ScienceDaily (Jan. 4, 2012) — Warming in the North Atlantic over the last 32 years has significantly reduced winter sea ice cover in harp seal breeding grounds, resulting in sharply higher death rates among seal pups in recent years, according to a new Duke University-led study.
“The kind of mortality we’re seeing in eastern Canada is dramatic. Entire year-classes may be disappearing from the population in low ice years—essentially all of the pups die,” said David W. Johnston, research scientist at the Duke University Marine Lab. “It calls into question the resilience of the population.”
The study, recently published in the peer-reviewed journal PLoS ONE, is the first to show that seasonal sea ice cover in all four harp seal breeding regions in the North Atlantic has declined by up to 6 percent a decade since 1979, when satellite records of ice conditions in the region began.
Harp seals rely on stable winter sea ice as safe places to give birth and nurse their young until the pups can swim and hunt on their own. Female seals typically seek out the thickest, oldest ice packs in sub-Arctic waters each February and March, and have adapted to the spring melt by developing unusually short, 12-day nursing periods.
“As a species, they’re well suited to deal with natural short-term shifts in climate, but our research suggests they may not be well adapted to absorb the effects of short-term variability combined with longer-term climate change and other human influences such as hunting and by-catch,” Johnston said.
To assess the cumulative impacts of these factors, the researchers analyzed satellite images of winter ice from 1992 to 2010 in the Gulf of St. Lawrence—a major breeding region off Canada’s east coast—and compared them to yearly reports of dead seal pup strandings in the region. They also compared the stranding rates to recorded measurements of the relative strength of the North Atlantic Oscillation (NAO), a climate phenomenon that controls the intensity and track of westerly winds and storms and greatly affects winter weather and sea ice formation in the region. These analyses revealed that higher pup mortalities occurred in the Northwest Atlantic harp seal herd in years with lighter ice cover and when the NAO was weaker.
Analysis of older data revealed that NAO-related changes in seasonal ice cover may have contributed to major declines in seal populations on the east coast of Canada from 1950 to 1972, and to a period of steady recovery from 1973 to 2000.
“This clearly shows that harp seal populations across the Atlantic fluctuate pretty much in synch with NAO trends and associated winter ice conditions,” Johnston said. “But there’s a caveat. Regardless of NAO conditions, our models show that sea ice cover in all harp seal breeding regions in the North Atlantic have been declining by as much as 6 percent a decade over the study period. The losses in bad years outweigh the gains in good years.”
A key unanswered question, he added, is whether seals will be able to respond to the long-term trend by moving to other, more stable ice habitats.
Recent reports that some harp seals are whelping in new breeding grounds off East Greenland indicate some shifting may be taking place, but thousands still return each year to traditional breeding grounds in the Gulf of St. Lawrence or along the Front, off Newfoundland, regardless of ice conditions.
“There’s only so much ice out there, and declines in the quantity and quality of it across the region, coupled with the earlier arrival of spring ice breakup, is literally leaving these populations on thin ice,” Johnston said. “It may take years of good ice and steady population gains to make up for the heavy losses sustained during the recent string of bad ice years in eastern Canada.”
Co-authors of the study are doctoral student Matthew T. Bowers and research scientist Ari S. Friedlaender, both of Duke, and David M. Lavigne, science advisor at the International Fund for Animal Welfare, which funded the study.
Note; Taking a population to extinction by destroying their habitat, in this case the sea ice. Only if their food sources relocate will the breeding colonies be able to also relocate.
Carbon Dioxide Is ‘Driving Fish Crazy’
ScienceDaily (Jan. 20, 2012) — Rising human carbon dioxide emissions may be affecting the brains and central nervous system of sea fishes with serious consequences for their survival, an international scientific team has found.
Carbon dioxide concentrations predicted to occur in the ocean by the end of this century will interfere with fishes’ ability to hear, smell, turn and evade predators, says Professor Philip Munday of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
“For several years our team have been testing the performance of baby coral fishes in sea water containing higher levels of dissolved CO2—and it is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival,” Prof. Munday says.
In their latest paper, published in the journal Nature Climate Change, Prof. Munday and colleagues report world-first evidence that high CO2 levels in sea water disrupts a key brain receptor in fish, causing marked changes in their behaviour and sensory ability.
“We’ve found that elevated CO2 in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life,” Prof. Munday says.
Prof. Munday and his colleagues began by studying how baby clown and damsel fishes performed alongside their predators in CO2-enriched water. They found that, while the predators were somewhat affected, the baby fish suffered much higher rates of attrition.
“Our early work showed that the sense of smell of baby fish was harmed by higher CO2 in the water—meaning they found it harder to locate a reef to settle on or detect the warning smell of a predator fish. But we suspected there was much more to it than the loss of ability to smell.”
The team then examined whether fishes’ sense of hearing—used to locate and home in on reefs at night, and avoid them during the day—was affected. “The answer is, yes it was. They were confused and no longer avoided reef sounds during the day. Being attracted to reefs during daylight would make them easy meat for predators.”
Other work showed the fish also tended to lose their natural instinct to turn left or right—an important factor in schooling behaviour which also makes them more vulnerable, as lone fish are easily eaten by predators.
“All this led us to suspect it wasn’t simply damage to their individual senses that was going on—but rather, that higher levels of carbon dioxide were affecting their whole central nervous system.”
The team’s latest research shows that high CO2 directly stimulates a receptor in the fish brain called GABA-A, leading to a reversal in its normal function and over-excitement of certain nerve signals.
While most animals with brains have GABA-A receptors, the team considers the effects of elevated CO2 are likely to be most felt by those living in water, as they have lower blood CO2 levels normally. The main impact is likely to be felt by some crustaceans and by most fishes, especially those which use a lot of oxygen.
Prof. Munday said that around 2.3 billion tonnes of human CO2 emissions dissolve into the world’s oceans every year, causing changes in the chemical environment of the water in which fish and other species live.
“We’ve now established it isn’t simply the acidification of the oceans that is causing disruption—as is the case with shellfish and plankton with chalky skeletons—but the actual dissolved CO2 itself is damaging the fishes’ nervous systems.”
The work shows that fish with high oxygen consumption are likely to be most affected, suggesting the effects of high CO2 may impair some species worse than others—possibly including important species targeted by the world’s fishing industries.
Note; Do ‘crazy’ fish have the sense to relocate?