Restore habitat for marine and freshwater mammals

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

55%
Certainty

30%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Degraded habitats that are important to marine and freshwater mammals, such as reefs, seagrass meadows, mangrove forests, rivers and beaches, may be actively restored. This may involve planting vegetation species, transplanting natural materials, such as sediment or rocks, and improving water quality. Habitat restoration is often carried out in combination with habitat protection, which may prohibit degrading activities and allow restored habitats to recover.

Study locations

Key messages

One study evaluated the effects of restoring habitat for marine mammals. The study was in the Kattegat sea (Denmark).

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (1 STUDY)

Abundance (1 study): One before-and-after study in the Kattegat sea found that harbour porpoise activity increased at a stony reef after it was restored with boulders and fishing was prohibited.

BEHAVIOUR (0 STUDIES)

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A before-and-after study in 2006–2012 of a stony reef in the Kattegat sea, Denmark (Mikkelsen et al. 2013) found that restoring the reef, along with prohibiting fishing, resulted in harbour porpoise Phocoena phocoena echolocation clicks being recorded more often and for longer periods than before restoration and protection. The average number of minutes with porpoise recordings and the average duration of porpoise encounters were higher at the reef in each of four years after the reef was restored and fishing prohibited (13–15 minutes/day; 4–5 minutes) than during two years before (6–10 minutes/day; 3 minutes). Porpoise activity at an intact reef 10 km away decreased over the same period (‘before’: 11–15 minutes/day; ‘after’: 3–7 minutes/day). In June–September 2008, a total of 100,000 t of norite boulders were dumped over 19 days to restore a 45,000 m² cavernous stony reef. Fishing was prohibited around the restored reef in 2009–2012. Porpoise activity was recorded with acoustic data loggers (two at the restored reef; two at an intact reef) for 33–75 days in June–August in each of two years before restoration and protection (2006 and 2007) and each of four years after (2009–2012).
Study and other actions tested
Referenced paper
Mikkelsen L., Mouritsen K.N., Dahl K., Teilmann J. & Tougaard J. (2013) Re-established stony reef attracts harbour porpoises Phocoena phocoena. Marine Ecology Progress Series, 481, 239-248.

Please cite as:

Berthinussen, A., Smith, R.K. and Sutherland, W.J. (2021) Marine and Freshwater Mammal Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation

Related Actions

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Leave anthropogenic structures in place after decommissioning Action Link	No evidence found (no assessment)	0	Synopsis Link
Create artificial habitat for marine and freshwater mammals Action Link	No evidence found (no assessment)	0	Synopsis Link
Restore habitat for marine and freshwater mammals Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link