On October 18, 2023 an interesting study appeared in the Proceedings of the Royal Society B: Biological Sciences entitled Survival improvements of marine mammals in zoological institutions mirror historical advances in human longevity. The study, conducted by a 41-author team, led by Species360 and Dr. Morgane Tidiere of the University of Southern Denmark, noted that there is an "intense public debate" over marine mammals held in captivity based on "the assumption that survival in zoological institutions remains lower than the wild." However, the study's findings "contradict arguments of poor or lower survival in zoological institutions than in natural habitats."
The study focused on four species of marine mammals: harbor seal (Phoca vitulina), California sea lion (Zalophus californianus), polar bear (Ursus maritimus) and the common bottlenose dolphin (Tursiops truncatus). The study assessed long-term changes (1829-2020) in population welfare among 8,864 individuals in the four species group which represented 63.4% of all marine mammals recorded in the global Species360 Zoological Information Management System (ZIMS). The study employed two demographic measures – life expectancy (the average lifespan in a population) and lifespan equality (the concentration of deaths at older ages relative to life expectancy). For the California sea lion and polar bear, the study was divided into four periods for comparison: pre-1975, 1975-1989, 1990-2004 and 2005-2020. For the harbor seal and bottlenose dolphin, it was three periods: pre-1990, 1990-2004 and 2005-2020.
The study concluded that:
Our findings highlight the effects of improvements in species-specific knowledge, management and care practices in modern zoological institutions, as the four species analysed today live on average 1.65–3.55 times longer than their wild counterparts. In addition, we found a significant increase in first-year and adult survival across time in marine mammal facilities. Thus, our results contradict arguments of poor or lower survival in zoological institutions than in natural habitats. [Emphasis added.]
The improvements in life expectancy and first-year survival for the bottlenose dolphin and California sea lion confirmed other reports as to these two species as well as for the killer whale where longer lifespans in zoological settings also have been observed (albeit debated). However, this was the first reported indication of improvements in longevity for harbor seals and polar bears in zoological institutions. The authors compared these results to similar historical trends among humans:
Among humans, increases in life expectancy and lifespan equality have been attributed to the effect of social, economic and public health advances on mortality rates. Similarly, animals living in modern zoological institutions are shielded from many pressures affecting mortality (e.g. starvation, disease, parasites, environmental impacts). Interestingly, at the population level, the demographic patterns of marine mammals in zoological institutions across time (and between wild and zoo populations) are qualitatively similar to those observed during the industrial revolution in humans. Specific changes in zoological management practices over the last decades . . . likely have contributed to the demographic improvements we found. In the nineteenth century, many zoological institutions started as menageries, where conditions for animals were poor, and survival was low. In the 1960s and 1970s, practical experience increased, and laws were passed to improve species conservation in the wild and animal care in zoological institutions (e.g. the Animal Welfare Act and the Marine Mammal Protection Act in the USA). In the 1970s and 1980s, the establishment of regional zoo associations, accreditation standards coordinated breeding programmes, shared databases, and professional networks further enabled zoological institutions to acquire and share knowledge about their animals and collectively improve welfare standards.
So the debate over whether animals should be held in exhibition facilities such as zoos goes on. But this study undermines the animal activist argument that animals in a zoological setting live shorter lives than their free-ranging counterparts.
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