Diet of Bottlenose Dolphin, Tursiops truncatus (Montagu, 1821), in the Northwestern Mediterranean Sea

Round 1

Reviewer 1 Report

As is commented by the authors, this type of analysis are difficult to carry out because the patience to care for and handle the samples, which takes money, time, and expertise. But on balance, they offer a lot of information not only about the diet of the animals but also about the biodiversity of the environment. Thanks for the effort. I encourage you to continue and enrich this line of research.

 

Some comments and tips:

 

Introduction

lines38-40: I miss adding some reference about distribution in the Med. Sea. 

line 57: change "died" to "diet"

 

Materials and methods:

Two minor considerations, can be ignored:

line 63: I would consider deleting "investigated" as it describes the area where the stranded animals appeared, but the area itself is not investigated. We really do not know the movements of the animals, so the area where the animals appeared is described

line 65: As before, I would consider changing "the study area" to "the coast of the area" or simply "the coast" or something like that. 

 

To consider:

lines 76-79: It is described the number of stomach selected for the analysis. I guess "calves nursed by the mother" include stomachs with milk. It would have been interesting to describe the number and the size of those specimens, in one sentence. This information provides data on when the pups begin to eat solid food. It is just an advice.

It is also described that individuals with very scarce stomach content, not representative of the diet, were not considered. Why have you considered that it is not representative of the diet? Table 5 includes a specimen with 3 preys with 5gr. weight , which is scarce but is included though. Perhaps it could be clarified, is it possible that the remains not included were not identifiable?

 

line 82: Just only a tip for preserving otoliths from stomach contents. After the content being washed, it is important to separate the otoliths and keep them dry, since it has been seen that ethanol can degrade them over time and therefore impede their correct identification.

 

Results

Results are methodical and orderly. Good tables, simple and visual graphs. 

Some comments

Line 240: Finish the sentence with "...where found in two stomachs.", as it is described "during the stomach content analysis", so repeating "stomachs analysed" could be reiterative. And relative to this sentence and paragraph: Two animals appeared with clear signs of bycatch, and in these two animals were found some remains of set nets in the stomachs. My question is, what kind of remains? fibers? something bigger like net pieces? I mean, were no other remains or foreign objects found in the stomachs of the rest of the animals?

 

Discussion

lines 258-259: "....animals found dead (e.g. stranded after accidental death, after by catch)": it would be better to include the most general causes in parentheses, I mean: "(either by natural causes or by an interaction with anthropogenic activities)"

lines 261-264: "As a matter of fact, in our case most of the SC were found....". The situation described as "in our case" is in fact the most frequent in the study of the stomach content from cetaceans. What is more, it is anecdotal to find the entire prey without digestion, being this more common in dead animals by bycatch. So, I would change the sentence, something like: ". As in this study, most of the stomach contents are frequently found highly digested....-...- and rocker bones) are observed."

lines 265-267: Any reference of this? I mean, beaks remain longer period than bone or otoliths.

 

 

The following paragraphs describe the high diversity found in the stomachs, but is also highlighted the importance by number and weight of some of them. It could be right to include some comments about the secondary digestion in the analysis of the stomach contents, as some of the minor species could be preys of the mayor. For example, the case of Merluccius, hake, which includes some of the prey found in this study in its diet (Bozzano et al-Scientia Marina 61(1): 1-8 (1997); Carpentieri et al.Fish. Bull. 103:411–416 (2005)).

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The paper is a useful foundational paper but it is similar to many stomach content analysis studies out there. It would be nice to integrate this diet studies with actual information on dolphin movement and behavior in the area. Also, can you compare past studies with your data and note any changes in dietary patterns over the years? Is there any time series available? 

The Introduction and the paper in general obviously needs some English editing but that is ok. 

Discussion is weak and is a bit one-sided on the prey side - but not all results are fully discussed. I have asked some additional questions in my comments about some missing information.

Cetacean studies are now becoming increasingly integrative and multidisciplinary - so to elevate this study to something significant and valuable, recommend collaborating with dolphin researchers and ecologists to include dolphin and environmental factors to better explain the foraging ecology and observed dietary patterns - since as you note there will be biases with stomach content samples. 

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

This paper reports some new, relevant findings on the diet of Tursiops in the Mediterranean, however authors must improve the appeal of their manuscript before it will be suitable for publication. In particular they have to increase the interest for the rider avoiding long, boring, detailed lists of preyed species and of their mophometric parameters. All these data and tables must be transferred to the "Supplementary Material" online section. In the following some suggestions to re-addres the mauscript are given.

Major changes

Title: "The diet of an apical predator: the feeding of bottlenose dolphin in the NW Mediterranean". This or a similar title may be more appealing for the rider.

Abstract:  More than half of this short Abstract is dedicated to the methods, please give more space and evidence to your findings, e.g. add the percentage of lactant calves; the percentage of youngs and adults with empty stomachs; the relations  between size/age or life stages (youngs, adults and olds, if any) of stranded dolphins and taxa richness and Diversity Indexes of their diet (is there any difference between male and females at this level?); benthic, demersal, pelagic ratio; please, underline the relative high amount of Conger conger and Ophium barbatum found, indicating a nocturnal hunting activity of T. truncatus and, for the second species, the ability of the dolphin to capture, at night, soniferous fishes.

Introduction                                                                                        Expand this section and  the references concerning the diet of Tursiops worldwide (also those dealing with other congeneric species) and add  some comments on the previous findings by other authors and on the (eventual) lack of a deeper knowledge on the topic (the need of research on annual cycle of diet, on local geographic differences, you reported in the Conclusions, should be included here.

Material and Methods.  At line 69-79 Authors have mentioned 47 stomachs 28 of which have been examined for their content. The others 19 were empty or have a scarce content or belong to lactating calves, therefore were not examined in this paper, however this should be a result of some interest, how many dolphins were starved? This finding should be mentioned  in the Results and Discussion.  Tab. 1 and 2 should be transferred to Supplementary Material.

Results. In this section should be reported the main findings previoulsy suggested. In particular, at line 94, together with the IRI index reported,  Diversity Indexes should be included and compared synthetically, while tables 3 and 5 should be transferred to the Supplementary Material. Table 4 should be somehow reduced and condensed. Table 6 too should be transferred to the Supplementary Material as the only significant difference between male and female diets  is reported at lines 231-232 and in Fig. 7.

Some additional change.

Abstract

lines 21-22 "......according to available data or from.............area." - Delete this sentence.

line 22 Please, add before "The trophic spectrum......." this sentence: Overall 2201 bony fishes and 406 cephalopods were examined.

line 23 - before "Nevertheless" (that can be deleted) add the values of Diversity Indices.

line 25 "..the interesting finding that.." - Delete

Introduction

line 34 "..is a regularly present species in the Mediterranean Sea" - change in: is a common Mediterranean species

lines 39-40 "..may also be present deeper waters" - may be found in deeper waters.

line 44 "..feeds on...prey species .." - delete prey

line 58 please, delete males and females.

MM

line 60 ".. the biggest MPA." - the largest MPA

lines 69-79 - You can report the finding of 19 stomachs of lactating calves or starved individuals in the Results  and comment this  in the Discussion section.

line 94 and following - Refer here to the Diversity Indices you will apply.

line 105 - "..the available parameters data.." - The available allometric relationships.

line 109 "..were used" - Were applied.

Tab. 1, 2, 3, 5, 6 - Must be transferred to the Additional Material on line (as reported above).

line 229 "..significant difference" -Any significant difference..

line 230 "except for....the contribution of Octopodidae" - Change in: Only the contribution of Octopodidae was significantly different, being higher in the diet of females.

Fig. 7 legend: "Boxplots about" -Boxplots of

 

Discussion

line 260 "..could continue to be digested by the acid residues present in the stomachs.." -....the digestion of the stomach content continue after death.

line 272 "..belonging mainly to bony fishes and some cephalopod species" - belonging to bony fishes and to some cephalopods.

lines 292-293 " but they were composed of a wide number of species.." - Sparidae, also if an high number of species was found, can be considered as preys of secondary relevance in our study (due to their lower frequency or biomass?)

line 299 "During the presence of calves and juveniles, females.."  - During nursering females may be less mobile...

line 305 "..similar abundances of our study - abundances similar to those we found.

lines 306-315 and 326-335 These findings are quite relevant and can be reported also in the Abstract.

line 316 "abundant presence " - abundance

line 329-330 "..are not as abundant as intead the stomach contents of T. truncatus led us suppose." - change in: are not so abundant as the stomach contents of T. truncatus suggest.

line 342 "..dead produced." - of dead.

line 347 "intersting" -delete

line 350 "..it is suggested "- We suggest to...

line 354-357 to much species in a few lines, delete the firs one (..defined as: "ecologically relevant"...)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The paper still requires extensive editing. The track changes make it difficult to read but there are numerous communication and presentation issues, which must be fixed to make it suitable for publication. 

Author Response

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Reviewer 3 Report

Also if the MS was impoved and several, mainly minor changes were made, however I don't believe it is still suitable for publication.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Thanks for getting the manuscript edited.

 

 

Reviewer 3 Report

The MS has been improved and is now sutable for publication.

Please, revise a little the English form; as an example:

Abstract line 30 among sexes; between is better.

Introduction

line 78 ..the dophin - dolphins

Please, control if the position of the single words is alwais correct in the improved MS.

A last question about the title: while "food and feeding" ? I don't found this difference in your findings. Are there 2 different kind of findings in your paper? Diet should be better.