Beel den Stormer Presents the Only Fishery Blog You Need

Fish, Fisheries and Queryomics

Carp as Snitches: Using the Judas Fish Technique

(photo source)

The common carp Cyprinus carpio was intentionally introduced into the USA in the 1800s.  The history of these introductions is obscure, however, in 1877 the US Fish Commission imported carp from Germany and, by 1885, was actively stocking lakes and rivers throughout the country.

The introduction of carp by the US Fish Commission was made to provide carp as a food fish.  Carp were were popular in Germany and other European countries, but, says Beel, never caught on in the USA.

Since their introduction, carp have become wildly distributed and abundant throughout the USA, often causing problems.  Carp feed on bottom dwelling organisms and, as a result, uproot aquatic vegetation and muddy the water while searching for food.

So, how does one take these carp out?  Peter Sorensen, director of the Minnesota Aquatic Invasive Species Research Center at the University of Minnesota, has been using what is called the “Judas technique” to locate and remove carp from lakes.

The technique receives its name, from the biblical character who betrayed Jesus.  Carp are captured from a lake, implanted with radio transmitters, and then re-released back into the lake.  These fish then mingle with their fellow carp and radio receivers can then be used to locate  the tagged carp and their associates. 

According to a recent report, Sorenson plans to use Judas fish implanted with transmitters to locate congregtaions of in Staring Lake in Eden Prairie, Minnesota.  A commercial fisherman then will net the unwanted carp, estimated at about 26,000 fish.

So, sounds a bit too good?  Sorenson has used this technique before- with some success.  Friends, please allow Beel to present a few results from a 2011 paper by Przemek Bajer and colleagues (one of whom is Sorenson).

Bajer and colleagues attached radio transmitters to carp in three Minnesota lakes.  The results for Riley Lake (below) are representative.  Carp were dispersed throughout the lake during much of the year but began to aggregate in winter once water temperatures dropped to 10oC (50oF).  These aggregations became even denser when the temperature dropped to 5oC (41oF).

)photo source)

Locations of radio-tagged carp (circles) in Lake Riley, Minnesota during the winters of 2008-2009 (left) and 2009-2010 (right).  Carp aggregations documented on 19 January 2009, 15 February 2010, and 3 March 2010 were targeted with a seine net.  The shaded polygon depicts the area seined.  Depth contours represent 3-m depth increments.  (source: Bajer and colleagues 2011)

Once carp were found to be aggregated, they were targeted with a 500-m long, 15-m deep seine net.  The netting operation was conducted by local commercial fishermen. 

The fisherman began by cutting a 5 x 5 m opening in the ice, through which the net was deployed. A series of holes were drilled in a V-shaped pattern that surrounded the aggregation.  Ropes were stretched under the ice between the holes using remote-controlled submersibles. The ropes were used to pull in both sides of the net, with power winches, and the net was landed through a 5 x 5 m opening cut near shore so that fish could be removed (see below).

Netting a carp aggregation (photo source)

Netting a carp aggregation (photo source)

That’s a lotta carp, says Beel.

Bajer and colleagues have performed these carp removals on four occasions, on three different lakes.  They estimate they removed between 52 and 94% of the carp in these lakes. 

On the plus side, this is a pretty effective way of reducing carp populations.  On the minus side, however, there is no hope of removing all the carp from a lake of any size and the population will rebound in a handful of years- carp are very fertile, which is one of the reasons they are so problematic. So, this technique provides only a temporary solution.

Note that the manner in which fish were captured by Bejar and colleagues- using a large net deployed under the ice- is very similar to fishing techniques used in the festivals in Hulun Lake,
Ullunger Lake, and Chagan Lake, Mongolia, China.  These festivals target winter aggregations of various Asian carps.


Przemek Bajer and colleagues.  2011. Using the Judas technique to locate and remove wintertime aggregations of invasive common carp.  Fisheries Management and Ecology, Volume 18, pages 497–505.


One comment on “Carp as Snitches: Using the Judas Fish Technique

  1. Pingback: Which Fish are Safe to Eat in the Savannah River? – My Augusta Blog

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This entry was posted on January 21, 2013 by in Conservation, Natural History and tagged , , , , .
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