An attempt to estimate changes in the fish stock of Lake Jeziorak on the basis of the fishing yield of seines

Alina Bonar

doi:10.3750/aip1991.21.2.09

Abstract

Analyses were performed of changes in the fishing yield and fish composition of catches obtained with seine nets in Lake Jeziorak in 1967-1985. The results were compared with similar data for 33 lakes of pikeperch type. It was found that average fishing yield of seines in Lake Jeziorak amounted to 362.87 kg, being 115.98 kg higher than the average calculated for 33 lakes of pikeperch type. Fishing yield showed an increasing trend at decreasing fishing effort and increasing fish catches. These differences and trends were caused by: change of the protective size for bream, so that specimens smaller than 0.5 kg were caught, and increased predation which reduced prey fish stocks, mainly that of roach.

Highlights

Seines are very popular in inland fishery due to the possibility of performing a catch in a relatively short time, gigh effectiveness, and low risk of being damaged
Fishing yield of the gear depends on gear construction, and methods and season of fishing on the one hand, and species composition of the ichthyofauna, biomass of parti cular fish populations and protective fish sizes on the other (Dementieva 1960, Dli· browski 1964, Dllbrowski et al 1964b, Bonar 1987a, b, 1989, 1990)
Any change of protective sizes will be reflected in the fishing yield (Bonar 1974, 1987a, b)

Summary

Introduction

Seines are very popular in inland fishery due to the possibility of performing a catch in a relatively short time, gigh effectiveness, and low risk of being damaged (by poachers or touristes). Share of seine nets in total intensity of the exploitation in pikeperch lakes amounted to 40% (Bonar 1974, Bonar 1987b). Fishing yield of the fishing gear, in this of seines, was frequently used to assess changes in fish biomass and densities of the fish stocks and fish populations (D browski, Leopold, Nowak 1964a, b, Kozlowska-Filar 1971, Forney 1977, Johnson 1977, Johnson and Hale 1977, Bonar 1987a,b, 1989, Bonar and Kempa 1987a,b). The objective of the study was to assess changes in the exploited fish stock in Lake Jeziorak on the basis of the fishing yield of seines

Objectives

Results

Conclusion