Concurrent exposure of bottlenose dolphins (Tursiops truncatus) to multiple algal toxins in Sarasota Bay, Florida, USA

Sentinel species such as bottlenose dolphins (Tursiops truncatus) can be impacted by large-scale mortality events due to exposure to marine algal toxins. In the Sarasota Bay region (Gulf of Mexico, Florida, USA), the bottlenose dolphin population is frequently exposed to harmful algal blooms (HABs) of Karenia brevis and the neurotoxic brevetoxins (PbTx; BTX) produced by this dinoflagellate. Live dolphins sampled during capture-release health assessments performed in this region tested positive for two HAB toxins; brevetoxin and domoic acid (DA). Over a ten-year study period (2000–2009) we have determined that bottlenose dolphins are exposed to brevetoxin and/or DA on a nearly annual basis (i.e., DA: 2004, 2005, 2006, 2008, 2009; brevetoxin: 2000, 2004, 2005, 2008, 2009) with 36% of all animals testing positive for brevetoxin (n = 118) and 53% positive for DA (n = 83) with several individuals (14%) testing positive for both neurotoxins in at least one tissue/fluid. To date there have been no previously published reports of DA in southwestern Florida marine mammals, however the May 2008 health assessment coincided with a Pseudo-nitzschia pseudodelicatissima bloom that was the likely source of DA observed in seawater and live dolphin samples. Concurrently, both DA and brevetoxin were observed in common prey fish. Although no Pseudo-nitzschia bloom was identified the following year, DA was identified in seawater, fish, sediment, snails, and dolphins. DA concentrations in feces were positively correlated with hematologic parameters including an increase in total white blood cell (p = 0.001) and eosinophil (p<0.001) counts. Our findings demonstrate that dolphins within Sarasota Bay are commonly exposed to two algal toxins, and provide the impetus to further explore the potential long-term impacts on bottlenose dolphin health.     

Florida red tide and brevetoxins: Association and exposure in live resident bottlenose dolphins (Tursiops truncatus) in the eastern Gulf of Mexico,U.S.A.

Bottlenose dolphins (Tursiops truncatus) along the Gulf of Mexico are frequently exposed to blooms of the toxic alga, Karenia brevis, and brevetoxins associated with these blooms have been implicated in several dolphin mortality events. Studies on brevetoxin accumulation in dolphins have typically focused on analyses of carcasses from large‐scale die‐offs; however, data are scarce for brevetoxin loads in live individuals frequently exposed to K. brevis blooms. This study investigated in vivo brevetoxin exposure in free‐ranging bottlenose dolphins resident to Sarasota Bay, Florida, utilizing samples collected during health assessments performed during multiple K. brevis blooms occurring from 2003 to 2005. Brevetoxins were detected by ELISA and LC‐MS in 63% of bottlenose dolphins sampled (n= 30) concurrently with a K. brevis bloom. Brevetoxins were present in urine and gastric samples at concentrations ranging from 2 to 9 ng PbTx‐3 eq/g, and in feces at concentrations ranging from 45 to 231 ng PbTx‐3 eq/g. Samples from individuals (n= 12) sampled during nonbloom conditions (≤1,000 cells/L) were negative for brevetoxin activity. Brevetoxin accumulation data from this study complement dolphin carcass and prey fish data from the same study area, and aid in evaluating impacts of harmful algal blooms on sentinel marine animal species along the west Florida coast.     

Genomewide investigation of adaptation to harmful algal blooms in common bottlenose dolphins (Tursiops truncatus)

Harmful algal blooms (HABs), which can be lethal in marine species and cause illness in humans, are increasing worldwide. In the Gulf of Mexico, HABs of Karenia brevis produce neurotoxic brevetoxins that cause large‐scale marine mortality events. The long history of such blooms, combined with the potentially severe effects of exposure, may have produced a strong selective pressure for evolved resistance. Advances in next‐generation sequencing, in particular genotyping‐by‐sequencing, greatly enable the genomic study of such adaptation in natural populations. We used restriction site‐associated DNA (RAD) sequencing to investigate brevetoxicosis resistance in common bottlenose dolphins (Tursiops truncatus). To improve our understanding of the epidemiology and aetiology of brevetoxicosis and the potential for evolved resistance in an upper trophic level predator, we sequenced pools of genomic DNA from dolphins sampled from both coastal and estuarine populations in Florida and during multiple HAB‐associated mortality events. We sequenced 129 594 RAD loci and analysed 7431 single nucleotide polymorphisms (SNPs). The allele frequencies of many of these polymorphic loci differed significantly between live and dead dolphins. Some loci associated with survival showed patterns suggesting a common genetic‐based mechanism of resistance to brevetoxins in bottlenose dolphins along the Gulf coast of Florida, but others suggested regionally specific mechanisms of resistance or reflected differences among HABs. We identified candidate genes that may be the evolutionary target for brevetoxin resistance by searching the dolphin genome for genes adjacent to survival‐associated SNPs.     

Severe Karenia brevis red tides influence juvenile bottlenose dolphin (Tursiops truncatus) behavior in Sarasota Bay,Florida

Harmful algal blooms (HABs) are natural stressors in the coastal environment that may be increasing in frequency and severity. This study investigates whether severe red tide blooms, caused by Karenia brevis, affect the behavior of resident coastal bottlenose dolphins in Sarasota Bay, Florida through changes to juvenile dolphin activity budgets, ranging patterns, and social associations. Behavioral observations were conducted on free‐ranging juvenile dolphins during the summer months of 2005–2007, and behavior during red tide blooms was compared to periods of background K. brevis abundance. We also utilized dolphin group sighting data from 2004 to 2007 to obtain comparison information from before the most severe recent red tide of 2005 and incorporate social association information from adults in the study area. We found that coastal dolphins displayed a suite of behavioral changes associated with red tide blooms, including significantly altered activity budgets, increased sociality, and expanded ranging behavior. At present, we do not fully understand the mechanism behind these red tide‐associated behavioral effects, but they are most likely linked to underlying changes in resource availability and distribution. These behavioral changes have implications for more widespread population impacts, including increased susceptibility to disease outbreaks, which may contribute to unusual mortality events during HABs.     

Demographic Clusters Identified within the Northern Gulf of Mexico Common Bottlenose Dolphin (Tursiops truncates) Unusual Mortality Event: January 2010 - June 2013

A multi-year unusual mortality event (UME) involving primarily common bottlenose dolphins (Tursiops truncates) was declared in the northern Gulf of Mexico (GoM) with an initial start date of February 2010 and remains ongoing as of August 2014. To examine potential changing characteristics of the UME over time, we compared the number and demographics of dolphin strandings from January 2010 through June 2013 across the entire GoM as well as against baseline (1990-2009) GoM stranding patterns. Years 2010 and 2011 had the highest annual number of stranded dolphins since Louisiana’s record began, and 2011 was one of the years with the highest strandings for both Mississippi and Alabama. Statewide, annual numbers of stranded dolphins were not elevated for GoM coasts of Florida or Texas during the UME period. Demographic, spatial, and temporal clusters identified within this UME included increased strandings in northern coastal Louisiana and Mississippi (March-May 2010); Barataria Bay, Louisiana (August 2010-December 2011); Mississippi and Alabama (2011, including a high prevalence and number of stranded perinates); and multiple GoM states during early 2013. While the causes of the GoM UME have not been determined, the location and magnitude of dolphin strandings during and the year following the 2010 Deepwater Horizon oil spill, including the Barataria Bay cluster from August 2010 to December 2011, overlap in time and space with locations that received heavy and prolonged oiling. There are, however, multiple known causes of previous GoM dolphin UMEs, including brevetoxicosis and dolphin morbillivirus. Additionally, increased dolphin strandings occurred in northern Louisiana and Mississippi before the Deepwater Horizon oil spill. Identification of spatial, temporal, and demographic clusters within the UME suggest that this mortality event may involve different contributing factors varying by location, time, and bottlenose dolphin populations that will be better discerned by incorporating diagnostic information, including histopathology.     

Where to catch a fish? The influence of foraging tactics on the ecology of bottlenose dolphins (Tursiops truncatus) in Florida Bay,Florida

Observations of bottlenose dolphins ( Tursiops truncatus ) in Florida Bay, Florida, between 2002 and 2005 revealed the use of three distinct foraging tactics. The goal of this study was to identify ecological correlates with tactic use and describe the impact of foraging specializations on the overall habitat use and distribution patterns of this dolphin population. Foraging tactics showed strong association with contrasting environmental characteristics, primarily depth. Locations of two of these tactic groups were spatially repulsed. Analyses of sighting histories of individual dolphins observed at foraging events determined that dolphins which employed one tactic never employed the other, and vice versa . Although bottlenose dolphins have plastic foraging behaviors, dolphins in Florida Bay appear to specialize in one tactic and subsequently limit their overall distribution patterns to coincide with habitats that facilitate success using that foraging tactic. This study demonstrates how foraging behavior can be an ecological determinant of overall dolphin habitat use patterns and works to create spatial structure within a population due to consistent mapping of tactics onto environmental variation. These foraging specializations potentially impact the social and demographic patterns of this dolphin population. The possible evolutionary mechanisms behind this intraspecific variation, including resource limitation and social learning, are considered.     

Fine-scale population structure of bottlenose dolphins (Tursiops truncatus) in Tampa Bay, Florida

Some populations of coastal bottlenose dolphins ( Tursiops truncatus ) comprise discrete communities, defined by patterns of social association and long-term site fidelity. We tested the hypothesis that bottlenose dolphins in Tampa Bay, Florida, form a single community. The longitudinal study of dolphins in Sarasota Bay, adjacent to Tampa Bay, allowed us to ground-truth the definition of community and test whether our approach was robust to small sample sizes of resightings. We conducted photo-identification surveys in Tampa Bay during 1988–1993, and identified 102 dolphins with 10 or more sightings. We used hierarchical cluster analysis to examine the locations and association indices of these dolphins. We used analysis of variance (ANOVA) to test for differences in mean locations and determine whether mean coefficient of association (CoA) values within a community were higher than among communities. Dolphins in Tampa Bay clustered into five putative communities differing significantly in location and CoA values. Kernel estimates of the ranges of these five communities exhibited little overlap; some communities had no overlap at all. We conclude that five discrete communities of bottlenose dolphins exist in Tampa Bay and that such fine-scale structure may be a common feature of bottlenose dolphin populations throughout the southeastern United States.     

GROWTH OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE INDIAN RIVER LAGOON SYSTEM, FLORIDA, U. S. A.

Gompertz growth models were fitted to total lengths and ages from tooth sections of 199 stranded bottlenose dolphins ( Tursiops truncatus ) from the Indian River Lagoon system, eastern Florida. Based on the model, dolphins from this population are estimated to be born at 119 cm and reach asymptotic length at 250 cm. No apparent pubescent growth acceleration was noted for either sex. Males appeared to grow to slightly longer lengths than females. There were small size differences between Indian River dolphins and those in Texas and Sarasota, indicating general size similarities between North Atlantic and Gulf of Mexico bottlenose dolphins stocks.     

Recovery rates of bottlenose dolphin (Tursiops truncatus) carcasses estimated from stranding and survival rate data

Recovery of cetacean carcasses provides data on levels of human‐caused mortality, but represents only a minimum count of impacts. Counts of stranded carcasses are negatively biased by factors that include at‐sea scavenging, sinking, drift away from land, stranding in locations where detection is unlikely, and natural removal from beaches due to wave and tidal action prior to detection. We estimate the fraction of carcasses recovered for a population of coastal bottlenose dolphins (Tursiops truncatus), using abundance and survival rate data to estimate annual deaths in the population. Observed stranding numbers are compared to expected deaths to estimate the fraction of carcasses recovered. For the California coastal population of bottlenose dolphins, we estimate the fraction of carcasses recovered to be 0.25 (95% CI = 0.20–0.33). During a 12 yr period, 327 animals (95% CI = 253–413) were expected to have died and been available for recovery, but only 83 carcasses attributed to this population were documented. Given the coastal habits of California coastal bottlenose dolphins, it is likely that carcass recovery rates of this population greatly exceed recovery rates of more pelagic dolphin species in the region.     

Lacaziosis and lacaziosis-like prevalence among wild, common bottlenose dolphins Tursiops truncatus from the west coast of Florida, USA

Lacaziosis (lobomycosis; Lacazia loboi) is a fungal skin disease that naturally occurs only in humans and dolphins. The first reported case of lacaziosis in a bottlenose dolphin Tursiops truncatus occurred in 1970 in Sarasota Bay, Florida, USA, and subsequent photo-ID monitoring of the Sarasota Bay dolphin population has revealed persistence of the disease. The objectives of this study were to estimate lacaziosis prevalence (P) in 2 bottlenose dolphin populations on the west coast of Florida (Sarasota Bay and Charlotte Harbor) and compare disease occurrence to other published estimates of lacaziosis in dolphin populations across the globe. Historic photographic records of dolphins captured and released for health assessment purposes (Sarasota Bay) and photo-ID studies (Charlotte Harbor) were screened for evidence of lesions consistent with lacaziosis. Health assessment data revealed a prevalence of lacaziosis in the Sarasota Bay bottlenose dolphin population between 2 and 3%, and analyses of photo-ID data provided a lacaziosis-like prevalence estimate of 2% for Charlotte Harbor dolphins. With the exception of lacaziosis prevalence estimates for dolphins inhabiting the Indian River Lagoon (P = 0.068; P = 0.12), no statistically significant differences were seen among Sarasota Bay, Charlotte Harbor, and other published estimates. Although lacaziosis is a rare disease among these dolphin populations, studies that assess disease burden among different populations can assist with the surveillance of this zoonotic pathogen.     

Brevetoxin exposure,superoxide dismutase activity and plasma protein electrophoretic profiles in wild-caught Kemp's ridley sea turtles (Lepidochelys kempii) in southwest Florida

Because of their vulnerable population status, assessing exposure levels and impacts of toxins on the health status of Gulf of Mexico marine turtle populations is critical. From 2011 to 2013, two large blooms of the red tide dinoflagellate, Karenia brevis, occurred along the west coast of Florida USA (from October 2011 to January 2012 and October 2012 to April 2013). Other than recovery of stranded individuals, it is unknown how harmful algal blooms affected the Kemp's ridley sea turtles (Lepidochelys kempii) inhabiting the affected coastal waters. It is essential to gather information regarding brevetoxin exposure in these turtles to determine if it poses a threat to marine turtle health and survival. From April 2012 to May 2013, we collected blood from 13 immature Kemp's ridley turtles captured in the Pine Island Sound region of the Charlotte Harbor estuary. Nine turtles were sampled immediately after or during the red tide events (bloom group) while four turtles were sampled between the events (non-bloom group). Plasma was analyzed for total brevetoxins (reported as ng PbTx-3 eq/mL), superoxide dismutase (SOD) activity, total protein concentration and protein electrophoretic profiles (albumin, alpha-, beta- and gamma-globulins). Brevetoxin concentrations ranged from 7.0 to 33.8 ng PbTx-3 eq/mL. Plasma brevetoxin concentrations in the nine turtles sampled during or immediately after the red tide events were significantly higher (by 59%, P = 0.04) than turtles sampled between events. No significant correlations were observed between plasma brevetoxin concentrations and plasma proteins or SOD activity, most likely due to the small sample size; however alpha-globulins tended to increase with increasing brevetoxin concentrations in the bloom group. Smaller (carapace length and mass) bloom turtles had higher plasma brevetoxin concentrations than larger bloom turtles, possibly due to a growth dilution effect with increasing size. The research presented here improves the current understanding of potential impacts of environmental brevetoxin exposure on marine turtle health and survival.     

Common bottlenose dolphin (Tursiops truncatus) social structure and distribution changes following the 2008 Unusual Mortality Event in the Indian River Lagoon,Florida

In animal societies with fission-fusion dynamics, demographic disturbances can influence the social and spatial structure of the population. Within the Indian River Lagoon (IRL), Florida, common bottlenose dolphins (Tursiops truncatus) have experienced recurrent unusual mortality events (UMEs) providing an opportunity to examine postdisturbance population and social cluster restructuring. This study investigates the impact of the potentially nonepizootic 2008 UME on the IRL dolphin population. Photo-identification surveys conducted from August 2006 to May 2010 were stratified into pre- (August 2006–April 2008) and post-UME (September 2008–May 2010) time periods. Social network and spatial (univariate kernel density) analyses were limited to individuals sighted 5+ times per period (pre-UME = 183, post-UME = 134), and indicated a change from 11 to ten social clusters, although individuals did not always reassociate with pre-UME cluster associates. Despite the social and spatial disconnect between IRL proper and Mosquito Lagoon clusters, both network density and core area spatial overlap increased post-UME allowing for increased intercluster interactions. However, intracluster associations increased as well, allowing the population to maintain multiple social clusters within a loosely connected network. This study shows the important role sociality may play in the adaptability of cetaceans to environmental and demographic changes.     

Extraction and analysis of lipophilic brevetoxins from the red tide dinoflagellate Karenia brevis

Efficient extraction and accurate analysis of lipophilic brevetoxins (PbTxs), produced by the harmful algal bloom (HAB) species Karenia brevis, are essential when assessing the toxicological potential of this dinoflagellate. One of the most commonly used brevetoxin extraction methodologies employs C18 solid-phase extraction (SPE). In this study, C18 SPEC discs were tested for extraction of spiked PbTx-3 in seawater and naturally produced brevetoxins from K. brevis. Quantification of brevetoxin in the extracts was determined using four independent methods: receptor binding assay (RBA), radioimmunoassay (RIA), neuroblastoma (N2A) cytotoxicity assay, and liquid chromatography/mass spectrometry (LC/MS). In addition to quantification of the brevetoxin concentration, LC/MS analysis provided identification of individual congeners and each of their hydrolyzed products. SPEC disc extractions prepared from sonicated cultures of non-brevetoxin-producing Karenia mikimotoi cultures spiked with PbTx-3 yielded extraction efficiencies of 108, 99, and 125% as determined by the RBA, RIA, and N2A cytotoxicity assay, respectively. In SPEC disc extracts of brevetoxin-producing K. brevis (isolate SP3) cultures, LC/MS analysis yielded the highest total concentrations, possibly due to the concurrent detection of hydrolytic brevetoxin congeners that accounted for up to 20% of the congener profile. Relative to the brevetoxin concentration as determined by LC/MS, the RBA, RIA, and N2A cytotoxicity assay detected 73, 83, and 51% of the total brevetoxin concentration. Stability experiments demonstrated that brevetoxins remain stable on the SPEC discs for at least 30 days, making this extraction method suitable for shipboard collections.     

Fatal Asphyxiation in Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon

Multiple single case reports of asphyxiation in dolphins caused by fish lodged in the esophagus exist. However, the significance of this cause of mortality in a single population has not been documented. We performed a retrospective evaluation of pathology records from stranded bottlenose dolphins (Tursiops truncatus) from the Indian River Lagoon to evaluate the impact of this cause of death on this population. From 1997 to 2011, asphyxiation due to choking was identified as the cause of death in 14 of 350 cases (4%). Sampling of an unrelated but adjacent population over this same period yielded 186 necropsy cases of bottlenose dolphins with no cases of asphyxiation. Asphyxiated animals presented with a fish lodged in the cranial esophagus associated with a dislocated and obstructed or compressed larynx. There was no clear sex predilection. Affected animals included 12 adults and two juveniles. The fish species involved included sheepshead, black chin tilapia and striped mojarra. In five cases, recreational fishing gear was also present. Cetacean choking is related to selection of prey fish species with strong dorsal spines and may be secondarily associated with fish attached to fishing gear. Prey abundance and dolphin behavior may influence these selections. Environmental alterations leading to changes in prey availability or increased interactions with fishing gear may change the significance of fatal choking in dolphin populations.     

Factors determining the interaction between common bottlenose dolphins and bottom trawlers off the Balearic Archipelago (western Mediterranean Sea)

Factors determining bottlenose dolphin association with bottom trawlers were studied off the Balearic Islands, western Mediterranean, by studying dolphin distribution around the islands and their interaction with fishing operations. Results showed that bottlenose dolphins avoided the upper shelf (shallower than 50 m) in the warm season, but not in the cold season and that the slope was avoided all year round. Bottlenose dolphins approached most of the trawlers surveyed in the continental shelf, but seldom interacted with those operating in the slope in the warm season. As a consequence, the average depth of trawling operations that attracted dolphins was shallower than those not attracting dolphins. No statistical difference was observed in the average catch of hauls conducted in the presence or in the absence of dolphins. However, discriminant analysis showed differences in catch composition between hauls with and without dolphin presence, but this difference was not attributed to the palatability of the catch, but to influence of trawling depth on the catch. It is concluded that depth is the main factor ruling occurrence of interaction.     

Age structure of strandings and growth of Lahille's bottlenose dolphin (Tursiops truncatus gephyreus)

This study describes the age structure and sex-specific growth patterns of Lahille's bottlenose dolphins (Tursiops truncatus gephyreus), a subspecies endemic to the Southwest Atlantic Ocean (SWAO). The ages of 120 animals collected in southern Brazil between 1976 and 2017 were determined. We found high frequencies of young animals, mostly males, with no sex bias among adults. A temporal change in the age structure of strandings was observed, and we conclude it is a consequence of increased bycatch rates of young dolphins after 2000. The oldest male and female were 27 and 44 years old, respectively, suggesting that females live longer than males in southern Brazil. Growth curve analysis using Gompertz and Laird-Gompertz growth models estimated asymptotic lengths of 316.5 cm for females and 351.6 cm for males, (reached around 13 and 18 years old, respectively), supporting sexual size dimorphism for the subspecies. A second growth pulse was identified for males. Our work highlights the benefit of long-term studies and contributes valuable information toward understanding the life history of Lahille's bottlenose dolphin. It will serve as baseline for future studies that seek to understand mortality patterns of bottlenose dolphins elsewhere and the effects of anthropogenic actions on the survival of these animals.     

Evoked potential audiometry of 13 Pacific bottlenose dolphins (Tursiops truncatus gilli)

Evoked potential audiograms were measured in 13 Pacific bottlenose dolphins (Tursiops truncatus gilli) to determine the variability in hearing sensitivity and range of hearing. The auditory evoked potential system used a transducer embedded in a suction cup to deliver sinusoidal amplitude modulated tones to each dolphin through the pan region of the lower right jaw. Evoked potentials were recorded noninvasively using surface electrodes, and hearing thresholds were estimated by tracking the amplitude of the envelope following response, an evoked potential that is phase‐locked to the stimulus modulation rate. Frequencies tested ranged from 10 to 180 kHz in each animal. Variability in the range of hearing and age‐related reductions in hearing sensitivity and range of hearing were consistent with those observed in Atlantic bottlenose dolphins. Comparison of audiograms to a captive population of Atlantic bottlenose dolphins demonstrated that the Pacific bottlenose dolphins tested in this study had significantly lower thresholds at frequencies of 40 and 60–115 kHz. Differences in thresholds between the groups are unlikely to be due to methodological factors.     

Effect of salinity on the distribution, growth, and toxicity of Karenia spp.

The first recorded bloom of Karenia spp., resulting in brevetoxin in oysters, in the low salinity waters of the Northern Gulf of Mexico (NGOMEX) occurred in November 1996. It raised questions about the salinity tolerance of Karenia spp., previously considered unlikely to occur at salinities <24 psu, and the likelihood that the bloom would reoccur in the NGOMEX. Salinity was investigated as a factor controlling Karenia spp. abundance in the field, using data from the NGOMEX 1996 bloom and Florida coastal waters from 1954 to 2004, and growth and toxin production in cultures of Karenia brevis (Davis) G. Hansen and Moestrup. During the NGOMEX bloom, Karenia spp. occurred much more frequently at low salinities than in Florida coastal waters over the last 50 years. The data suggest that the NGOMEX bloom started on the NW Florida Shelf, an area with a higher frequency of Karenia spp. at low salinities than the rest of Florida, and was transported by an unusual westward surface current caused by Tropical Storm Josephine. The minimum salinity at which growth occurred in culture ranged between 17.5 and 20 psu, but the optimal salinity ranged between low values of 20 or 25 and high values of 37.5–45 psu, depending on the clone. The effect of salinity on toxin production in one clone of K. brevis was complex, but at all salinities brevetoxin levels were highest during the stationary growth phase, suggesting that aging, high density blooms may pose the greatest public health threat. The results demonstrate that Karenia spp. can be a public health threat in low salinity areas, but the risk in the NGOMEX is relatively low. No bloom has occurred since the 1996 event, which was probably associated with a special set of conditions: a bloom along the Florida Panhandle and a tropical storm with a track that set up a westward current.     

“Porpicide” in California: Killing of harbor porpoises (Phocoena phocoena) by coastal bottlenose dolphins (Tursiops truncatus)

Between 2007 and 2009, we witnessed three aggressive interactions between harbor porpoises and bottlenose dolphins in Monterey Bay, California. This is the first time such aggression has been documented in the Pacific, and the first time a harbor porpoise was collected immediately after witnessing its death, inflicted by bottlenose dolphins. Of the bottlenose dolphins present, 92% were males either confirmed (61%) or putative (31%). Since 2005, 44 harbor porpoise deaths inflicted by bottlenose dolphins were documented in California. Aberrant behavior was rejected as a cause of aggression, based on widespread documentation of similar behaviors in other populations of free‐ranging bottlenose dolphins. The evidence for interspecies territoriality as a form of competition for prey was weak: there is little dietary overlap and there are differences in bottlenose dolphin and harbor porpoise distribution patterns in California. Object‐oriented play was plausible as a form of practice to maintain intraspecific infanticidal skills or a form of play to maintain fighting skills between male associates. Contributing factors could be high‐testosterone levels, as attacks occurred at the height of the breeding season, and/or a skewed operational sex ratio. Ultimately, we need more information about bottlenose dolphin social structure at the time of the aggression.     

Environmental drivers of habitat use by common bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon,Florida, USA

Anthropogenic impacts in estuarine systems can influence marine mammal habitat use, population dynamics, fitness, and mortality events. The objective was to examine habitat use among the resident common bottlenose dolphin (Tursiops truncatus) population inhabiting the Indian River Lagoon, Florida, and the influences of variation in environmental factors and prey availability in 2003–2015. We utilized photo-identification surveys, stratified random samples of prey, and environmental variables collected monthly. Kernel density estimation was used to determine the magnitude-per-unit area of dolphins across the IRL by wet and dry seasons each year, the values were used as a response variable in classification and regression tree analyses with fish community and environmental variables as predictors. Spatial patterns in dolphin density in the IRL were associated with salinity and dissolved oxygen levels, which are in part associated with freshwater discharges of nutrient and algae laden waters from the region's storm water management system. These findings isolate locations of concern for management of dolphin habitat, and anthropogenic drivers of dolphin distributions requiring further research.