Biodiversity and Ecosystem (EO 1)

Common Indicator 4: Population abundance of selected species - Marine Mammals

Geographical scale of the assessment:
Regional, Mediterranean Sea
Contributing countries:
Mid-Term Strategy (MTS) Core Theme:
2-Biodiversity and Ecosystems
Ecological Objective:
EO1: Biological diversity is maintained or enhanced. The quality and occurrence of coastal and marine habitats and the distribution and abundance of coastal and marine species are in line with prevailing physiographic, hydrographic, geographic and climatic conditions.
IMAP Common Indicator:
Common Indicator 4 (CI4): Population abundance of selected species (related to marine mammals)
Indicator Assessment Factsheet Code:

GES Definition

  • For cetaceans: The species population has abundance levels allowing to qualify to Least Concern Category of IUCN.
  • For Monk Seal: Number of individuals by colony allows to achieve and maintain a favourable conservation status10.

GES Targets:

  • State: (for cetaceans) Populations recover towards natural levels.
  • State:(for monk seal) Continual recovery of population density.



Robust information on population parameters such as abundance and density is pivotal to inform conservation and management at the diverse temporal and spatial scale. They are also relevant to ensure that conservation measures, mitigation actions and management measures that are already in place are effective by providing a yardstick to evaluate their effectiveness (e.g. by evaluating population trends). Cetaceans in the Mediterranean Sea are protected under statutory regulations (e.g. the Habitat Directive and the Marine Strategy Framework Directive) and by several international agreements such as ACCOBAMS among the others, which not only dictate to some extent the priorities in terms of conservation but also clearly state the details of monitoring activities that should be in place. By consequence, this information and the process to gather it are necessary to abide national and international regulations.

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Assessment methods               

Visual aerial and vessel surveys.

Before conducting any type of monitoring of animal populations aimed at assessing the species abundance and density, it is essential to define the main objectives of the programme, alongside with the collection of relevant information on the target study area and the species presence and occurrence. These elements are critical to choose the right data collection methodology, survey design approach and analytical framework. Visual aerial- and vessel-based surveys, as well as acoustic surveys from both static platforms and vessels, have proven to be successful to assess the density and abundance of many species, providing robust estimates.

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Results and Status, including trends

This assessment presents a brief overview of the key results and status of twelve species of marine mammals, one seal and 11 cetaceans, that are regularly present in the Mediterranean Sea and face several threats due to heavy anthropogenic pressures throughout the entire Mediterranean basin.

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Some of the cetaceans species present in the Mediterranean Sea are migratory species, whit habitat ranges extending over wide areas. It is therefore highly recommended to monitor these species at regional or sub-regional scales for the assessment of their population abundance. Priority should be given to the less known areas, using online data sources, such as Obis Sea Map and published data and reports as sources of information.

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Key messages 

  • Effort should be dedicated to provide density and abundance estimates at the Mediterranean level, with synoptic surveys, such as that currently ongoing with the ACCOBAMS Survey Initiative.
  • The conservation priorities listed by the European Directives and the Ecosystem Approach should be implemented.

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