Multiple Pressures negatively impact marine mammals
There are numerous pressures on marine mammals across the North-East Atlantic caused by human activities. Their relative importance varies between species and OSPAR Regions, depending on the extent of the respective activities and the sensitivity of the species in its Region.
Climate change will affect marine mammals throughout the OSPAR Maritime Area, including directly on abundance and distribution, and also indirectly; details are provided in the Climate Change section.
The main other pressures affecting marine mammals are fishery (incidental by-catch in fishing gears, reduction in prey density, habitat loss) and shipping activities (mortality / injury due to collision with ships), disturbance (including tourism, shipping and wind farm activities), anthropogenic sound (including military sonar and pile-driving), litter (ingestion of plastics), man-made substances (e.g. bioaccumulation of toxic contaminants) and physical loss or disturbance of the sea-bed (which affects the prey of marine mammals). Seals are also under pressure on land (when breeding or moulting) from disturbance (e.g., tourism or coastal development) and habitat loss due to land reclamation.
Trends in the pressures are difficult to elaborate, but trends in the human activities exerting them could provide a suitable proxy for trends in the pressures themselves.
Human activities are creating multiple pressures, which have been shown to have negative impacts on marine mammals at both individual and population level (Butterworth et al., 2017; Avila et al. 2018). These impacts range from increased stress and higher energetic costs, through sub-lethal effects on reproduction and immune function, to mortality and therefore declining populations (Hammond et al., 2008).
These pressures fall under several MSFD headings, as shown in square brackets [ ].
OSPAR acts as a coordination platform in the North-East Atlantic for the regional implementation of the EU Marine Strategy Framework Directive (MSFD) that aims to achieve a Good Environmental Status (GES) in European marine environments, as well as for the coordination of other national frameworks. The characteristics of GES are determined by the individual EU member states, based on criteria elements, threshold values and methodological standards set regionally or at EU level.
Norwegian, Icelandic, United Kingdom, Greenlandic and Faroese marine areas are not covered by the MSFD.
Pressures are ranked comparatively. The number in brackets indicates the comparative ranking.
(1) Selective extraction of species, including non-target catches [Biological]: Fish and shellfish harvesting, at either professional or recreational level, can result in fisheries by-catch as well as entanglement, causing injury or mortality of marine mammals (Silva et al., 2011; Reeves et al., 2013). By-catch is widely considered to be the primary human-induced cause of mortality in marine mammals (Lent and Squires, 2017).
Marine mammals may be at risk of becoming incidentally by-catch depending on their behaviour and the fishing gears being used to harvest fish and shellfish. For example, static gears such as gillnets are prone to entangle harbour porpoises and seals. Pelagic pair trawlers have been identified as inducing by-catch of common dolphins, and creel pots can result in entanglement and by-catch, particularly of large baleen whales such as minke whales (ICES 2019).
(2) Input of anthropogenic sound (impulsive, continuous) [Substances, litter and energy]: Activities that emit anthropogenic noise into the environment include shipping, seismic surveys, tourism activities, aquaculture, military operations, dredging, mineral extraction, and the construction and operation of devices such as renewable energy turbines and water pumps, as well as oil and gas platforms. Underwater noise can be divided into two forms of pressure:
- Loud impulsive noise, typically from sonar, seismic surveys, pile-driving and explosions (Gordon et al., 2003);
- Continuous noise, typically offshore renewable energy turbines, water pumps, shipping and acoustic deterrent devices (Erbe et al., 2018).
Anthropogenic noise is a form of energy that can have behavioural and physiological impacts on marine mammals. The behavioural impacts can be changes in resting, breathing, diving patterns and vocalizations, changes in spatial relationships, and avoidance behaviour. Anthropogenic noise masking may interfere with social interaction, communication and foraging. Physiological impacts can be temporal threshold shift (TTS) or permanent threshold shift (PTS) (Saunders and Dooling, 2018). In the worst case, underwater noise can lead to injury or even death (Weilgart, 2007).
Input from noise and the pressure on marine mammals is linked with environmental impacts in the Underwater Noise Thematic Assessment .
Dead porpoise. © Shutterstock
(3) Disturbance of species (e.g. where they breed, rest and feed) due to human presence [Biological]: Disturbance leads to (temporary) habitat loss or deterioration, displacement, lost energy acquisition and higher energy expenditure, with consequences for survival and reproduction, in marine mammals. Human activities that disturb marine mammal species, due to their presence, include: (i) coastal development for physical restructuring of either rivers, coastline or seabed (water management), tourism and leisure infrastructure, nuclear energy, land claim (Nelms et al., 2021); (ii) offshore constructions for the production of energy or extraction of non-living resources (with offshore wind farms occupying a large surface area) (Bailey et al., 2014; Copping et al., 2020); (iii) maritime traffic in any form (including fisheries and renewable energy) (Schoeman et al., 2020); (iv) military operations (Siebert et al., 2022); and (v) tourism and leisure activities (examples: recreational boating, sailing, wind-surfing, kite-surfing, coastal swimming, hiking) (Machernis et al., 2018).
(4) Extraction of, or mortality/injury to, wild species (other activities) [Biological]: Collisions with vessels and tourism and leisure activities (e.g., whale- watching boats, recreational vessels, jet skis), lead to injury/mortality and can remove individuals from the population and the ecosystem (Panigada et al., 2006; Van Waerebeek et al. 2007; Evans et al. 2011, Schoeman et al., 2020). The expansion of tidal energy production has the potential to injure marine mammals through collisions with moving components of turbines (Wilson et al., 2007, Hastie et al., 2018, Onoufriou et al., 2019; 2021). Rotor speeds are often relatively high, three times the collision speeds thought to kill large cetaceans during ship strikes (Vanderlaan and Taggart, 2007).
(5) Extraction of, or mortality/injury to, wild species (by commercial and recreational fishing) [Biological]: The removal of target species of fish and shellfish can cause reduced prey availability, affecting marine mammal abundance and health. In some countries in the OSPAR Regions, marine mammals are also still the targets of either commercial or traditional whaling and hunting, which leads to mortality (Clapham and Baker, 2009; Jog et al., 2022).
Whale struck by a boat. © Tyler Ingram
(6) Input of other substances (e.g., synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, atmospheric deposition, acute events [Substances, litter and energy]: Synthetic and non-synthetic substances can cause physical harm to marine mammals. These substances can be spilt into the marine environment during activities such as oil and gas extraction, non-renewable energy generation, shipping, waste disposal, agriculture and mineral extraction (Das et al., 2003). Marine mammals are often predators at the top of the food chain, indicating that they are sensitive to bioaccumulation, whereby toxic contaminants build up throughout the food chain, with the highest concentration found in its top predators (Moore, 2008). For example:
- Polychlorinated biphenyls (PCBs) can lead to reduced reproduction success or complete failure of the reproductive organs (Stuart-Smith and Jepson, 2017). See: OSPAR Pilot Assessment of Status and Trends of Persistent Chemicals in Marine Mammals .
- Mercury (Hg) can cause cancer, decreased learning abilities and damage to the nervous system (Kershaw and Hall, 2019).
- Lead (Pb) is highly toxic and can cause cancer and decreased learning ability (Das et al., 2003).
- Cadmium (Cd) can also cause cancer and further reduces bone strength (Das et al., 2003).
- Other, novel, persistent organic pollutants, such as polybrominated diphenyl ethers (PBDEs) or per- and polyfluoroalkyl substances (PFASs), can be found in high concentration in marine mammals. While they have not yet been attributed as the cause of decreased fecundity in those species, they have known effects on other species (Rotander et al., 2012; Fair and Houde, 2018).
- This all impacts the abundance, demography and distribution of marine mammals (Desforges et al., 2016).
Inputs from other substances and their pressures on marine mammals are closely linked with environmental impacts in the Hazardous Substances Thematic Assessment .
(7) Input of litter (solid waste matter, including micro-sized litter) [Substances, litter and energy]: The introduction of litter, whether land-based (e.g. rivers, industrial sources, tourism) or marine-based (e.g. shipping, fishing, aquaculture) can cause ingestion and entanglement leading to injury or death (Collard and Ask, 2021). For example, if a marine mammal is caught in lost fishing nets, the result can be injuries, reduced movement or even drowning (Simmonds, 2017). Input of litter into the environment can also affect the health and biological fitness of marine mammals (Fossi et al., 2018; Senko et al., 2020).
The input of litter and the pressure on marine mammals is linked with the environmental impacts of the Marine Litter Thematic Assessment .
(8) Physical loss (due to permanent change of seabed substrate or morphology and to extraction of seabed substrate) [Physical]: Loss of haul-out sites and the associated deterioration of habitat, particularly from coastal developments, coastal and flood defences and land claim, have consequences for the reproduction, distribution and habitat use of seals (Kovacs et al., 2008; Baker et al., 2020). Loss of marine habitats due to the installation of infrastructure and the associated vessel activity can impact all marine mammals (Culloch et al., 2016; Benhemma-Le Gall et al., 2021).
Lost fishing gear. © Shutterstock
(9) Physical disturbance to seabed (temporary or reversible) [Physical]: Bottom-trawling fisheries, extraction of minerals, land claim, the construction of infrastructures (e.g. oil/gas/renewables) and the laying of cables and pipelines reduce prey availability and result in habitat loss (Todd et al., 2015).
(10) Input of other forms of energy (including electromagnetic fields, light and heat) [Substances, litter and energy]: Electricity and communications cables can create electromagnetic fields (EMF). Cetaceans can sense EMFs and use the earth’s geomagnetic field to navigate during their migration. Therefore, marine mammals could be sensitive to minor changes in the geomagnetic field. Depending on the persistence and magnitude of the EMF, the effects may include temporary change in swim direction, detours in migration routes or alteration of hunting behaviour (Torres, 2017). The result can be habitat loss and a change in distribution (Gill et al., 2014; Kremers et al., 2014; Ferrari, 2017).
(Unranked) Several impacts of anthropogenic climate change exert pressures on marine mammals in the North-East Atlantic. The changes in environmental conditions driven by climate change are likely to be exacerbating pressures, as follows:
- Extraction of, or mortality/injury to, wild species (other activities) [Biological];
- Physical loss (due to permanent change of seabed substrate or morphology and extraction of seabed substrate) [Physical];
- Disturbance of species (e.g. where they breed, rest and feed) due to human presence [Biological];
- Selective extraction of species, including non-target catches [Biological];
- Input of anthropogenic sound (impulsive, continuous) [Substances, litter and energy];
- Input of other substances (e.g. synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, atmospheric deposition, acute events [Substances, litter and energy].
The impacts of human-induced climate change are described in more detail in the dedicated Climate Change section.
Climate change and the pressures on marine mammals are closely linked with environmental impacts in the Underwater Noise Thematic Assessment .
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