Shrinking whales show danger signs
RESEARCH into shrinking whales could help save other marine species from overfishing.
Scientists from Tasmania have contributed to a study that reveals the decreasing body size of whales during commercial hunting last century was an early warning sign some species were headed for global collapse.
The most rapid shrinkage was seen in sperm whales, which were 4m shorter in the 1980s than in 1905.
Scientists from the Institute for Marine and Antarctic Studies in Tasmania and Switzerland’s University of Zurich have studied historical whale records to reveal the smaller sizes of commercially harvested whales indicated the species were in danger up to 40 years before their collapse.
The researchers say the ability to predict when population collapses will occur is vital for the sustainable management of commercially exploited wild fish stocks.
IMAS co-author Julia Blanchard said body size could be a warning sign, used to complement other indicators of decline.
She said the study, published today in the international journal Nature Ecology & Evolution, could help pinpoint early warning signs that a population was at risk of collapse from pressures such as overfishing and climate change.
“In the face of global envi- ronmental change it’s important that we can predict which species are at risk so appropriate conservation measures can be taken,” Associate Professor Blanchard said.
She said the findings could help our understanding of how commercial fish varieties were faring, including popular species such as flathead.
“This is highly relevant to other species, and flathead is a type of population that would be ideal to look at.”
The researchers used International Whaling Committee records of abundance and body size of four whale species between 1900 and the commercial whaling moratorium in 1985.
They looked at catch sizes of blue whales, fin whales, sei whales and sperm whales — showing the average body size dropped rapidly during the second half of the 20th century.
Lead author Chris Clements from the University of Zurich said the declining sizes were detectable up to 40 years before the species’ collapsed.
Dr Clements said sperm whales taken in the 1980s were 4m shorter on average than those taken in 1905, shrinking from about 1.8m to 1.4m.
The research could be valuable to detect overfishing in other species, said IMAS coauthor, Professor Mark Hindell.
“Overfishing, which is likely to get worse with an increasing human population, is a threat faced by many marine species and can lead to changes in body size as well as the collapse of fish stocks that can take many decades to recover,” he said.