Boom-bust cycles in gray whales associated with dynamic and changing Arctic conditions

Climate change is affecting a wide range of global systems, with polar ecosystems experiencing the most rapid change. Although climate impacts affect lower-trophic-level and short-lived species most directly, it is less clear how long-lived and mobile species will respond to rapid polar warming because they may have the short-term ability to accommodate ecological disruptions while adapting to new conditions. We found that the population dynamics of an iconic and highly mobile polar-associated species are tightly coupled to Arctic prey availability and access to feeding areas. When low prey biomass coincided with high ice cover, gray whales experienced major mortality events, each reducing the population by 15 to 25%. This suggests that even mobile, long-lived species are sensitive to dynamic and changing conditions as the Arctic warms.

Co-occurrence of gray whales and vessel traffic in the North Pacific Ocean

All species of large whales are susceptible to vessel strikes, but the true scale and geographical extent of such strikes is not known. This paper provides a qualitative assessment of the range-wide risks posed to gray whales Eschrichtius robustus by vessels, by comparing patterns of whale distribution with the density of vessel traffic seasonally throughout the North Pacific in 2019. Areas of very high vessel density were evident year-round near many coastlines, along inter-continental trade routes, and at hubs of commercial shipping near port entrances. Gray whales were exposed to vessel strikes throughout their range and in their feeding, southbound migration, wintering, and northbound migration periods. Areas of apparently high risk were in the Russian Far East (Kamchatka peninsula and Okhotsk Sea), Bering Sea (including the Aleutian Islands), Gulf of Alaska, and along the entire west coast of North America. Risk appeared greatest during south- and northbound migration when much of the gray whale population is moving through waters near shore. Tanker, container, and bulk-carrier ships represent considerable risk to whales in the North Pacific Ocean, but the large geographical extent of commercial fishing activities suggests that fisheries are also a substantial source of risk. Vessel-strike risk maps indicate the relative extent of exposure of gray (and other) whales to underwater vessel noise. The number of gray whales killed by ship strikes each year may be in the tens, or perhaps the low hundreds. Additional analyses, including quantitative assessments, are warranted to further clarify the risk of vessel strikes to gray whales.

Apex marine predators and ocean health: Proactive screening of halogenated organic contaminants reveals ecosystem indicator species

Despite decades-long bans on the production and use of certain chemicals, many halogenated organic compounds (HOCs) are persistent and can bioaccumulate in the marine environment with the potential to cause physiological harm to marine fauna. Highly lipid-rich tissue (e.g., marine mammal blubber) functions as a reservoir for HOCs, and selecting ideal indicator species is a priority for retrospective and proactive screening efforts. We selected five marine mammal species as possible indicators for the Southern California Bight (SCB) and applied a non-targeted analytical method paired with an automated data reduction strategy to catalog a broad range of known, known but unexpected, and unknown compounds in their blubber. A total of 194 HOCs were detected across the study species (n = 25 individuals), 81% of which are not routinely monitored, including 30 halogenated natural products and 45 compounds of unknown structure and origin. The cetacean species (long-beaked common dolphin, short-beaked common dolphin, and Risso's dolphin) averaged 128 HOCs, whereas pinnipeds (California sea lion and Pacific harbor seal) averaged 47 HOCs. We suspect this disparity can be attributed to differences in life history, foraging strategies, and/or enzyme-mediated metabolism. Our results support proposing (1) the long- and short-beaked common dolphin as apex marine predator sentinels for future and retrospective biomonitoring of the SCB ecosystem and (2) the use of non-targeted contaminant analyses to identify and prioritize emerging contaminants. The use of a sentinel marine species together with the non-targeted analytical approach will enable a proactive approach to environmental contaminant monitoring.

Bacterial Species Identified on the Skin of Bottlenose Dolphins Off Southern California via Next Generation Sequencing Techniques

The dermis of cetaceans is in constant contact with microbial species. Although the skin of the bottlenose dolphin provides adequate defense against most disease-causing microbes, it also provides an environment for microbial community development. Microbial community uniqueness and richness associated with bottlenose dolphin skin is a function of varying habitats and changing environmental conditions. The current study uses ribosomal DNA as a marker to identify bacteria found on the skin of coastal and offshore bottlenose dolphins off of Southern California. The unique microbial communities recovered from these dolphins suggest a greater microbial diversity on the skin of offshore ecotype bottlenose dolphins, while microbial populations associated with the coastal ecotype include species that are more closely related to each other and that suggest exposure to communities that are likely to be associated with terrestrial runoff.

Migratory behavior of eastern North Pacific gray whales tracked using a hydrophone array

Eastern North Pacific gray whales make one of the longest annual migrations of any mammal, traveling from their summer feeding areas in the Bering and Chukchi Seas to their wintering areas in the lagoons of Baja California, Mexico. Although a significant body of knowledge on gray whale biology and behavior exists, little is known about their vocal behavior while migrating. In this study, we used a sparse hydrophone array deployed offshore of central California to investigate how gray whales behave and use sound while migrating. We detected, localized, and tracked whales for one full migration season, a first for gray whales. We verified and localized 10,644 gray whale M3 calls and grouped them into 280 tracks. Results confirm that gray whales are acoustically active while migrating and their swimming and acoustic behavior changes on daily and seasonal time scales. The seasonal timing of the calls verifies the gray whale migration timing determined using other methods such as counts conducted by visual observers. The total number of calls and the percentage of calls that were part of a track changed significantly over both seasonal and daily time scales. An average calling rate of 5.7 calls/whale/day was observed, which is significantly greater than previously reported migration calling rates. We measured a mean speed of 1.6 m/s and quantified heading, direction, and water depth where tracks were located. Mean speed and water depth remained constant between night and day, but these quantities had greater variation at night. Gray whales produce M3 calls with a root mean square source level of 156.9 dB re 1 μPa at 1 m. Quantities describing call characteristics were variable and dependent on site-specific propagation characteristics.

Phenotypic variation in dorsal fin morphology of coastal bottlenose dolphins (Tursiops truncatus) off Mexico

Geographic variation in external morphology is thought to reflect an interplay between genotype and the environment. Morphological variation has been well-described for a number of cetacean species, including the bottlenose dolphin (Tursiops truncatus). In this study we analyzed dorsal fin morphometric variation in coastal bottlenose dolphins to search for geographic patterns at different spatial scales. A total of 533 dorsal fin images from 19 available photo-identification catalogs across the three Mexican oceanic regions (Pacific Ocean n = 6, Gulf of California n = 6 and, Gulf of Mexico n = 7) were used in the analysis. Eleven fin shape measurements were analyzed to evaluate fin polymorphism through multivariate tests. Principal Component Analysis on log-transformed standardized ratios explained 94% of the variance. Canonical Discriminant Function Analysis on factor scores showed separation among most study areas (p < 0.05) with exception of the Gulf of Mexico where a strong morphometric cline was found. Possible explanations for the observed differences are related to environmental, biological and evolutionary processes. Shape distinction between dorsal fins from the Pacific and those from the Gulf of California were consistent with previously reported differences in skull morphometrics and genetics. Although the functional advantages of dorsal fin shape remains to be assessed, it is not unlikely that over a wide range of environments, fin shape may represent a trade-off among thermoregulatory capacity, hydrodynamic performance and the swimming/hunting behavior of the species.

Newly Identified DDT-Related Compounds Accumulating in Southern California Bottlenose Dolphins

Nontargeted GC×GC-TOF/MS analysis of blubber from 8 common bottlenose dolphins (Tursiops truncatus) inhabiting the Southern California Bight was performed to identify novel, bioaccumulative DDT-related compounds and to determine their abundance relative to the commonly studied DDT-related compounds. We identified 45 bioaccumulative DDT-related compounds of which the majority (80%) is not typically monitored in environmental media. Identified compounds include transformation products, technical mixture impurities such as tris(chlorophenyl)methane (TCPM), the presumed TCPM metabolite tris(chlorophenyl)methanol (TCPMOH), and structurally related compounds with unknown sources, such as hexa- to octachlorinated diphenylethene. To investigate impurities in pesticide mixtures as possible sources of these compounds, we analyzed technical DDT, the primary source of historical contamination in the region, and technical Dicofol, a current use pesticide that contains DDT-related compounds. The technical mixtures contained only 33% of the compounds identified in the blubber, suggesting that transformation products contribute to the majority of the load of DDT-related contaminants in these sentinels of ocean health. Quantitative analysis revealed that TCPM was the second most abundant compound class detected in the blubber, following DDE, and TCPMOH loads were greater than DDT. QSPR estimates verified 4,4',4″-TCPM and 4,4'4,″-TCPMOH are persistent and bioaccumulative.

Nontargeted biomonitoring of halogenated organic compounds in two ecotypes of bottlenose dolphins (Tursiops truncatus) from the Southern California Bight

Targeted environmental monitoring reveals contamination by known chemicals, but may exclude potentially pervasive but unknown compounds. Marine mammals are sentinels of persistent and bioaccumulative contaminants due to their longevity and high trophic position. Using nontargeted analysis, we constructed a mass spectral library of 327 persistent and bioaccumulative compounds identified in blubber from two ecotypes of common bottlenose dolphins (Tursiops truncatus) sampled in the Southern California Bight. This library of halogenated organic compounds (HOCs) consisted of 180 anthropogenic contaminants, 41 natural products, 4 with mixed sources, 8 with unknown sources, and 94 with partial structural characterization and unknown sources. The abundance of compounds whose structures could not be fully elucidated highlights the prevalence of undiscovered HOCs accumulating in marine food webs. Eighty-six percent of the identified compounds are not currently monitored, including 133 known anthropogenic chemicals. Compounds related to dichlorodiphenyltrichloroethane (DDT) were the most abundant. Natural products were, in some cases, detected at abundances similar to anthropogenic compounds. The profile of naturally occurring HOCs differed between ecotypes, suggesting more abundant offshore sources of these compounds. This nontargeted analytical framework provided a comprehensive list of HOCs that may be characteristic of the region, and its application within monitoring surveys may suggest new chemicals for evaluation.