Diversity and Seasonal Variation in Live Baits Caught in Hann Bay, Dakar, Senegal

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study presents valuable empirical data on the diversity and seasonal dynamics of live bait species in Hann Bay, Senegal, which is a fishery that has been critically understudied despite its significant ecological and economic implications. Although the research addresses an important gap and employs rigorous field methodology, the manuscript requires substantial revision to improve clarity, statistical reporting, ecological interpretation and alignment with the journal's scope. The core data is robust, but the presentation and analysis could be improved.

Comments for author File: Comments.pdf

Author Response

Minor comments

1. Abstract

'Remains a small study' should be replaced with 'Remains poorly studied'.

It's done

'...for the exploitation of tropical tunas remains...' Clarify whether it was initiated in Senegal in

the 1950s.

It's done

 

2. Methods

Specify the mesh size used for each haul, if it varied (12 mm or 20 mm BS; different purse

seine dimensions). Was the mesh size randomised or fixed per season/site?

We specified the mesh sizes of the nets. The mesh size remained consistent throughout the entire sampling campaign. The same fishing gears were used from the beginning to the end of the sampling periods."

'Landed individuals' must be replaced by 'captured individuals' as they were caught

experimentally and not necessarily landed commercially.

It’s done

Clarify whether diversity indices were calculated per haul and then averaged per season, or on

pooled data per season/gear.

Yes, this information is clearly detailed in Table 2. The indices were calculated by fishing gear and by season, but the means were calculated by fishing gear across all seasons combined.

 

3. Results

"Miscellaneous category accounted for 33.5%"; in Table 1, it was 33.85%.

It has been corrected

'Other bait species less than 2% each of the total' changed to 'each accounting for less than 2%

of the total number of individuals'.

It’s done

'Rapid rise of the two dominance curves' changed to 'Rapid initial rise of the dominance curves'.

It’s done

'Suggesting low species diversity' changed to 'Consistent with low species diversity'.

It’s done

Table 3: 'Size ranges varied from 42 mm (M. curema) to 233 mm (Ethmalosa fimbriata).' This

seems to refer to BS catches. Make this clear ('For beach seine catches...'). The PS size range

(13 mm to 242 mm) follows.

It’s done

 

4. Discussion and conclusion

'Despite the absence of repeated sampling', this phrasing is confusing. Sampling was repeated

monthly. It should be rephrased as 'despite the monthly sampling resolution'.

It has been corrected

'Increased Shannon diversity did not reflect the addition of new species, but rather a narrowing

of abundance distribution'. This seems counterintuitive. Narrowing usually implies lower

evenness and a reduction in H'. Clarify the point being made with the Tamdrari (2007)

reference.

It has been corrected

'Constant availability... year-round' is slightly overstated, as the study only covered 10 months,

missing December and January.

It has been corrected

'These bycatches are more substantial in purse-seine operations.' Support this claim with data

from the results, such as the higher percentage of miscellaneous species in purse seine

operations (67% vs 8% in beach seine operations).

It’s done

 

The conclusion effectively summarises the main findings. Ensure that the stable availability

statement reflects the stability of the bait species' abundance/biomass, rather than overall

ecosystem stability.

The conclusion has been rewritten.

5. References

The formatting needs to be checked for consistency (journal names should be italicised or

abbreviated, and author lists should be consistent).

It’s done

Ensure that all in-text citations appear in the reference list, and vice versa. For example, Poulard

and Blanchard (2005), cited in section 4.3, are reference 30.

This verification has been carried out completely.

 

Ref. 11: The Fishbase URL should be www.fishbase.se, and the access date should be specified.

It’s done

Ref. 31: 'Robert, E., 2012' was misplaced and incomplete.

It has been corrected

6. Typos

Page 1 Abstract: "a small study This study" Add a full stop "a small study. This study"

It’s done

Page 2, Introduction: 'Fishing C Operating' should be changed to 'Fishing Activities Operating'.

It’s done

Page 2, Introduction: 'Juvenile exploitation' should be changed to 'unregulated exploitation of

juveniles'.

It has been corrected

Page 3, Methods: 'Salmoneter' should be changed to 'salinometer'.

It has been corrected

Page 3, Methods: 'Length at first sexual maturity (1.50)' should be changed to '(L50)'.

It has been corrected

Page 4, Results: S. maderenis should be changed to S. maderensis.

It has been corrected

Page 5, Table 1: Sardinella maderenis should be changed to Sardinella maderensis; '% weight'

headers; total weight values.

It has been corrected

Page 7: Mugil carena should be changed to Mugil curema (in the Fig. 5 caption and Table 3).

It has been corrected

Page 8: Move the definition of "L50: length at first sexual maturity" to the Methods section

(2.2), where it is first mentioned.

It’s done

Page 11: 'Distribution and availability of S. modernis should be changed to S. maderensis.

It’s done

Author contributions: Should "Oumar Sadio" or "Oumar Sadi" be included in the author list?

It’s Oumar Sadio

Reviewer 2 Report

Comments and Suggestions for Authors

General comments

This paper investigates the ichthyological diversity of Hann Bay, Dakar, and explores seasonal variations in species used as live bait, based on ten fishing campaigns using beach seine and purse seine gears in 2023. The topic is of applied interest, especially in the context of sustainable baitfish management for tuna fisheries. However, the current version of the manuscript presents several methodological, analytical, and interpretive shortcomings that limit its scientific contribution. Substantial revisions are needed before the paper can be considered for publication.

First, the manuscript relies heavily on descriptive statistics and a single non-parametric Wilcoxon test to assess seasonal differences, which limits the analytical depth. Community-level variation is not sufficiently addressed. To better understand the drivers of changes in species composition and diversity, multivariate analyses such as PERMANOVA, NMDS, or redundancy analysis (RDA) are strongly recommended. These methods could provide a more comprehensive understanding of seasonal and gear-related differences in assemblage structure.

Second, the Results and Discussion sections are largely repetitive, with limited ecological interpretation. Although biodiversity indices such as Shannon index and Pielou’ s evenness index are reported, their seasonal variation is not fully explained in ecological terms. The manuscript would benefit from a deeper discussion on what these patterns suggest about ecological processes, such as recruitment cycles, environmental changes, or gear selectivity. Additionally, little attention is given to the ecological roles or life history traits of the dominant bait species, which would enhance the scientific insight of the findings.

Third, gear selectivity is mentioned but not adequately analyzed. Given the different mesh sizes and operational characteristics of the beach seine and purse seine, more discussion is needed on how these factors may have influenced the observed species composition and size structure. Comparative analysis of catch profiles between gear types would provide a clearer understanding of methodological biases and resource targeting implications.

Fourth, although the study aims to inform sustainable baitfish management, the conclusions remain vague and offer limited practical guidance. The authors are encouraged to elaborate on how their findings could support gear selection, seasonal management, or juvenile fish conservation in bait fisheries.

Fifth, the sampling period spans most months but lacks clarity in its design. The manuscript should explain the rationale behind the number and timing of surveys and consider potential spatial heterogeneity within Hann Bay, which may influence species diversity patterns.

In summary, while the dataset is valuable and the topic relevant, the manuscript requires major revision in terms of analytical rigor, interpretation depth, and language quality before it can be considered for publication.

Specific comments

1. The introductory section contains overly lengthy paragraphs. It is recommended to split them into 2–3 shorter ones. Additionally, the relationships among rod fishing and live bait use, the primary sources of live bait, target species, and relevant management regulations or legal frameworks are insufficiently addressed. It is recommended to supplement this information.
2. The introductory section features overly long sentence structures, insufficient logical connectors, and an overuse of technical terminology. A careful language review and appropriate refinement are recommended. For instance, lines 29–31 could be revised as: “Senegal’s fishing sector benefits from favorable natural conditions, including a 718 km coastline and a 200-nautical-mile EEZ rich in marine resources (Mbaye 2014).”
3. Lines 45–52: There are many references to older literature (e.g., Gobert 1983). It is recommended to supplement or replace them with more recent and relevant research findings.
4. Lines 46–47: The description of the “Live bait fishing is allowed throughout Senegalese jurisdictional waters, except in the area defined by the line connecting the following coordinates: L = 14°40'08" N and G = 17°25'02" W and L = 14°44'18" N and G = 17°21'00"  47 W. According to Senegalese fishing regulations” is somewhat vague. It is recommended to briefly explain the reason for its designation as a prohibited area.
5. Line 57: The sentence “some fishing c operating in Hann Bay...” Not clear. Try to reformulate.  
6. Lines 57–59: The concluding statement “...which raises concern” is abrupt. It is recommended to clearly identify specific issues such as resource depletion, biodiversity loss, or ecosystem degradation.
7. Lines 65–67: The description of Hann Bay’s geographic location lacks clarity. The sentence “Hann Bay is located in the traditional village of the same name” followed by “from Bel-Air Point to Mbao village” appears disorganized. A clearer geographical description is recommended.
8. The longitude coordinates in Figure 1 are incomplete. It is recommended to revise the figure to ensure full and accurate display of the map legend.
9. The Materials and Methods section is relatively brief. It is recommended to include more detail and to provide the formulas or explanations for Shannon index and Pielou’s evenness index in Section 2.3.
10. Line 105: The unit for salinity is missing. Figure 2(a) also does not include a salinity unit label. It is recommended to ensure unit consistency and add the necessary labels.
11. Section 3.2 of the Results lacks a comparative summary between beach seine and purse seine in terms of species composition, live bait proportion, and weight distribution. It is recommended to add a summary statement.
12. Section 3.2 of the Results presents data on quantity, weight, and species in a mixed manner, affecting the logical flow, particularly in distinguishing between beach seine and purse seine. For example, in line 142, the sentence “Non-bait species represented 67% of individuals” does not specify which gear type it refers to. Clarification is recommended.
13. Lines 133–134: Terminology such as “the most abundant species” and “Other bait species each represented less than 5% of the total” is inconsistent or slightly ambiguous. It is recommended to specify whether these refer to abundance or biomass.
14. Lines 156–165: It is recommended to describe the Shannon index and Pielou’s evenness index results separately for each gear type to avoid overlapping information that may hinder understanding.
15. The legend in Figures 3 and 4 uses “solid blue = warm season, dashed red = cold season,” which contradicts common color conventions (red typically denotes “warm” and blue “cold”). It is recommended to adjust the colors to avoid reader confusion.
16. The four paragraphs in Section 3.5 of the Results are structurally repetitive. It is recommended to reorganize and integrate them to enhance readability, and to clearly specify which type of fishing gear is referred to by “this gear” avoiding the use of ambiguous pronouns.
17. Section 4.1 of the Discussion repeatedly mentions environmental factors such as “temperature,” “transparency,” and “fishing pressure,” but does not analyze how these factors influence the responses of live bait species.
18. Section 4.2 of the Discussion frequently mentions the dominance of E. encrasicolusand S. maderensis, but lacks analysis of the mechanisms underlying this dominance, includinglife history traits and habitat preference.
19. Section 4.3 provides only a brief explanation of the differences in diversity indices between the two gear types. It is recommended to explore potential influencing factors such as gear structure, operational methods, and mesh selectivity.
20. Discussions often referred to ‘not significant’ without further explanation of possible causes or ecological impacts. It is recommended that influences such as sample size, data distribution or variability in fishing activities be explored.
21. The discussion includes assumptive statements such as ‘alteration of aquatic food webs’ and ‘impairment of ecological functions and structures’, but lacks supporting data or references. It is recommended that relevant ecological models or studies be cited to strengthen the argument.
22. Many of the arguments in the discussion are not supported by references. It is recommended that additional citations be provided.

 

Comments on the Quality of English Language

The manuscript frequently has language problems, including repetitive and redundant wording, especially in the results and discussion sections. Descriptive statements about species richness and abundance are repeated multiple times with minimal explanation added. In addition, the manuscript contains many grammatical and syntactical errors, as well as unclear sentence structure. These issues hinder readability and weaken overall scientific communication. Thorough linguistic revision is strongly recommended, with particular attention to eliminating repetition, improving clarity, and ensuring consistency in terminology and wording.

Author Response

Major Comments

1. Abstract

Eleven species were identified as live bait, yet the results in Section 3.2 (Table 1) list only ten

species for beach seine and eight for purse seine. This inconsistency needs to be resolved.

Pielou’s evenness index indicated a more balanced assemblage in the cold season for beach

seine and in the warm season for purse seine, but it does not include the actual index values

reported in Table 2. Key values should be included.

 

It has been corrected.

 

2. Sampling

There is unequal effort in sampling. The design specifies two purse seine hauls per month (for

a total of 20), but only one beach seine haul per month (for a total of 10). This difference in

sampling effort between the two methods makes direct comparisons of absolute

abundance/biomass (389,000/9,400 individuals) potentially misleading. The analysis should

therefore focus primarily on relative metrics, such as diversity indices, proportions and CPUE

(catch per unit effort). Acknowledge this limitation when comparing absolute catches.

Emphasise CPUE in the results and discussion sections where appropriate.

 

We have clearly explained the methodology in response to your comments. What should be noted is that this is not a comparison between the two fishing gears. That is not the objective of our study.

 

Were all hauls conducted at the same location? If multiple sites within Hann Bay were used,

this should be clearly stated, and potential spatial variability should be discussed as a factor

influencing the results alongside seasonality.

 

This section has been thoroughly supported following your comment. Yes, all hauls were conducted in the same locations: two stations for the purse seine and one station for the beach seine throughout the entire sampling campaign.

Figure 1 is crucial for understanding the spatial context, but it is referenced only and not included. There is a limitation in temporal resolution: Sampling only during the 'last week of each month' may result in important intra-monthly or sub-seasonal variations being missed.

Sampling campaigns were conducted once per month during the second half of each month, over a period of ten months. Although this strategy may not capture certain intramonthly or sub-seasonal variations, it ensures temporal consistency and comparability across months, with the aim of analyzing broader seasonal patterns in the diversity of live bait species.

 

3. Data Presentation and Statistical Analyses

- Table 1

Similar to the '% Number' columns, the '% Weight' columns lack clear headings to distinguish

between gear types. Label them explicitly, for example, "% Weight BS" and "% Weight PS".

The 'Total' row for weight has different values compared to the text and to the values within the

table: 1743 kg BS vs 306 kg PS, and 1742.72 kg BS, 305.8 kg PS, respectively. Round the

weights appropriately (1742.7 kg and 305.8 kg).

The requested modifications have been incorporated into Table 1.

 

The species names require consistent formatting and correction. For example, Sardinella

maderenis is used in Table 1, but maderensis is used elsewhere. Similarly, Sardina pitchardus

is used in one place, but the standard pilchardus is used elsewhere. Finally, Mugil carena is

used in one place, but curema is used elsewhere.

The species names have been properly formatted.

 

The 'Miscellaneous category' requires further clarification. Providing a list of the number of

species or dominant non-bait families/groups would significantly improve understanding of the

broader community impacted.

 

A table listing all the species caught by gear type has been prepared and included in the Appendix section.

 

- Table 2

The species richness (S) values for beach seine cold (40) and purse seine cold (30) seem

surprisingly low compared to the total number of species reported (65 for beach seine and 62

for purse seine). Please explain this discrepancy (fewer species were encountered per haul in

the cold season?).

The values 65 and 62 were calculated across all seasons combined, whereas the seasonal analysis of catches revealed different levels of species richness. The correction is clearly shown in Table 2.

 

The 'Shannon Index (0-In(S))' is unclear. It is typically reported as H' (base e or 2). Specify the

base used (likely base e?).

The logarithm used in the Vegan package in R is the natural logarithm (base e).

The values in parentheses (0–3.97) are not explained. Are these ranges across hauls or standard

deviations?  

These are the limitations of the Shannon index, which ranges from 0 to log(S), with S representing species richness.

Reporting the mean ± standard deviation (SD) for diversity indices per season/gear

would be far more informative than reporting single values, unless these represent a single

pooled sample per season/gear, in which case this should be stated.

It’s done

'Chaude' and 'Froide' should be translated as 'Warm' and 'Cold'.

It’s done

- Table 3

The gear codes (PS and BS) should be defined in either the table caption or a footnote. Ensure

that species names are consistent (e.g. Sardinella maderensis).

It’s done

 

- Statistical tests

Report the actual test statistics (W) and p-values for all relevant comparisons in the main text.

For salinity, transparency and depth, where p>0.05, report W and the p-value, as was done for

temperature and bait catches. State which tests were used for diversity indices (if any beyond

descriptive statistics).

It’s done

4. Interpretation of diversity and dominance

The interpretation of the K-dominance curves in Figures 3 and 4 needs to be strengthened.

While the rapid rise indicates low diversity is clear, this should be linked more explicitly to the

Shannon and Pielou values in Table 2.

 

The requested corrections have been taken into account.

Explain why dominance patterns differ between gears and seasons (beyond environmental

variation).

Dominance patterns differ between fishing gears and seasons not only due to environmental factors but also because of the selectivity and operational characteristics of the gears themselves. Different fishing gears have varying mesh sizes, fishing depths, and deployment methods, which influence the size and species composition of the catch. For example, one gear may be more efficient at capturing smaller, schooling species, while another targets larger, solitary species. Additionally, seasonal behavioral changes of fish, such as migration, spawning, and changes in habitat use, affect their availability and vulnerability to specific gears.

 

Furthermore, fishing effort and fishermen’s practices may vary seasonally, altering catch composition. The combined effect of gear selectivity, fish behavior, and fishing practices results in differing dominance patterns that cannot be fully explained by environmental variation alone.

We agree with the reviewer on these additional pieces of information.

 

Are the dominant bait species (E. encrasicolus and S. maderensis) responsible for these

patterns?

The dominance of Engraulis encrasicolus and Sardinella maderensis certainly contributes to the observed patterns, as these species often represent a large proportion of the catch due to their abundance and schooling behavior. However, these patterns are also influenced by other factors such as gear selectivity, seasonal availability, and environmental conditions. Therefore, while these dominant species play a key role, they are not the sole drivers of the patterns observed.

 

The extremely high dominance of E. encrasicolus (83% by number) in beach seine catches

requires further discussion. Is this typical? What ecological or behavioural factors make it so vulnerable?  What are the implications of such extreme dominance for ecosystem resilience and the

sustainability of fisheries?

This is explained in the section: Seasonal Variation in Species Dominance.

5. Juvenile Exploitation and Sustainability

The high percentage of juveniles in bait catches (often over 80%, sometimes reaching 100%) is a critical finding with significant implications for management. This issue is not adequately addressed in the Discussion (Section 3.6, Table 3). While the discussion (Section 4.5) rightly raises concerns about the impact, it needs to explicitly  link these concerns to the empirical evidence of high juvenile exploitation presented in the results. It is important to emphasise that live bait fishing primarily targets juveniles of key small pelagic species. The potential consequences for stock recruitment and ecosystem structure should be discussed in more detail. Although the conflict between bait use and other uses (human consumption and fishmeal production) is mentioned, it needs to be framed more strongly within the context of unsustainable juvenile removal.

The questions regarding juveniles are addressed in the chapter "Proportion of juvenile live baits in the catches". These results are discussed in section "4.7. Juvenile exploitation and implications for sustainability".

6. Discussion

The discussion is lengthy and repetitive, and could be streamlined. The focus should be more sharply on interpreting the key novel findings, such as the specific diversity patterns (differences between gears and seasons), the extreme dominance of certain species, the consistently high proportion of juveniles and the lack of seasonal variation in bait abundance and biomass despite changes in diversity. In section 4.1, the authors simply reiterate existing results and do not offer much new interpretation. Relevant environmental points (high turbidity……) should be integrated into discussions about species distribution or catchability where appropriate, rather than being presented in a standalone section. More directly compare the dominance findings (E. encrasicolus BS, S. maderensis PS) with the cited literature (Sieben, 2020; Ngom Sow et al., 2020). How do the dominance levels compare?

The entire discussion section has been revised taking your comments into account.

 

The conclusion about ecological stability, based on consistent S. maderensis catches, requires further consideration. Does high stability in the catch of one dominant species equate to ecosystem stability? Could it mask underlying degradation, such as the loss of other species

 

The Conclusion section has been completely revised, still taking your observations into account.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your efforts. All the requested revisions have been implemented in accordance with the reviewer's comments.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1. Lines 32 and 33 should be merged into a single paragraph.
2. The discussion section contains too many subsections; it is recommended to merge
   some of them appropriately.
3. In several sections of the discussion (e.g., 4.2, 4.3, 4.4), results are presented
   together with interpretations or inferences. It is recommended to separate data
   description from ecological interpretation for better clarity.
4. Lines 354–355: The expression “purse seine… caught by beach seine” is unclear
   and should be verified for accuracy.
5. Line 359: The explanation of environmental preferences for some species (e.g., S. maderensis relative to the 359 temperature vector may indicate a preference for cooler
   waters ) is inconsistent with the earlier conclusion (S. maderensis preferred warmer
   waters ) and should be clarified or verified for accuracy.
6. The conclusions on “seasonal differences” in sections 4.2 and 4.4 appear to
   conflict with the statement of “no significant seasonal variation” in section 4.6. The
   applicable conditions for each conclusion should be clarified.
7. The expression “juvenile individuals’ key prey” is unclear and should be
   rephrased

Author Response

Please see the attachment

Author Response File: Author Response.docx