Restore habitat for marine and freshwater mammals
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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.
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