The Influence of Flow Regime on Ecological Quality, Bird Diversity, and Shellfish Fisheries in a Lowland Mediterranean River and Its Coastal Area

Abstract

Designing environmental flows in lowland river sections and estuaries is a challenge for researchers and managers, given their complexity and their importance, both for nature conservation and economy. The Ebro River and its delta belong to a Mediterranean area with marked anthropogenic pressures. This study presents an assessment of the relationships between mean flows (discharges) computed at different time scales and (i) ecological quality based on fish populations in the lower Ebro, (ii) bird populations, and (iii) two shellfish fishery species of socioeconomic importance (prawn, or Penaeus kerathurus, and mantis shrimp, or Squilla mantis). Daily discharge data from 2000 to 2015 were used for analyses. Mean annual discharge was able to explain the variation in fish-based ecological quality, and model performance increased when aquatic vegetation was incorporated. Our results indicate that a good ecological status cannot be reached only through changes on discharge, and that habitat characteristics, such as the coverage of macrophytes, must be taken into account. In addition, among the different bird groups identified in our study area, predators were related to river discharge. This was likely due to its influence on available resources. Finally, prawn and mantis shrimp productivity were influenced up to a certain degree by discharge and physicochemical variables, as inputs from rivers constitute major sources of nutrients in oligotrophic environments such as the Mediterranean Sea. Such outcomes allowed revisiting the environmental flow regimes designed for the study area, which provides information for water management in this or in other similar Mediterranean zones.

Environmental Flows in the Lower Ebro River and Delta: Current Status and Guidelines for a Holistic Approach

“…Some studies in the Ebro have recently been carried out to evaluated the relationship between the flow regime of the river and some components of biodiversity such as the abundance of protected species of birds in the delta, as well as the ecological quality of the final stretch of the river, measured through fish community [34,48]. Such studies showed that flow regime was significantly related to only a few deltaic bird species, and likely due to an indirect effect on prey availability in rainy years.…”

“…River effects are most noticeable in oligotrophic seas (e.g., Mississippi River in the Gulf of Mexico, [60]; Rhône River in the Mediterranean, [61]) and in semi-enclosed systems such as the Black Sea [62]. Several studies have shown the influence of river inputs and other environmental factors on coastal fisheries, especially in oligotrophic seas [34,60,62,63]. Some of these studies were carried out in the coastal zone influenced by the Ebro River discharge [34,61,63,64].…”

“…Several studies have shown the influence of river inputs and other environmental factors on coastal fisheries, especially in oligotrophic seas [34,60,62,63]. Some of these studies were carried out in the coastal zone influenced by the Ebro River discharge [34,61,63,64]. In these studies, both pelagic fish (European anchovy, Engraulis encrasicolus) and shellfish (caramote prawn, Penaeus kerathurus and mantis shrimp, Squilla mantis) landings showed to be positively influenced by the Ebro River runoff.…”

“…Gauging stations, weirs, dams and tributaries are also represented, as well as the location of the city of Tortosa and the island of Gràcia. Source: modified from Belmar et al [34].…”

Environmental typology of rivers from the Brazilian semiarid as a first step for the application of the index of biotic integrity: The case of the Chapada Diamantina

“…Fish‐based methods to assess ecological quality of running waters have proved to be very useful in the detection of human‐induced impacts on the aquatic ecosystems. These methods were able to detect, not only water quality impacts, but also environmental disfunctions related with insufficient discharge (Belmar, Ibáñez, Forner, & Caiola, ; Belmar, Vila‐Martínez, Ibáñez, & Caiola, ; Caiola, Ibáñez, Verdú, & Munné, ). The development of an IBI for the Chapada Diamantina running waters is, thus of great importance.…”