Dear Dr. Español and co-authors,

Your revised manuscript has much improved, but I have some final comments, which I encourage you to account for. These are listed below. In five cases I think you could improve the answer to the comments by the referees. These are indicated as well.
The remaining comments are minor and technical issues.

Comment from referee #1:
Did you also look into associated calls (i.e. calls produced preceding and following these downsweeps)?

EDitor: Please answer this question from referee #1 and add info in the manuscript text

Comment from referee #1 (page and line refer to first version):
P14, line 214-217: Did you also investigate to what extent the background noise conditions differed between the recording sessions and if this might have affected the quality of the recordings in one year and as a result may have affected the measurements? How do you explain the differences in characteristics in the recorded calls between years?
Your Response: Background noise was not part of this investigation. Future research will be conducted to characterize acoustic pollution background and traffic.

EDitor: Please answer also the last question of referee #1 and add info in the text

Comment from referee #2 (page and line refer to first version):
Line 114: The hydrophone deployment method is a little unclear. Was the hydrophone suspended for up to 5 days over the side of the vessel? How many recording stations were conducted? What were the positions (lat/longs)? What was the sampling rate? How were the data recorded? Are these archival recorders, or were you using a computer, a recording deck, etc, and if so, what equipment was included?
Response: the methodology was change as follow: Opportunistic and planned recordings were carried out depending on the weather conditions and the vessel location. In 2017 the hydrophones were deployed for 2 to 5 days in 3 locations. In these cases, hydrophones were deployed at a depth of 5 or 10 meters on rocky bottom with no more than 40 meters depth. Hydrophones were hold on a row with an anchorage in the end and superficial buoys in the opposite side. In both years, during the day or night, hydrophones were deployed at a depth of 5 and 10 meters from the stationary vessel. In the opportunistic recordings, recordings were continuously, but in the night when the vessel was anchorage, the recordings were in intervals between 10-30 minutes each hour for guarantee the capacity of the acoustic personal to study the recording in the next day.

EDitor: I think referee #2 is asking for more info than you supplied here. Please also supply the remaining info.

Comment from referee #2 (page and line refer to first version):
Lines 119-123: This section is completely lacking in any detail on the analyses. How were the sounds reviewed? Using spectrograms? What page size, what FFT? How were signals from sei whales distinguished from other species, such as blue whales (which also produce similar low-frequency downsweeps)? How were measurements conducted? Issues with measurements such as low and high frequency that are strongly affected by spectrogram parameters and SNR have been recognized in the literature; Raven and other software packages (i.e. Ishmael) offer a set of more “ro- bust” analyses; these need to be used as well. It appears that two software packages were used (Audacity and Raven). What was each one used for?
Your Response: the methodology was change as follow: Audio data were analyzed using Raven Pro 1.5 (Cornell University, Ithaca, NY). Low and high frequency (Hz), frequency range (Hz), peak frequencies (the frequency at which the maximum power occurred within a call) and duration (s) for all calls found and attributed to sei whales were analysed from spectrograms and waveform plots created in Raven Pro 1.5 (Hann window; 50% overlap; window size 14563 samples; DFT 16384 samples).

EDitor: You have improved the method section, but I think you did not answer all questions of referee #2. Please add info also to the text

Comment from referee #2 (page and line refer to first version)
Figure 1: Which whale tail corresponds to which year? Also, the area where putative sei whales were detected appear very close to recording sites where they were not detected. Is there any explanation for why this might be?
Your Response: we incorporate a table with more detail about the sei whale recordings at the Penas Gulf and we explain this difference in the discussion: The few calls obtained in both expeditions maybe was due the duration of recorded in each site since they were opportunistic recordings, so visual observations, tagging efforts and genetic studies are needed to verify this hypothesis.
Discussion: Overall, there is no discussion of one of the main outcomes of this study – that despite the number of sites sampled, putative sei whales were only detected very rarely, and only in two locations. Why might this be? Could this have to do with the sampling scheme (ie duration of samping at each site) or noise conditions (ie masking of signals)? How does this conform to your expectation?
Your Response: the response above explain better the idea.

EDitor: I think there is more in this. Please expand


I think in the abstract some info should be added in what way these vocalizations were obtained, i.e. from sightings, which have an inherent uncertainty.

L43 For example, in the North Atlantic Ocean …
L46-47 Furthermore, the genetic divergence between North Pacific and North Atlantic stocks is well known …

L116-118 Is there possibly a cruise report of these cruises, that could be cited?
L130-131 at a depth of 5 or 10 m on rocky bottom with about 40 meters bottom depth.

L132 I am not sure I understand this. “… with an anchorage in the end and superficial buoys in the opposite side.” I suggest “…with a mooring at the end and surface buoys on the opposite side.” Is that correct?

L134-135 I suggest: Opportunistic recordings were continuous …
L135 “when the vessel was at anchor” instead of “when the vessel was anchorage”

L136-137 I suggest to change this to: … intervals of 10-30 minutes each hour to guarantee the capacity of the acoustic personnel to study the recording during the next day.

L157 between 8 and 10 May (change format)
L158 delete the second “were”

L173, 174 7 May, 10 May (change format)

Table 1 Hydrophone depth instead of Hydrophone Deep
Table 1 In L130 you write that the depth of the hydrophones is 5 or 10 m. In the table this is 13 m. Please correct where needed.

L183 This must be changed to something like: only sounds were detected without associated calls which we assign to sei whales

L220-222 “low frequency is higher and 220 downsweep had been accompanied in the recorders by the Southeast Pacific type 2 221 (SEP2) (Saddler et al., 2017),” I do not understand this. Please rephrase for better understanding.

L233 upper instead of superior
L260-261 “The few calls obtained in both expeditions maybe was due the 260 duration of recorded in each site” This sentence is not clear to me. Please make clear.

L281-283 “An other factor that could be important in the discussion about the acoustic behavior is background noise, which might be masking biologically important signals …”

L305 referees
L357 (30–80°E)

L359-360 Please add a translation of the title in English.
L375 update of reference: Conservation Genetics, 19, 1007-1024, 2018.

L392 delete [abstract only]
L396 22 instead of XXII

Thanks and best wishes
Mario Hoppema

Dear Dr. Español-Jiménez and co-authors,

Thank you for revising your manuscript. I am satisfied with your modifications and answers, but do have some technical issues that I encourage you to account for in the final submission of your manuscript.

Please add a sentence in the Abstract on the conditions of detection, i.e. that they were done opportunistically.

L124 “frequency response 60000Hz ±3 dB” Is this correct? Hz ± dB? Please clarifiy.
L142 … using Raven Pro 1.5 (Cornell University, Ithaca, NY) software. (add: software)

Table 1: Usually S and W are placed behind the numbers of latitude and longitude, respectively

L190-194 SD is standard deviation, I guess. Usually σ (sigma) is used here, I request to use that notation.

Table 2 title: … timing of recorded calls of sei whales in the present study … (add: of sei whales)

Table 2: In the last three lines, the values for the frequencies are very different from those of the remaining studies. Is this correct? Are possibly other whales concerned here?

L223-224 Modify to: … the minimum frequency of blue whales is higher than that in our results …

L224-225 “downsweep had been accompanied by the Southeast Pacific type 2 (SEP2)” It is not clear here what SEP2 stands for. Is it a signal? Please clarify in the text.

L377-381 Please separate the two references
L444-445 I think this is not the full list of authors. Please complete to add all authors.

With best wishes
Mario Hoppema