Texas Marine Mammal Stranding Network

Construction-related loss of habitat, degradation of existing habitat, noise pollution, and vessel activity are growing issues for Indo-Pacific humpback dolphins (Sousa chinensis) that occur in the shallow, near-shore, highly industrialized waters off Lantau Island, Hong Kong. We studied the occurrence of dolphins in discrete locations, fine-scale movement patterns, and dolphin behavioral activity states. Potential explanatory variables varied and included year, season, time of day, dolphin group size and behavioral activity state, proximity to construction activity, and vessel type and number. Land-based observations and theodolite tracking of dolphins and vessels were conducted from seven locations to the north of Lantau Island, Hong Kong, and marine construction activities near survey sites were identified. A total of 636 groups of dolphins were recorded, totaling 150.91 h of tracking, from 405 days of observation effort. Hurdle models were used to analyze dolphin occurrence, multivariate generalized additive models were used to analyze fine-scale movement patterns, and log-likelihood ratio and binomialzscorepost hoctests were used to analyze behavioral activity states. Dolphin occurrence was lower in historically important areas near long-term, low-intensity construction activity, and dolphin swimming speed was higher in response to vessel presence. Overall, foraging and traveling were the most frequently observed behavioral activity states and resting behavior was observed off only one location that was not in proximity to construction activities. Temporal overlap in adjacent marine construction areas may displace animals for extended periods and nearby ecologically similar habitats should be identified and designated as marine protected areas to mitigate effects of such disturbance.

The whale watching industry in Juneau, Alaska relies primarily on the presence of North Pacific humpback whales (Megaptera novaeangliae). To meet demands from the rapidly growing tourism industry, the number of whale watching vessels in this region has tripled over the last 18 years. As a result, increased vessel presence could have negative effects on humpback whales, ranging from short-term behavioral disturbance to long-term impacts. The current humpback whale viewing regulations are outdated and may not be as effective as they were 18 years ago, when both the whale watching industry and humpback whale population were smaller. The present study assessed how humpback whale movement and behavioral patterns were affected by (1) vessel presence and number of vessels present, and (2) time spent in the presence of vessels. The study also determined how humpback whale behavioral state transitions were affected by vessel presence. A total of 201 humpback whale focal follows were conducted during summer 2016 and 2017. Based on linear mixed effects models, whales in the presence (vs. absence) of vessels exhibited 38.9% higher deviation in linear movement (p = 0.001), 6.2% increase in swimming speed (p = 0.047) and a 6.7% decrease in inter-breath intervals (IBI) (p = 0.025). For each additional vessel present, deviation increased by 6.2% (p = 0.022) and IBI decreased by 3.4% (p = 0.001). As time spent in the presence of vessels increased, respiration rate increased (p = 0.011). Feeding and traveling humpback whales were likely to maintain their behavioral state regardless of vessel presence, while surface active humpback whales were likely to transition to traveling in the presence of vessels. These short-term changes in movement and behavior in response to whale watching vessels could lead to cumulative, long-term consequences, negatively impacting the health and predictability of the resource on which the industry relies. Current formal vessel approach regulations and voluntary guidelines should be revisited to reduce vessel pressure and mitigate potential negative effects of this growing whale watching industry.

On 20 January 1990, twenty-three Tursiops truncatus (Common Bottlenose Dolphin) carcasses were found scattered around the interior shoreline of East Matagorda Bay, TX. Few accounts exist to document the presence of live or dead Common Bottlenose Dolphins inside the boundaries of East Matagorda Bay before or after the die-off. We conducted a review of areal data for East Matagorda Bay and the original investigation of the January 1990 mass die-off. Information we examined included the history of natural and anthropogenic changes to the area, dolphin stranding records, small-boat visual surveys, and dolphin dorsal-fin photographic identification. Natural events preceding the discovery of the dolphin carcasses were likely factors in the mortalities; however, the timing of engineering projects that modified access points between the bay and the Gulf of Mexico may be an additional factor that contributed to the cause of this unusual mortality event.

A northern Gulf of Mexico (GoM) cetacean unusual mortality event (UME) involving primarily bottlenose dolphins (Tursiops truncatus) in Louisiana, Mississippi, and Alabama began in February 2010 and continued into 2014. Overlapping in time and space with this UME was the Deepwater Horizon (DWH) oil spill, which was proposed as a contributing cause of adrenal disease, lung disease, and poor health in live dolphins examined during 2011 in Barataria Bay, Louisiana. To assess potential contributing factors and causes of deaths for stranded UME dolphins from June 2010 through December 2012, lung and adrenal gland tissues were histologically evaluated from 46 fresh dead non-perinatal carcasses that stranded in Louisiana (including 22 from Barataria Bay), Mississippi, and Alabama. UME dolphins were tested for evidence of biotoxicosis, morbillivirus infection, and brucellosis. Results were compared to up to 106 fresh dead stranded dolphins from outside the UME area or prior to the DWH spill. UME dolphins were more likely to have primary bacterial pneumonia (22% compared to 2% in non-UME dolphins, P = .003) and thin adrenal cortices (33% compared to 7% in non-UME dolphins, P = .003). In 70% of UME dolphins with primary bacterial pneumonia, the condition either caused or contributed significantly to death. Brucellosis and morbillivirus infections were detected in 7% and 11% of UME dolphins, respectively, and biotoxin levels were low or below the detection limit, indicating that these were not primary causes of the current UME. The rare, life-threatening, and chronic adrenal gland and lung diseases identified in stranded UME dolphins are consistent with exposure to petroleum compounds as seen in other mammals. Exposure of dolphins to elevated petroleum compounds present in coastal GoM waters during and after the DWH oil spill is proposed as a cause of adrenal and lung disease and as a contributor to increased dolphin deaths.

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.

Involution of lymphoid tissues in relation to age has not been defined for bottlenose dolphins (Tursiops truncatus). Twenty-five bottlenose dolphins from the coast of Texas and western Louisiana were examined and complete necropsies were performed with histological samples taken of nearly all tissues. Ages ranged from several days to 27 years. The histology of four lymphoid organs-thymus, pharyngeal tonsil, mucosa-associated lymphoid tissue (MALT) of the colon, and anal tonsil-was assessed. Numerical scores were assigned to specific morphological features, thus creating an involution score. Definable and scorable features of each organ were selected for evaluation and determination of loss of lymphoid elements. Neonatal dolphins were recorded as the reference standard for no involution. The highest score for each organ represented the greatest amount of retention of tissue elements. Thus, the lower the score, the greater degree of involution. Comparing involution scores to tooth age permitted an assessment of involution over time. The greatest degree of involution was found in the MALT of the colon. The MALT of the colon declined dramatically so that after age 10 it was absent from 4 of 14 animals and minimally present in 8 others. Thymic tissue also suffered a precipitous drop in volume after about age 5, but was found in animals up to 24 years of age. Involution was moderate and variable in both pharyngeal and anal tonsils. In some animals, these tissues were reduced in volume early, and prominent in others well into adult life (over 20 years).

During necropsy of cetaceans stranded or accidentally net-captured along the western coast of the Gulf of Mexico from 1991 to 1996, we found 13 of 59 (22%) animals had abnormalities of the atlanto-occipital and/or humeroscapular joints, the synovial joints. A few cases demonstrated mild roughening of the articular cartilage, while the majority exhibited complete erosion with thickened synovium and bony proliferation. The lesions resulted in ankylosis of both joints in one animal. In humans and terrestrial mammals, synovial joint diseases are known to be debilitating. Cetaceans depend on neck and flipper movement for locomotion, feeding, avoiding danger, and reaching the water's surface for breathing. Therefore, synovial joint disease may be significant mortality factor in these marine animals.