Nothing to add here except that this question wins the January award for "Most Awesome" research question. Well done, sir. My hat is off to you.

YIKES !! You might want to consider the use of artificial substrates such as Hester-Dendy samplers. These are deployed in the river and then retrieved after a few weeks with the macroinvertebrates that have colonized then. The samplers are easily made or are available commercially and there is a significant literature on their use.

Nothing to add here except that this question wins the January award for "Most Awesome" research question. Well done, sir. My hat is off to you.

Awesome question; like what mr.paul said there are artificial substrates avail to collect the the organisms which depends on rocky substratum, but there are macro organisms which made their habitat along the river bank vegetation. please make note on all dwelling places (substratum, vegetation and soil) while going for the collection.

do well and good

The issue depends very much on the exact river and site you want to sample, and the species of crocodile(s) that live(s) there. I have done much sampling (herps and fish) in numerous rivers and swamps in all parts of Gabon, many of them ''infested'' with crocodiles. Mecistops and Osteolaemus are not at all an issue for your safety as long as you do not approach or threaten them. Only Crocodylus potentially are a problem, if there are large enough individuals (local villagers will know). Even if there are large Crocodylus, there are still of lot of sampling activities that can take place if some precautions are taken. But the best option is then to change to another site where there are no large Crocodylus, again villagers will be able to tell you where to go. Another issue with crocodiles you might have to consider is that they are very curious, and like to come inspect and bite or destroy your nets or traps. This happened to me numerous times, especially with Osteolaemus.

Quickly!

Use such dredges which can be operated from large sized boats, which keeps you away from the reach of crocodiles and collection will be conducted scientifically.

Awesome question. What about unexperienced undergrad students? They might not realize what they run into ;) - Greetings from a Swiss Monday morning

When I worked in Australia we had 'crocodile awareness training' before setting out in the field - it mostly seemed to consist of NOT hitting crocodiles over the head with your canoe paddle. Apparently that makes them a bit cross.

You need to be working as a team ( two or more) so that others are always keeping an eye on the surrounding waters.. when you get to a sampling point you must ensure that you survey the who stretch of the river before you venture in. I have heard that throwing one or two stones may keep the crocs at bay.You might as well move with an ellectrofisher to just scare them of.

I suggest take the samples at high water when crocodiles are spread in a larger area. At low waters (dry season) crocodiles are concentrated in a small area. In the Ibera wetlands we use a network with long metal handles operated from a small aluminum boat during the day. We have two species Caiman latirostris and Caiman yacaré, the last with high density.

Like Kate Searle, I too am from Australia and have had crocodile awareness training - I definitely recommend attending something like it (maybe ask university researchers or a zoo to help you?). We had it at Steve Irwin's Australia Zoo, and it was run by crocodile experts who gave us a lot of information. We got to recognise slide marks on the bank, that indicate that crocodiles are present. We also got to see some captive saltwater crocodiles disappearing into turbid water an becoming invisible right near the edge! Some people have said not to sample where there are crocodiles, but that is potentially most of northern Australia (and of course many other parts of the world). Every site is different, and like some others have said, local knowledge from villagers, farmers, etc. can be useful. Get to know your species - for some, the worst time to be in the water is around dusk, so best not to sample then. Sometimes you have to trust your gut instinct - some sites definitely feel more "crocodilian" than others and make the hairs on the back of your neck stand up!

You are asking about sampling in rivers that are crocodile-infested though, so you already know that crocodiles are there... In rivers with turbid water (where a crocodile could be 1 metre away from you and you wouldn't even know) I've sampled macroinvertebrates from the edge with a dip net on a long pole. It isn't ideal, but it is better than being attacked - but some crocodiles can lunge out of the water to attack you, so be wary of this... We always work in a team of 2 or more people. In crocodile areas, one person samples and the other keeps watch, holding a whistle to use in case any floating logs are sighted. I have also heard of some people sampling macroinvertebrates with a dip net from a boat. You need to be quick - don't hang around the site for too long, and don't leave arms dangling out of the boat for very long! Crocodiles nest on the banks so also be wary of the time of year you are sampling, and whether any crocodiles could be on the bank near you... Good luck!

I have attached the crocodile awareness protocol that we follow for field work. Hope it is useful.

Fantastic that Australian researchers have crocodile awareness training. Thanks for the protocol, which I have downloaded for future reference. Macro-invertebrate sampling doesn't always need boats, as other replies have indicated. We usually sample from the river bank, with an armed guard if possible. Light trapping at dusk has its own hazards, and a bright torch to spot the eyes, which glow red at night when you shine a light at them. Its always quite nerve wracking sampling in croc infested waters.

Also in Australian Rivers, we have sampled from boats, using a rake or some other device to distrubte the habitat where you can then follow with your sampling net. This method of boat based sampling is actually preferred in sampling manuals here in Australia, because of crocs.

Most of the rivers we deal with are not deep enough for boats, though yes, I can certainly see the advantage of being in a boat if possible.

Snappily...? Sorry, I'll get my coat.

I would like to thank everyone for the helpful hints, advice and comments. At least I am now able to design my research to fit in with our nile crocodile infested rivers.

Thank you for the protocol Alisha. This question arise also in African streams. So your experience is very interesting!

While it be in any waters researcher should be well trained as well as be equipped

For some reason my first post did not appear ?

I suggest using artificial substrates like Hester-Dendy samplers - they can be deployed and retrieved by boat without getting into the water. We are using them with a lot of success in arctic rivers.

Just picking up on your comment Paul, the use of artificial substrates, do you have any references where I can learn more? Sounds interesting!

Hi Nathan, one reference (& some other references therein:

Methods for sampling benthic macroinvertebrates in tropical lentic systems

Lynette H. L. Loke et al., Aquatic Biology 01/2010; 10(2):119-130. DOI:10.3354/ab00274.

Cheers

In response to NATHAN WALTHAM here is a site that specializes in these samplers and also provides methodological links.

http://www.hesterdendy.com/

Very, very carefully :o)

ohh.. I was also going for the joke of " very very carefully", and fast.. haha

Good luck ! ;-)

thank you Alisha. wish we had that protocol when we were up in the NT trapping for Macrobrachium prawns on the E alligator and Daly rivers and associated billabongs back in the early 90s.

i would also add: when at likely croc waters try to avoid repeating the same activities at the same times on successive days. The crocs can track this sort of activity and they may plan accordingly.

Great post. I've been sampling in the Darwin harbour area for about one month. My RA would watch out for possible danger and I walked in shallow water to collect mudskippers .... I was just lucky, I guess. When we both attended one of those "jumping-crocodiles" tours for tourists we realised we would not have a chance.

Silent, virtually invisible, fast, powerful. Visibility is just a few cm in those waters.

Alisha thank you so much for the document. I'm working in Brunei now. Not such an issue like in northern Australia, but salties are here as well.... thanks again.

Change Your expertese area ;-)

Hi Maria Nunez,

Are you saying, I should change my career?

I would have done ut!

Alisha is right. I work in the tropics of Australia in crocodile waters. The best thing to do is to do crocodile awareness training and sample with something like a Van Dorn bottle that you can throw into the water from a distance. If there are crocs there you may lose the bottle, but its better than losing your life. It would also pay to go sampling with someone experienced in those waters.

Hi Todd,

As you've probably experienced in your fieldwork with Jens, adult Odonata are excellent surrogates of overall macroinvert diversity. Better still, you can identify to species level and often can just identify species through binoculars.

Cheers, KD

Hi Klaaus-Douwe,

You are right. I finally decided on using adult Odonata as most parts of the stream could not be sampled because of crocodile infestations. I am glad that you came when we are almost concluding the study.

Thanks alot. I really value your contribution.

Cheers, Todd

Good luck, Todd, and remember to share your results with Jens. Cheers, KD

Will surely do. Thanks a lot.

Regards, Todd

Cast nets offer flexibility in the depth of areas sampled and a relatively quick so high rates of replication can be achieved

There are a few sampling devices that lend themselves to not getting your hands and arms ripped off or mangled. The Hester Dendy Invert sampler, a colonisation sampler set, and various artificial structures. They can be dropped in with a float and anchor or tied to trees and retrieved with hook poles, from a boat or at a distance from the water edge. There are also drift nets that can be set up and retrieved from boats. Having seen the results of alligator attacks on scientists who where sampling I guarantee you don't want even a small

Hello Daniel. I'd suggest you consider a kick net or suber and keep crocs away from you with an electrofisher when in shallow water (>0.75m) and in deep water (>0.75m) use and boat. In RSA we sample in the Kruger National Park regularly. Regards

Gordon 

Hi Gordon,

What is the effective range of these electrofishers? Are they also affordable!

Todd

Gordon, Todd

backpack shockers can run a little expensive depending on what you get up 10- 20K around here. Gators get the heck out of there when they feel it hit.  I've seen them used without neoprene waders but they can uncomfortably shock you if you are using goretex waders especially if it's hot and you are sweating.  The boat mounted ones will incapacitate you if you are in the water.  In the US you have to have a permit and you should have a person there to rescue you if you were to become overcome.  Also, more mobile inverts will try to take off and avoid the shocker by burying or swimming, while some will be incapacitated by the shock.  Just like the fish that they were intended for.  There are pluses and minuses.  Having never used a shocker for bug collection I don't know but I would guess that most diving inverts would float and aquatic stage inverts would sink.  The plus being that most reptiles don't like it.  But I have also seen snakes, specifically water moccasins, get really upset by the shocks and not avoid it because they try to hide . If you are good and have observation time you can dial in the frequency and voltage to specific values that crocodilians don't like.

you can make your own for cheaper.  If you look it up there are designs and specs out there.  

Are there hippos around? anything that you can stand a hippo won't even care if they view you as a threat.  Just like bulls who want to fight.

some people modify an electric fence unit to do the job, also you can run wires from a gas motor ignition, but it's a little hot and fast.  You would definitely want someone around for the motor trick, and with all shockers, you can drown if you aren't careful.

Much depends on the invertebrates that you intend to study.  However, remote sampling would be what I would consider but there may be problems with snagging on submerged objects such as waterlogged dead trees.  Should the density of the invertebrates be high then sampling using a basket dredge or Van-Veen type grab might just be sufficient for your study.  Diving may be an option under some circumstances but whether this something that you would be covered on your life -insurance policy is something else.