The Importance of Including Water Temperature Simulations in a 2D Fish Habitat Model for the St. Lawrence River

Valerie Ouellet,Jean Morin,Yves Secretan,Stephen J Dugdale,Marc Mingelbier,André St-Hilaire

doi:10.3390/w13131736

Abstract

Extreme climatic conditions likely caused a massive fish mortality during the summer of 2001 in the St. Lawrence River. To corroborate this hypothesis, we used a physical habitat simulation approach incorporating hydraulic and water temperature models. Spawning Habitat Suitability Indices (HSI) for common carp (Cyprinus carpio) were developed using fuzzy logic and applied to the model outputs to estimate habitat weighted usable area during the event. The results revealed that areas suitable for common carp spawning (HSI > 0.3) were severely reduced by high water temperatures, which exceeded 28 °C during the mortality event. During the mortality event, the amount of suitable habitat was reduced to <200 ha/day, representing less than 15% of the maximum potential suitable habitat in the study reach. In addition, the availability of cooler habitats that could have been used as thermal refuges was also reduced. These results indicate that the high water temperature in spawning areas and reduced accessibility to thermal refuge habitats exposed the carp to substantial physiological and environmental stress. The high water temperatures were highly detrimental to the fish and eventually led to the observed mortalities. This study demonstrates the importance of including water temperature in habitat suitability models.

Highlights

Understanding and quantifying the effects of habitat availability on fish populations is crucial for protecting habitats from anthropogenic pressures [1,2,3]
The specific objectives of this study were (1) to develop an Habitat Suitability Indices (HSI) for common carp spawning based on a fuzzy logic approach, (2) to estimate the importance of water temperature as a carp habitat variable by exploring its spatial distribution and dynamics at different time scales and (3) to spatially and temporally quantify common carp spawning habitat during the 2001 mortality event
Our study highlights the importance of including water temperature in habitat suitability models

Summary

Introduction

Understanding and quantifying the effects of habitat availability on fish populations is crucial for protecting habitats from anthropogenic pressures [1,2,3]. Since the mid-1970s, simple habitat preference curves have been used to represent fish habitats, allowing for the development of Habitat Suitability Indices (HSI) Such habitat predictions can be helpful to inform water resources managers, prioritize conservation decisions and contribute to environmental assessments [4,5,6]. With advances in computational power, it is becoming increasingly possible to implement spatial habitat models over large areas [8,9,10] and incorporate additional variables into the models, increasing their accuracy [11]. A deeper understand of the drivers of thermal heterogeneity within rivers and the impact of this upon river habitats and organisms is, needed [22,23,24,25]

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