Wintering White Sharks: possible migrations along U.S. east coast

A possible migration corridor has been identified for great white sharks on the east coast of the U.S. A satellite tagging study was initiated in the fall by the Massachusetts Division of Marine Fisheries and some of the early results are intriguing. It is possible that the great white sharks that appear off the New England coast during the summer months - suspected of feeding on seal populations there - travel south during the winter months based on the results of a tagged shark who has appeared as far south as Jacksonville, Florida.

Satellite tagging has been used on great whites and other shark species to record location, speed, depth, and ambient temperature. Typically, a well-placed tag will record data for 30 to as long as 90 days then release itself, float to the surface, and download its data to satellites overhead. Researchers must wait patiently then sift through a mountain of data when it is downloaded all at once. Satellite tags can provide more long-range data than regional telemetry tags (like those documented in my film, Island of the Great White Shark) but are also subject to being dislodged prematurely. A newer technique, SPOT tagging, bolts the tag to the shark to insure a significantly longer monitoring period, but requires that the shark be caught and brought on board; a technique that has raised considerable controversy because of the physical impact imposed on the shark during the procedure.

In the summer months, several species of shark inhabit the New England coastline, from basking sharks to thresher and blue sharks to the great white white (although not in significant numbers). This new tagging study is the first indication that, like their distant cousins throughout the world who exhibit distinct migratory patterns, white sharks could very well be moving up and down the east coast based on seasonal temperature changes and any changes in prey populations that those seasons impose.

Great whites have already been shown to migrate from the west coast Farallon Islands to the mid-Pacific; same for the white sharks at Isla Guadalupe. White sharks have been monitored moving from South Africa all the way to Australia and back. While there can always be the occasional exception, there is continuing evidence that these sharks and other pelagic species develop critical migratory patterns. Our concern would be, what would happen to these sharks if their migrations were intercepted by commercial fishing fleets? Or what would happen to the overall health of their populations with changes in ocean temperature due to global warming? How ingrained are these patterns and what would happen if external factors were altered - could the sharks successfully adjust?

Sea Birds: not immune to environmental issues

There's one marine animal that, frankly, I don't pay much attention to in this blog and that is sea birds. Except for concern over their uncanny ability to bomb our cars, hats, and docks with globs of white, many people don't give them much thought - maybe the occasional shot of an oil-soaked sea gull catches our eye, but beyond that . . .

But these animals are at the mercy of environmental change like pollutants or global warming, just like any other species. And their loss would be ours too, as they play a role in maintaining a balanced ecosystem.

I was reviewing summaries of several scientific papers and found some interesting issues confronting several species:

One study looked at red knots that frequent the U.S. east coast. This time of year, red knots congregate in the Delaware Bay to feed on horseshoe crab eggs before they continue their northward Arctic migration to breed. The demand for horseshoe crabs as bait has dramatically increased over the past two decades, thereby greatly reducing the supply of eggs for the red knots. This has impacted the survivability rate of the red knot and returning populations in the Delaware Bay have dropped as much as 75 %. Of concern is that while efforts have been made to increase the horseshoe crab population, the number of red knots has not increased in kind.

Another study showed that Cassin's auklet, a cold-water sea bird, could face serious population declines due to climate change because, as a zooplankton feeder, it depends on prey like the copepod N. cristatus whose population drops when warmer waters are prevalent. The study showed that in past years, the population of the auklet fluctuated in direct correlation with copepod numbers that were impacted by warmer water temperatures. As temperatures consistently warm up, the auklet is at risk.

Not all is necessarily bad news. While some animals suffer from climate change because of an inability to adapt, the razorbill seems to be adjusting as it's dispersal and range has reported to have increased northward into the Canadian Arctic due to the northward movement of its fish prey, like capelin. As temperatures increase and a variety of flora and fauna expand their range, some animals are able to adjust, while others perish due to loss or reduction of prey or food.

If you adhere to the evolutionary concept of birds being ancestors of ancient dinosaurs, then it can truly be said that they are highly adaptive creatures. But with their long range migrations and breeding habits based on certain environmental conditions, there is a question as to their future in the face of what is happening today. Research is ongoing to determine the long-term effects of pollution and climate change on our feathered friends.

Birds in Flight: climate change is threatening their range

Many of the discussions regarding climate change revolve around the impacts seen at the opposing polar regions: the Arctic and Antarctic. Loss of animal habitat, encroachment by previously foreign animal and plant species - with these events we often consider what has happened or will happen in these areas as indications of future events in the more populated warmer regions of the earth.

But there are changes taking place right now in "our backyard" that can be documented as was recently done by the National Audubon Society regarding North American bird migrations and changes in their range or territory. The Society tabulated winter migration data over the past 40 years from 2,000 locations nationwide. The data shows that 58% of the 305 most common North American species have shifted their ranges northward and inland by an average of 35 miles. In a few cases, the distance was much greater, as with the purple finch, common in Missouri but now moving 300 miles north towards Canada.

"Too many people hear about melting glaciers and polar bears and conclude that the impacts of global warming are far into the future and far from home," said NAS president, John Flicker. "But the impact of climate change can be seen right now in the birds that are right outside our door - or not," referring to the possibility that many species may be unable to exist in new locations and extinction becomes a real possibility.

While there are those who debate the cause of climate change, man-made or cyclical, one thing is for sure: we must consider the implications of what is happening now and in the near future - before our efforts to reduce greenhouse gases take effect or before the next cyclical change, depending on your favored position. Birds are a crucial part of plant pollination and seed germination by virtue of the plants and insects they feed upon. How will these natural processes be impacted? How will those impacts affect the large agricultural areas we have come to depend on for fruits, vegetables, or grain?

We are faced with many unknowns and there is much to be studied and hypothesized - waiting until we have a definitive result may be too late as changes in nature can move deceptively slow but with tremendous momentum. Time to act. It's not just "for the birds."

Download National Audubon Society report.