Assessing the Fish Stock Status in Lake Trichonis: A Hydroacoustic Approach

Triantafyllia-Maria Perivolioti,Jaroslava Frouzova,Dimitra Bobori,Michal Tušer

doi:10.3390/w12061823

Abstract

Fish stock monitoring is an important element for the sustainable management of inland water resources. A scarcity of data and the lack of systematic monitoring for Lake Trichonis precludes an up-to-date assessment. To assess the current status of pelagic fish stock, a hydroacousting survey was conducted for the first time in Lake Trichonis, Greece. In October 2019, the lake was acoustically surveyed with two, horizontally and vertically mounted, 120 kHz transducers during day and night. A decreasing gradient in pelagic fish density from the western to the eastern shores of the lake was observed. Fish density was significantly higher in the intermediate layers of the water column, in the eastern region, compared to the western region. The lake appears to host primarily communities of small-sized fish (TL: 0–5 cm), whereas larger fish (TL: 5–50 cm) are a small minority of the total fish stock. The overall average estimated fish length was approximately 2.4 cm. The adoption of routine inland fish stock monitoring through hydroacoustic methods could be a promising step in the effort to improve the understanding of unique inland water ecosystems with minimum impact on endemic species, as well as to mitigate human impact and achieve long-term sustainable management.

Highlights

Within Europe, in order to eliminate or mitigate freshwater degradation, the Water FrameworkDirective (WFD) calls for all the natural aquatic ecosystems to achieve a “good” ecological status.To date, inland fisheries management is focused on improving the aquatic environment for biodiversity, allowing the sustainable exploitation of the resources and verifying conservation and protection of fish and fisheries [1]
The purpose of this study is to use a hydroacoustic method for obtaining a detailed overview In of particular, we aimed to (i)status quantify freshwater fish biomass andthe fish density, (ii) fish size the freshwater fish stock in Lake
Acoustic biomass detected per sampling unit (Figure 2) did not exhibit diurnal heterogeneities

Summary

Introduction

Within Europe, in order to eliminate or mitigate freshwater degradation, the Water FrameworkDirective (WFD) calls for all the natural aquatic ecosystems to achieve a “good” ecological status.To date, inland fisheries management is focused on improving the aquatic environment for biodiversity, allowing the sustainable exploitation of the resources and verifying conservation and protection of fish and fisheries [1]. The methodologies adopted by researchers for the monitoring of freshwater fish stocks, such as gillnetting, are often unable to support an ecosystem–based management approach [2], as they fail to comprehensively address the spatiotemporal variability of fish stocks [3], require high effort [4] and often result in a reduction of fish biomass [5]. In this context and considering the proposed WFD goals, there is a strong demand for standardized, reliable, reproducible and non-invasive methods for routine monitoring programs. Hydroacoustic methods have been applied in all kinds of aquatic ecosystems in order to acquire detailed information about aquatic fauna, and especially about fish [8]

Objectives

Methods

Results

Conclusion