Optimizing Flow Conditions and Fish Passage Success in Vertical Slot Fishways: Lessons from Fish Behavior Observations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

This study investigated the behavior of mid length Squalius cephalus under turbulent conditions in experimental vertical channel fish ponds. The velocity and turbulence intensity were characterized using PIV data. Turbulence conditions are improved by adding one or three vertical rigid cylinders to the pool. The research findings provide valuable insights and information for understanding the relationship between fish behavior and hydraulic conditions. However, the manuscript still needs to undergo the following modifications and checks before being accepted:

1. The introduction briefly describes the research content of the article, and it is recommended to give a detailed introduction and explain the innovations of the article compared to related studies.

2. Section 2.2 of the article mentions that the average water temperature in the experiment was controlled at 16°C, but it does not specify the water temperature of the fish used in the experiment during the migration period, and whether this temperature matches the actual migration water temperature.

3. The arrows in Figure 5 of the article are not of the same thickness, and it is suggested that the phenomenon be described in some words.

4. In the analysis of the results of the article, four thresholds are mentioned that consider horizontal and turbulent kinetic energy according to the spatial average velocity standard. The results of the study are shown and described in Figure 6 . It is recommended to add the formation of causes and effects.

5. The conclusion section describes the work as well as the advantages of the article in a more concise manner. It is recommended to add future research directions.

6. Please increase the clarity of the image in Figure 1.

7. L149 formula format problem.

8. Please briefly describe the fish species tested.

9. There are many errors in the citation style of references.

Author Response

We thank the reviewer for his/her suggestions and evaluation of our manuscript. In the following, the comments of the reviewer are uncoloured, our answers are coloured in blue.

1. The introduction briefly describes the research content of the article, and it is recommended to give a detailed introduction and explain the innovations of the article compared to related studies.

The introduction has been modified

2. Section 2.2 of the article mentions that the average water temperature in the experiment was controlled at 16°C, but it does not specify the water temperature of the fish used in the experiment during the migration period, and whether this temperature matches the actual migration water temperature.

Initially, the experimental protocol did not necessarily involve working at a temperature similar to that corresponding to the natural migration period of the chub. The objective was to work at a temperature that was neither too cold nor too hot, so that the fish would be active and their stabulation would not be too complicated. As natural migration conditions cannot be mimicked to perfection in the laboratory, the aim was to make a relative comparison of biological results obtained under different experimental conditions, without seeking absolute results that could be quantitatively extrapolated to unmanipulated, motivated individuals in their native environment.

However, previous research has shown that (in France) ‘a monthly temperature above 12°C is necessary for reproduction, which takes place in spring from mid-April to mid-June, when the water temperature exceeds 15°C’ (Keith et al., 2020).

We therefore specified in the manuscript that ‘the water temperature during the experiments was very close to the optimum used by this species during its movements and breeding behavior (Keith et al., 2020)’.

Keith P., Poulet N., Denys G., Changeux T., Feunteun E. & Persat H. (coords), 2020. Les poissons d'eau douce de France. 2nde édition. Biotope Editions, Mèze. Muséum national d'histoire naturelle, Paris (collection Inventaires et biodiversité), 704 p.

3. The arrows in Figure 5 of the article are not of the same thickness, and it is suggested that the phenomenon be described in some words.

Added into manuscript: “Upstream and downstream movements were observed. These movements can be continuous or discontinuous with stops in the pool. A detailed study of the trajectories reveals a very marked movement pattern. The most frequent trajectories are identified by the thicker arrows. 98.9% of the fish entered the pool directly into the ZBL. From the ZBL zone, 81.9% of the fish directly crossed the upstream slot and entered the upper pool without having entered any other zone of the pool. Fish movement patterns differ according to whether or not individuals have stopped in one of the zones of the basin. The movements of the fish that stopped for a moment in the pool were more diversified: they crossed the basin making a maximum of 16 movements between zones, while the fish that did not stop made a maximum of 5 movements across the pool. ”

4. In the analysis of the results of the article, four thresholds are mentioned that consider horizontal and turbulent kinetic energy according to the spatial average velocity standard. The results of the study are shown and described in Figure 6 . It is recommended to add the formation of causes and effects.

We have been used term “zone” for location inside the pool used by fish and the term “area” for localisation inside the pool based on hydraulic conditions.

The manuscript have been modified in order to explain and define the four areas (figure 5) based on definition of thresholds: “ First, in terms of Intensity, the aim was to identify areas in the pool where intensities could be quite low and stable enough to be predictable and sustainable for fish. Four areas were considered (Figure 6), respect to two threshold values of space averaged velocity norm and turbulence kinetic energy, which could be considerate as criteria to define the hydrodynamic environment of fish, see [2]. The choice of thresholds is only based on these hydraulic criteria. The aim is to identify locations in a pool where the flow could be considered as “barrier” for fish. These values were respectively set at 0.282.V_th^  (velocity) and 0.017.V_th^2 (turbulence kinetic energy). In F11 areas (Figure 6), velocity and turbulence kinetic energy values were both over their respective threshold value. Inside these areas, the flow might be unpredictable for fish. In F00 areas, velocity and kinetic energy values were both under their respective threshold value. These areas might be considered as suitable for fish resting and/or for initiating an upstream movement and, as seen before, corresponded to the preferential areas used by fish during the experimental trials. In F10 areas (respectively F01), the velocity value (respectively the turbulence kinetic energy value) was the only value higher than its threshold value.”

5. The conclusion section describes the work as well as the advantages of the article in a more concise manner. It is recommended to add future research directions.

 The conclusion has been modified

6. Please increase the clarity of the image in Figure 1.

The correction is done.

7. L149 formula format problem.

The correction is done.

8. Please briefly describe the fish species tested.

Added into manuscript: “We used young-of-the year fish to carry out the tests. The chub (Squalius cephalus L.) is a very generalist species, colonising many rivers. It is highly adaptable to water temperature conditions and habitat characteristics. Its migratory behaviour is less marked than other species as brown trout (Salmo trutta L.), but individuals regularly move between habitats.”

9. There are many errors in the citation style of references.

The corrections have been done.

Reviewer 2 Report

Comments and Suggestions for Authors

Optimizing flow conditions and fish passage success in vertical slot fishways: lessons from fish behaviour observations by Calluaud et al.

 

 

The manuscript describes the flow conditions of the fish passaage and their beahavior. The research is designed well. The fish manupuliaitons and observations were performed and results compared. The hydraulic conditions created by the addition of 3 cylinders resulted  in a significantly higher rate of chub passage (47.4 %) when compared to the VSF configuration without any cylinder (26.2%). Their results show the importance to optimize flow characteristics in VSF pools in order to maximize fish passage success, for example by modifying the length to width ratios of vertical slot passes.

 

There are few places mentioning the significat reults but they are not actually proved by the statisitical tests, I therefore recommend authors to run the statisitical tests for the values pressented.

Author Response

We thank the reviewer for his/her suggestions and evaluation of our manuscript. In the following, the comments of the reviewer are uncoloured, our answers are coloured in blue.

There are few places mentioning the significat reults but they are not actually proved by the statisitical tests, I therefore recommend authors to run the statisitical tests for the values pressented.

Added into manuscript: “Non-parametric statistical analysis (Kruskal-Wallis and Mann-Whitney tests) were used to compare (i) fish transit time through the pool, (ii) fish trajectories between the 3 different zones and (iii) the fish passage efficiency. We also used homogeneity Χ² test with Yates continuity correction to compare the distribution of fish associated with different patterns of using the zones inside the pool.” and “ There are statistically significant differences in the use of the three zones identified for each configuration studied (χ², p<0,05). Nevertheless, note that the median transit time increased from 6.4 s in the configuration without any cylinder to 9.8 s in the experimental configuration with 3 cylinders (Kruskall-Wallis, p=0,12).”