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Year: 1999
Author: G. Gerosa and P. Casale
Publisher: UNEP; Regional Activity Centre for Specially Protected Areas (RAC/SPA); Tunis, Tunisia.
ISBN: 9973-9926-6-0
Pages: 59 pages

Published as a resource document for UNEP’s Mediterranean Action Plan for marine turtles, this volume sets an important precedent. Various international instruments for marine turtle conservation are being developed in different parts of the world: the western hemisphere (Frazier 2000a), the Indian Ocean and South-East Asia (Anon 2000; Hykle 2000; Al-Ghais & Frazier 2001), and west Africa (CMS 2000), as well as the Mediterranean. The measures included in these instruments, and the actions implemented by the Parties and Signatory States, will depend ultimately on political decisions. To increase the chances of these decisions being informed, and relevant to the issues that need to be resolved, it is imperative that up-to-date, balanced documents be made available to decision-makers in each of the participating nations. At the same time, these resource documents must be clear, informative, and succinct; there is little chance that bureaucrats will wade through reams of documentation, much less be able to synthesize and extract the most pertinent problems and solutions.

The book, published by UNEP, Tunisia, meets the criteria for informing decision-makers. Beginning with the front cover, where one colour photo vividly portrays a turtle hooked in the mouth and another shows hatchling turtles hopelessly entangled in a gill net, the effort has been to drive the message home quickly.

After the introduction, the following nine chapters deal with longlines, trawls, gill nets, indirect mortality, the Mediterranean fishing fleet, zones frequented by turtles, possible ways to reduce fishing induced sea turtle mortality, reducing Mediterranean fishery-sea turtle interaction: available options, and assessing/evaluating Mediterranean fishery-sea turtle interaction: some priorities. The stated object of the report is to provide a general summary of the problem of fisheries interactions in the Mediterranean, and to help identify priority areas for research and conservation. It makes clear that there is still a great deal to be learned, and that much of the available information is difficult to interpret.

The booklet presents a valuable synthesis of literature on incidental capture of marine turtles in the Mediterranean, and is further enhanced by drawing from a number of key publications on fisheries, not directly related to marine turtles. Incidental capture is of course a fisheries issue, and as such can only be understood and resolved by understanding fisheries.

The authors rightly emphasise the primary importance of reducing fishing effort, not only for the sake of marine turtles, but also for other animals impacted by fishing as well as for marine environments. In their discussion of different types of fishing gear, Gerosa and Casale make a number of interesting points, including economic and social insights as to why certain types of fishing are carried out. In so doing, they correctly show that just technological considerations are inadequate for understanding and resolving marine conservation issues. It is also important to appreciate that many fishing vessels in the Mediterranean employ a variety of different gear types, so during certain seasons they may longline, and during others they may trawl. Clearly, this adds other layers of complication, notably for analyses of fleet sizes, distribution and fishing effort; managing and implementing measures for these multi-purpose fleets will also be complex.

The authors point out that some of the species identifications may be erroneous, for fishermen may confuse one turtle with another: there is a tendency to group all marine turtles as the most common/best-known species, Caretta caretta. This could explain, in part, why there are so few records of Chelonia mydas in fisheries interactions.

Their review leads them to the conclusion that: 1) loggerheads are the only species known to be significantly impacted by fisheries, and 2) the Spanish longline fleet has far greater (perhaps 61 times) probability of catching a turtle than do any of the other fleets in the eastern basin of the Mediterranean. Hence, although the Spanish fleet is but a few hundred vessels, the evidence indicates that it has far more impact than other fleets that are much greater (the Italian and Greek fleets both number in the thousands of vessels).

They rightly explain that a large number of parameters must be considered when assessing a fishing activity and its impacts, including gear, environment fished (depth of water, depth fished, bottom type, currents, etc.), time of day, season, weather conditions, “soak time” of the gear, and so on. Hence, it is not uncommon for expert opinions about various aspects of incidental capture to vary, or even contradict each other.

Gerosa and Casale point out that documenting direct, or observed, mortality is not sufficient, for all types of gear can produce delayed mortality: pieces of netting may be left entangled on a live animal, later to produce necrosis and debilitation; hooks in live animals may cause infections or perturbations to the digestive system; forced submersion in any gear can result in physiological stress and consequent debilitation.

In general, it seems that Mediterranean fishermen (from the lack of any reference to “fishers,” it appears that there are few, if any, women in the Mediterranean who fish) have no desire to catch turtles, nor have they any use for them – indeed in some societies it is regarded as bad luck to catch and harm turtles, and in some cases there is even appreciation that these are endangered species and merit special consideration. However, in some places the meat and blood are relished, so there is a stimulus for keeping and selling turtles, even if they are caught accidentally.

Gill nets are categorised as potentially dangerous: their use is widespread throughout the Mediterranean, and mortality rates for entangled turtles are generally quite high. It is remarkable that some of this gear has been in use in the Mediterranean for centuries, if not millennia: surface longlines since 177 BC and drifting gill nets since 171 AD. Because ostensibly passive nets with entangled fish may actively attract turtles, they question the apparently simple categorisation of gear into “passive” and “active”. However, the usual meaning of “active” gear is that it is actively moved through the water in an effort to catch prey, not that it is or is not attractive.

There are unfortunately a number of confused or dubious statements that detract from the value of the book, notably in the Introduction.

The claim (page 5) that “Mediterranean populations of both species [Caretta caretta and Chelonia mydas] seem to be genetically isolated from the Atlantic ones” appears to be an error of translation, for the authors cite the studies of Bowen et al. (1993) and Laurent et al. (1993) which clearly argue that a significant proportion of the C. caretta sampled from the Mediterranean show genetic markers comparable to individuals known to nest on west Atlantic beaches; hence the “Mediterranean populations” of this species are in fact mixed stocks.

Likewise the statement (page 5) “the bigger (older) a specimen is, the greater is its contribution to the demographic growth of the population” seems to imply that size and age are directly related to each other, and also to reproductive contribution. There is no question that “large” adults have a greater reproductive value to the population than “small” juveniles. However, the situation with the “larger” sizes is not so clear; there is no certainty that every individual larger than the minimum known breeding size is reproductively mature. Individuals, even from the same population, do not become sexually mature at the same size, and several studies have shown that near adulthood, size and age are not directly related (e.g., Limpus et al., 1994a; 1994b). Hence, the “bigger” animals do not always have a greater reproductive value. Furthermore, demographic studies (including those cited by Gerosa and Casale, 1999) do not claim that the older an adult is, the more it contributes (thus, negating any effect from senility), but rather that a breeding adult – as a member of an age class - contributes more, and hence is worth more to the population, than a juvenile. Experienced breeders may contribute more, on average, than inexperienced breeders, but this is not the same as an across the board generalisation that older individuals contribute more.

Some statements cut corners to draw generalised conclusions. For example, the claim (page 5) that “[m]arine turtles go through two main ecological phases during their lives, first pelagic and then demersal” is used to make the point that turtles (presumably adults and large juveniles) in coastal waters are more important to a population than those on the high seas. Certainly, the terrestrial phase (incubation in the nest and nesting by females), although it is an extremely brief proportion of the total life cycle, is not only of critical importance for reproduction, but also the time when the animals are exposed to exceptionally intense sources of mortality.

The conclusion that pelagic/surface longlines are of little significance to leatherback turtles (Dermochelys coriacea) may be in strict keeping with the available evidence (page 9), but it is not in keeping with the precautionary principal: the lack of scientific evidence/proof is not sufficient basis for ignoring conservation needs. What is known of this species in other seas has been enough to raise global concern about the dangers of pelagic fisheries, especially longlines (e.g., Eckert & Sarti 1997; Spotila et al., 2000). This is not the first time that conservation requirements of the leatherback have been obscured by “scientific logic” (Frazier 2000b), and it emphasises the pressing need to develop realistic policies based on the best available scientific information, but also sensitive to the limitations of contemporary science.

The statements that gill nets can be used “to catch exactly the target species they want” and that they “are almost species specific” (page 23) are hard to accept. Likewise, the conclusion that surface longlines in the Mediterranean “seems to be a very homogenous method” (page 7) is remarkable, for it is followed by a series of possible sources of variation in this technique.

These, and various other questionable nuisances that are less than convincing evidently stem from language problems. The value of the publication would have been enhanced had it been given a final “polishing” for language.

J. FRAZIER, Conservation and Research Center, 1500 Remount Road, Front Royal, Virginia 22630 USA.

Al-GHAIS, S. & J. FRAZIER. 2001. Workshop on the Western Indian Ocean. Marine Turtle Newsletter 92:17-25

BOWEN, B. W., J. C. AVISE, J. I. RICHARDSON, D. MARGARITOULIS & S. HOPKINS-MURPHY. 1993. Population structure of the loggerhead turtle Caretta caretta in the northwest Atlantic Ocean and Mediterranean Sea. Conservation Biology. 37 (4): 834-844

CMS (Convention on Migratory Species) 2000. Conservation Measures for Marine Turtles of the Atlantic Coast of Africa. CMS Technical Series Publication No. 5; Bonn. 157 pp.

ECKERT, S. A. & L. SARTI M. 1999. Distant fisheries implicated in the loss of the world’s largest leatherback nesting population. Marine Turtle Newsletter. 78:2-7.

FRAZIER, J. 2000a. Guest Editorial: Advances with the Inter-American Convention for the Protection and Conservation of Sea Turtles. Marine Turtle Newsletter 90:1-3.

FRAZIER, J. 2000b. Leatherback Sea Turtle. In: R. P. Reading and B. Miller (eds.) Endangered Animals: A Reference Guide to Conflicting Issues. Greenwood Press; Westport, Connecticut. pp. 171-177.

HYKLE, D. 2000. Indian Ocean – South East Asia Marine Turtle MoU Concluded under CMS. Marine Turtle Newsletter 90:21-24.

LAURENT, L., J. LESCURE, L. EXCOFFIER, B. BOWEN, M. DOMINGO, M. HADJICHRISTOPHOROU, L. KORNARAKI & G. TRABUCHET. 1993. Etude génétique des relations entre les populations méditerranéenne et atlantique d’une torut marine (Caretta caretta) à l’aide d’un marquer mitochondrial. C. R. Acad. Sci. Paris 316: 1233-1239.

LIMPUS C. J., P. J. COUPER & M. A. REED. 1994a. The green turtle, Chelonia mydas, in Queensland: population structure in a warm temperate feeding area. Mem. Queensland Museum 37(1):139-154.

LIMPUS, C. J., P. J. COUPER & M. A. REED. 1994b. The loggerhead turtle, Caretta caretta, in Queensland: population structure in a warm temperate feeding area. Mem. Queensland Museum 37(1):195-204.

SPOTILA, J. R., R. D. REINA, A. C. STEYERMARK, P. T. PLOTKIN & F. V. PALADINO. 2000. Pacific Leatherback faces extinction. Nature 405: 529-530.