Last weekend, I visited lovely Monterey, California to check out Whalefest Monterey, an annual celebration of marine science hosted by the town's Fisherman's Wharf Association

In the course of reporting a story about leatherback sea turtles that I wrote for the San Jose Mercury News, I learned that leatherback hatchlings, which start life small enough to fit in your palm, grow up into adult turtles that can weigh as much as a ton. Turns out leatherbacks are seasonal visitors to California's coast, which was news to me, though their numbers are dwindling rapidly and they're considered critically endangered

To learn why paying attention to the source of the swordfish you eat could help leatherbacks make a comeback, check out my newspaper story here

A leatherback hatchling makes its way to the ocean. 

(Image by Ken Clifton via Flickr; creative commons license)

Turtle footage

In several of the video clips, a loggerhead sea turtle, shell studded with barnacles and matted with an undulating crop of green algae, is flanked by an entourage of fish, apparently eating the bounty of food growing on the turtle’s shell or perhaps using the large turtles for cover (adult loggerhead sea turtles are typically about three feet long).

In another clip, a turtle, evidently in response to the shadowy presence of a shark, flips over so its shell is facing the threat and swims away.

These and other natural loggerhead sea turtle behaviors were captured on video by a remotely operated vehicle, or ROV, deployed off the coast of New Jersey, Delaware, and Maryland, by a group of researchers from the Coonamessett Farm Foundation and the Woods Hole Laboratory of the Northeast Fisheries Science Center, both based in Massachusetts. They recently published their findings in the Journal of Experimental Marine Biology and Ecology – and, as the scientists note in their paper, the “study represents the first example of an ROV for tracking sea turtles.”

The scientists spotted the turtles from a boat, focusing on areas where loggerhead sea turtles have been active in the past; when they found one, they launched their ROV, tethered to the boat, and followed the turtle wherever it went. Over their 10 research trips (during which they recorded footage of 70 turtles), the researchers found that they could maneuver the ROV to within about three to five yards of the turtle without disturbing it.

From that vantage point, the scientists were able to observe a number of apparently natural behaviors which would have been difficult to capture by other means, such as human divers, cameras attached to turtle shells, and tracking tags implanted into turtles, all of which have been used to study sea turtles in the past. “[T]he ROV add[s] a new technique that complements existing technologies while overcoming several of the limitations,” the researchers write.

ROVs appear to be a new and useful tool for scientists attempting to understand how loggerhead sea turtles behave in their natural environment, and how they interact with each other and other animals.

Loggerhead sea turtles are typically about three feet long and weigh about 250 pounds.

(Image by Richard Ling via Flickr/Creative Commons license)

Turtle bycatch

When you’re standing knee-deep in a stream, branches growing together into a leafy green tunnel above your head, slippery cobbles under your feet, expecting to find a steelhead or two in the net you just jerked out of the water, it can be a little startling to see a five-inch crayfish staring back at you, waving its claws.

Sometimes at work, when I’m lucky, I get to step outside my office for a little while and help the graduate students in my lab as they collect samples and data in the field. The project I work on the most involves scooping up fish in hand-held nets, but occasionally we capture other things, too – organisms we weren’t targeting or trying to catch, like that five-inch crayfish. In the fisheries world, this accidental take is called bycatch. Usually when scientists and managers are studying or trying to regulate bycatch, they’re dealing with marine life, but it happens in freshwater fisheries, too – and not just with crayfish.

When I catch a crayfish in my net, I pull it out and set it back in the stream where it came from (carefully, to preserve my fingers), but that’s not always possible in other situations. Some fishing nets are set underwater, and left to soak and collect fish for several hours before the catch is retrieved; that can be a problem if air-breathing aquatic animals – like turtles – also get caught.

A team of Canadian scientists recently published a case-study of freshwater turtle bycatch in a small lake in the journal Aquatic Conservation: Marine and Freshwater Ecosystems. They estimated the effectiveness of two methods for reducing turtle bycatch in Lake Opinicon, in southeast Ontario, Canada, which supports a small commercial fishery: adding “exclusion devices” to fish net openings that would keep most turtles out but let fish in, and shortening the fishing season.

The researchers measured the shells of four species of female turtles, and found that the smaller exclusion device they evaluated (which had an opening about two inches wide) would keep most turtles out of the fishnets – between 92 and 100 percent of three turtle species in the lake had shells too large to fit through the device. For the fourth and smallest turtle species the scientists studied, however, the exclusion device was not as successful – only 27 percent of those turtles were bigger than the opening.

If managers close the fishery during the time when turtles are most active, that can reduce turtle bycatch; to evaluate the effect of closing the fishery a month earlier in the spring, the scientists measured how active the turtles were during May and June. Only one turtle species was most active right before the current closing date of June 20, but, as the authors note, “[w]hile seasonal activity rates vary among species, a shortened fishing season would still decrease the total number of turtles captured, provided that there is no compensatory increase in fishing effort.”

Based on demographic traits like the current number of turtles in the lake, how old female turtles are when they first reproduce, and the proportion of female turtles that reproduce each year, the researchers estimated how the population of each turtle species might increase or decrease over the next 500 years under different bycatch scenarios. They determined that for three of the turtle species, just one or two female turtle deaths due to bycatch each year could lead to a complete loss of the population from the lake within that timeframe.

When I catch a crayfish in my hand-held net I can let it go right away, but turtles caught in underwater fishnets don’t have that option. The unintended capture of turtles during fishing can have disastrous consequences – as the authors write, “it is imperative that appropriate bycatch mitigation measures . . . are put in place to ensure the long-term persistence of freshwater turtles.”

Researchers studied four turtle species in Lake Opinicon, in southeastern Ontario, Canada, including the painted turtle. 

(Image by Micheal Jewel via Flickr)