for dolphins in the study area.

160

140

120

100

60 # Individuals

0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536 # Sightings

Figure 7. Sighting frequency of individuals in the study area 1982 to May 2007.

350

300

250

200

150

# of Individuals 100

0 12345678910111213141516171819202122232425 Span of Years Seen

Figure 8. Span of years seen within the Charlotte Harbor study area for 1,154 individuals.

500

450

400

350

300

250

200

Number of Individuals 150

100

0 Summer Only Winter Only Summer and Winter

Figure 9. Number of individuals sighted in the study area during Summer only, Winter only, or both field seasons.

250

193 Resighted within the 200 Same Region?

150

100 # of Dolphins of # 50 13 0 Yes No

Figure 10. Dolphins with 10 or more sightings seen before and after Hurricane Charley. Yes = dolphin was resighted in the same region before and after Hurricane Charley, No = dolphin was resighted in a different region after the hurricane.

28 Figure 11(a). Sightings of ‘BITM’: 1990 – 2006.

29 Figure 11(b). Sightings of ‘BMTH’: 1993 – 2006.

30 Figure 11(c). Sightings of ‘F301’: 2004-2006.

31 Figure 11(d). Sightings of ‘HAIG’: 1990-2006.

32 Figure 11(e). Sightings of ‘HSLI’: 1990-2006.

33 Figure 11(f). Sightings of ‘HSRE’: 1991-2006.

34 Figure 11(g). Sightings of ‘LAST’: 1993-2006.

35 Figure 11(h). Sightings of ‘LRBD’: 1996-2006.

36 Figure 11(i). Sightings of ‘M233’: 1996-2006.

37 Figure 11(j). Sightings of ‘MTMS’: 1990-2006.

38 Figure 11(k). Sightings of ‘POTP’: 1990-2006.

Figure 11(l). Sightings of ‘SILA’: 1991-2006.

40 Figure 11(m). Sightings of ‘SMRF’: 1990-2007.

41 Figure 11(n). Sightings of ‘STIM’: 1990-2006.

42 Figure 11(o). Sightings of ‘TPMI’: 1990-2006.