Study

Impacts of sex ratio reduction on male aggression in the critically endangered Hawaiian monk seal Monachus schauinslandi

  • Published source details Johanos T.C., Becker B.L., Baker J.D., Ragen T.J., Gilmartin W.G. & Gerrodette T. (2010) Impacts of sex ratio reduction on male aggression in the critically endangered Hawaiian monk seal Monachus schauinslandi. Endangered Species Research, 11, 123-132.

Actions

This study is summarised as evidence for the following.

Action Category

Remove individual marine and freshwater mammals exhibiting aggressive behaviours that may limit population recovery

Action Link
Marine and Freshwater Mammal Conservation
  1. Remove individual marine and freshwater mammals exhibiting aggressive behaviours that may limit population recovery

    A before-and-after study in 1983–2005 on an island in the North Pacific Ocean, Hawaii, USA (Johanos et al. 2010) found that removing individual adult male Hawaiian monk seals Monachus schauinslandi exhibiting aggressive behaviours resulted in fewer injured and greater survival of adult female seals compared to before removal. After removal of aggressive adult males, a greater proportion of adult female seals survived each year (average 99.7% survived; total 3 seals died) than before the males were removed (average 95.9% survived; total 30 seals died). The average proportion of injured (but not killed) adult female seals each year was lower after aggressive males were removed (2%) than before (11%, numbers not reported). In 1984–1994, a total of 37 adult males exhibiting aggressive behaviours (attacking or harassing female seals) were removed from an island and either released in a different area (30 seals), were taken into captivity permanently (five seals) or died during capture/in captivity (two seals). Seals were monitored daily on the island for 3–9 months during spring and summer in each of 10 years before (1983–1994) and after (1995–2005) the removal of aggressive adult males.

    (Summarised by: Anna Berthinussen)

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