Why does the west west whaling population of the West Atlantic grow much slower than those of southern whales, a sister species recovering from a disappearance close to commercial whaling?
NOAA fishermen researchers and colleagues have analyzed the question more closely and concluded that maintaining adult lives amongst the population is by far the most effective way to promote population growth and recovery. Most of these deaths are attributable to tangle in fishing gear and collisions with ships. The findings are reported in The Royal Society opens science.
"If the Korean Atlantic whales have risen to the annual rate we prove to be capable of, the population will be almost double by now and their current situation is not that tough," said Peter Corkeron, the lead author of paper and heads of whale research effort at NOAA Fishing "Northeast Fisheries Science Center.
The right Atlantic Bale, Eubalaena glacialis, is one of the three correct whale species. Of the three, he lives in the most industrialized habitat and migrates near the shore.
From 1970 to 2009, 80% of all deaths caused by whales in the North Atlantic (70 out of 87), for which the cause is known, were man-induced, mainly due to entanglement in fishing gear and collisions with ships. By comparison, most of the southern whale deaths that were observed were calves in the first year of life, and very few were directly attributable to human activities.
Qualities are a measure
"We studied four straight whale populations, three South American South African and South West Austrians, plus the Western North Atlantic population that had data comparable to time series and minimum number of calves known to be born every year, Corkeron said. "The intensive aerial research of the whale habitat in the North Atlantic began in 1992, which marked the beginning of our comparison."
The researchers compared the number of calves between 1992 and 2016 for each of the four populations. By this index, the annual growth rate of whales in the North Atlantic (about 2% per year) was much lower than that of southern whales (between 5.3 and 7.2% per year).
Estimate the intrinsic growth rate for whales in the North Atlantic
The researchers then looked at the extent to which this difference in annual growth is related to man-made lesions and deaths, and not to ecologically inherent growth rates for each population.
They have built a population design model for the right whales in the North Atlantic, using the highest annual survival estimates available from recent analyzes of resources by using photographs and assuming four years between deliveries. This led to an estimated growth rate of 4%, about twice as high as observed.
The results of the model also showed that adult female deaths accounted for about two-thirds of the gap between the estimated intrinsic growth rate and what was observed.
Researchers also looked at other factors and differences in the North Atlantic and Southern populations. Eighty-three percent of all individual whales in the North Atlantic have been entangled in fishing gears at least once in their lives, and 59% have been entangled two or more times.
Energy requirements from traction associated with entanglement may reduce the likelihood that a woman can reproduce successfully. Years between births also increase for females given the required recovery period in the physical costs of entanglement, which may last from months to years. By comparison, pushing into fishing gear is almost nonexistent for southern whales.