Crayfish season 2010 – reliable catch predictions support development of the crayfish industry

According to crayfish catch monitoring by the Finnish Game and Fisheries Research Institute, signal crayfish stocks are robust, and a large number of noble crayfish were left in Finland’s waterways last season. The period of hot weather that followed Midsummer will have promoted crayfish growth and speeded up moulting. There are also plenty of young crayfish in the waterways growing up for future seasons. Therefore we have good reason to expect good crayfish catches during this year’s crayfish season, which begins at 12.00 on 21 July 2010 and ends at the end of October.

The number of signal crayfish caught by the Institute’s crayfish catch counters increased in Finland’s principal and largest signal crayfish waters during the monitoring period 2006–2008. The growth in catch per unit effort levelled off last year in those waters where signal crayfish stocks have stabilised. Because of introductions, the number of new signal crayfish areas is increasing, leading to more crayfish catching opportunities.

For professional fishermen catching crayfish, last year was surprising: the demand for crayfish dropped off in the middle of the season, and many hung up their traps in August instead of mid-September as in a normal year. This means that crayfish of catch size were left in the waterways, and therefore we may expect not only a good catch of noble crayfish this year but also that there will be large individuals.



Unit catches of noble crayfish are clearly larger than those of signal crayfish, due to the differences in catching methods. By contrast, more than half of the signal crayfish catch consists of large individuals (more than 10 cm long), as opposed to only one fourth of the noble crayfish catch.

Weather has short-term and long-term effects

The weather in early summer affects when the crayfish become most active and what the size of the crayfish in the first catches will be. There was a brief warm period in spring 2010, and in Lake Päijänne – where the signal crayfish population is monitored around the year – the crayfish became active in early June. The hot weather in late June and early July warmed up the waters, and the development of roe and hatchlings as well as moulting were ahead of schedule. The start of the crayfish season seems set to be much more lively than last year.

In autumn 2009, the waters cooled early, and there was concern for the number of signal crayfish hatchlings this year. Fortunately, this turned out to be unnecessary: in test catches in the spring, female crayfish were found to have large quantities of good-quality roe under their tails. We may deduce from this that this summer will have produced a large number of hatchlings and that there will therefore be plenty of crayfish to catch in coming years.


The cluster of roe under the tail of this female signal crayfish, caught in a test catch in early June, is almost perfect and should yield some 200 hatchlings around the turn of July. Males with large pincers (right) have been observed in large numbers in early summer.

Crayfish plague

Cases of crayfish plague were observed in 12 stocks of noble crayfish last year, a normal number. In the current year, only one confirmed case has been recorded; this was in North Savo, where the plague wrought havoc last year too. Mostly crayfish with suspected infections are not submitted until the crayfish season has begun. The most extensive crayfish plague epidemic of recent years, the one in River Kemijoki, would seem to be continuing to spread upstream. All suspected cases of crayfish plague are investigated at the Kuopio unit of the Finnish Food Safety Authority (Evira).

Plenty to catch, but is there enough demand?

In 2009, for the first time in a long time, there were signs of saturation in the crayfish market. This had a particularly great impact on sales of noble crayfish, which are transported from long distances to markets in the south of Finland. The reasons for this slump may include the economic recession and also the fact that the proliferation of signal crayfish meant that many more shore dwellers and summer cottage residents could catch their own crayfish.

In 2008, the crayfish catch in Finland was 5.9 million noble and signal crayfish (260 tonnes) in amateur fishing and about 153,000 signal crayfish (7 tonnes) for registered professional fishermen. The majority of crayfish caught are thus for personal needs, and perhaps the needs of neighbours. Signal crayfish stocks in particular have developed so well, according to the Institute’s monitoring, and spread so wide that the entire nationwide population increase is probably not being utilized. There is thus no longer a need for introductions of signal crayfish to increase the crayfish catch, which was still the case a few years ago.

The majority of Finns do not live or have a summer cottage along waters where crayfish catches are good, and not all waterways ever become good sources of crayfish, so many consumers will continue to buy their crayfish. We may hope that the crayfish trade and Finnish crayfish products will develop to make full use of the valuable continuously growing crayfish population in our natural waters and thus make this delicacy easily available to everyone.

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