Abstract
The social strain situation related to decreasing of fishing profitability arose in the Lake Ladoga region in North-Western Russia. Commercial fisheries representatives believe the Ladoga ringed seal depredation on nets to be the main reason. Besides, fishermen claim that the seal population number has increased drastically over the last decade and they observe certain changes in seals' behavior reflecting adaptation to foraging from fishing gear. In order to clarify the situation we conducted series of questionnaire surveys among commercial and individual fishermen, poachers and controlling authorities in Leningrad region and Karelian Republic in 2007–2012. As a result of the survey the following conclusions were made:
1. Seal depredation on nets became more active and seal-fisheries conflict achieved its critical point in 2005–2006. Total number of seals by-caught in nets in 20072 was 454 seals in Leningrad region; an average number of animals caught was 8 seals/km of nets. For 2011, 381 cases of seal by-catch were registered. At the same time there was a decline in fishing effort related to shutting down of several fishing organizations and reduction of total time spent by the fishermen out in the Lake.
2. The conflict is characterized by distinct seasonality. Maximum proportion of seals by-caught in nets is registered in May–June (38%). Most of the animals caught were less than 20kg and were assumed to be juveniles which started to feed independently. The second spike in by-catch rate can be noticed in September and October - about 29% and is associated with intensive harvest of white fish in this period.
3. The conflict level differs from region to region. The by-catch rate is traditionally high in the southern part of the Lake, where the commercial fishing is the most active - up to 90% of fish catch comes from the Leningrad region.1
4. Feeding from nets; ringed seal prefer valuable fish species - Coregonidae and Salmonidae families. The seals can take large fish from the nets, which is not typical for the ringed seals foraging on "wild" fish.
5. Majority of by-catch cases occur in fyke-nets and white-fish nets with strong netting.
6. The respondents reported cases when the animals followed the vessel going to fishing area orientating by its engine's sound. The vessels had to make a zigzagging track so that they could break away.
7. Most of the respondents noticed decline of Ladoga Lake biological productivity rate, in particular salmonids catches are insignificant (up to a few tons per year) and the amount of white fish catches has decreased.
The Ladoga ringed seal depredation on nets is a significant factor which leads to negative social consequences. The Ladoga ringed seal by-catch rate is about 10% of the total population number per year which is a major factor affecting the subspecies. It is necessary to develop a complex project on assessment of Ladoga Lake fish stocks.
Acknowledgements
We are grateful to the Marine Mammal Commission (USA) for the support of our research in 2012.
* Presenting author
Literature Cited
1. Leonov AG, Teslia A.Ya. 2009. Fish resources of the Ladoga Lake and their use in the beginning of 19th century. Pp. 121–137 in Fishery study of big lakes in northwestern Russia. Collection of scientific papers. Issue 334.
2. Verevkin M, Trukhanova I, Sipila T. 2010. Relationships of the Ladoga seal (Pusa hispida ladogensis Nordquist, 1899) and commercial fishery in the Ladoga Lake. The Ladoga seal (Phoca hispida ladogensis) population status problems and conservation ways. Proceedings of international conference. St. Petersburg. 74 p.