Guest Post: A review of the Field Guide for Sharks of the Genus Carcharhinus

Dr. David Ebert is the Director of the Pacific Shark Research Center at Moss Landing Marine Laboratories. He is one of the world’s leading experts on shark taxonomy, and has described new species of sharks, skates, rays, and chimaeras. Dr. Ebert has written over 100 publications, five books, and dozens of IUCN Red List assessments. He generously agreed to review a new taxonomy guide, Field Guide for Sharks of the Genus Carcharhinus, for Southern Fried Science. He has provided a thorough list of citations backing up his points, but all opinions are his own. 

The shark genus Carcharhinus is one of the largest and perhaps most important genera of sharks, with many common and wide-ranging species. These sharks are mostly marine occurring from close inshore to the outer continental shelf and upper slope, but a few species inhabit estuaries and freshwater rivers and lakes. This group is by far one of the most important shark genera for fisheries globally, with various species being taken in commercial and sport fisheries, and in artisanal fisheries. Given the high profile and importance of this genus and the associated problems in identifying them to individual species in the field, an identification guide to the group would be most welcomed.

The book, “Field Guide for Sharks of the Genus Carcharhinus” by Matthias Voigt and Dietmar Weber, could have been that guide, with an exceptionally nice layout, beautiful illustrations, and tooth plates, but unfortunately the text does not stand up to the same high quality of the illustrations. The book cover is quite attractive and eye-catching, and upon initially thumbing through the illustrations and layout of the individual species accounts, I thought wow this looks to be an interesting and possibly useful guide to this shark group, even though I was unfamiliar with the authors, whom to be candid I had never heard of before.

The lateral view color illustrations of each individual Carcharhinus species are perhaps some of the best I have seen for this group of sharks, rivaling the outstanding color illustrations by Roger Swainston in the recent Sharks and Rays of Australia (Last and Stevens, 2009), and appear to be fairly accurate, at least for those species I am familiar with. The layout for each species also includes key characteristics such as a ventral surface illustration, a close-up of the nostril, dermal denticles, and tooth illustrations that are all quite nice, and well presented. Many of the illustrations, however, especially of the jaws and teeth, appear to have been taken directly from the lines drawing of Garrick (1982, 1985). A problem with the tooth drawings though is that the size and sex of the shark illustrated is different in this book from what Garrick (1982, 1985) reported which will cause confusion for those trying to use this guide to identify individual shark species. Sexual and ontogenetic heterondonty may be weak to strong in this shark genus as the teeth can change ontogenetically with growth in some species and sexual dimorphism can be quite strong in some species. The tooth plates and images at the back of the book are also quite nice in their presentation, but I am not certain how they came by some of the type specimens teeth, which are still intact in the jaws of some type specimens. Also, some of the images from type specimens appear to be from the types of species that have been synonymized which may cause considerable confusion.

The maps on species distribution while nice are a bit uneven in their presentation, with the color of each shark’s distribution being either bluish or purple. However, this is a minor criticism to the overall presentation, the larger issue is that the distribution for some species is not well known in some areas, and is considered questionable at best, but here the authors do not always distinguish between confirmed or questionable records. For example, C. isodon is well known from the Western Atlantic, but most researchers consider its occurrence in the Eastern Atlantic questionable at best, yet the authors simply list it as occurring in this area without comment.

Despite the appealing and attractive layout of the book, however, the real problems are within the text and the information presented within it, which I found to be quite disappointing in comparison to the illustrations. The English grammar is quite poor and although I realize that English is a second language for these authors, and I can certainly make some allowance, the more I read the more frustrating it became in trying to understand what they were often trying to convey. The book would have benefitted immensely if someone fluent in English could have worked closer with them to improve the English grammar. Also, a knowledgeable taxonomist on this genus could have probably helped the authors avoid some of the egregious mistakes that will likely further complicate the taxonomy of this genus in the future.

The back-cover of the book and in their advertisement of the book the authors state that most previous works on this genus listed and discussed a maximum of 30 species. In contrast, they describe 33 species; a statement which certainly grab my attention. The additional 3 species discussed includes C. acarenatus, a species considered by most taxonomists of this group to be a junior synonym of C. brachyurus, C. leiodon which they state was hitherto recorded only once by Garrick (1985), and Carcharhinus species A. They also mention possible subdivisions within C. brevipinna. The authors also resurrect another species, C. wheeleri, which has been considered a valid species until recently, and may in fact still be a good species, but the authors do not explain why they consider it to be valid.

The resurrection of C. acarenatus is curious since these authors base their recognition of this species on their review of the literature, and not apparently on examination of the type material with a comparison to C. brachyurus material. In fact, they state (page 35) that they did not examine type material because it was unavailable. The literature they cite as having based their information on in recognizing this species as valid consists of four publications, including the original description by Moreno and Hoyos (1983) that in itself was quite poor and with a very poor quality line drawing of the holotype which in the caption states that it is a male, but the line drawing is clearly of a female. Of the other three literature citations, all of which come from non-peer reviewed sources, one is by one of the original descriptors, Moreno (1995).  Also, I noticed that in their Key to the Genus Carcharhinus they have both species as lacking an interdorsal ridge, but in the species account (page 36, Misidentifications) they state that the difference between C. acarenatus and C. brachyurus is that the latter species lacks an interdorsal ridge while the former species has it present. Whether C. acarenatus is a good species or not, it will require a critical examination of the types specimens and comparison with other similar congeners such as C. brachyurus.

In the authors account of C. leiodon they appear to question its validity, and feel that because it is known from only a single specimen that it may be a mutation of another Carcharhinus species, possibly C. brevipinna, C. limbatus, or C. wheeleri since all these species occur in the same area. They base their conclusion on the similar body size and coloration of C. leiodon to C. brevipinna, and C. wheeleri, and on tooth shape and counts being similar to C. limbatus. However, whereas Garrick (1985), who was a well known and very good taxonomist who spent over 20 years of his career examining Carcharhinus species, based his description on material he actually examined these authors, who have no previous taxonomic background on this genus that I could find, initially dismissed Garrick’s description of C. leiodon.  However, at the end of their account of this species they had to retract their earlier statements in a separate paragraph at the end of the “Authors note” section by adding that Alec Moore in a presentation at the Sharks International conference (June 2010) presented information on additional specimens of this species. This paper, which is now published (Moore et al., 2011), provides additional detailed information on this species. However, the authors’ assertion that this may not be a good species, without any real supporting evidence other than their interpretation of literature accounts highlights the major shortcomings of this field guide.

The recognition of Carcharhinus sp. A is also curious since all the authors really state is that they apparently agree with Compagno (1988) that this is not C. porosus, but they also state that they cannot tell whether this species is a Carcharhinus or not. Most of the account is based on information found in Garrick (1982), Compagno (1988), and Compagno et al. (2005). It is curious why the authors did not attempt to locate some of this material, which apparently is deposited in the Paris Museum.

Although the authors have compiled a considerable amount of information, the book appears to largely be a compilation of other author’s previous work (e.g. primarily Garrick 1982, 1985; Compagno 1984, 1988; Compagno et al., 2005), which is not a problem, but they often present the information as though it were mostly their own original work when in fact it is difficult to determine what original work they contributed.  In the introduction section (page 15), Table 2, they give the number of specimens used to calculate the morphometric mean values for the creation of graphs, which I presume is for the tables and figures at the end of the book. However, this is not clear and it is not clear if the authors took these values themselves, or they came from the literature, or both? Also, the deposition of the specimens they measured (e.g. were these museum specimens) is not available and there is no indication if these specimens are still in existence.

Another problem I had was that they occasionally cited nearly verbatim sentences from Compagno (1984) or Garrick (1982), but did not correctly cite the authorship. For example, Carcharhinus falciformis, on page 62, they state in the food section that this shark “Mainly bony fishes, e.g. sea catfish, mullets, mackerel, yellowfin tuna, porcupine fish, but also cephalopods (squids, paper nautiluses) and pelagic crabs.” This information is attributed to Cabrera Chavez-Costa (2003), a Ph.D. dissertation, but in Compagno (1984, page 472) he states “Primarily a fish-eater, eating teleosts including sea catfish, mullets, mackerel, yellowfin tuna, and porcupine fish, but also squids, paper nautiluses and pelagic crabs”. It would have been better if they had attributed the citation for this information to its proper authority (Compagno, 1984). There are other examples throughout of the information being attributed to or ascribed to the wrong authority. I also found that marginal references were often given equal weight to more established and accepted peer review references.

Overall, despite the excellent illustrations and nice layout, the text is very poor grammatically, uneven, and had numerous errors that will likely only further complicate this genus. The book’s text rather than help in identifying members of this problematic genus will only serve to infuse more confusion and uncertainty into an already complicated genus.

Field Guide for Sharks of the Genus Carcharhinus. Matthias Voigt and Dietmar Weber. 2011. Verlag Dr. Friedrich Pfeil, München, Germany. ISBN: 978-3-89937-132-1. 151 p. 38 € (US$ 52) (soft cover).

Cabrera Chavez-Costa, A.A. 2003. Feeding habits of the silky shark, Carcharhinus falciformis (Bibron, 1839) in the western coast of Baja California Sur. Unpubl. Ph.D. Dissertation.

Compagno, L.J.V. 1984. FAO Species Catalogue. Vol. 4, Sharks of the World. An annotated and illustrated catalogue of shark species known  to date. FAO Fisheries Synopsis No. 125. vol. 4, pt. 2  (Carcharhiniformes), pp. x, 251-655, United Nations Development Programme/ Food and Agriculture Organization of the United Nations.

Compagno, L.J.V. 1988. Sharks of the Order Carcharhiniformes. Princeton  University Press, Princeton, New Jersey, pp. 1-572.

Compagno, L.J.V., Dando, M., and Fowler, S. 2005. Sharks of the World. Princeton University Press, 368 p.

Garrick, J.A.F. 1982. Sharks of the genus Carcharhinus. Nat. Ocean. Atmosph.   Adm. USA, Tech. Rep., Nat. Mar. Fish. Serv. Circ. (445): 194 p.

Garrick, J.A.F. 1985. Additions to a revision of the shark genus Carcharhinus: synonymy of Aprionodon and Hypoprion, and description of a new species of Carcharhinus. NOAA Tech. Rep., Nat. Mar. Fish. Serv. (34): 26 p.

Last, P.R. and Stevens, J.D. 2009. Sharks and rays of Australia. CSIRO Division of Fisheries, Melbourne, Australia, 644 pp.

Moore, A., White, W., Ward, R., Naylor, G., & Peirce, R. (2011). Rediscovery and redescription of the smoothtooth blacktip shark, Carcharhinus leiodon (Carcharhinidae), from Kuwait, with notes on its possible conservation status Marine and Freshwater Research, 62 (6) DOI: 10.1071/MF10159

Moreno, J.A. 1995. Guia de los tiburonesde Atlantico Nororiental y Mediterraneo. Pirámide, Madrid. 310 p.

Moreno, J.A. and Hoyos, A.1983. Carcharhinus acarenatus, nov. sp., nouveau requin

Carcharhinidae de l’Atlantique Nord-Oriental et de la Mediterranee Occidentale. Cybium, 7(1): 57-64