UK dolphin and porpoise conservation strategy: technical report

Section 2 – Vulnerability Assessment and Scores

Vulnerability Assessment

6. The vulnerability assessment adopted in this strategy consists of two components: sensitivity to pressure and exposure to the pressure. Together (Figure 1) they indicate the vulnerability of the species to impact at the population scale. The assessment is made at the UK scale but, where applicable, issues that might be locally/regionally significant are presented in more detail in Table 4.

7. Table 1 (below) gives a summary of vulnerability scores by species for UK waters and the confidence in that score. This is split by the type of pressure and the activities which give rise to these pressures. The various combinations of species, pressures and activities presented in Table 1 have been assessed and vulnerability scored using the following system:

• L = shows species and pressure-activity combinations for which vulnerability was assessed to be low
• M = shows species and pressure-activity combinations for which vulnerability was assessed to be medium
• H = shows species and pressure-activity combinations for which vulnerability was assessed to be high

8. Superscripts denote a ‘low’ confidence in the vulnerability score and are explained in more detail below the table.

Confidence

9. The confidence in the resulting vulnerability score has been assessed, and scored, using the confidence decision tree (Figure 2).

10. The confidence in the vulnerability assessment is fundamentally based on the available evidence; against which we judge whether or not the UK population of a species is impacted by a pressure.

11. The scoring is derived from a consideration of the available evidence demonstrating a species vulnerability to a pressure. Confidence has been scored as:

• L* = low because of contradictory evidence
• L = low
• M = moderate
• H = high

12. More detail on the confidence decision tree, sources of evidence and a table including the evidence used for this strategy is in Section 4 and Table 4 of this document.

13. Confidence in the vulnerability has been considered with regards to the actual impact of each pressure/activity on a species, driven by the available evidence (literature and monitoring data).

14. In the absence of evidence about the impact, the confidence in the vulnerability outcome would not necessarily be low if there is good evidence of the exposure. The level of confidence in the exposure is an important consideration if the pressure/species vulnerability outcomes are to be appropriately prioritised for action.

Table 1: Summary of UK vulnerability scores by species

	Pressure: Removal of non-target species (i.e. bycatch or entanglement)
	Creeling and Potting				Drift net fishing				Trawling and purse seine				Set (fixed) net
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	H	M	M∞	L*	H	L	L	M	H	M	M$	L*	H	M	M	H
Common dolphin	H	M	M∞	L*	H	L	L	M	H	M	M	H	H	M	M	H
Atlantic white-sided dolphin	H	L	L	H	H	L	L	H	H	M	M	M	H	M	M†	L
White-beaked dolphin	H	M	M∞	L*	H	L	L	M	H	M	M	M	H	M	M	M
Bottlenose dolphin (offshore)	H	L	L	H	H	L	L	H	H	M	M$	L*	H	M	M	M
Bottlenose dolphin (coastal)	H	M	M∞	L*	H	L	L	M	H	M	M	M	H	M	M	M
Risso’s dolphin	H	M	M∞	L*	H	L	L	M	H	M	M	M	H	M	M	M
Long-finned pilot whale	H	L	L	H	H	L	L	H	H	M	M	M	H	M	M	M
Killer whale	H	M	M	M	H	L	L	H	H	L	L	H	H	L	L	H
Minke whale	H	M	M	M	H	L	L	H	H	L	L	H	H	L	L	H

Monitoring of bycatch has focused on set nets and until recently, pelagic trawls. There is limited monitoring of drift nets in the current UK monitoring scheme and there has been limited targeted at-sea monitoring of creels

∞ Bycatch events in creels and pots are very rare, which suggests that individuals may be able to avoid them.

^$ Monitoring bycatch of harbour porpoises and offshore bottlenose dolphins, in pelagic trawls, has shown this gear to be low risk to these species.

† Monitoring of set nets tends to focus on waters off southwest England, therefore evidence of bycatch in more northern species and gear is unknown.

	Pressure: Acoustic disturbance
	Cumulative impacts of acoustic disturbance				Seismic/geophysical surveys				Underwater explosions				Pile driving
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	H	M∞	L	M	L	L	M	M	L	L	M	M	L	L	M
Common dolphin	M	H	M∞	L	M	L	L	M	M	L	L	M	M	L	L	H
Atlantic white-sided dolphin	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	M	H
White-beaked dolphin	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	L	M
Bottlenose dolphin (offshore)	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	L	H
Bottlenose dolphin (coastal)	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	L	M
Risso’s dolphin	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	L	M
Long-finned pilot whale	M	H	M∞	L	M	L	L	M	M	L	L	M	M	L	L	H
Killer whale	M	H	M∞	L	M	L	L	M	M	L	L	H	M	L	L	H
Minke whale	M	H	M∞	L	M	L	L	M	M	L	L	M	M	L	L	M

Sound introduced in the marine environment by human activities is one of the key areas of concern with regards to potential detrimental effects. Whilst the vulnerability to an activity may be low, when multiple operations and/or different activities occur at the same time, or over an extended period, the impact is likely to be greater.

∞The impact of this sound on fecundity and survival is not well understood and there is a lack of evidence, particularly when multiple sound sources act cumulatively.

	Pressure: Acoustic disturbance
	Operational offshore windfarms				Operational oil and gas platforms				Acoustic Deterrent Devices$				Fish finders and depth sounders†
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	L	L	L∞	M	L	L	L∞	M	M	L	L	M	L	H	L	M
Common dolphin	L	L	L∞	H	L	L	L∞	H	M	L	L	M	L	H	L	M
Atlantic white-sided dolphin	L	L	L∞	H	L	L	L∞	M	M	L	L	H	L	H	L	M
White-beaked dolphin	L	L	L∞	M	L	L	L∞	M	M	L	L	M	L	H	L	M
Bottlenose dolphin (offshore)	L	L	L∞	H	L	L	L∞	M	M	L	L	H	L	H	L	M
Bottlenose dolphin (coastal)	L	L	L∞	M	L	L	L∞	M	M	L	L	M	L	H	L	M
Risso’s dolphin	L	L	L∞	M	L	L	L∞	M	M	M	M	M	L	H	L	M
Long-finned pilot whale	L	L	L∞	H	L	L	L∞	M	M	L	L	H	L	L	L	M
Killer whale	L	L	L∞	H	L	L	L∞	M	M	L	L	M	L	H	L	M
Minke whale	L	L	L∞	M	L	L	L∞	M	M	L	L	M	L	H	L	M

∞ Noise from operational platforms is not thought to be a significant concern.

^$ Evidence for the effect of permanently placed ADDs associated with aquaculture is limited but has the potential to affect movement patterns and may be locally significant. Disturbance impacts have been demonstrated for some species. ADDs are also used as mitigation prior to offshore construction and for ordnance detonation.

†Fish finders and depth sounders occur on almost all vessels.

	Pressure: Acoustic disturbance
	Pingers				Mining and dredging activities				Vessel noise				Military activity and sonar
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M
Common dolphin	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M
Atlantic white-sided dolphin	M	L	L∞	H	M	L	L$	H	M	L	L	H	M	L	L^	M
White-beaked dolphin	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M
Bottlenose dolphin (offshore)	M	L	L∞	H	M	L	L$	H	M	L	L	M	M	L	L^	M
Bottlenose dolphin (coastal)	M	L	L∞	M	M	L	L$	M	M	M	M†	M	M	L	L^	M
Risso’s dolphin	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M
Long-finned pilot whale	M	L	L∞	H	M	L	L$	H	M	L	L	H	M	L	L^	M
Killer whale	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M
Minke whale	M	L	L∞	H	M	L	L$	M	M	M	M†	M	M	L	L^	M

∞ Pingers are used to alert animals to the presence of nets to reduce bycatch risk. Evidence shows they can be effective for some species. Pingers are currently used only on gillnet vessels >12m in length, which is a small proportion of the UK gillnet fleet.

^$Noise emitted during dredging operations is broadband and unlikely to cause damage to marine mammal auditory systems, but masking and behavioural changes are possible.

^†Behavioural reactions have been observed in response to vessels. Vulnerability is highest in areas of busy shipping lanes.

^{^}Overall low vulnerability across UK but locally/regionally high at certain times when operations are occurring.

	Pressure: Physical Disturbance
	Scientific studies (e.g. tagging, photo ID, biopsy)				Recreation and wildlife tourism$
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	L	L∞	H	M	L	L	H
Common dolphin	M	L	L∞	H	M	L	L	M
Atlantic white-sided dolphin	M	L	L∞	H	M	L	L	H
White-beaked dolphin	M	L	L∞	H	M	L	L	H
Bottlenose dolphin (offshore)	M	L	L∞	H	M	L	L	H
Bottlenose dolphin (coastal)	M	L	L∞	H	M	M	M	H
Risso’s dolphin	M	L	L∞	H	M	L	L	H
Long-finned pilot whale	M	L	L∞	H	M	L	L	H
Killer whale	M	L	L∞	H	M	M	M	M
Minke whale	M	L	L∞	H	M	L	L	M

^∞ Limited in UK waters, with certain activities requiring licensing. Some work is taking place in UK waters, which is predominantly photo ID. Disturbance from research vessels is a small component of all vessel traffic.

^$ There are multiple studies indicating behavioural impacts concerning tourist boat interactions with cetacean species. This may be locally significant.

	Pressure: Change to habitat
	Barrier to movement				Change/removal of supporting habitat				Reduction in availability of prey				Localised temperature change
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	L	L∞	H	M	L	L$	M	M	M	M	H	L	L	L^	H
Common dolphin	M	L	L∞	H	M	L	L$	M	M	M	M	H	L	L	L^	H
Atlantic white-sided dolphin	M	L	L∞	H	M	L	L$	H	M	M	M	M	L	L	L^	H
White-beaked dolphin	M	L	L∞	H	M	L	L$	M	M	M	M	M	L	L	L^	H
Bottlenose dolphin (offshore)	M	L	L∞	H	M	L	L$	H	M	M	M	M	L	L	L^	H
Bottlenose dolphin (coastal)	M	L	L∞	H	M	L	L$	M	M	M	M	M	L	L	L^	H
Risso’s dolphin	M	L	L∞	H	M	L	L$	H	H	M	M	M	L	L	L^	H
Long-finned pilot whale	M	L	L∞	H	M	L	L$	H	M	M	M†	L*	L	L	L^	H
Killer whale	M	L	L∞	H	M	L	L$	H	M	M	M	M	L	L	L^	H
Minke whale	M	L	L∞	H	M	L	L$	M	M	M	M	M	L	L	L^	H

∞ Evidence of barrier to movement it very limited but may be locally significant.

^$ Very little evidence of changes to or removal of supporting habitat, but may be locally significant.

^† Changes in prey availability due to competition with other marine predators, fishing or climate change, may have an impact. Post mortem examinations can provide some evidence of the occurrence of starvation, but not cause and effect. For some species, starvation has never been recorded as a cause of death in post mortem examinations.

^{^} Local water temperature changes, for example cooling water discharges from power stations, is unlikely to have population level effects due to its localised nature.

	Pressure: Physical injuries/mortality
	Vessel strikes				Collision with renewable energy devices				High energy acoustic events (e.g. removal of unexploded ordnance)
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	H	M	M∞	H	H	L	L$	H	H	L	L†	H
Common dolphin	H	M	M∞	H	H	L	L$	H	H	L	L†	H
Atlantic white-sided dolphin	H	L	L	M	H	L	L$	H	H	L	L†	H
White-beaked dolphin	H	M	M∞	M	H	L	L$	H	H	L	L†	H
Bottlenose dolphin (offshore)	H	M	M∞	M	H	L	L$	H	H	L	L†	H
Bottlenose dolphin (coastal)	H	M	M∞	M	H	L	L$	H	H	L	L†	H
Risso’s dolphin	H	M	M∞	M	H	L	L$	H	H	L	L†	H
Long-finned pilot whale	H	L	L	M	H	L	L$	H	H	L	L†	H
Killer whale	H	M	M∞	M	H	L	L$	H	H	L	L†	H
Minke whale	H	M	M∞	M	H	L	L$	H	H	L	L†	H

∞ Vessel strike is recorded as a cause of death from some species, although it is not of high concern. There is no requirement for vessels to report strikes occurring at sea and carcasses may not wash up on land.

^$ Limited wet renewable devices in place and limited understanding or evidence of impact, but potentially may be locally significant.

^† Loud noises can result in injury to cetaceans, particularly to their hearing, although there is very little evidence.

	Pressure: Marine pollution
	Oil pollution				Chemical pollution (e.g. PCBs Butyl tins, PAHs, Radionuclides, heavy metals)				Plastic pollution (ingestion)				Entanglements in marine litter and ghost nets
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	L	L∞	H	H	H	H$	H	H	L	L†	H	H	L	L^	H
Common dolphin	M	L	L∞	H	H	H	H$	H	H	L	L†	H	H	L	L^	H
Atlantic white-sided dolphin	M	L	L∞	H	H	M	M	M	H	L	L†	M	H	L	L^	M
White-beaked dolphin	M	L	L∞	H	H	H	H$	M	H	L	L†	M	H	L	L^	M
Bottlenose dolphin (offshore)	M	L	L∞	H	H	M	M	M	H	L	L†	M	H	L	L^	M
Bottlenose dolphin (coastal)	M	L	L∞	H	H	H	H$	H	H	L	L†	M	H	L	L^	M
Risso’s dolphin	M	L	L∞	H	H	H	H$	M	H	L	L†	M	H	L	L^	M
Long-finned pilot whale	M	L	L∞	H	H	M	M	M	H	L	L†	M	H	L	L^	M
Killer whale	M	L	L∞	H	H	H	H$	H	H	L	L†	M	H	L	L^	M
Minke whale	M	L	L∞	H	H	H	H$	M	H	L	L†	M	H	L	L^	M

∞ No records of any spills in which a cetacean was affected in the UK. Globally there are few examples of oil spills having direct negative effects on cetaceans.

^$ Impacts of contaminants on cetaceans is well documented for some species, including impacts on immune system and reproduction. Limited or no data for some species.

^† Plastic ingestion is monitored through post-mortem examination of stranded animals. There have been post-mortems of all species within this strategy, but for some the sample sizes are too small.

^{^} Very little evidence of impacts in UK waters from strandings data.

	Pressure: Marine pollution
	Eutrophication, sewage pathogens
Species	Sensitivity	Exposure	UK vulnerability score	Confidence in score
Harbour porpoise	M	L	L∞	H
Common dolphin	M	L	L∞	H
Atlantic white-sided dolphin	M	L	L∞	M
White-beaked dolphin	M	L	L∞	M
Bottlenose dolphin (offshore)	M	L	L∞	M
Bottlenose dolphin (coastal)	M	L	L∞	M
Risso’s dolphin	M	L	L∞	M
Long-finned pilot whale	M	L	L∞	M
Killer whale	M	L	L∞	M
Minke whale	M	L	L∞	M

∞ Nutrient enrichment in areas of agriculture, aquaculture or sewage may pose a threat to an individual cetacean, but the consequence of exposure to the population is unlikely to be a concern