Estimation of European eel migration and improvement of stock estimation methods on inland waterbodies. 

Project code: 8-2/T10172PKPK
Project duration: 01.11.2010-30.10.2013
EFF funding: 53 685,78

According to the European Council Regulation (EC) No 1100/2007 and the Estonian eel management plan (EMP) it is essential to evaluate the natural migration of European eel (Anguilla anguilla) between inland waterbodies as well as silver eel escapement from the lakes where they have been stocked. Also, a report on different obstacles (dams, turbines, traps etc.) concerning the migration route had to be given. Council Regulation (EC) No 1639/2001 declares refining of data collection methods on yellow and silver eel to determine the escapement rate per catchment basin and to estimate the size of both yellow and silver eel fishable stock.

The most important outcome in the first period of the project was the collection of data that helped to fulfill the EMP’s action report (30.06.2012). The implementation of the requirements in the EMP were also neccessary for getting additional funding for the eel stocking programme in Estonian lakes. The main purpose of the EMP is to expand the eel population in Estonian waterbodies to increase the possibilities for the reproduction of the species and with that the growing of fishable eel stock.

The project commited foremost to ascertain the eel stocks of small lakes (L. Saadjärv, L. Kuremaa, L.Kaiavere and L. Vagula) using the mark-recapture method and to determine the escapement of eels during catchment period. The results helped to verify whether the escapement rate of silver eel was in accordance with the 40% target set by the European Council Regulation (EC) No 1100/2007. If the results in studied lakes are scientifically proven it is possible to apply for 50% additional funding for eel stocking in the next frame programme period. A third of the funds reserved for stocking come from the professional fishermen fyke net licence fees used on certain lakes.

One of the goals of the project was experimenting with different types of fyke nets to assure sustainable eel fisheries in studied waterbodies. The results allowed a change in the legislation to change the mouth sizes of fyke nets to make them more efficient. According to current legislation fishing on the outflows of small lakes is permitted. Also possible obstacles and barriers concerning the outflows of small lakes were studied.

One of the objects of the project was to estimate the age of eels using new methods, tagging eels and stocking glass eels and elvers to small lakes.

In total 875 eels were tagged with Carlin type of tags from which 139 were recaptured.

To estimate the age from extracted eel otoliths, „cracking and burning“ method was used. In total 1325 eel otoliths were treated with the method from which 1143 were suitable for age reading. On small lakes it is rather difficult to measure the age of eels due to the stress marks on otholiths. That is why usually the specimens are estimated older and the growth rate slower. Other methods like mass marking of eels with chemicals should be used in the future to get more accurate results.

The analysis of eel landings showed that most of the eel caught in Estonia is obtained by professional fishermen. The recreational landings make up around 3-6% of the total on the studied lakes. 90% of eel caught by professionals are acquired using fyke nets and the other 10% using long lines. Recreational fishermen mostly use long lines but in waterbodies with high transparency harpoons are also used. In Lake Saadjärv and Lake Kuremaa eels caught with a harpoon make up 70% of recrational landings and 10% of total landings respectively. Due to different stocking volumes and to compare stocking efficency in various lakes a stocking productivity index was worked out. It was found that on lakes where the index is under 4 the stocking isnt economically sustainable altough it can be used as a measure of reproducing the species.

The stocking of eels in small lakes has been continous from 2002 and in some of the lakes eel abundance has risen critically high. In the following years a break (2-3 years) in stocking has to be considered in the lakes (L. Saadjärv, L. Kuremaa, L.Kaiavere and L. Vagula) where fishable eel abundance is high enough. Stocking to waterbodies that have connection with the coastal sea (L. Ermistu, L. Tõhela etc.) should be thought over instead.

To measure the abundance of eel in lakes where the fishable stock can not be estimated directly an index was worked out using mark-recapture data and the CPUE (Catch per unit effort) of long lines. That index enables to roughly calculate fishable eel stock size in the lakes that have enough long line data available. The experiments with fyke nets showed that in deeper lakes (L. Vagula and L. Kuremaa) fishing with limited number of larger mouth size fyke nets should be allowed.

According to the results of this project the conditions for eel fishing should stay the same as of now. Considering the 40% escapement target from Narva River Basin District including the escapement from Lake Võrtsjärv the requirement stated in the EMP is filled.