Establish handling and release protocols for mammals captured by fisheries

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • One study evaluated the effects on marine mammals of establishing handling and release protocols for mammals captured by wild fisheries. The study was in the Great Australian Bight (Australia).



  • Survival (1 study): One before-and-after study in the Great Australian Bight found that introducing a code of conduct for releasing dolphins trapped in nets, along with avoiding dolphins during fishing, resulted in lower mortality of short-beaked common dolphins.


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 2004–2006 of a pelagic area in the Great Australian Bight, Australia (Hamer et al. 2008) found that introducing a code of practice for releasing dolphins trapped in fishing nets, along with avoiding dolphins during fishing, resulted in fewer deaths of short-beaked common dolphins Delphinus delphis. The study did not distinguish between the effects of releasing and avoiding dolphins. Mortality rates of dolphins in purse-seine nets were lower after the code of conduct was put in place (0.01 dolphins killed/net) than before (0.4 dolphins killed/net). The code of practice was introduced to a sardine Sardinops sagax fishery in September 2005. At least one crew member/vessel was required to observe for dolphins. Fishing was delayed or relocated if dolphins were present. Release procedures for encircled dolphins included opening the net or a dolphin gate within the net, using weights to submerge the float line, physical removal of dolphins or stopping fishing. An independent observer recorded dolphin encirclements and deaths during 49 fishing events by eight vessels in November–June 2004/2005 (before the code of conduct) and 89 fishing events by 12 vessels in November–June 2005/2006 (after).

    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?

List of journals searched by synopsis

All the journals searched for all synopses

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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