Seasonal movements of Gulf of Mexico sperm whales following the Deepwater Horizon oil spill and the limitations of impact assessments

Morano, Janelle L.; Tielens, Jamey T.; Muirhead, Charles A.; Estabrook, Bobbi J.; Sullivan, Patrick J.; Dugan, Peter J.; Clark, Christopher W.; Rice, Aaron N.

doi:10.1016/j.marpolbul.2020.111627

Cited by 6 publications

(3 citation statements)

References 54 publications

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“…Similarly, we assumed no seasonal movement of populations and used an annual average density surface to estimate the number of animals exposed. While there is no definitive evidence of seasonal movement, there is, for example, evidence for seasonal fluctuations in passive acoustic detections of sperm whales at sites along the continental shelf (Morano et al 2020). If definitive information about seasonal movements were available, it could be incorporated into the model by using a seasonal density surface or adding an animal movement component.…”

Section: Discussionmentioning

confidence: 99%

Population consequences of the Deepwater Horizon oil spill on pelagic cetaceans

Marques

Thomas

Booth

et al. 2023

Mar. Ecol. Prog. Ser.

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The Deepwater Horizon disaster resulted in the release of 490000 m3 of oil into the northern Gulf of Mexico. We quantified population consequences for pelagic cetaceans, including sperm whales, beaked whales and 11 species of delphinids. We used existing spatial density models to establish pre-spill population size and distribution, and overlaid an oil footprint to estimate the proportion exposed to oil. This proportion ranged from 0.058 (Atlantic spotted dolphin, 95% CI = 0.041-0.078) to 0.377 (spinner dolphin, 95% CI = 0.217-0.555). We adapted a population dynamics model, developed for an estuarine population of bottlenose dolphins, to each pelagic species by scaling demographic parameters using literature-derived estimates of gestation duration. We used expert elicitation to translate knowledge from dedicated studies of oil effects on bottlenose dolphins to pelagic species and address how density dependence may affect reproduction. We quantified impact by comparing population trajectories under baseline and oil-impacted scenarios. The number of lost cetacean years (difference between trajectories, summed over years) ranged from 964 (short-finned pilot whale, 95% CI = 385-2291) to 32584 (oceanic bottlenose dolphin, 95% = CI 13377-71967). Maximum proportional population decrease ranged from 1.3% (Atlantic spotted dolphin 95% CI = 0.5-2.3) to 8.4% (spinner dolphin 95% CI = 3.2-17.7). Estimated time to recover to 95% of baseline was >10 yr for spinner dolphin (12 yr, 95% CI = 0-21) and sperm whale (11 yr, 95% CI = 0-21), while 7 taxonomic units remained within 95% of the baseline population size (time to recover, therefore, as per its definition, was 0). We investigated the sensitivity of results to alternative plausible inputs. Our methods are widely applicable for estimating population effects of stressors in the absence of direct measurements.

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Section: Discussionmentioning

confidence: 99%

Population consequences of the Deepwater Horizon oil spill on pelagic cetaceans

Marques

Thomas

Booth

et al. 2023

Mar. Ecol. Prog. Ser.

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“…Odontocetes possess biosonar and are likely capable of detecting oil slicks (Geraci et al, 1983), however there is no evidence of oil avoidance in coastal proxies (Smultea and Wursig, 1995). Similarly, oceanic cetaceans were observed, directly both visually and acoustically, within the DWH oil slick, with no evidence of avoidance or reduced presence (Hildebrand et al, 2015;Dias et al, 2017;Frasier et al, 2019;Morano et al, 2020). Initial acute exposure to surface oil through inhalation, ingestion, and dermal contact for a portion of the major stocks is certain.…”

Section: Shallow-and Deep-diving Oceanic Cetaceansmentioning

confidence: 99%

The Open-Ocean Gulf of Mexico After Deepwater Horizon: Synthesis of a Decade of Research

et al. 2022

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The scale of the Deepwater Horizon disaster was and is unprecedented: geographic extent, pollutant amount, countermeasure scope, and of most relevance to this Research Topic issue, range of ecotypes affected. These ecotypes include coastal/nearshore, continental shelf, deep benthic, and open-ocean domains, the last of which is the subject of this synthesis. The open-ocean ecotype comprises ~90% of the volume of the Gulf of Mexico. The exact percentage of this ecotype contaminated with toxins is unknown due to its three-dimensional nature and dynamics, but estimates suggest that the footprint encompassed most of its eastern half. Further, interactions between the water column and the deep benthos may be persistent, making this synthesis one of time (a decade) rather than event conclusion. Here we examine key elements of the open-ocean ecosystem, with emphasis on vulnerability and resilience. Of paramount importance relative to the Gulf nearshore and shelf ecotypes, pre-disaster baseline data were lacking for most of the fauna. In such cases, inferences were drawn from post-disaster assessments. Both phytoplankton and mesozooplankton vulnerabilities were quite high, but resilience appeared equally so. The phytoplankton situation was a bit more complex in that toxin-imposed reductions may have been offset by nutrient injection via high freshwater discharge in 2010. Intermediate trophic levels exhibited population-level depressions, ostensibly due to high vulnerability and low resilience. Apex predator impacts were variable. Certain large epipelagic fishes may have avoided the highest concentrations of hydrocarbons/dispersant, and thus larval abundances returned to pre-disaster levels of variability and abundance within a few years after a steep initial decline. Oceanic cetaceans, particularly shallow-diving stenellid dolphins, did not appear to avoid oiled waters and exhibited strong declines in the northern Gulf. Given that population declines of many open-ocean taxa appear to be ongoing a decade later, we conclude that this largest of Gulf ecosystem components, like its deep-benthic counterpart, is as fragile as it is voluminous. This is particularly concerning given the rapid, and likely irreversible, shift to deeper waters by the US and Mexican oil industries in concert with the higher likelihood of accidents with increasing platform depth.

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“…Photo courtesy of the US Navy abundance decline across all major invertebrate and fish deepwater taxa (Sutton et al 2020) that has coincided with the DWH spill and is coincident with the discovery of elevated PAH levels and other biochemical changes provides strong circumstantial evidence of a toxicological triggering event. Changes in the mesopelagic prey base were accompanied by shifts in the distribution of major marine mammal predators, including whales and dolphins (Fraiser, 2020;Fraiser et al, 2020), although seasonal movements in species such as sperm whales (Physeter macrocephalus) were apparent (Morano et al, 2020). While direct oil contamination may have elicited many of the toxicological impacts seen in other species, disruption of chemosensory abilities may be particularly important as an outcome for deep-sea biota.…”

Section: Monitoring Toxicological Impacts In the Fieldmentioning

confidence: 99%

Impacts of Petroleum, Petroleum Components, and Dispersants on Organisms and Populations

Murawski

Grosell

Smith

et al. 2021

Oceanog

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Following the Deepwater Horizon blowout, oil, degraded oil, oil mixed with dispersants, and management responses to the spill affected a variety of Gulf of Mexico organisms. This review provides examples of various documented impacts, common patterns, and trends across organisms and/or their environments, and discusses future implications as well as directions for future research. Organism effects are generally characterized as lethal and sublethal. Sublethal can be short term, long term, or permanent and multigenerational. We present individual examples of effects on behavioral response, olfaction, vision, cardiac function, and gene shift, based on research done in laboratories, mesocosm settings, and the field. Future research should emphasize collection and analysis of routine toxicological baselines and examine how and if molecular impacts cascade up to populations. This research will require development of rapid molecular tools and testing procedures to determine exposure compared to field-relevant exposure levels and to be able to extrapolate laboratory results to the field, especially given the mosaic of differing contaminant concentrations (below, at, or exceeding critical concentrations that result in lethal or sublethal effects) occurring in the environment. Recent chemical studies have identified a detectable suite of polycyclic aromatic hydrocarbon metabolites for which there are no toxicity data; further research is needed to determine their impacts on food webs.

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Seasonal movements of Gulf of Mexico sperm whales following the Deepwater Horizon oil spill and the limitations of impact assessments

Cited by 6 publications

References 54 publications

Population consequences of the Deepwater Horizon oil spill on pelagic cetaceans

Population consequences of the Deepwater Horizon oil spill on pelagic cetaceans

The Open-Ocean Gulf of Mexico After Deepwater Horizon: Synthesis of a Decade of Research

Impacts of Petroleum, Petroleum Components, and Dispersants on Organisms and Populations

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