The book of Honu: Pioneering citizen-based science

Image source here

We began as two sport divers with an interest in underwater photography. We weren’t marine biologists and had no background in conservation. We knew nothing about the Hawaiian green turtle, or honu as the Hawaiians call them.

Peter Bennett and Ursula Keuper-Bennett start their book with these phrases. Originally from Canada, Peter and Ursula had their first underwater experience with a sea turtle in 1998, on the reefs of Honokowai, in the Hawaiian island of Maui. They named her Clothahump. The Bennets kept returning back to Maui every year up until today (at least I hope-their last video in their youtube channel is from 2013). All these years, they have spent countless hours observing and documenting the local Hawaiian green sea turtle population in a dedicated and consistent way, that probably very few – if any – people had done before them. They summarised their accumulated knowledge in their book, The book of Honu: Enjoying and learning about Hawai’i’s sea turtles, published by the University of Hawai’i’ Press in 2008.

This book is a treasure. Really. They provide highly detailed information about the underwater life and habits of the Honus like no other before, scientist or not. Not any modern and fancy sea turtle behaviour study technique like GPS fine scale tracking, accelerometers, remotely operated vehiclescameras attached to sea turtles, or even, the so popular these days, use of drones, can provide such a great insight into the daily routine of sea turtles that resulted from their dedication and enthusiasm for more than 2 decades. (the linked studies and videos however provide very useful insights of different nature and they are highly recommended!). It is not surprising that

We attended the 13th annual sea turtle symposium in Georgia. Once the turtle specialists heard that we’d been observing turtles underwater for years, they began asking us questions: How did we tell them apart, whether they got along together, if they had favorite spots, just what is it that they did all day long-the same sort of queries that everyone had.

The Bennetts give many answers (or at least insights) to questions of the above type in their book.

  • “Upon approach from humans, young turtles are caught up in a delicate dance between curiosity and caution”.
  • “Juvenile turtles seem to enjoy play. A dance of round-and-round where one would try to nip the tail of the other”.
  • “Male-male mounting turns out to be so common. Perhaps it is a dominance behaviour”.
  • “Some honu occupy exactly the same spot year after year. Some have 2 or 3 favorite places, while others are content to stay in the same small area”.
  •  “They scratch the tops and bottoms of their shells, their throats, their heads”.
  • “We’ve concluded that the honu create their own cleaning stations”.
  • “They mostly do the same things we do at home: eat and sleep”.
  • “They don’t seem to have a pecking order. We have never seen one honu consistently dominating another. Even size is not a reliable predictor of which turtle will prevail in a confrontation. At times, we’ve seen the smaller honu chase off the larger”. I can personally confirm this last one.
A honu cleaning station on Maui island. 

The book is full of descriptions of the above style. Notice the absence of dry scientific language. In fact positive, turtle-huggy emotions are overflowing:

There is no better experience – no happier time – for us than resting with old friends on the ocean bottom.

But that should not discourage people, even highly qualified marine biologists, to read this book and take its content into serious account. Of course sea turtle behaviour of the above kind is hard to quantify and it is open to many explanations – even I disagree with a couple of their interpretations. But if I was writing a book about my own underwater sea turtle encounters, I hardly imagine I would use a much different tone.

Photo identification

One of the first questions that people ask after hearing about our turtle experience, is “How do you tell them apart?”

The Bennetts were among the first people (if not the first) who consistently used photo id techniques to distinguish individuals: their facial scales (scutes) are practically unique, like a human fingerprint. Until the end of 2004, they had logged more than 750 unique individuals. They gave names to turtles that were repeatedly observing and naturally they became attached to them. It is really enjoyable, to read their narrations about the lives of known turtles, how they first met, how they were reacting in their presence as well as with other turtles, and about their transition from being young juveniles to mature adults. This emotional attachment however sometimes came with a cost.


Example of a Hawaiian green turtle with fibropapilloma tumours. This is an alive turtle basking on a beach.

Seeing an afflicted turtle will probably disturb you. It certainly upsets us.

Fibropapillomatosis (FP) was firstly recorded in Florida, in 1938 and in Hawaii in 1958. It is a disease that gives the turtles nasty external and internal tumours that can be more than 10cm large in diameter. The tumours grow steadily, sometimes, blinding the turtle, while the tumours on the skin, neck and plastron, make swimming difficult. The cause and how FP spreads still remains a great mystery. Some healthy turtles have remained healthy even if they live close to infected ones. A herpesvirus seem to play a role in the disease, as well as poor quality of water, even though infected turtles have been found in clean waters. The Marine Turtle Specialist group consider FP as one of the key unsolved mysteries of sea turtle biology.

The Bennetts were unfortunate to see many of their friends dying from the disease, including Clothahump itself.

We saw her only once in 1993. The white spots had mushroomed into tumors. We both cried underwater. That day, we vowed to tell Clothahump’s story and somehow help the ocean community on her reef.

And so they did. Their long term observations of affected turtles led to a better understanding on how the disease appears, progresses and disappears. They discovered that the tumours start from the eyes, and in general one can tell the severity of an affected turtle, by assessing the eye tumours. They also discovered that it affected primary young turtles, and that most adult turtles recover within 3 or 4 years. They collaborated with George Balazs, an expert on Hawaiian sea turtles, and they published a series of scientific papers and reports, like this one and this one (page 37) (also available here).  The Bennetts comforted their readers:

Our records and other studies show that FP isn’t nearly as deadly as was first feared. FP related deaths are not affecting the chances for survival of the whole population. It certainly kills some, but others live and grow to reproduce and replenish the population. There’s comfort in knowing that.

Nevertheless, for these two people that see turtles as individuals and not as part of a population, many sea turtle deaths were like losing a friend.

In a population level things are looking great till today indeed.

The future looks very optimistic for the sea turtles of Hawaii. The population is increasing and very recently it was characterised as least concern by the IUCN.

Peter and Ursula have contributed a lot in our knowledge of sea turtle biology with their observations. But they have inspired us even more with their passion…

Peter and Ursula’s webpage (made in 1995!)

Peter and Ursula’s youtube channel



How many sea turtles do we want? The case of Kyparissia bay, Greece.


The story of loggerhead sea turtle nesting area of Kyparissia bay is an interesting one. Several issues have been risen during the last years, both in a political and a conservation level. In this post, we will focus on the latter. Situated in the western part of Peloponnese, Greece, the whole bay has total length of 44 km with the majority of loggerhead nests (around 85%) concentrated in the south 9.5 km. The average nest number in this core area used to be, up a decade ago, around 550-600 nests (a bit more in the whole bay), see this paper. It was considered to be the second largest reproductive site for the species in the Mediterranean, after Laganas bay, Zakynthos, where typically double the amount of nests were laid each year. However, unlike Zakynthos, the Kyparissia nests were suffering from mammal predation (e.g. dogs, foxes) as well as severe flooding due to large waves. Hence intensive conservation efforts began in the early 90’s by Archelon, the Sea Turtle Protection Society of Greece, with the objective to reduce these effects. Metal grids were placed on top of nests to reduce predation and nests laid close to the sea were being relocated into a safer place. It goes without saying that this requires a tremendous effort every year, by dedicated young volunteers. The result: hatchling production was steadily increasing every year. Hence, 15 years after (around 2007) Kyparissia’s nests started increasing as well. Up to then, its nest numbers, as well as the ones of Zakynthos was pretty much stable. Given the fact that the minimum sexual maturation age for loggerheads is 14-15 years (check here the source), this increase, as expected, is naturally attributed to the increased hatchling production since the beginning of the 90’s. In fact Kyparissia’s nesting data itself could lead to a nice scientific paper regarding sexual maturation age and other general parameters of the demographics of the Mediterranean loggerheads.

Two of the main conservation measures in Kyparissia bay: nest relocation in order to avoid inundations and protective metal grids to reduce predation.

 And this increase continues till today. Last summer (2016), the 9.5 core sector had around 2650 nests,  a truly unprecedented number. Projections elevate this number to more than 3000 nests for the whole bay. To compare with, the most nests that Zakynthos ever had was a bit more than 2000, in 1995. We should note here that 2016 was an exceptional year for the whole Mediterranean with record breaking nest numbers in many areas.

It is also worth noting that unless our assumptions on demographic parameters are wrong, this current increase has not hit yet its exponential phase. This is because the turtles that nest for the first time (neophytes) still belong to the first generation of hatchlings that were born after the conservation measures.  So very very roughly, until now, the gain in neophytes every year, should directly correlate to the number of hatchlings that were “saved” 15 years due to conservation measures. That should theoretically result in a linear increase these days, i.e., a fixed amount of “saved” neophytes is added every year. It could be the case that 15 years after the first increase of the nest numbers (i.e., around 2022), the second generation of hatchlings will be mature enough to start laying eggs as well.

Will the nest numbers explode then? If yes, is that necessarily something good? Is it always true that the more nests, the better? With how many nests will we be happy? And at which point, conservation stops and intervention begins?

The IUCN marine turtle specialist group, the world authority in sea turtle writes on its website:

We envision marine turtles fulfilling their ecological roles on a healthy Planet where all Peoples value and celebrate their continued survival.

While this statement does not give a straight answer, to how many sea turtles we would like to have out there, it implies that a healthy population is desirable, meaning that its dynamics are driven by natural powers only while the anthropogenic impact is absent. In order to find out these ideal population numbers we would have to use a time machine and go many years back in time. How many years back though? Scientists and conservationists often suffer from the baseline syndrome: The tendency to regard healthy population levels as the ones that one sees at the beginning of her/his career, see for instance here and here. Regarding Kyparissia bay, nobody can know what the correct baseline is (i.e., the population number in equilibrium where no anthropogenic effects have acted). Let us note that given the fact that Kyparissia’s beaches are pretty much pristine, the main anthropogenic effect is that of the fishing industry. In fact, it is estimated that (source), over 44000 sea turtles die every year because of the fishing industry. (Note: however, all these do not belong to the Mediterranean population, as the majority of sea turtles in the west part of the Mediterranean basin come from the Atlantic populations. Thus, always with regards to conservative estimations, the number of deaths of local Mediterranean turtles should be less). It could be the case that the average nest number in the 80’s, around 600 nests per year, was an equilibrium point driven by a combination of natural dynamics and interactions with fishing industry. Of course with such long lived species, as sea turtles are, we cannot even be certain if this number was actually an equilibrium or not.

In any case, current conservation measures in Kyparissia address only nest predation and inundation, which are both natural processes (though even that is still debatable; are predator numbers what they should be? where they always predating nests? does climate change increase inundations?). Moreover, it could be the case that even these measures do not come without a cost. In fact, given that low nest incubation temperatures produce male hatchlings, nest inundations could be a natural mechanism to boost male turtle production in, what seems to be, a female biased population, see here (page 67). Also, sea turtles lay their nest away from the surf, something that has resulted as a natural selection process. One could argue that by relocating a doomed nest, that would result in survival of hatchlings that will keep doing the same wrong choice of nest site. However in this interesting study for an Australian loggerhead population, it was shown that

…doomed-egg relocation does not substantially distort the gene pool in the eastern Australian loggerhead stock and should not be abandoned as a strategy for the conservation of marine turtle populations.

Still further research is required on this topic. Taking all the above into account, my opinion is:

The current conservation measures in Kyparissia are only justified if they are considered as counter-measures to sea turtle mortality in the sea. If the anthropogenic sea turtle mortality was zero then they shouldn’t exist in the first place.

Of course the above statement, implies that we are trying to solve a problem (anthropogenic mortality), not by dealing with the problem directly but sort of by patching it up. Of course, this is not big news in sea turtle conservation. Mortality at sea due to fishing industry is extremely difficult to control and hence reduce. Thus, it looks like that start of conservation measures in the beginning of the 90’s was well justified indeed.


But what about in the future? Should we always celebrate after another record breaking year? Nest numbers are starting to blow up, making the protection of every single nest, an almost impossible task.  Unless any density effects come into play, introducing some negative dynamics, this increase is likely to continue (?).  We have seen cases where nesting beaches host a huge number of nesting females, like the case of Raine island in Australia (see this impressive video), the largest green sea turtle rookery in the world with tens of thousands females every year. In fact, Raine island is an example where, turtles are just too many. So many in fact, that they destroy each other’s nests, resulting in an extremely low nesting and hatching success (just Google “Raine island reproductive failure”).

Yet, the young conservationist in Kyparissia has a decision to make: protect or not the nest she/he just found? Depending on if none, half or all the nests are decided to be protected, the long term equilibrium nest number that corresponds to each decision will be different (and currently unknown).  None decision seems right or wrong at the moment, but we should definitely dream of a time where sea turtle population dynamics are only driven by natural processes.

This post is dedicated to those, who have walked thousands kilometres, poured hundreds kilos of sweat and spent countless sleepless nights at the beaches of Kyparissia.