Marine Birds Thematic Assessment

Pressures on marine birds

Human activities exert numerous pressures on marine birds across the North-East Atlantic. Their relative importance varies greatly between species and OSPAR Regions, depending on the extent of the respective activities and the sensitivity of the species.

Climate change has pervasive and fundamental implications for marine birds throughout the OSPAR region, including indirect effects on food supply and direct effects on bird physiology; given its importance the effects are detailed in a dedicated Climate Change section. 

The main other pressures affecting marine birds, according to the main reporting sources, are direct disturbance from various activities (including recreation, shipping and wind farm activities), fisheries impacts (including extraction of forage fish such as sandeels and mortality from incidental by-catch in fishing gear), physical disturbance of the seabed (e.g. bottom-trawling fisheries which affect the habitats of birds’ prey) and mortality caused by collisions with offshore structures such as wind turbines. Breeding birds are under pressure from invasive non-indigenous mammalian predators and from habitat loss due to land reclamation. The ranking in the Pressures section is based only on the information available from main reporting sources (OSPAR, EU Marine Strategy Framework Directive 2008/56/EC (MSFD), EU Birds Directive (Directive 79/409/EEC)). The confidence in such assessment was considered low because of various information gaps identified in the reporting sources considered.

A more detailed ranking of the importance of pressures affecting marine birds is provided in the bow-tie section based on analysis of "Exposure" (comprising spatial and temporal overlap) and "Consequence" (comprising pressure persistence, likely impact and ecosystem recovery potential), see: Cumulative Effects . Some differences in the relative rankings of individual pressures were highlighted, and a caveat inserted, in the bow-tie section. 

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.

Owing to the large number of marine bird species, which use various kinds of marine habitat and belong to five different feeding guilds, it is not straightforward to identify the most important anthropogenic pressures acting on this ecosystem component. In order to investigate these pressures in the OSPAR Maritime Area, various sources of reporting were reviewed. As reporting methods are not consistent among Contracting Parties and EU Member States, respectively, and because different terminology was used for the pressure categories, it is challenging to aggregate information about pressures across countries and conventions at the same level. Here, all information has been translated into the pressure categories used in the MSFD.

In order to identify the main pressures impacting marine birds in the North-East Atlantic, the following reporting sources were investigated:

• OSPAR MPA database;
• MSFD Art 8 reporting; 
• MSFD Art 16 reporting; 
• Birds Directive Reporting, Art 12.

For each reporting source, the relative importance of individual pressures impacting marine birds was assessed and assigned to a qualitative category (high-medium-low-no importance). An overall assessment for each pressure was then obtained by averaging the relative importance ranks obtained from all reporting sources.

Details of this analysis and confidence gaps are described in this Supplementary Material .

Although the picture can vary slightly depending on the source, it is generally apparent that disturbance and additive mortality are the most important pressures. While disturbance is caused by various activities, additive mortality mostly refers to incidental by-catch in fishing gear and hunting (Table P.1). A number of pressures were found to be of medium importance, with physical loss of habitat, physical disturbance of the seabed, input of anthropogenic sound and the occurrence of non-indigenous species (here mostly invasive mammalian predators in breeding colonies) also of high importance in one or other source. A full overview of the levels of importance shown by this analysis is given in Table P.1. It should be noted that this table does not consider new and emerging pressures (or recent step-changes to the prevalence of existing ones) such as the Highly Pathogenic Avian Influenza (HPAI). Major impacts on seabird species from HPAI were observed in 2021 and 2022, including also species that were unaffected in previous outbreaks. 

The overall confidence in the assessment of relative importance of individual pressures is considered low. Various gaps were highlighted in the four reporting sources analysed, ranging from (often severe) uncertainties regarding the pressure categories used, and incomplete coverage of OSPAR Regions, to limited details / coverage of the bird species reported. For details see Supplementary Material .

Table P.1: Pressures by MSFD pressure category showing relative importance as derived from sources related to OSPAR MPAs, MSFD and Birds Directive. * Owing to the different terminologies used, incidental by-catch can be placed in different pressure categories, and therefore the MSFD category “Selective extraction of species” is not included in the overall assessment.

Summary of pressures on marine birds

Various effects arising from human-induced climate change exert pressure on marine birds world-wide; these are observed also in the North-East Atlantic. A section dedicated to this topic describes the connections in more detail: Climate Change . The pressures from climate change in the OSPAR region are exacerbated by the following additional pressures:

Disturbance of species (e.g. where they breed, rest and feed) due to human presence [Biological]:
Disturbance to marine birds can be caused by visual stimuli and above-water noise and the disorientation caused by the introduction of artificial light. Important examples of sources of visual disturbance are recreation, shipping, fisheries and windfarm activities. Disturbance at sea can displace birds from foraging areas or other important areas, leading to (temporary) habitat loss, higher energy expenditure (flights for food, migration distances), with consequences for survival and reproduction (including carry-over effects from non-breeding to breeding season) (Burger et al., 2019; van der Kolk, 2021; Krüger, 2016; Fliessbach et al., 2019; Linssen et al., 2019; Mendel et al., 2019; Peschko et al., 2020).  

Lighting can disorient or displace sensitive species. Birds can be drawn to lighted vessels and structures offshore and may become disoriented and collide with them. The young of species that fledge at night, such as Atlantic puffin, Manx shearwater and storm-petrels, are particularly susceptible to disorientation caused by artificial light on land and offshore (Rodríguez et al., 2017, 2022; Ryan et al., 2021).

Disturbance of adult birds at breeding sites can leave chicks and eggs vulnerable to chilling or predation. Continued disturbance at nesting sites can lead to reduced breeding success or desertion (see e.g., Buxton et al., 2017, for airborne anthropogenic sound effects). 

Extraction of, or mortality / injury to, wild species (by commercial and recreational fishing and other activities) [Biological]:  

Selective extraction of species, including non-target:  

Seabird by-catch: Seabirds and some waterbirds are accidentally caught and killed in fishing gear (commercial, recreational or artisanal) in the OSPAR Maritime Area. (Oliveira et al., 2015; Christensen-Dalsgaard et al., 2019; Northridge et al., 2020), Pilot Assessment of Marine Bird Abundance - Non-Breeding Offshore Birds . This can happen when birds are foraging for fish caught in trawls or purse seines or used for bait on longline hooks, or if they enter fixed nets when diving below the sea surface. Gillnets and / or hook gears (hand- and longlines) are reported to be the deadliest fishing gears for marine birds (Pott and Wiedenfeld, 2017; ICES, 2013). Most recorded gillnet by-catch relates to species that undertake plunge or pursuit diving, such as seaducks, auks and shearwaters ((Žydelis et al., 2013; Pott and Wiedenfeld, 2017), but fulmar was the most common by-catch in gillnet fisheries on the Norwegian coast, probably through entanglement while the gillnets were being set (Bærum et al., 2019). Mortality due to incidental by-catch in longlines mainly occurs in birds that are feeding at the surface - species such as shearwaters, fulmar, gannet and gulls (Anderson et al., 2011; Dunn and Steel, 2001).

Impacts on the food supply for marine birds: The extraction of fish and invertebrates can reduce the prey available to marine birds through competition for the same species (e.g., intertidal bivalves, sandeels, sprat, and small herring) (Cury et al., 2011). (Food webs Thematic Assessment - Response Section - Case Study). A reduction in available prey can lead to immediate reductions in fitness, which can affect survival and reduce the numbers attempting to breed. If food is scarce during the chick-rearing period, breeding success can also be reduced or whole colonies may fail to produce any young (Camphuysen et al., 2002; Frederiksen et al., 2008, 2013; Cury et al., 2011; Cook et al., 2014; Mitchell et al., 2020; Carroll et al., 2017; Cook et al., 2014; Fayet et al., 2021).

Hunting, egg harvesting and control: All of these directly remove individuals and offspring from marine bird populations (Merkel and Barry, 2008). The hunting and harvesting of eggs and chicks for human consumption is permitted for certain species and regulated in the OSPAR Maritime Area under national and international legislation (Nørrevang, 1986; Trinder, 2016; Murray, 2018). The killing of certain species or the destruction of their nests / eggs is also permitted and regulated to protect other wild birds, to preserve public health and safety or air safety, or to prevent damage to crops or inland fisheries. 

Physical disturbance to seabed (temporary or reversible) [Physical]:
Physical disturbance impacts the feeding habitats of marine birds by reducing prey availability. For example, the construction of infrastructure, aggregate extraction, bottom trawling fisheries, kelp trawling and the laying of cables and pipelines all disturb, reduce and / or remove the benthic fauna (including demersal fish) that serve as bird prey, with consequences for feeding and reproduction (Cook and Burton, 2010; Christensen-Dalsgaard et al., 2020). 

Extraction of, or mortality/injury to, wild species (other activities) [Biological]:

Death or injury by collision above water: Collisions with offshore windfarm turbines / tidal devices, vessels / aircraft and offshore structures such as oil and gas platforms remove individuals from populations and thus cause additive mortality (Busch and Garthe, 2018; García-Barón et al., 2019; Kelsey et al., 2018; Merkel and Johansen 2011; King, 2019; Potiek et al., 2019; Searle et al., 2019). The risk of collision with an obstacle is a function of birds’ flight height in relation to an obstacle and of their ability to avoid it. Offshore wind turbines are becoming the most significant obstacles in some areas. The flight height of some seabirds, particularly large gulls, kittiwake, gannet, cormorant and shag, is such that they could potentially collide with turbines (Furness et al., 2013; Johnston et al., 2014; Mendel et al., 2014; Johnston and Cook, 2016).

Death or injury by collision below water: Diving seabirds such as auks and shag could potentially be injured or killed by collision with tidal stream turbines below the surface (Furness et al., 2012). A lack of information exists regarding the collision risk of seabirds with underwater structures, including wave energy generators (Grecian et al., 2012)

Input or spread of non-indigenous species [Biological]:
The deliberate or accidental introduction of mammal predators to places where they would not naturally occur has had catastrophic impacts on bird populations around the world (see for example Courchamp et al., 2003; Jones et al., 2008; Towns et al., 2006; Dias et al., 2019). Most marine bird species nest on the ground or in burrows, where they are potentially accessible to mammalian predators. Predation of eggs and young birds can cause reductions in breeding success and could lead to the desertion of whole colonies (Mitchell et al., 2004). In the OSPAR Maritime Area, seabird colonies are at risk from introduced non-native predatory mammals such as brown rats, cats and American mink and also from native mammals such as hedgehog, stoat and fox, which have been introduced by humans to offshore islands that they otherwise could not reach unassisted (Stanbury et al., 2017; Mitchell et al., 2018). The presence of invasive native and non-native mammals can limit the amount of safe nesting habitat available and therefore impact the distribution and size of breeding population of marine bird species (e.g., Mitchell et al., 2004; Ewins and Tasker, 1985).

The Non-indigenous Species Thematic Assessment only considers the introduction and spread of marine NIS, which excludes the impacts of mammals on marine birds.

Physical loss (due to permanent change of seabed substrate or morphology and to extraction of seabed substrate) [Physical]:
Loss of nesting sites or intertidal feeding areas is particularly associated with land reclamation and coastal development, coastal nuclear energy power stations, coastal and flood defences, bottom trawling, aggregate extraction and offshore renewables, with consequences for feeding and reproduction among marine birds.

Input of other substances (e.g. synthetic substances, non-synthetic substances, radionuclides) - diffuse sources, point sources, atmospheric deposition, acute events [Substances, litter and energy]:
In bird species, the input of other substances into their environment can cause contamination of the food chain. These substances can be spilt into the marine environment during activities such as oil and gas extraction, non-renewable energy generation, shipping, agriculture and extraction of minerals. Such contamination can take the following forms:

• Polybrominated diphenyl ethers (PBDE) in biota can impact behaviour, learning and hormonal function. 
• Polychlorinated biphenyl (PCB) in biota can cause genotoxic effects, immune suppression, inflammatory response and endocrinal effects. 
• Radionuclides in biota can cause genetic, reproductive, cancerous and acute effects. 

PBDE and PCB both cause reduced reproduction and bioaccumulation in benthic, fish, bird and mammal species (Sagerup et al., 2009; Millow et al., 2015).

Oil can contaminate and adhere to plumage, causing its insulating effect to be lost. This and the ingestion of oil during grooming can lead to the death of affected birds (Jenssen, 1994). The impacts of oil depend upon the timing and location of spills, and are likely to be more severe when they occur around breeding colonies, when birds are highly concentrated.

Inputs of other substances and these pressures on marine mammals are closely linked with environmental impacts in the Hazardous Substances Thematic Assessment .

Input of litter (solid waste matter, including micro-sized litter) [Substances, litter and energy]:
Litter introduced from land and via rivers (e.g., industrial sources, tourism) and directly into the marine environment (e.g., from shipping, fishing, aquaculture) can impact marine birds’ health and also kill them. Surface-feeding seabirds such as fulmars ingest plastics that they mistake for food, and these accumulate in their stomachs (Kühn and Van Franeker, 2020), Plastic Particles in Fulmar Stomachs in the North Sea . Plastic ingestion can lead to the accumulation of endocrine-disrupting compounds in body tissues (Wang et al., 2021) and reduce the space for food in the digestive tract of seabirds, but little is known about the population-level effects for the species inhabiting the OSPAR Maritime Area. Marine birds can become entangled in litter (e.g., discarded fishing gear), often leading to injury or death. This can occur in breeding colonies where some species use litter as nest material, which can then ensnare adults and young and lead to reduced reproductive rates (O'Hanlon et al., 2019). Input of litter into the environment can also cause loss or degradation of breeding and nesting habitats, alterations to suitable foraging habitats, and diseases, all of which affects the abundance of marine birds. 

The input of litter and the pressure on marine birds is linked with environmental impacts in the Marine Litter Thematic Assessment .

Input of anthropogenic sound (impulsive, continuous) [Substances, litter and energy]:
Military operations that produce impulsive noise into the marine environment can have behavioural and physiological impacts on marine birds. 

Underwater noise can also trigger behavioural responses which have potential detrimental effects for marine birds (Anderson Hansen et al., 2020).

In the worst case, underwater noise can lead to injury or even death (insufficient knowledge as yet). 

Input of noise and the pressure on marine birds is linked with environmental impacts in the Underwater Noise Thematic Assessment .

New, emerging and increasing activities and pressures

Large increases in offshore wind infrastructure, especially in Greater North Sea, are projected, owing to the dual imperatives of increased energy security and carbon-reduction. Offshore wind infrastructures can lead to mortality and disturbance (including permanent displacement) in marine birds.

Highly Pathogenic Avian Influenza: Although assessed as relatively low impact in QSR 2023, it has already been seen to have a major impact in 2021 and 2022 (outside the reporting period), and to impact seabird species which in previous outbreaks were unaffected (Rijks et al., 2022).