Legally protect habitat for marine and freshwater mammals

How is the evidence assessed?
  • Effectiveness
    70%
  • Certainty
    60%
  • Harms
    0%

Source countries

Key messages

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (4 STUDIES)

  • Abundance (2 studies): One before-and-after study in the North Atlantic Ocean found that a population of Mediterranean monk seals increased during eight years after the islands they inhabited were legally protected. One before-and-after study in the North Sea found that a population of bottlenose dolphins was estimated to be a similar size before and after part of its range was protected.
  • Survival (2 studies): One before-and-after study in the South Pacific Ocean found that the survival rate of Hector’s dolphins was higher after a coastal area was legally protected than before. One before-and-after study in the Port River estuary found that after the area became legally protected a similar number of Indo-Pacific bottlenose dolphin strandings were recorded compared to before protection, but the number of strandings caused by humans decreased.

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

  1. A before-and-after study in 1984, 1989 and 1992–1998 of three islands in the North Atlantic Ocean, Portugal (Pires & Neves 2001) reported that after the area became legally protected, a population of Mediterranean monk seals Monachus monachus increased over eight years. Results are not based on assessments of statistical significance. The number of monk seals inhabiting the islands was estimated to be higher eight years after legal protection was put in place (20 seals) than six years before legal protection (6–8 seals). Annual pup production was higher during 5–8 years after legal protection (2–3 pups/year) than during one year before legal protection (1 pup/year). The islands (and surrounding waters to a depth of 100 m) were legally protected and designated as a nature reserve in 1990. Controlled commercial fishing without nets was permitted in one half of the reserve. Wardens patrolled the islands daily by boat and educated fishers. In 1992–1998, seals were photographed and observed with binoculars for 5 h/day at 12–24 points located along the three islands. Data for 1984 and 1989 were from previous studies.

    Study and other actions tested
  2. A before-and-after study in 1986–2005 of a coastal area in the South Pacific Ocean, New Zealand (Gormley et al. 2012) found that after the area became legally protected the survival rate of Hector’s dolphins Cephalorhynchus hectori was higher than before protection. The average annual survival rate of Hector’s dolphins was 5.4% higher after the area became legally protected (0.92) than before (0.86). However, the authors state that the survival rate may still have been too low for population recovery. In 1988, the 1,170 km2 coastal area was designated as a marine mammal sanctuary. Commercial fishing with gill nets was prohibited in the protected area, and amateur fishing with gill nets was restricted to specific times and locations to reduce dolphin entanglements. Hector’s dolphins (462 individuals) were identified from photographs taken during boat transects (number not reported) along the shore in November–February before (1986–1989) and after (1990–2005) the sanctuary was established.

    Study and other actions tested
  3. A before-and-after study in 1990–2010 in an inlet of the North Sea, Scotland, UK (Cheney et al. 2014) reported that after the area was protected, the resident population of bottlenose dolphins Tursiops truncatus was estimated to be of a similar size to before protection. The total bottlenose dolphin population was estimated to be 102–157 individuals/year during the 15 years before the area was protected, and 143–178 individuals/year during the six years after, although the difference was not tested for statistical significance. Overall, the population was estimated to be stable or increasing over the entire 21-year period. In 2005, part of the bottlenose dolphin population’s range was designated as a protected area. In May–September 1990–2010, the area was surveyed during 10–39 boat surveys/year along fixed (1990–2000) or flexible routes (2001–2010). All dolphins encountered were recorded and photographs were taken of the left and right side of their dorsal fins. Annual abundance and population trends were estimated using sightings of distinctive individuals (26–92 individuals/year) and mark-recapture models.

    Study and other actions tested
  4. A before-and-after study in 1987–2012 in the Port River estuary, South Australia (Adamczak et al. 2018) found that after the area became legally protected a similar number of Indo-Pacific bottlenose dolphin Tursiops aduncus strandings were recorded compared to before protection, but the number of strandings caused by humans decreased. There was no significant difference in the average number of dolphin strandings recorded before (1.1 strandings/year) and after (2.3 strandings/year) the area became legally protected. However, the authors note that more data may be required over a longer time period to detect changes. The proportion of dolphin strandings caused by humans (intentional killing, boat collisions, entanglement in fishing gear) vs. non-human causes (disease, natural causes, live strandings) was lower after the area became legally protected (2 vs. 20 strandings respectively) than before (6 vs. 9 strandings). The area (118 km2) was adjacent to a major port and urban/industrial area and became a legally protected dolphin sanctuary in 2005. This involved higher fines for intentional harm, fishing restrictions (commercial and recreational), enforcement patrols and an education and awareness raising programme. Dolphin strandings (live and carcasses) were recorded before (1987–2004) and after (2005–2012) the area was legally protected.

    Study and other actions tested
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?

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Marine and Freshwater Mammal Conservation

This Action forms part of the Action Synopsis:

Marine and Freshwater Mammal Conservation
Marine and Freshwater Mammal Conservation

Marine and Freshwater Mammal Conservation - Published 2021

Marine and Freshwater Mammal Synopsis

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