Tuesdays with Turtles – Green Turtles Deluged?

Following up on the fishing issues from last week, here’s word that lights used to lure tuna towards longline fisheries attract juvenile sea turtles as well.

Article – Science & Technology – Lightsticks may hold deadly attraction for sea turtles

RALEIGH, N.C. Longline fishermen use lightsticks similar to the glowing tubes that delight trick-or-treaters to lure tuna and swordfish to baited hooks. New research by University of North Carolina-Chapel Hill scientists suggests that for endangered sea turtles the lights may hold a fatal attraction.

Lab experiments by Ken Lohmann, a University of North Carolina biology professor and John Wang, a graduate who is now a research associate at the University of Hawaii and National Marine Fisheries, found that young loggerhead turtles in a tank tended to swim toward lights.

It’s well known that hatchling turtles on a beach will crawl toward lights as they try to find the surf. But researchers did not know whether juvenile loggerheads in the water shared that attraction. Young loggerhead and leatherback sea turtles, which are protected because of declining numbers, are inadvertently hooked during longline fishing.

Well, not so surprising, is it? Bioluminescence is a common enough phenomenon that especially at night, animals will be attracted to light as it can signal food. It’s tricky, but when you try to catch fish, tyou will catch other animals as well. So, when you change something about the way you catch fish, you need to study how it affects other endangered species…

Off topic, but it is ironic that I read this in the ocregister, which is a newspaper from Orange County, California. It reported on work done by UNC Chapel Hill, which is in Orange County, North Carolina.

Depressing as always, but this is a yearly headline around turtle nesting season.

1,000 Giant Turtles Wash Ashore in India, Bangladesh

It’s nesting season for the sea turtles of Bangladesh and India, but this year the beaches where the animals lay their eggs are eerily still.

Nearly a thousand dead turtles have washed ashore along the coasts of both countries in the past few weeks, conservation workers report.

About 200 dead reptiles have appeared in the past week alone along a single stretch of beach, pictured here, in the Bangladeshi tourist town of Cox’s Bazar (see Bangladesh map).

A team of scientists visiting the beach on Monday to investigate the mysterious mass deaths concluded that fishing nets were to blame.

Sea turtles swarming the shores to nest are getting entangled in poorly laid nets and drowning, the experts told Bangladesh’s Financial Express.

The survival rate of turtle hatchlings is estimated at anywhere between 0.1 and 1%. Assuming 0.5%, this represents 20000 hatchlings. Assuming a hatching success (not all eggs hatch successfully) of about 2/3rds, that is 30,000 eggs, or between 200-250 nests. In my two years of turtle conservation work on an approximately 3 mile stretch of beach, we relocated about a 100 nests. These aren’t the same turtles (they tend to come back to nest very close to where they hatched), but there’s my two seasons of work down the drain and then some!

Turtle safe fishing is a well researched technology and is not expensive. As I have mentioned before in a similar context, the gaps between the availability of a certain technology and its actual adoption and use are depressingly huge.

When it comes to serious problems like global warming, all the talk is going to be about the cool science and innovative solutions, but how the technology transfers to India and China, how it is implemented, and the nature of the interactions between the traditional powers and the emerging ones is going to be more critical than the science. Something to remember as a scientist!

You see the hatchlings as they dig out of the nests all small and helpless and make a beeline towards the sea. You see the adult female as she comes back to lay her eggs. You see adult males when you go snorkeling , but the juveniles had kept a low profile, until now…

Sea turtles’ mystery hideout revealed – LiveScience – MSNBC.com

Once sea-turtle hatchlings hit the surf, they vanish for up to five years. Where the half-dollar-size tots spend these ‘lost years’ while ballooning to the size of dinner plates has been a mystery, until now.

New research, published in the online edition of the journal Biology Letters, indicates the green sea turtles (Chelonia mydas) hide out in the open ocean, where they feast on jellyfish and other marine creatures.

Turns out that they’ve been “hiding out” in the open ocean eating meat to augment their vegetarian adult diet. I have not seen the paper (reference below), but the study was based on an analysis of their shell content. Carbon and Nitrogen isotope analysis was used as a marker for diet and location.

The ‘lost years’ of green turtles: using stable isotopes to study cryptic lifestages

Kimberly J. Reich, Karen A. Bjorndal, Alan B. Bolten

Archie Carr Center for Sea Turtle Research, Department of Zoology, PO Box 118525, University of Florida, Gainesville, FL 32611, USA

An interesting paper featuring a North Carolinian turtle researcher Larry Crowder from Duke University:

Blackwell Synergy – Conservation Biology, Volume 21 Issue 1 Page 79 – February 2007 (Full Text)

Abstract: Although some sea turtle populations are showing encouraging signs of recovery, others continue to decline. Reversing population declines requires an understanding of the primary factor(s) that underlie this persistent demographic trend. The list of putative factors includes direct turtle and egg harvest, egg predation, loss or degradation of nesting beach habitat, fisheries bycatch, pollution, and large-scale changes in oceanographic conditions and nutrient availability. Recently, fisheries bycatch, in particular bycatch from longline fisheries, has received increased attention and has been proposed as a primary source of turtle mortality. We reviewed the existing data on the relative impact of longline bycatch on sea turtle populations. Although bycatch rates from individual longline vessels are extremely low, the amount of gear deployed by longline vessels suggests that cumulative bycatch of turtles from older age classes is substantial. Current estimates suggest that even if pelagic longlines are not the largest single source of fisheries-related mortality, longline bycatch is high enough to warrant management actions in all fleets that encounter sea turtles. Nevertheless, preliminary data also suggest that bycatch from gillnets and trawl fisheries is equally high or higher than longline bycatch with far higher mortality rates. Until gillnet and trawl fisheries are subject to the same level of scrutiny given to pelagic longlines, our understanding of the overall impact of fisheries bycatch on vulnerable sea turtle populations will be incomplete

Adult sea turtle killing by humans occurs due to

1. Harvest, killing them deliberately for food
2. Incidental bycatch in fishing nets
3. Habitat loss

The paper focuses on long line fishing and its effects on turtle mortality. So, if like me, you’re not a fisherperson, what is long line fishing and what are some other kinds of fishing techniques that have effects of sea turtles? Well, the Duke Project GloBal research team on studying bycatch has a nice primer. Some highlights:

1. Longlines: As the word suggests, longlines are very long (>10 km) lines of 2000+ individually baited hooks that drift close to the surface and are used to catch tuna, swordfish, halibut, etc. Crowder’s paper suggests that while each individual longline hook has low probability of catching a turtle, because of their number and ubiquitousness, they catch many many turtles.
2. Gillnets: These are giant rectangular mesh nets, either stationary or drifting, that catch marine life indiscriminately. There’s not much that can be done by way of reducingsea turtle catch in gillnets, except monitoring, observation and just using less of them
3. Trawls: Big funnel shaped bags that catch fish. Bottom trawling fishing boats used to, and still catch turtles at an alarming rate. Trawls are now (at least in the U.S and other “developed” countries) required to be outfitted with Turtle Excluder Devices (TEDS) to let turtles swim to safety.
4. Purse Seines: These are weighted on the bottom and float at the corners. They are indiscriminate, and especially hard on dolphins. It appears that mitigation efforts aimed at reducing dolphin mortality have the unintended effect of increasing sea turtle catch. Battle of the cute species!!

Take home message? Catching fish causes a lot of turtles to die. While trawl fishing is the worst culprit, it is also the most studied and the technique for which a viable mitigation strategy exists. THe other kinds of fishing are less studied, and there is precious little that can be done to avoid sea turtle bycatch.

Happy fishing!

Well, since this blog gratuitously takes its name from a sea turtle, it’s only fair that there needs to be a turtle post at least once a week! Why Tuesday? Because it alliterates. Why not Thursday? Because apparently, Tuesday’s the day that you do things with other things, ask Morrie.

I confess to knowing very little about the flatback. It’s only found around Australia and is listed as threatened. This news item caught my attention (for obvious reasons)

Turtles may fall victim to Australian gas project – International Herald Tribune

The peak nesting season is just drawing to a close for the flatbacks, a threatened species of sea turtle found only in Australia, when thousands of palm-sized hatchlings emerge from eggs buried under the sand and race to the sea. Every second counts: Between them and the ocean lies an army of hungry predators: lizards, dogs, foxes and gulls. Most of the turtles will never taste saltwater.

Development is another threat. Until now, the flatbacks could find some respite off the coast west of here, on Barrow Island, one of the country’s oldest nature reserves. But now environmentalists say that Barrow’s flatbacks may be among the victims of a plan by the oil giant Chevron to use Barrow Island for a roughly $8.6 billion project meant to supply natural gas to Japan and other energy-hungry nations.

“The environment is being made to pay for a poor business development model,” said Chris Tallentire, director of the Conservation Council of Western Australia in Perth.