Fri 29 May 2009

300 entangled horseshoe crabs rescued at Mandai Besar mangrove

Category : marine

Carcinoscorpius rotundicauda is one of four species of horseshoe crabs in the world. It is found in the inshore waters of the Indo-West Pacific and associated with the mangrove-mudflat ecosystem. In Singapore waters, from eyewitness accounts alone, their numbers have depleted significantly since the 80's. This is not unexpected given the massive quantity of habitat loss and increased pollution over the past three decades along the Johor Straits.

They still are found in the mangrove-mudflats of north-western Singapore, off the Johor Straits. However, nearshore fishing is unregulated, and Mandai mangrove and mudflats are not provided with any special protection by the law. It's fate appears to be undecided as yet. Meanwhile something else threatens its ancient denizen.

Telsons poking out of the net give an indication of the number of trapped animals in this section of a long net

Frequently over the past decades, monofilament gill nets have been left behind over several tidal cycles in several mangrove patches in north-west Singapore. These poorly frequented areas without popular access are commonly only visited only by recreational fishermen and researchers. Fishermen normally harvest fish caught in a gill net after a single tidal cycle as the dead fish would rot very quickly. However, many nets I have encountered are unattended for days and are regarded as "ghost nets". Entangled fish will die once exposed but arthropod mangrove residents, can survive trapped in the net for several tidal cycles. Eventually it is the heat of the sun during the exposed low tide or starvation that kills them.

In several instances, I have found entire lengths of "ghost nets" with the still-trapped carcasses of animals in an advanced state of decay. In other instances, I have been fortunate enough to detect them early enough to release the living indiviudals. A few of such instances are featured in Habitatnews over the years, e.g. in March 2005 and July 2008. Members of the Nature Society Singapore Horseshoe crab research and rescue team scour Kranji mangroves on a quarterly basis to release trapped individuals as well [link].

Given the reduced population size of these Xiphosurans ("sword tail"), the the impact of indiscriminate capture by gill nets has been heightened and it tragic to see the senseless slaughter of these animals, mirroring the larger-scale problem in the world's oceans.

Two nights ago (27 May 2009) I chanced upon a gill net and the sound of horseshoe crabs struggling to be free at about 11pm. My labmates from Ecolab and myself had been in the area for about four hours and were leaving as the tide rose. Regretfully, we left behind the trapped horseshoe crabs.

I reassured myself that the incoming tide would keep them relatively safe, even if they could not bury themselves.

The next morning I returned alone to release the animals, thinking it would be a one or two hour job as was usually the case. Instead I discovered I had badly miscalculated the numbers trapped in the darkness of the previous night. And I had come directly without help or breakfast! But it was getting hot so I decided I'd best just work as fast as I could.

Mandai Besar mangrove, 27 May 2009

In the end it took five hours (8.45am - 1.45pm) to remove some 300 mangrove xiphosurans from a 100 metre gill net. They were in relatively good condition, being able to struggle reasonably vigorously. There was no mortality except for predator attack (possibly heron) on a two mature gravid females. Otherwise the other females were not full of eggs.

I cut the net into several sections and dragged them into different lengths of a stream through some thigh-deep mud. I turned the thick bundles over every couple of hours (or when I thought the carapace looked alittle too dry) to ensure that all the individuals were kept wet. Thankfully there were intermitted clouds that reduced that stress on the animals. I cut out an individual at a time, removing the entangled net with the help of a pair of scissors.

I tried to keep the cuts to a minimum to reduce littering the mud with short lines. By first removing the main tense filaments restricting the animal, the scissors was then used like a pair of forceps to pull loose any line entangled amongst its segmented legs. This often required cuts at either ends to remove knots before pulling a line free with the scissor tip - it helped that I was using a narrow-point scissors with a slightly dulled blade tip.

I had to be careful not to cut and injure a grasping leg or a telson - the latter looks like a twig so I kept saying to myself, "there are no twigs"! So the release was a very deliberate exercise and it was important to be vigilant while working quickly. Sand grains and the filaments were wearing into my skin and I was thankful the water was brackish and not salty.

As each animal was cleared of all filament, it was released away from the net to prevent re-entanglement - horseshoe crabs can move away quite fast in precisely the wrong direction sometimes! I bundled the net fragments away from the stream for collection later. Thunder crabs and forceps crabs were set aside as they require a much finer pair of scissors and would take too much time. Those I would bring back to the Systematics & Ecology lab at NUS for release and return later.

It was hot and I ran out of water but that spurred me to work faster before these creatures dried up. By creating sections, I turned a large job into a series of smaller jobs to encourage myself with intermediate success. By 10.30am (1 hour 45 minutes) I estimated that I had released over a hundred horseshoe crabs. By then I was sitting in the mud and pretty much covered with it as bending over and even squatting was too tiring.

As the tide rose, I went back to turn over individuals that had returned to a belly up position. I was encouraged when I saw some crawl off but did not examine them. As they were submerged, I cleared the cut nets and stuffed them into large plastic bags I found amongst the trash on the forest floor. Rain threatened but did not come, unfortunately. Eventually, the last individual was released about five hours after I had first started.

I dreamt of them later and woke up in the middle of the night hoping they were all okay.

Until the next ghost net appears.

Photos on Flickr

Posted at 6:50PM SGT by N. Sivasothi | permalink | , .

Fri 25 Jul 2008

Video clip of horseshoe crab rescue at Mandai mangroves

Category : marine

During the mangrove horseshoe crab yesterday, I had Kah Ming shoot this video clip with my Panasonic Lumix when Theresa and I were disentangling the crabs from the monofilament gill net. The battery ran out and I uploaded the film clip warts and all. The camera's output was a 718.2MB 640 x 480 mov file; within QuickTime, I used DivX export which reduced the filesize to 72.4MB - almost a 10 times reduction!

I uploaded this video to Vimeo since YouTube can't handle DivX formats yet and Google Video is experiencing some error which has them challenging the copyright on all my videos. Isn't it always nice to have alternatives and the means to distribute videos for free?

The horseshoe crabs appear dead so its important to check each individual. The scissors are very important as it eliminates the need to pull the filament against the limbs which can accidentally cut the animal! Just keep going snip, snip, snip after every filament joint and gently pull each cable one way or the other until it comes free with little resistance. An alert assistant able to work patiently with the persn doing the cutting can be invaluable! We later took out an additional, smaller scissors to tackle some very tough knots buried at the base of the animal's legs. Amongst the horseshoe crabs was a single, defensive forceps crab! We did lose count of the number released but hey, we were focusing on completing the release and the need to continue with our recce!

Posted at 12:46AM SGT by N. Sivasothi | permalink | , .

Thu 24 Jul 2008

Horseshoe crabs rescued from a ghost net in Mandai mangrove

Category : marine

Horseshoe crabs have been around for at least 445 million years, predating the dinosaurs and they are facing their greatest challenges during the Anthropocene - habitat loss, pollution, over-fishing and ghost net entanglement. The latter arises when fishermen abandon or lose their strong mono-filament gill nets; these do not degrade but will instead repeatedly entangle all sorts of animals in mangroves, rocky shore, coral reefs, sea grass and sandy shores.

This is happening in Singapore too. Like my fellow naturalists and field biologists, I have had to rescue horseshoe crabs, forceps crabs, birds and even snakes over the past two decades. Habitatnews has highlighted just a couple of these rescues (e. g. Lazarus Island, 2004; Mandai, 2005) and the Nature Society (Singapore) has a regular rescue team that works the Mandai mudflats. These days it seems almost every low tide trip to a mangrove reveals ghost nets - e.g. shooting for Once Upon a Tree 2, a shore visit suring the last Pedal Ubin and the recent Lim Chu Kang mangrove cleanup as well.

Mandai mudflats and mangroves have such a high incidence of ghost nets that I pack a scissors and factor in time for gill net removal each time before I set out - film shoot, education trip or work trip. Unfortunately, today was no different - NUS biology honours student Theresa Su, Raffles Museum Toddycat Teo Kah Ming and myself carefully released about 20 mangrove horseshoe crabs that were still living. Kah Ming had counted 87 carapaces entangled and adacent to the net so most had died some time ago.

We checked each individual to be sure and carefully removed the nylon filaments that had weaved between and around their limbs. The chelicerates (horseshoe crabs are not crabs) were not feisty but happily not too limp - so they were recent entanglements but probably not last night's. Once freed, we left them clustered in various tide pools nearby with some hope that they would survive. The net was cut into three lengths and carried out in a bag made from a large-mesh ghost net lying nearby.

There are still nets out there, I know, and with research trips increasing, hopefully it will come to a time when my scissors can stay in the bag!

Posted at 11:01PM SGT by N. Sivasothi | permalink | , .

Wed 18 Apr 2007

"Say no to plastic bags"

Category : coastalcleanup

"Say no to plastic bags." By Lee U-Wen. Today, 18 Apr 2007.

YOU may not realise it, but each day, nearly every one of us brings a pest into the home. They are small, mostly pink, blue or white in colour, adaptable to land and water, and have caused the deaths of countless animals and fish around the world.

This lethal monster is none other than the plastic bag, a flimsy everyday item that we simply cannot do without, yet has been the scourge of many cities, even countries, which have rallied to impose taxes or ban them altogether.

The global war against plastic bags - something that most people use for only a short while but takes hundreds of years to break down - is picking up steam, most notably in San Francisco, which last month became the first American city to ban non-biodegradable plastic bags. Shoppers there now must use paper bags when they buy groceries, or carry their own bags from home. The move came after weeks of intense lobbying from environmentalists.

San Francisco joins a select group that has taken a major step forward in saving the earth, including Rwanda, Bangladesh, South Africa, Mumbai and Bhutan which have already imposed their own ban. Paris will join the list at the end of this year, with the rest of France following suit by 2010.

Why, then, is Singapore, a much smaller city and one that has serious aspirations of making its mark as a champion of green technology, not following suit in a big way?

A National Environment Agency (NEA) study revealed that Singaporeans use about 2.5 billion plastic bags each year - the equivalent of 19 million kilogrammes of waste.

In Apr 2005, TODAY raised the plastic bag issue to national debate.

Ever since a heated debate on plastic bags was sparked off in this newspaper some two years ago, the awareness of the problem has gone up somewhat. A national campaign to encourage the use of reusable bags has taken off well with more than 100,000 such bags sold at many major supermarkets.

More significantly, today marks Singapore's first Bring Your Own Bag Day, where more than 200 supermarkets will encourage customers to use reusable bags. That it is not just a one-off campaign, but one that will take place every first Wednesday of the month, is also laudable.

But we can do better. We need to speed up the push to bring down the use of plastic bags here.

The Government certainly believes enough in Singaporeans' changing attitudes towards environment issues, seeing how it is investing millions of dollars to study clean energy and launching eco-friendly flats in Punggol.

But time and again, whenever the plastic bag problem surfaces, we get the same message from the lawmakers, that it prefers not to impose legislation, but rather work with voluntary schemes and allow consumers and the market to take the lead.

Encouragingly, the door to legislation is not fully closed, as NEA chief executive Lee Yuen Hee said last week that he had not ruled out making it a law if the plastic bag situation does not improve here.

Then the question is, when is that breaking point for such a move to happen? What would it take for lawmakers here to introduce a law in Parliament? I believe that if we continue to take the ground-up route, we can never expect any significant progress to be made in a country where people have grown up expecting plastic bags to be given to us free.

Realistically, banning plastic bags completely is not completely feasible, given our heavy dependence on them, be it at the wet market or to contain garbage at home.

A plastic tax is perhaps the best way to make consumers think twice about whether they really need that bag when they buy their pack of cigarettes, a newspaper or a loaf of bread. Such a tax is already taking off in many countries around the world. If you're out shopping in Taiwan or Ireland, be prepared to fork out anywhere from five to 20 cents for a plastic bag.

Last June, Ikea stores in the United Kingdom started charging its customers 10 pence (30 cents) per bag, a move which the furniture giant said could cut down plastic bag usage by a whopping 20 million by this year. Its two stores here recently became the first retail stores to start charging for plastic bags.

How Singapore can do one better is to promise that every single cent collected from its plastic bag tax goes towards green effort, be it for more recycling centres, running environmental programmes in schools, or to various non-profit groups such as the Environmental Challenge Organisation and the Singapore Environment Council.

You do the maths - a nominal tax of, say, five cents multiplied by 2.5 billion bags would add up to an astonishing $125 million to fund meaningful causes. But until then, let us try to cut down our usage in whatever small way we can.

With April 22 being Earth Day - a special day to celebrate the Earth and remind ourselves of its scarce resources - each of us can do our part by refusing that plastic bag when we go shopping, or even better, bring along a reusable bag.

That would be the best present you could ever give to Mother Nature. And it's much better than having to deal with yet another law breathing down our necks.

Links

San Francisco, first US city to ban plastics bag distribution at large supermarkets.

• "San Francisco to ban plastic grocery bags." Reuters (at CNN), 28 Mar 2007. San Francisco's Board of Supervisors voted ... to become the first U.S. city to ban plastic bags from large supermarkets to help promote recycling.

• CNN video. "We can't sleepwalk into the future. The end of the era of cheap oil is here."

• "San Francisco Nears Ban on Plastic Grocery Bags." By Richard Gonzales. NPR, 14 Apr 2007. Audio file and transcript.

• "Paper or plastic? San Francisco decides." By John M. Glionna. L. A. Times, 28 Mar 2007.

• "Plastic-bag ban full of holes." USA Today, 01 Apr 2007. The real culprit is the slob who litters or refuses to recycle either one — or communities that don't provide the means for him to do so. Our throwaway society is to blame as well. ... Each individual can do more to help the environment by reusing whatever bags groceries distribute or buying a canvas sack to carry goods.

• Google News and Yahoo! News. For emerging reactions from other counties, states and countries.

• Google News Archives

Some highlights from recent efforts in Singapore

• WildSingapore: News about plastic consumption. Efforts to reduce use of plastic bags, issues, discussions.

• "NEA launches campaign to encourage shoppers to use reusable bags." By Wong Mun Wai. Channel NewsAsia, 11 Apr 2007

• "Ikea to start charging customers for plastic bags." By Tania Tan. The Straits Times, 11 Apr 2007. Retailer hopes to cut waste; from April 22, shoppers will pay up to 10 cents for them.

• "Campaign to reduce wastage of plastic shopping bags." Habitatnews, 10 Feb 2006 - campaign and background to problem.

• "Make the difference." Today, 28 Oct 2005. Every gesture contributes to improving our environment.

• "Semakau landfill to last 15 more years as recycling reduces waste." Channel News Asia, 16 Jul 2005.

• "Is S'pore a nation of plastic bag junkies?" Habitatnews, 26 Apr 2005 - Lee U-Wen's article title (25 Apr 2005) and Yvonne Lim's editorial, "Say no to plastic bags." (26 Apr 2005).

• "IKEA will not distribute plastic bags on Earth Day weekend." Habitatnews, 11 Apr 2005 - about The Straits Times report, and comments based on data from ICCS 2004 and NEA Clean Card 2005.

Impact on Marine Life and Public Education

• "Battling the Curse of Marine Litter" - article that explains the problems, special impact of plastic, volunteeer efforts on the international coastal cleanup especially mangroves and what the data tells us.

• "Drowning in an ocean of plastic." Habitatnews, 07 Jun 2004 - highlights from article of that title in Wired News, 5th June 2004 by Stephen Leahy.

• "More than 100 horsehoe crabs rescued from gill net at Mandai." Habitatnews, 13 Mar 2005.

• "Lazarus Island rescue for crabs and coral." Habitatnews, 28 Jul 2004.

• "Two dead turtles, guts choked with marine rubbish (Australia)." Habitatnews, 15 Jul 2006 - Univ. Queensland report.

• "Reaching heartlanders on World Environment Day - EnviroFest 2006." Habitatnews, 23 Jun 2006 - One way that various groups promote nature/environment education in Singapore.

• "What an Albatross ate." Habitatnews, 06 Mar 2004 - Link to a Shifting Baselines feature on plastics.

• "L. A. Times "Altered Oceans" features the plague of plastics." Habitatnews, 05 Aug 2006 - excellent web resource!

International Coastal Cleanup Singapore

• ICCS webpage - 2006 results.

• "Battling the curse of marine litter - volunteers around the globe take to the shores." Habitatnews, 18 Sep 2006.

• "Here's the dirt on S'pore's beaches." Habitatnews, 05 Dec 2005 - ST report by Radha Basu on the 2005 International Coastal Cleanup Singapore; 'Singapore has had an anti-littering campaign for more than three decades. Yet we seem to have a long way to go.'

• "Worldwide Coastal Cleanup Bags 4,000 Tons of Debris." Habitatnews, 21 May 2005.

• "World Oceans Day - ICC director speaks at the United Nations." Habitatnews, 09 Jun 2005.

• "Coastal Cleanup data in FHM." Habitatnews, 22 Mar 2005.

• "Reflections of Cedar Primary students." Habitatnews, 13 Oct 2005 - "The beach was very dirty. I think we P4s have done a good job in picking up the litter. But I wonder why there were so much litter. Does that mean we singaporeans don't care for our environment. In future, I wish I could see Singapore's beach clean." Hema Roshini 4-3.

• Rubbish in Johor Straits - '15 tonnes collected daily'. Habitatnews, 23 Jul 2006 - NST article: "Tonnes of rubbish from polluted strait."

• "Clean, Green S'pore? Not the beaches." By Radha Basu. The Straits Times, 22 Oct 2004.

Posted at 3:28PM SGT by N. Sivasothi | permalink | , .