If it’s real, could it be an eel?
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Abstract
Previous studies have estimated the size, mass, and population of hypothetical unknown animals in a large, oligotrophic freshwater loch in Scotland based on biomass and other observational considerations. The ‘eel hypothesis’ proposes that the anthrozoological phenomenon at Loch Ness can be explained in part by observations of large specimens of European eel ( Anguilla anguilla ), as these animals are most compatible with morphological, behavioural, and environmental considerations. The present study expands upon the ‘eel hypothesis’ and related literature by estimating the probability of observing eels at least as large as have been proposed, using catch data from Loch Ness and other freshwater bodies in Europe. Skew normal and generalized extreme value distributions were fitted to eel body length distributions in order to estimate cumulative distribution functions from which probabilities were obtained. The chances of finding a large eel in Loch Ness are around 1 in 50, 000 for a 1-meter specimen, which is reasonable given the loch’s fish stock and suggests some sightings of smaller ‘unknown’ animals may be accounted for by large eels. However, the probability of finding a specimen upwards of 6 meters is essentially zero, therefore eels probably do not account for ‘sightings’ of larger animals. The existence of exceedingly large eels in the loch is not likely based on purely statistical considerations.
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Peer review report
Title: If it’s real, could it be an eel?
version: 2
Referee: Dr Derek W Evans
Institution: AFBINI
email: derek.evans@afbini.gov.uk
ORCID iD: 0009-0002-1981-2693
General assessment
Interesting paper and a useful attempt at answering a crypto-zoological questions using real data, although some of the data used is not quite relevant to the cold waters of Ness. There was no figure 2 included with the manuscript. A description of eel behaviour outlining how they do not swim upwards and out of the water akin to “Nessie” breaching would be useful.
Essential revisions that are required to verify the manuscript
A map of locations. Corrected inclusion of Figure 2. Some wider eel biometric data such as that to be found in any of the ICES WG Eel annual reports; reference to The eel book by Tesch 2003 for comments on eel …
Peer review report
Title: If it’s real, could it be an eel?
version: 2
Referee: Dr Derek W Evans
Institution: AFBINI
email: derek.evans@afbini.gov.uk
ORCID iD: 0009-0002-1981-2693
General assessment
Interesting paper and a useful attempt at answering a crypto-zoological questions using real data, although some of the data used is not quite relevant to the cold waters of Ness. There was no figure 2 included with the manuscript. A description of eel behaviour outlining how they do not swim upwards and out of the water akin to “Nessie” breaching would be useful.
Essential revisions that are required to verify the manuscript
A map of locations. Corrected inclusion of Figure 2. Some wider eel biometric data such as that to be found in any of the ICES WG Eel annual reports; reference to The eel book by Tesch 2003 for comments on eel behaviour and comments on biometry.
Other suggestions to improve the manuscript
Inclusion of some images of very large 1m plus eels for comparative purposes
Decision
Verified with reservations: The content is academically sound but has shortcomings that could be improved by further studies and/or minor revisions. By way of edits suggested above
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Author response
Response to Dr Don Jellyman:
I thank Dr Jellyman for their polite and complimentary comments on the manuscript. Because no essential revisions or other suggestions were requested by Jellyman, I have not made revisions to the manuscript in response to their review.
Response to Dr Derek W Evans:
I thank also Dr Evans for their careful consideration of the manuscript.
Evans notes that “some of the data used is not quite relevant to the cold waters of Ness”. This is an important limitation. Accordingly, I have expanded the limitations paragraph of the Discussion section to read: “environmental conditions such as temperature and available biomass impact eel growth and length, therefore comparisons to other environments such as Zeeschelde may not be appropriate, i.e., some of the data cited may not be relevant to the …
Author response
Response to Dr Don Jellyman:
I thank Dr Jellyman for their polite and complimentary comments on the manuscript. Because no essential revisions or other suggestions were requested by Jellyman, I have not made revisions to the manuscript in response to their review.
Response to Dr Derek W Evans:
I thank also Dr Evans for their careful consideration of the manuscript.
Evans notes that “some of the data used is not quite relevant to the cold waters of Ness”. This is an important limitation. Accordingly, I have expanded the limitations paragraph of the Discussion section to read: “environmental conditions such as temperature and available biomass impact eel growth and length, therefore comparisons to other environments such as Zeeschelde may not be appropriate, i.e., some of the data cited may not be relevant to the relatively cold waters of Loch Ness.”
I apologise for causing some confusion around “Figure 2”. In the manuscript, I refer in multiple places to a “Figure 2” and a “Figure 4” which never appear in the text, e.g. “Oliver et al. (2015, Figure 2)” and “Meulenbroek et al. (2020, Figure 4).” What I meant by these references were the respective figures in those publications, i.e., “Figure 2 of Oliver et al. (2015)” and “Figure 4 of Meulenbroek et al. (2020)”. I see how my orginal wording was entirely confusing and I apologise for not making this at all clear. Correspondingly, I have revised the wording of the manuscript throughout as follows: “Oliver et al. (2015, Figure 2)” → “Figure 2 of Oliver et al. (2015)” “Simon (2007, Figure 2(b))” → “Figure 2(b) of Simon (2007)” “Melia et al. (2006, Fig. 2)” → “Fig. 2 of Melia et al. (2006)” “(Macnamara et al., 2014, Fig. 2)” → “(Fig. 2 of Macnamara et al., 2014)” “Meulenbroek et al. (2020, Figure 4)” → Figure 4 of Meulenbroek et al. (2020)”
I hope that these changes to the figure references above now make it clear that I was citing figures within other published works, rather than a missing figure in my own manuscript. Evans requested that I reference ‘The Eel’ by Tesch (2003). In this revision, I have included additional comments with citations to three chapters of ‘The Eel’, including Kloppmann (Chapter 1: Body Structure and Function, in ‘The Eel’) in the Introduction of the manuscrupt (third paragraph); Tesch and Thorpe (Chapter 2: Developmental stages and distribution of the eel species, in ‘The Eel’) in the Discussion of the manuscript (third paragraph); and Tesch and Thorpe (Chapter 3: Post-larval ecology and behaviour, in ‘The Eel’) in the Discussion of the manuscript (second paragraph).
Another suggestion was made to cite the work of the ICES Working Group on Eels (WGEEL) on eel biometric data, of which I note Evans is a member and so has extensive knowledge of this body of literature. To this end, I have added to the manuscript citations to the latest Report to ICES on the eel stock, fishery and other impacts in UK, 2020–2021, from the Joint EIFAAC/ICES/GFCM Working Group on Eels (WGEEL) Country Reports 2020–2021. I use biometric data from this report to compare Mackal’s eel lengths in Loch Ness to those collected elsewhere in Scotland in the same decade (Discussion, first paragraph) and to estimate ages of 1- and 6- meter eel specimens based on eel growth rates from a Scottish river (Discussion, second paragraph).
Finally, Evans requested a map of locations, which I have now provided links to in the online Supplementary Information (mentioned at the end of the Methods section), and inclusion of some images of very large 1-meter-plus eels for comparative purposes, which I have now also provided links to in the online Supplementary Information (mentioned in the Discussion; because I do not own the copyrights for these images, I do not feel comfortable reproducing them directly in the manuscript).
I hope that these changes are satisfactory, and that the reviewer feels that the manuscript may now be verified without reservations. I am grateful for the reviewers’ feedback, and I believe that their recommendations have greatly improved the manuscript. Accordingly, I have added Evans and Jellyman to the Acknowledgement sections of the manuscript to express my appreciation.
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Peer review report
Title: If it’s real, could it be an eel?
version: 2
Referee: Dr Don Jellyman
Institution: National Institute of Water and Atmosphere (New Zealand)
email: don.jellyman@niwa.co.nz
ORCID iD: 0000-0002-6941-2703
General assessment
An interesting assessment that verifies the obvious – that any monster of ~ 6 m cannot be an eel (Anguilla anguilla), although there is a reasonable likelihood that eels of ~ 1 m could account for some of the “sightings” of elongate animals in the loch. However, even though the outcome is unsurprising, the author approaches the subject in a rigorous and systematic way. As such, the manuscript is of value in eliminating eels as possible candidate species for the mythical monster.
The manuscript is well written and referenced.
Essential revisions that are required to verify the manuscript
Nil
O…
Peer review report
Title: If it’s real, could it be an eel?
version: 2
Referee: Dr Don Jellyman
Institution: National Institute of Water and Atmosphere (New Zealand)
email: don.jellyman@niwa.co.nz
ORCID iD: 0000-0002-6941-2703
General assessment
An interesting assessment that verifies the obvious – that any monster of ~ 6 m cannot be an eel (Anguilla anguilla), although there is a reasonable likelihood that eels of ~ 1 m could account for some of the “sightings” of elongate animals in the loch. However, even though the outcome is unsurprising, the author approaches the subject in a rigorous and systematic way. As such, the manuscript is of value in eliminating eels as possible candidate species for the mythical monster.
The manuscript is well written and referenced.
Essential revisions that are required to verify the manuscript
Nil
Other suggestions to improve the manuscript
Nil
Decision
Verified: The content is academically sound, only minor amendments (if any) are suggested.
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