Prohibit or restrict hunting of marine and freshwater mammal species

Supporting evidence from individual studies

1. A study in 1979–1986 of a coastal area in the Kattegat and Skagerrak seas, Denmark and Sweden (Heide-Jørgensen & Harkonen 1988) reported that after hunting was prohibited, the abundance of harbour seals Phoca vitulina increased over seven years. Results are not based on assessments of statistical significance. The total abundance of harbour seals in the area was higher nine years after hunting was prohibited (maximum 5,608 seals) than two years after (maximum 2,345 seals). Overall, abundance was estimated to increase by 13% per year during seven years after hunting was prohibited. Hunting of harbour seals was prohibited in 1967 in Swedish waters and in 1977 in Danish waters. Aerial surveys were carried out across the area in each of seven years in 1979–1986. Each year, all haul-out sites in the area (number not reported) were photographed from the air at the end of August using the same methods, equipment, and surveyors. Seal counts were obtained from aerial photographs.

   Study and other actions tested

   Referenced paper

   Heide-Jørgensen M.P. & Harkonen T.J. (1988) Rebuilding seal stocks in the Kattegat-Skagerrak. Marine Mammal Science, 4, 231-246.

2. A review in 1971–1990 in the North Atlantic, North Pacific and Southern Hemisphere (Best 1993) found that after legislation to prohibit hunting was introduced, significant increase rates were recorded for 10 of 12 baleen whale (Mysticeti) populations of five species or species groups. Estimated increase rates during 7–21 years after hunting was prohibited were significant for four right whale Eubalaena spp. populations (0.07–0.13), three humpback whale Megaptera novaeangliae populations (0.09–0.14), one bowhead whale Balaena mysticetus population (0.03), one gray whale Eschrichtius robustus population (0.03), and one blue whale Balaenoptera musculus population (0.05). Increase rates for the two other monitored populations (one right whale, one humpback whale) were not significant. However, the authors note that more data may have been needed. Four legal agreements were put in place between 1935 and 1968 to protect 44 depleted baleen whale populations from exploitation. Twelve populations were monitored for 7–21 years between 1971 and 1990 using shore, aerial or shipboard counts or mark and recapture methods. The other 32 populations were not monitored.

   Study and other actions tested

   Referenced paper

   Best P. (1993) Increase rates in severely depleted stocks of baleen whales. ICES Journal of Marine Science, 50, 169-186.

3. A before-and-after study in 1962 and 1984–1992 of a pelagic area in the South Pacific Ocean, Australia (Paterson et al. 1994) reported that after legislation to prohibit hunting was introduced, sightings of migrating humpback whales Megaptera novaeangliae increased over 30 years. Results are not based on assessments of statistical significance. The average number of sightings of migrating humpback whales was higher 30 years after commercial whaling was prohibited (14.4 sightings/10 h) than during the final year of whaling (8.5 sightings/10 h). Daily sightings during the peak four-week migration period were estimated to increase by an average of 12% each year from 22 to 30 years after whaling was prohibited. Legal protection from commercial whaling began in 1963. Whale sightings were collated from multiple studies (see original paper for details). Migrating whales were observed from a headland during daylight hours during at least 4 days/week in June–August in 1984–1992. Data for the final year of whaling were collected by whaling boats assisted by aircraft in 1962.

   Study and other actions tested

   Referenced paper

   Paterson R., Paterson P. & Cato D.H. (1994) The status of humpback whales Megaptera novaeangliae in east Australia thirty years after whaling. Biological Conservation, 70, 135-142.

4. A before-and-after study in 1984–2007 in a pelagic area in the North Atlantic Ocean, Greenland (Heide-Jørgensen et al. 2012) found that after legislation to prohibit hunting was introduced, the abundance of humpback whales Megaptera novaeangliae increased over 22 years. The estimated abundance of humpback whales in summer feeding grounds was higher 22 years after hunting was fully prohibited (1,020 whales) than before (99–271 whales). Overall, abundance was estimated to increase by 9.4% per year from 1984 to 2007. Commercial whaling of humpback whales was prohibited in 1955, although low level harvesting continued until full protection was put in place in 1985. Aerial transect surveys were conducted in July–September during one year before full legal protection (1984) and during seven years after (1985–1989, 1993, 2005 and 2007). Aircraft flew over the area at 600–750 feet and 3–4 observers recorded sightings of humpback whales along 41–103 transects/year.

   Study and other actions tested

   Referenced paper

   Heide-Jørgensen M.P., Laidre K.L., Hansen R.G., Burt M.L., Simon M., Borchers D.L., Hansen J., Rasmussen M. & Dietz R. (2012) Rate of increase and current abundance of humpback whales in west Greenland. Journal of Cetacean Research and Management, 12, 1-14.

5. A before-and-after study in 1968–1978 and 2009 of a pelagic area in the Southern Ocean, Western Australia (Carroll et al. 2014) found that 31 years after legislation to prohibit hunting was introduced, the number of mature male sperm whales Physeter macrocephalus in the area did not differ significantly compared to before protection. The average number of mature male sperm whales observed in the area did not differ significantly before (6–13 whales/survey) or 31 years after hunting was prohibited (2–3 whales/survey). However, the authors state that other factors may have limited population recovery (e.g. entanglement in fishing nets, chemical and noise pollution). The sperm whale population had declined by 74% in 1955–1978 due to commercial whaling. Full legal protection was put in place after 1978 to prohibit whaling. Data for before protection were collected by aircraft used to assist in hunting whales in 1968–1978. Aircraft flew over the area at 1,500 feet and observers recorded mature male sperm whales (>11 m long) during 42–73 surveys/year. The same area was surveyed in September–December 2009 (21 surveys) using similar methods and a standard grid of 12 transects to provide comparable data 31 years after protection was put in place.

   Study and other actions tested

   Referenced paper

   Carroll G., Hedley S., Bannister J., Ensor P. & Harcourt R. (2014) No evidence for recovery in the population of sperm whale bulls off Western Australia, 30 years post-whaling. Endangered Species Research, 24, 33-43.