Web edition: October 18, 2009
QUEBEC CITY, CANADA - This isn’t a cop convention. These are marine mammal biologists, but they do care about speed limits.
At the 18th Biennial Conference on the Biology of Marine Mammals, manatee researcher Edmund Gerstein stands unwrapping what looks like a fine piece of chocolate a companion has presented — maybe this wasn’t the best moment to walk up with a question about boat speeds and gory collisions with manatees.
Gerstein, a marine mammal researcher at Florida Atlantic University in Boca Raton, is the guy at this meeting who has been arguing what sounds just backward at first. In circumstances such as murky water, he says, slow boats are more likely to hit manatees than are fast boats. Fortunately, he’s also a gracious guy who’s willing to mix manatee death and chocolate.
Slow boats don’t make as much noise within the manatee hearing range, he says. So when manatees have to rely on sound to detect boats, the animals don’t pick up the warning until too late.
Cautionary note to boaters: Sorry, folks. Gerstein is not, repeat not, arguing for lifting speed limits on boats. He does not, repeat not, favor roaring as fast as possible through manatee habitats. Instead he argues that boats need to slow down and also broadcast the right kind of manatee-warning sound.
Florida’s subspecies of the West Indian manatee falls under the protection of the U.S. Endangered Species Act, and wildlife managers have identified boat collisions as a significant threat. Regulations restrict speed in manatee zones, but boats keep hitting the animals. In 2007, Florida reported 73 manatees dead in boat collisions. Gerstein says some animals get clobbered dozens of times during their lives.
He objects to suggestions he hears that manatees are just too stupid to learn to avoid boats. Details of their hearing could explain the repeated strikes. At this meeting, he, Laura Gerstein and their colleagues presented data on just one of the conditions that turns slow boats into a risk: the hopper dredges that scoop up sand. The researchers noted that in Florida’s St. Johns River, manatee deaths tend to rise during years with lots of dredging. Researchers monitored dredging noise, compared it with manatee hearing capabilities and calculated that hopper dredging operations drowns out the noise of fast boats within 250 meters. For slow and quiet boats, the dredging operations keep manatees from hearing an approach in a timely way throughout an area up to 4 kilometers away from the dredge.
As a solution, he proposes equipping boats with an alerting system that beams a narrow signal in front of the boat’s path. In his tests, he reported at the meeting, most of the manatees he spotted ahead moved aside when he cruised along slowly with the alert. When he cruised without it, mostly he had to do the avoiding.
It’s not just manatee fans who muse about speed limits. Boats collide with whales along the U.S. East Coast and pose a dire threat to the faltering remnants of the right whale population. In 2008 NOAA slapped a 10-knot speed limit on commercial vessels 65 feet or longer in particularly busy and whalish spots during winter. The restrictions applied to a swath along coasts of Georgia and the Carolinas and more northern spots such as the waters of Norfolk, Philadelphia and New York. So far, though, it’s not clear that slap has even amounted to a slap, or a tap, on the wrist.
As Gregory Silber got up to report on the effects of this ban at the meeting, he said he was used to giving talks about the behavior of animals so he felt a little out of place talking about the behavior of people.
"Compliance was a little dismal," reported Silber of the NOAA Fisheries Service’s Office of Protected Resources in Silver Spring, Md. He and his colleagues reached that dismal opinion by looking at the basic information, including speed, that ships automatically broadcast as they travel. About 19 percent of the thousands of trips tracked through the slow-go zones last winter met the legal requirement of 10 knots or below, Silber said. Half of the journeys tracked fell into next category over the limit, up to 12 knots.
The risk to whales rises with vessel speed, according to a pretty steep curve that Silber showed. Whales may survive a collision with a slower boat, but as he put it, "At 20 knots, the possibility of death approaches 100 percent."
Silber presented his data in a matter-of-fact tone, but it was possible to imagine that biologists packed in that room were having cop fantasies.
Gerstein, Laura A., Pinto, Gerard; Barr, Seth; Gerstein, Edmund R. 2009. Zones of masking from hopper dredging impact the risk of vessel collisions with manatees. Abstract presented at 18th Biennial Conference on the Biology of Marine Mammals, Quebec City, 12 – 16 October 2009.
Gerstein, Edmund R., Gerstein, Laura A., Greenewald, Josiah. 2009. Field tests of a directional acoustic alarm designed to alert manatees of approaching boats. Abstract presented at 18th Biennial Conference on the Biology of Marine Mammals, Quebec City, 12 – 16 October 2009.
Silber, Gregory et al. 2009. Compliance with Vessel Speed Restrictions to Reduce Right Whale Ship Strikes. Abstract presented at 18th Biennial Conference on the Biology of Marine Mammals, Quebec City, 12 – 16 October 2009.
The Society for Marine Mammalology website [Go to]
Gerstein, Edmund. 2002. Manatees, Bioacoustics and Boats: Hearing tests, environmental measurements and acoustic phehomena may together explain why boats and animals collide. American Scientist. (March-April 2002) Vol. 90, No. 2, p. 154. doi: 10.1511/2002.2.154. Available at [Go to]