Spatiotemporal Trends Spanning Three Decades Show Toxic Levels of Chemical Contaminants in Marine Mammals

Abstract

Despite their ban and restriction under the 2001 Stockholm Convention, persistent organic pollutants (POPs) are still widespread and pervasive in the environment. Releases of these toxic and bioaccumulative chemicals are ongoing, and their contribution to population declines of marine mammals is of global concern. To safeguard their survival, it is of paramount importance to understand the effectiveness of mitigation measures. Using one of the world’s largest marine mammals strandings data sets, we combine published and unpublished data to examine pollutant concentrations in 11 species that stranded along the coast of Great Britain to quantify spatiotemporal trends over three decades and identify species and regions where pollutants pose the greatest threat. We find that although levels of pollutants have decreased overall, there is significant spatial and taxonomic heterogeneity such that pollutants remain a threat to biodiversity in several species and regions. Of individuals sampled within the most recent five years (2014–2018), 48% of individuals exhibited a concentration known to exceed toxic thresholds. Notably, pollutant concentrations are highest in long-lived, apex odontocetes (e.g., killer whales ( Orcinus orca ), bottlenose dolphins ( Tursiops truncatus ), and white-beaked dolphins ( Lagenorhynchus albirostris )) and were significantly higher in animals that stranded on more industrialized coastlines. At the present concentrations, POPs are likely to be significantly impacting marine mammal health. We conclude that more effective international elimination and mitigation strategies are urgently needed to address this critical issue for the global ocean health.

Endocrine-Disrupting Chemical Exposure Induces Adverse Effects on the Population Dynamics of the Indo-Pacific Humpback Dolphin

“…PBDEs have been found to induce endocrine disruption of thyroid hormone levels in the blood in gray seal pups when concentrations exceed 1.5 mg/kg lw, and significant positive relationships with testosterone have been observed in coastal and offshore bottlenose dolphins . Exposure to DDTs has been associated with impacts on androgen and corticosteroid homeostasis in common bottlenose dolphins. , PCBs, widely recognized for their toxic impacts, affect thyroid hormone concentration above a threshold of 9 mg/kg lipid. , The elevated burden of EDCs in humpback dolphins may have triggered endocrine disruptions. A notable metabolic pathway for PBDEs involves hydroxylation, aligning with the metabolic route of thyroid hormones .…”

“…PBDE accumulation can potentially induce deleterious consequences, including immune suppression, endocrine disruption, and reproductive toxicity in marine mammals. , Despite a decline in PBDE concentrations in humpback dolphins over recent decades, there is a slight increase in concentrations in calves. Furthermore, there is a significant and positive correlation between annual calf stranding death rates and PBDE concentrations in calves .…”

Population genomics of the white-beaked dolphin (Lagenorhynchus albirostris): Implications for conservation amid climate-driven range shifts

“…Furthermore, this region has been identified as a high- risk area for strong anthropogenic impact from climate change, pollution, and fishing (Davidson et al 2012 ). Populations of white-beaked dolphins on the edge of their southern distribution are therefore likely to be impacted by climate-change associated habitat shifts (Lambert et al 2014 ), in addition to numerous direct threats (Stone and Tasker 2006 ; Bearzi et al 2006 ; Reeves et al 2013 ; Galatius, Bossi et al 2013 ; Williams et al 2023 ). A recent northward-shift in their distribution based on strandings data (IJsseldijk et al 2018 ; Williamson et al 2021 ) and predictive habitat modelling (Lambert et al 2014 ) is indicative of an ongoing contraction of suitable habitat around the British Isles and North Sea.…”

“…As SSTs in the North Sea are projected to further increase, more frequently exceeding the suitable threshold for white-beaked dolphins, the species risks facing a considerable northward-shift in this region (Dieterich et al 2019 ; Evans and Waggitt 2020 ; Johns et al 2003 ; Lambert et al 2014 ). Additionally, the species faces numerous direct anthropogenic pressures, such as bycatch in commercial fisheries (Reeves et al 2013 ), local unregulated harvesting (Takekawa 2000 ; Piniarneq 2021 ), prey depletion (Jackson et al 2001 ), anthropogenic noise and chemical contaminants (Stone and Tasker 2006 ; Galatius, Bossi et al 2013 ; Williams et al 2023 ). In order to understand the consequences of predicted habitat shifts and other threats, it is necessary to investigate how white-beaked dolphins are connected across their range.…”

Whales and dolphins of the Adriatic Sea

“…Cetaceans are long-lived mammals positioned at the top of marine food webs, making them susceptible to the accumulation and effects of chemical contaminants (Jepson et al, 2016;Williams et al, 2023). These effects can be either direct or indirect, and may result in impacts at the individual, community or population level (Reijnders et al, 1999).…”