My favorite turtle organization, the Chennai students’ sea turtle conservation network is in the process of getting a website together. It will be at http://www.sstcn.org, which is not much to look at right now!
So, blogging has been light this summer as Olive Ridley’s partner made her way to Canada and is settling in. Also, it is summer in BC and beautiful as hell, so the prospect of sitting down and typing on a computer with brains that are only half working, well, ain’t so hot! Also, Canada is just a much calmer place than the U.S. As I looked back at my many posts, most of them are bitter fulminations against American politics or the various shenanigans of the Emperor. Anyway, I am not under his rule any more, and while he’s gutting the Endangered Species Act as we speak, he will be history soon.
While Canadian policy debates are equally interesting, they are generally civil in comparison, except the occasional kerfluffle where old white men want their female opponents to go back to making tea, charming…
Anyway, I felt the blogging itch again and as always, it’s nice to get back with a story about turtles.
Researchers say they have figured out why sea turtles that normally feed and breed in shallow water or on land will, very rarely, go deep sea diving: the reptiles are on reconnaissance.
Leatherbacks have amazing diving capabilities and can get up to a kilometre below the surface. Why? for food, of course! More precisely, the promise of future food. Turns out that jellyfish (or jellyfish like animals) hang out in the deep during day time and surface at night. Leatherbacks go looking for them during the daytime down in the deeps so they can get them on the surface for dinner. It’s akin to you taking a leisurely walk around downtown looking for the perfect dinner spot.
Interesting. As always, very fascinating and sexy creatures, and critically endangered.
Expect more regularly scheduled blogging just in time for the late summer sweeps!
North American marine turtles are at risk if global warming occurs at predicted levels, according to scientists from the University of Exeter. An increase in temperatures of just one degree Celsius could completely eliminate the birth of male turtles from some beaches. A rise of three degrees Celsius would lead to extreme levels of infant mortality and declines in nesting beaches across the USA.
Like a lot of other reptiles, the sex of the hatchling is dependent on nest temperature. Warmer temperatures make female turtles (my mnemonic was hot females!), and even warmer temperatures just kill the eggs. But, I wonder if the turtles would adapt by nesting a little earlier. I don’t think it is yet clear when turtles decide to nest. If it is based on sea temperature, then they would eventually figure it out. This paper from 2004 appears to conclude that loggerheads in Florida do nest earlier than before, so there is hope.
John F. Weishampel, Dean A. Bagley, Llewellyn M. Ehrhart (2004) Earlier nesting by loggerhead sea turtles following sea surface warming Global Change Biology 10 (8), 1424–1427
The onset of spring, noted by the timing of wildlife migratory and breeding behaviors, has been occurring earlier over the past few decades. Here, we examine 15 years of loggerhead sea turtle, Caretta caretta, nesting patterns along a 40.5 km beach on Florida’s Atlantic coast. This small section of beach is considered to be the most important nesting area for this threatened species in the western hemisphere. From 1989 to 2003, the annual number of nests fluctuated between 13 000 and 25 000 without a conspicuous trend; however, based on a regression analysis, the median nesting date became earlier by roughly 10 days. The Julian day of median nesting was significantly correlated with near-shore, May sea surface temperatures that warmed an average of 0.8°C over this period. This marine example from warm temperate/subtropical waters represents another response of nature to recent climate trends.
So the truth lies somewhere between easy adaptation and giant swarms of frustrated female turtles!
An interesting paper featuring a North Carolinian turtle researcher Larry Crowder from Duke University:
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
- Harvest, killing them deliberately for food
- Incidental bycatch in fishing nets
- 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:
- 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.
- 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
- 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.
- 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.
Turns out that a small change in hook design can save a lot of turtles from getting caught in longline hooks. But the story’s not really about the shape of the hook. I’ve written about this before. The issue is rarely one of technology. The solutions have been developed and exist because a lot of work has gone into developing technological solutions. Implementation on the ground (or sea!) has lagged because it is much harder to effect change where it counts when you attempt to impose technology in a top-down fashion. Small scale fishers (new english here, to avoid the whole fishermen/fisherwoman/fisherperson nonsense, take out the gender specific suffix to every occupation describing verb! – Try it, it’s not weldman, or plumbwoman!) are in a world of hurt with declining fish stocks and widespread fisheries piracy by the so called “developed world”. Without developing and implementing the solution with the full participation of the people who have the most potential to be affected, the change will not be successful.
What did the WWF do differently this time?
Together with fishermen we are building a culture for sustainable fishing practices that will guarantee fish stocks in the long term
They emphasized the people, not the solution. And the results were great, 90% reduction in turtle catch, >95% of the turtles caught were released safely, and the fish yields were not affected. Everyone wins, right?
Good stuff. Those turtles are still endangered and we’ll run out of wild edible fish in 50 years, but hey, more like this and there’s a bit of hope.
Olive Ridley hatchlings emerge in Gahirmatha
Kendrapara (Orissa), April 10. (PTI): Millions of tiny olive ridley sea turtle hatchlings are now emerging out of nests at the Gahirmatha beach in Orissa’s Kendrapara district, wildlife officials said on Monday.
The eggs laid by thousands of adult females in the Nasi-2 and Babubali islands in the Gahirmatha marine sanctuary have began to hatch over the last two days, they said.
Wildlife officials stationed at the nesting grounds were witness to the phenomenon, but tourists and researchers were not allowed into the unmanned territory close to the Wheeler’s island where a defence test range is located.
India’s intermediate range nuclear-capable missile Agni III is likely to be test fired from there some time this week, defence sources said.
You know what, the fact that this area is under close military supervision because of India’s grandiose missile dreams may not be sucha bad thing (sacrilege!!!). The area is under so much development pressure that even military operations are better than the alternative.
For more about the Gahirmatha area, visit the official website. At this point in time, the Arribada is very tourist unfriendly, and there are few, if any volunteering opportunities. I will keep any eye open for changes
If you did not know already, sea turtles tend to nest on (or close to) the beaches they were born at. It is known that they use the Earth’s magnetic fields to navigate. Here’s an article on the navigational natations (I strain to alliterate at times, but natation means swimming!) of the Green Turtle.
I flagged this article not because it tells us much new, but just adds some nuances to sea turtle navigation.
The study has shown that the marine turtles’ navigation system allows them to maintain their course towards the egg-laying site wherever they find themselves. It is almost as if they were equipped with a compass pointing towards the beach in question. So they can correct any deflection they are subject to: transport by boat, ocean currents… But, unlike human navigators, they are not able to correct for ocean drift in plotting their course. So the movements recorded by the satellite are a combination of deliberate action by the turtles and the effect of currents. So it appears that the turtles’ navigation system is relatively simple and may cause them to be wander at sea for long periods during adverse ocean conditions. One turtle released 250 km from its egg-laying site on Europa traveled more than 3 500 km in two months before returning there!
Well, that’s interesting, if not surprising. It’s one thing to have a magnetic bookmark of a destination in your head (pretty wonderful thing, I wish I had it!) and swim continually towards this destination. It’s quite another thing to keep track of complex parameters like ocean drift and keep correcting continuously.
In essence, what they’re saying is that turtles home in on their destinations, but don’t always take the shortest way in because they tend to drift and not correct for this drift dynamically. It is not evolutionarily necessary because turtles probably do not get thrown way of course often enough that evolving even more sophisticated navigational systems (Garmin?) would provide a significant enough survival advantage.
In the Mozambique Channel, between the east coast of Africa and Madagascar, on the beaches of the French Islands of Europa and Mayotte, they caught turtles at the beginning of their egg-laying cycle, so that the animals were strongly impelled to return to this area to complete their cycle. After having Argos transmitters fitted to their shells in order to satellite track their return journey to the beach, the animals were released in open sea, several hundred kilometers from the egg-laying site.
Now that’s just mean! Imagine being kidnapped, tagged and released many miles away from home, and having to find your way back. Apparently, these turtles did it. Man, that would be such a cool navigational aid to have, quite a party trick!