Health Impacts and Recovery From Prolonged Freshwater Exposure in a Common Bottlenose Dolphin (Tursiops truncatus)

Impacts of the Bonnet Carré Spillway on common bottlenose dolphins in the Mississippi Sound from 2010 to 2021

In the last decade, the frequency of the use of the Bonnet Carré Spillway (BCS) to divert water from the Mississippi River by the United States Army Corps of Engineers (USACE) has dramatically increased. The BCS is designed to protect the city of New Orleans, Louisiana from levee breaches and devastating floods. In 2011 and 2019, during extreme flood events, the USACE diverted 6.4 trillion gallons and 10.07 trillion gallons of Mississippi River water into Lake Borgne and Biloxi Marsh, Louisiana, and the Mississippi Sound, Mississippi. The 2011 and 2019 diversions and lower-discharge diversions in other years have coincided with high freshwater discharges of coastal Mississippi streams, the appearance of common bottlenose dolphins (Tursiops truncatus, dolphins) with skin lesions, and large numbers of stranded dolphins. To determine what might be causing dolphin skin lesions and strandings, we investigated BCS and coastal stream discharges between 2010 and 2021 as possible drivers. Generalized additive, kriging, and seasonal-trend decomposition using loess models showed that the prevalence of skin lesions in the western Mississippi Sound and Biloxi Marsh was significantly related to BCS discharge and not to stream discharge. From 2010 to 2021, the frequency of stranded dolphins across the Mississippi Sound was significantly related to BCS discharges, while coastal stream discharges had localized effects. Between 2018 and 2019, the relationship between the frequency of dolphin strandings and BCS discharge was highly significant. In this model, the relationship between dolphin strandings and stream discharge was not significant. This research provides evidence that freshwater diversions through the BCS likely increase the prevalence of skin lesions on live dolphins, strandings, and mortality in the Mississippi Sound.

Development of single-pin, un-barbed, pole-tagging of free-swimming dolphins and sharks with satellite-linked transmitters

Background

To tag large marine vertebrates, without the need to catch them, avoiding using barbs for tag retention, and precisely controlling tag location, the remote Tag Attachment Device on a pole (TADpole) was developed. This allows single-pin tags (Finmount, Wildlife Computers) to be attached to the dorsal fins of free-swimming large marine vertebrates.

Results

TADpole comprises a pole-mounted holster that carries a tag. It uses compressed air, and a micro-controller, to rapidly insert a stainless-steel pin through a corrodible metal retaining ring in the first tag attachment wing, the animal’s dorsal fin, and then a press fit Delrin retaining ring in the tag wing on the other side of the fin. Tagging only occurs when the trailing edge of the dorsal fin touches a trigger bar in the holster, ensuring optimal pin placement. It was developed using fins from cadavers, then trialed on briefly restrained coastal dolphins that could be followed in successive days and weeks, and then on free-swimming animals in the field. The latter showed very short touch/response intervals and highlighted the need for several iterative revisions of the pneumatic system. This resulted in reducing the total time from triggering to tag application to ~ 20 ms. Subsequent efforts expanded the TADpole’s applicability to sharks. One free-swimming Atlantic spotted dolphin, two white sharks, and one whale shark were then tagged using the TADpole.

Conclusions

Being able to tag free-swimming dolphins and sharks remotely and precisely with satellite-linked telemetry devices may contribute to solving conservation challenges. Sharks were easier to tag than dolphins. Dolphin touch-to-response times were 28 ms or less. Delphinid skin has unique polymodal axon bundles that project into the epidermis, perhaps a factor in their uniquely fast response, which is 10 × faster than humans. Their primary reaction to tagging is to abduct the flippers and roll the fin out of the TADpole holster. This device has the potential to deliver high-quality tag data from large vertebrates with dorsal fins without the stress and logistics associated with catch-and-release, and without the trauma of tags that use barbs for retention. It also collects a dorsal fin biopsy core.

Causes of death and pathogen prevalence in bottlenose dolphins Tursiops truncatus stranded in Alabama, USA, between 2015 and 2020, following the Deepwater Horizon oil spill

Between 2010 and 2014, an unusual mortality event (UME) involving bottlenose dolphins Tursiops truncatus occurred in the northern Gulf of Mexico, associated with the Deepwater Horizon oil spill (DWHOS). Cause of death (COD) patterns in bottlenose dolphins since then have not been analyzed, and baseline prevalence data for Brucella ceti and cetacean morbillivirus, 2 pathogens previously reported in this region, are lacking. We analyzed records from bottlenose dolphins stranded in Alabama from 2015 to 2020 with necropsy and histological findings to determine COD (n = 108). This period included another UME in 2019 associated with prolonged freshwater exposure. A subset of individuals that stranded during this period were selected for molecular testing for Brucella spp. and Morbillivirus spp. Causes of death for all age classes were grouped into 6 categories, including (1) human interaction, (2) infectious disease, (3) noninfectious disease (prolonged freshwater exposure and degenerative), (4) trauma, (5) multifactorial, and (6) unknown. Two additional categories unique to perinates included fetal distress and in utero pneumonia. Human interaction was the most common primary COD (19.4%) followed closely by infectious disease (17.6%) and noninfectious disease (freshwater exposure; 13.9%). Brucella was detected in 18.4% of the 98 animals tested, but morbillivirus was not detected in any of the 66 animals tested. Brucella was detected in some moderately to severely decomposed carcasses, indicating that it may be beneficial to test a broad condition range of stranded animals. This study provides valuable information on COD in bottlenose dolphins in Alabama following the DWHOS and is the first to examine baseline prevalence of 2 common pathogens in stranded animals from this region.

Precision of the Abaxis VetScan VS2 for postmortem biochemical analysis of delphinid vitreous humor

Biochemical analysis of vitreous humor has several forensic applications, including toxicology, estimation of the postmortem interval, and as proxy for select antemortem serum analytes. Estimation of postmortem interval from vitreous humor analytes such as potassium has potential to be a valuable forensic tool for marine mammal strandings, as time of death is essential to provide spatial and temporal context for anthropogenic interactions. The Abaxis VetScan VS2 (VetScan) chemistry analyzer is inexpensive, compact, and requires low sample volume (100 μl), making it ideal for organizations with limited resources and limited samples. This pilot study compared accuracy of the Vetscan on delphinid serum/plasma (n = 7) to the Beckman Coulter AU480, validated the precision of the Vetscan for biochemical analysis of delphinid vitreous humor using the described sample processing protocol, and assessed analyte stability at room temperature in delphinid vitreous humor. Pooled samples (n = 12) of delphinid vitreous humor were serially analyzed and the between-run and within-run coefficient of variation of the VetScan was acceptable for most analytes tested but was not for creatinine, total bilirubin, amylase, and alanine aminotransferase. These results demonstrated the precision of the VetScan for the analysis of glucose, albumin, globulin, total protein, urea nitrogen, sodium, potassium, calcium, and phosphorus in delphinid vitreous humor.

Skin lesion and mortality rate estimates for common bottlenose dolphin (Tursiops truncatus) in the Florida Panhandle following a historic flood

Increasing evidence links prolonged freshwater exposure to adverse health conditions, immune deficiencies, and mortality in delphinids. Pensacola, Florida, experienced a record-breaking flood event in April 2014, after which, skin lesions evident of freshwater exposure were observed on common bottlenose dolphins (Tursiops truncatus). Here we assess the potential consequences of the flood on bottlenose dolphin health and mortality. Data from an ongoing study were used to evaluate the relationship between skin lesions (progression, prevalence, and extent) and the flood with respect to changing environmental conditions (salinity). Annual stranding records (2012–2016) from Alabama to the eastern Florida Panhandle were used as an indicator of dolphin health to test the hypothesis that the flood event resulted in increased annual mortality rates. Although salinities remained low for several months, results suggest that there was not the widespread skin lesion outbreak anticipated. Of the 333 unique individuals detected only 20% were seen with skin lesions. There was a significant increase in the proportion of dolphins seen post-flood with lesion extent above background levels (≥ 5%; p = 0.001), however, there were only 11 cases with lesion extent greater than 20%. Skin lesion prevalence increased overall following the flood (p < 0.001), but pairwise comparisons revealed a delayed response with significant increases not detected until the following fall (p = 0.01), several months after salinities returned to expected levels. Regression modeling revealed no significant effects of year, region, or year x region on mortality rates, except in Alabama, where increased mortality rates were likely due to residual impacts from the Deepwater Horizon Oil Spill. This study takes advantage of a natural experiment, highlighting how little is understood about the conditions in which prolonged freshwater exposure leads to negative impacts on dolphin health.

High site-fidelity in common bottlenose dolphins despite low salinity exposure and associated indicators of compromised health

More than 2,000 common bottlenose dolphins (Tursiops truncatus) inhabit the Barataria Bay Estuarine System in Louisiana, USA, a highly productive estuary with variable salinity driven by natural and man-made processes. It was unclear whether dolphins that are long-term residents to specific areas within the basin move in response to fluctuations in salinity, which at times can decline to 0 parts per thousand in portions of the basin. In June 2017, we conducted health assessments and deployed satellite telemetry tags on dolphins in the northern portions of the Barataria Bay Estuarine System Stock area (9 females; 4 males). We analyzed their fine-scale movements relative to modeled salinity trends compared to dolphins tagged near the barrier islands (higher salinity environments) from 2011 to 2017 (37 females; 21 males). Even though we observed different movement patterns among individual dolphins, we found no evidence that tagged dolphins moved coincident with changes in salinity. One tagged dolphin spent at least 35 consecutive days, and 75 days in total, in salinity under 5 parts per thousand. Health assessments took place early in a seasonal period of decreased salinity. Nonetheless, we found an increased prevalence of skin lesions, as well as abnormalities in serum biochemical markers and urine:serum osmolality ratios for dolphins sampled in lower salinity areas. This study provides essential information on the likely behavioral responses of dolphins to changes in salinity (e.g., severe storms or from the proposed Mid-Barataria Sediment Diversion project) and on physiological markers to inform the timing and severity of impacts from low salinity exposure.

Common Bottlenose Dolphin, Tursiops truncatus, Behavioral Response to a Record-Breaking Flood Event in Pensacola Bay, Florida

Common bottlenose dolphins, Tursiops truncatus, can suffer health complications from prolonged freshwater exposure; however, little is known about how dolphins behaviorally respond to flood events. We investigated whether dolphins mitigated their freshwater exposure by moving south towards the estuary mouth and/or towards deeper areas with higher salinities in response to a record-breaking flood in Pensacola Bay, Florida. In total, 144 dolphin groups observed during 45 population dynamic surveys were analyzed across two flood-impacted sampling sessions and their respective seasonal control sessions. Kernel density estimates demonstrated southern movement towards the estuary mouth during flood-impacted sessions, but this distribution change was limited. Species distribution models showed that dolphins did not move to deeper areas after the flood and dolphin distribution was not substantially altered by flood-induced salinity changes. The estuary system exhibits strongly stratified waters with broad salinity ranges even during the flood. Dolphins may have mitigated the severity of freshwater exposure by capitalizing on these stratified areas as they continued to use habitat affected by the flood. A lack of avoidance of low salinity could result in this dolphin population being at greater risk for health problems, which should be considered in future population management and conservation.

Fresh water skin disease in dolphins: a case definition based on pathology and environmental factors in Australia

A distinct ulcerative dermatitis known as “freshwater skin disease” is an emerging clinical and pathological presentation in coastal cetaceans worldwide. In Australia, two remarkably similar mortality events enabled the creation of a case definition based on pathology and environmental factors. The first affected a community of endemic Tursiops australis in the Gippsland Lakes, Victoria, while the second occurred among T. aduncus resident in the Swan-Canning River system, Western Australia. The common features of both events were (1) an abrupt and marked decrease in salinity (from > 30ppt to < 5ppt) due to rainfall in the catchments, with hypo-salinity persisting weeks to months, and (2) dermatitis characterized grossly by patchy skin pallor that progressed to variable circular or targetoid, often raised, and centrally ulcerated lesions covering up to 70% of the body surface. The affected skin was often colonized by a variety of fungal, bacterial and algal species that imparted variable yellow, green or orange discoloration. Histologic lesions consisted of epidermal hydropic change leading to vesiculation and erosion; alternately, or in addition, the formation of intra-epithelial pustules resulting in ulceration and hypodermal necrosis. Thus, the environmental factors and characteristic pathologic lesions, are necessary components of the case definition for freshwater skin disease.

Physiological Effects of Low Salinity Exposure on Bottlenose Dolphins (Tursiops truncatus)

Bottlenose dolphins (Tursiops truncatus) have a worldwide distribution in temperate and tropical waters and often inhabit estuarine environments, indicating their ability to maintain homeostasis in low salinity for limited periods of time. Epidermal and biochemical changes associated with low salinity exposure have been documented in stranded bottlenose dolphins; however, these animals are often found severely debilitated or deceased and in poor condition. Dolphins in the U.S. Navy Marine Mammal Program travel globally, navigating varied environments comparable to those in which free-ranging dolphins are observed. A retrospective analysis was performed of medical records from 46 Navy dolphins and blood samples from 43 Navy dolphins exposed to a variety of salinity levels for different durations over 43 years (from 1967–2010). Blood values from samples collected during low salinity environmental exposure (salinity ranging from 0–30 parts per thousand (ppt) were compared to samples collected while those same animals were in a seawater environment (31–35 ppt). Epidermal changes associated with low salinity exposure were also assessed. Significant decreases in serum sodium, chloride, and calculated serum osmolality and significant increases in blood urea nitrogen and aldosterone were observed in blood samples collected during low salinity exposure. Epidermal changes were observed in 35% of the animals that spent time in low salinity waters. The prevalence of epidermal changes was inversely proportional to the level of salinity to which the animals were exposed. Future work is necessary to fully comprehend the impacts of low salinity exposure in bottlenose dolphins, but the physiological changes observed in this study will help improve our understanding of the upper limit of duration and the lower limit of salinity in which a bottlenose dolphin can maintain homeostasis.