A recent scientific paper has highlighted the relationship between food scarcity and low reproduction of one of the North Pacific killer whale populations. These are the southern resident killer whales, a subpopulation of three pods that feed primarily on salmon and live permanently on the shores of Washington State and British Columbia.

The negative effect of the shortage of salmon on the abundance of these killer whales has been pointed out in previous publications, but it is the first time scientific evidence shows that prolonged periods of hunger can produce reproductive problems in cetaceans. This has been possible thanks to knowledge of the hormonal levels of orcas during pregnancy, which were described thanks to the research done with animals in the SeaWorld parks more than a decade ago. In this current research, scientists have been able to determine when orcas were pregnant by measuring the hormone concentration in their faeces and using as reference levels those published for orcas in zoos. In order to find the faeces of the orcas, trained dogs were used, so that hundreds of samples were obtained between the years 2008 and 2014. Faeces analysis also shows elevated levels of corticosteroid hormones (cortisol) associated with the scarcity of salmon, indicating that the animals were starving.

Thanks to this methodology researchers have determined that in the last six years only 37% of the pregnant females of that population gave birth successfully, that is to say, that more than two thirds of the pregnancies were interrupted. The authors compared this situation with the famine produced in Holland during the Second World War where births were reduced by 30%. There is no doubt that the systematic loss of more than 60% of offspring is unsustainable for this population of killer whales in the medium term, as it currently has only 78 individuals.

The mechanism of abortion is still not well understood, whether it is simply the malnutrition caused by lack of food or the mobilization of toxic substances due to the consumption of fat reserves. Killer whales are known to store large amounts of fat-soluble toxins in their fat reserves, and a prolonged period of famine can mobilize these fatty deposits and release toxins that would pass into the fetus through the blood. Even if a baby is born, it is known (thanks to research done in zoos) that these toxins are transmitted efficiently through the milk to the baby, which could compromise their weak immune system. The effects of these toxic substances on the immune system in killer whales are being studied by experts such as those at the University of Aarhus (Denmark) who took blood samples from Loro Parque orcas at the beginning of the year. These samples, which are still being analyzed in the United States, will serve to better understand how these substances impact on the health of killer whales and to predict the effects of rising levels of pollution at sea.

Once again it becomes clear how overfishing and pollution seriously affect the populations of cetaceans on our planet. But not only that, the authors of this research point out that this mechanism of lack of food and exposure to soluble organic pollutants could also be affecting communities of Native Americans who depend on salmon fishing in that area. We hope this research will enable the US administration to regulate salmon fisheries and the use of coastal and river habitat in the area to protect Native American populations and also one of the most endangered populations of killer whales.