There's probably no "right" methodology for berried females - they'll always be difficult to collect.

Westman et al. (1978) conducted night electrofishing for crayfish (cited below). I don't recall their success for berried individuals. You might also consider kick-seining or kick-sampling (e.g. Gladman et al. 2011), or the use of habitat bundles - which might be colonized by berried females (Parkyn et al. 2011). Depending on your system (water depth), you might also consider active searches by snorkeling or diving (Lamontagne and Rasmussen 1993).

I collected roughly 7,300 crayfish (combined for two species) over a year and a half for a life history study (on quite different species from P. leniusculus in wadeable, rocky streams), and found a total of 48 berried females (Larson and Magoulick 2008). Those were obviously constrained to a subset of sampling months (spring), where berried individuals constituted ~90% of all females collected for one species, but only ~20% for the second. There are enough life history studies out there interested in berried crayfish that you may be able to find better examples of sampling methodologies (and their efficacy) for your species and systems similar to yours; see Moore et al. (2013) for a recent (but North American-centric) review. Also specific to signal crayfish life history, I think Scott Lewis' thesis work (from a large lake system) from the native range is excellent, see here:

http://ir.library.oregonstate.edu/xmlui/handle/1957/14611

Important as well, see all references to Mason cited by Lewis, who did a great deal of work on signal crayfish reproduction and egg laying in the native range. Some of that may point to sampling methodology, as well.

Gladman, Z.F., W.E. Yeomans, C.E. Adams, C.W. Bean, D. McColl, J.P. Olszewska, C.W. McGillivray and R. McCluskey. 2011. Detecting North American signal crayfish (Pacifastacus leniusculus) in riffles. Aquatic Conservation: Marine and Freshwater Ecosystems. 20:588-594.

Lamontagne, S. and J.B. Rasmussen. 1993. Estimating crayfish density in lakes using quadrats: Maximizing precision and efficiency. Canadian Journal of Fisheries and Aquatic Sciences 50:623-626.

Larson, E.R. and D.D. Magoulick. 2008. Comparative life history of native (Orconectes eupunctus) and introduced (Orconectes neglectus) crayfishes in the Spring River drainage of Arkansas and Missouri. American Midland Naturalist 160:323-341.

Moore, J.M., R.J. DiStefano and E.R. Larson. 2013. An assessment of life-history studies for USA and Canadian crayfishes: identifying biases and knowledge gaps to improve conservation and management. Freshwater Science 32:1276-1287.

Parkyn, S.M., R.J. DiStefano and E.M. Imhoff. 2011. Comparison of constructed microhabitat and baited traps in Table Rock Reservoir, Missouri, USA. Freshwater Crayfish 18:69-74.

Westman, K., O. Sumari and M. Puriainen. 1978. Electric fishing in sampling crayfish. Freshwater Crayfish 4:251-256.

Thanks for the detailed answer. The Lewis (1997) thesis continues to be one of the best pieces of life history work I have found on signal crayfish (Although Guan and Wiles publications from the UK around the same time also contain lots of excellent material). Thank you for the references, I am currently awaiting confirmation of International Astacology Association membership, so am eagerly anticipating the opportunity to read the Freshwater Crayfish publications. Is kick-seining at two (or more) man job?

I have found these refuge traps (guidelines attached) to be highly effective (n=139 out of a total of 799 individuals caught (~50:50 M:F) in a 3 month study period, 6, two day-samples using 40 traps: 10 refuge, 30 baited) in catching berried Orconectes virilis females in a navigation channel in the South of England. I can only assume these traps work on a similar principal to those used in Parkyn et al (2011). I want to use them again but I'm not sure of their efficiency in untested habitat types.

Kick-seining can be done by a single person; effectively all of the Larson and Magoulick (2008) reference above was conducted solo by me. An additional person certainly helps, and would allow for a larger area to be sampled (two people can hold a wider seine, and disturb substrates over a larger area, than a single person). That may also be dependent on the habitat - I was working in fairly small, wadeable, and very rocky streams (with high crayfish densities).

Great to hear you've had success with the refuge traps; and that you've worked on O. virilis in England - an under-studied invader!

I agree that trapping is likely to be ineffective for collecting berried females. Electrofishing may also not be ideal because berried females are likely to be inactive under the substrate and may not surface. I have had success collecting berried females using kick nets in streams and turning over rocks by hand in the littoral zone of lakes, so depending on the habitat you are sampling, one of these two strategies may work well.

Thanks Lindsey, I suspect the study sites will include small gravel streams, small upland gravel/pebble rivers and hopefully a small lake, so I can foresee I wide variety of methods being employed. I was also not sure what electrofishing might do to the numbers of eggs being carried, whether the stress might cause egg loss. Still lots to find out!

Ovigerous females are usually hidden, and decreasing their activity. However, especially in oligotrophic lakes or reservoirs is effective to use a baited (fish meat) stick to elicit females from their shelters. Than you can catch them by hand. Some conclusion provides following paper: http://www.onema.fr/BFPP/bfpp/Article/376_377/376p675.pdf

For signal crayfish is probably effective also hand searching under banks or stones.

Both methods are little bit laboring but you can obtain ovigerous females in top condition (and without methodologically induced egg losses) in contrast to kick sampling or electrofishing. In addition, you see the real crayfish habitat or differences in foraging behavior etc.

Milos

I agree with the answers provided. In my experience with white-clawed crayfish, I have taken berried females in baited traps but best results have been sweep-netting under fringing vegetation, where the females have retreated. I would think electrofishing could be injurious. Best wishes, Julian

Using elecrofishing can be quite tricky, depending on substrate and depth. We have used it for testfishing Astacus astacus. There are difficulties since the crayfish tend to lose their legs (depending on voltage). This would most definitely also include loss of eggs. This is an ugly sight if you're trying to restore an endemic species. I would definitely use a manual method (hand picking). In lakes we have used diving and manually picking with great results. It's easy to spot females from above. Of course this is not possible in small streams. Night fishing can be be used, but we found no significant difference from catches during daytime. Though, we may have to execute our testfishing more scientifically. There is a report (however in Swedish, thank God for google translate...!): http://www.lansstyrelsen.se/jonkoping/SiteCollectionDocuments/Sv/djur-och-natur/fiske/Utbildning%20prov%20och%20elfiskeutvärdering/Kraftor%20och%20elfiske_2008.pdf

/Patrik

In streams with fine substrates (sand and clay), I have gotten more berried Orconectes by backpack electrofishing than by kick seining, probably because we can cover more ground faster while electrofishing. That said, the most I've ever gotten in one sample was from tearing apart some large, rotting logs in the streams. I have not studied the effects of electrofishing on eggs, but the berried Orconectes I have caught while electrofishing usually have very firmly attached eggs. Also, I've held a number of berried females (various genera) live in aquaria after capturing them via electrofishing, and a very high percentage of the eggs have hatched, producing viable offspring.

The problem id that the berried females stay in their burrows more than males. The sex ratio of signal crayfish will therefore change with the season. To catch the berried females you need to collect from riffles by stone turning or persist with traps especially in late August to october and again march to may. You will not dislodge them from burrows. Do not bother with electrofishing. What you do will depend on the question you need to answer.

I agree with Susan and Eric that trapping might not be your best method, but would provide some individuals.My experience is that the berried females are often hidden along the edge of the bank. They are usually associated with larger cobble, aquatic vegetation, or woody debris. I have not collected large percentages of berried females even though our primary method is electrofishing. The benefit of the electrofishing is that individuals that are hidden are stimulated by the current causing them to move. This method is a real benefit to flushing individuals out of cover. We have not seen eggs detached from the electrofishing current, nor have we had any problems caused with mortality in eggs that we have stripped from females and raised separately in watch glass containers. I am not of the opinion that you need to electrofish at night. We have done only a couple of comparison studies but did not see any real difference between relative abundance of individuals during four different diel periods. Crayfish were more active at dusk, but with the electrofishing gear you will be able to see them better during twilight or day conditions. I am not sure that kick seining would be a benefit

I agree that electrofishing is effective method, but my opinion is clear.

I can not use a method, which can cause any damages on animals, especially if I need them for research. I prefer much laborious and time-consuming methods, but gently for collected crayfish. That is necessary for any following behavioral, ecological or physiological experiments if we don't want to risk any bias in results. If you need crayfish only for morphological study, then the use of electrofishing can be probably OK (if you will not be interested in chelae and legs which are often lost during electrofishing). MB

Thank you for all your answers. Provided egg loss is minimal, damage to limbs, while not desirable, will not affect the information I wish to acquire, so I still think electrofishing could be employed (I am only interested in invasive species and there are no native crayfish in Scotland). I believe electrofishing has also generally been shown to be less sex/size selective than other methods (correct me if I'm wrong), and would therefore be useful to assess population structure (which I am also interested in).

I am intrigued by the baited stick methodology, and have read the Policar & Kozak (2005) paper with interest. Milos the link you sent did not work, was this referring to the aforementioned paper?

Apart from that, it seems that a general root around in good habitat (undercut banks, piles of debris etc), with nets and a bit of kick sampling is the only other way. I will probably employ all of these methods, as well as traps in order to increase chances, and allow comparison between methodologies when looking for berried individuals.

Roy- I think I should be conducting field work April-June, as I've been told the season is delayed slightly up in Scotland (I'll find out!). Also, as I believe you found in your 1999 paper on the River Great Ouse (my home river), pleopodal egg counts declined over winter, to a more realistic fecundity estimate in Spring, pre-hatching? So it makes sense to me to go for the spring.

Sorry for not working link, but you find the right paper. It is on-line available from KMAE journal.

Best regards

Milos

This is my small addition: I have experience with electrofishing of Orconectes limosus. A very important factor is water conductivity. In eutrophic waters with higher value (about 800-1000 uS/cm) many crayfish were immediately killed by an electric pulse (of course a voltage depending).

Regards

Jiri

Hi Rupert

You do indeed get high loss of claws among crayfish caught by electrofishing - as we found when doing a high power shock treatment to try to eradicate signal crayfish in a stream (details in my paper).

I recently came across this paper, which gives thresholds for response to electric field - it seems very low voltage may be the answer to encourage them to leave refuges, although I haven't tried it myself. Alonso used a low voltage system for electrofishing crayfish, but this is much lower.

http://scialert.net/qredirect.php?doi=jfas.2008.228.239&linkid=pdf

I have seen the baited stick in use, an interesting traditional method, but you still need to catch the crayfish by hand. A drop-net/ crabbing net is an alternative I've also seen and tried, but like the baited stick you have to sit and wait at one spot.  If the waterbody is shallow and clear, I have caught crayfish by hand-catching at night, including some berried ones. Putting out some oily fish bait helps to bring the crayfish out, although I don't usually do that if I'm doing a survey transect. Watch what happens if you peg out a kipper on the bed! I recommend you do  your catching  early in the breeding season however, as the female signal crayfish become progressively less responsive through October. 

When working with Austropotamobius pallipes, I have found there is a window of opportunity for catching females in the spring, in early to mid May (in Yorkshire), when the water starts to warm up, but before they become reclusive in the run up to the hatching period. They will sometimes go into traps, but hand-catching them at night, especially with bait present does produce a catch of berried females, albeit low compared to say August. You need to pick the time quite carefully - weekly visits may be needed to get the time of best response. I am not sure whether signals show the same response and it may be a little earlier, as they hatch young about 3 weeks or so before the white-clawed crayfish.

For a large and rapid catch of signal crayfish in a small stream I was amazed to see the response when we dewatered short sections at night, using temporary dams and diverting the flow. If there are berried females in the bank that would be an effective way of getting them out within minutes to an hour or so. One of the refuge sites for A.pallipes (ark sites) in Yorkshire was stocked by dewatering a section of stream in spring (by day), so berried females were translocated prior to the hatching period. Some signal crayfish emerge by day when you dewater, but not many (unlike A.pallipes, which come out readily). Even so you can catch far more on a drained bed than in running water. Dewatering at night is more effective for signal crayfish. You don't even have to dewater fully, so long as you expose the in-bank refuges. Consent would be needed from the environmental authorities for any dewatering. Salmonid fry would be likely to have emerged from gravels by May (if they haven't been predated by signal crayfish on emergence).

Regards

Stephanie