GIS assessment of shorelines during the last century and their effect on fishing activities in a Mediterranean Lagoon

Abstract

The Mediterranean region hosts more than 100 coastal lagoons, which play a crucial ecological role and offer vital goods and services for humans. This research focuses on monitoring the shoreline of Ghar El Melh lagoon in the Gulf of Tunis, Tunisia, to assess how environmental changes affect local fishing activities.

The methodology is based on a long-term diachronic study (1881-2021) of the lagoon's shoreline, using the statistical tool DSAS (Digital Shoreline Analysis System) along with a socioeconomic investigation. The fisheries survey responds to requests from regional fisheries authorities, specifically the national fishing and aquaculture department of the Ministry of Agriculture, Water Resources, and Fisheries of the Tunisian Republic. The goal is to collect data that accurately reflects the current state of lagoon fisheries.

The survey was conducted in Ghar El Melh city and involved 34 local lagoon fishermen over a period of one week, from March 20th to March 27th, 2022. The diachronic study revealed that the maximum erosion rate of the lagoon is -14.88 ± 0.20 m/yr in the southeast, while the accretion rate is +7.35 ± 0.20 m/yr in the northeast. The lagoon's surface area expanded by 400.9 hectares between 1881 and 2021, negatively impacting fishing activities and resulting in a 72% decline in annual fishing yield from 1993 to 2022.

Our findings demonstrate the significant impact on the lagoon's sedimentary dynamics, altering water flow patterns and affecting nutrient distribution, sediment deposition, and the transport of larvae and juvenile fish. Additionally, overfishing, along with increasing fishing efforts, accelerates the decline of the fisheries population and the deterioration of ecological conditions within the lagoon.