Health, Hibernation and Habitat
Author: Roman Muryn
13 August, 2011
Introduction
Last year I wrote about making ponds and keeping North American turtles outside in the UK. My interest came about as a result of the appalling strategies that we in the hobby adopted in trying to manage the burden of unwanted animals that resulted from the consequences of the Mutant Ninja Turtle craze. This included hundreds of animals being shipped from a country (UK) where they cannot breed to a country (Italy) where they can breed if they escape.
Since the start of that craze and up until the present, millions of animals have been imported into this country, most of which have ended up dead. The law that was passed in 1997 to prohibit the import of Red Eared Sliders was largely circumvented by the import of their look alike cousins the Yellow Belly Slider and the Cooter. However many thousands have survived often as a result of caring and informed homes. Human lives are transient and circumstances change, often resulting in the rehoming of the pet turtle; too often the pet cannot be rehomed and is released into a local pond.
This is illegal.
The majority of animals thus released are of the Slider and Cooter variety. These animals when adult are mostly vegetarian and have a similar diet to carp. They do not however, have the same metabolic rate as carp and those that have kept turtles with carp know that the fish always gets to the food first. In the wild their dietary needs are not great, vegetation, snails and invertebrates. Maybe part of the solution to these unwanted pets is to keep them in outside domestic ponds provided the pond is secure and they can't escape into the wild.
In previous articles I have described pond design and have outlined which animals could do well outside in a UK pond. There is a proviso though, they have to be healthy and their environment has to be suitable - this is harder that it at first seems and attrition rate is very high if factors are unsuitable. Death rates can be up to 50%.
Since writing those two articles last year more information has come to light as a result of scientific study and this article is really an attempt to stitch up all the technical threads and apply them in a hobby context. Very few if any hobby books describe the hibernation issues in detail and I hope I can fill in a few information gaps.
I have titled this article as Health, Hibernation and Habitat
Health
Let's start with the basic health of an animal; imported animals have never had to go through a natural selection process as they would in the wild. Contrary to popular opinion breeders are meticulous with their breeding regime and a very high proportion of their hatchlings survive. Yet in the wild a very small percentage of all eggs laid get transformed into hatchlings and predation by raccoons, skunks and human impact takes its toll. Once hatched they then run the gauntlet with other predators, now including fish, birds and of course humans. Any animal vaguely unfit is removed by nature, not so in the turtle farms.
During rearing they will have been kept in clinical conditions with no contact with natural pathogens and protection offered by anti-biotics, so no natural developed immunity has been developed. When introduced into the wild they will be susceptible to new pathogens - a bit like the spread of small pox with humans.
The young animals in nature have specific and balanced dietary needs along with the availability of natural sunlight and clean water. Regrettably, when bought for not very much on a whim, the animal will not fare well. All too frequently the result is a dead animal or an animal that has grown unnaturally, often with a deformed shell. If its body or organs have not have grown properly then it simply will not have all the tools to see it through hibernation as we shall see later.
I was fortunate enough to have visited Elmar Meier in Muenster Zoo and part of the discussion centred upon stress and the effect it had on the immune system; our own Kevin Eatwell echoed him in another similar discussion. This part of husbandry gets too little attention but the reader should be in no doubt that a stressed animal is extremely susceptible to falling sick. Some diseases such as herpes are always present but only surface when the host is under stress. Shingles in humans is a good parallel example. I have rehomed animals that have had real problems with introductions to the outside after prolonged imprisonment in a glass box. One little box turtle would not eat for months and only then when I put it into a small enclosure, it's taken 3 years to recuperated him.
The move from an aquarium to an outside world pond therefore does carry significant risk for all sorts of reasons.
Hibernation
There is a real dearth of plain speaking about turtle hibernation and it's a tricky subject to tackle as its littered with Old Wives Tales and wisdom borrowed from other hobbies.
There are many elements that contribute to a successful hibernation and each stands on its own by the end, the reader will see how they join up.
- It's commonly said that turtles dig themselves into the mud for the winter. Actually most turtles move about underwater during the hibernation period, seeking optimal water temperatures and oxygen levels. The extent this happens varies from species to species.
- Turtles have a liver that forms about 4% of body mass, this and their muscles store huge quantities of glycogen which is used as an energy reserve for the winter. It's commonly thought that fat is the energy store but fat cannot be metabolised without oxygen.
- Most turts are good at extrapulmonary (without use of lungs) oxygen uptake and whilst it is commonly thought it is through cloacal (vent) and/or buccopharyngeal (throat) exchange; it is diffusion through the skin that is the most significant oxygen supply mechanism. Sliders can stay underwater that has good oxygen content for 100+ days without going hypoxic.
- With deep still water anoxic (no oxygen in the water) layers can form in the pond. This can happen when bacteria oxidise detritus in the pond using oxygen at a greater rate than plants and nature can replace. The detritus also generates other dangerous gases eg hydrogen sulphide. This can happen in the summer but is not a problem as turtles then have a metabolic level where they can easily swim to the surface for oxygen.
In winter when ice forms it prevents surface gas exchange and matters are made worse when snow settles, as it stops the light getting to the plants, thus they stop producing oxygen and start using it. Very quickly the water is depleted of oxygen and becomes anoxic. - The turtles we see in the UK can be split into two groups for the purpose of this discussion. Those that are riverine species and those that are closed pond dwellers. The riverine species hibernate in frozen rivers but the water continues to flow and is generally rich in dissolved oxygen throughout the year. In this group belong the Sliders, the Cooters, the Map turtles, the soft-shell turtles, and Musk turtles. The other group is that which predominately inhabit ponds which have no great moving water source and that get totally frozen over in the winter. The Pond dwellers include the Painted turtles, the Snapper and the Spotted turtle.
It's an interesting thing but the riverine species are particularly adept at extrapulmonary oxygen intake but cannot cope well with water that is depleted of oxygen. A Slider (Trachemys) can survive in anoxic water no more than about 10 days, Cooters are a bit better so it varies from species to species. However the painted turtles can survive 150 days in anoxic water. The rest of the pond group too are good at dealing with anoxic conditions. - A recent paper has shown that with lower water temperatures less energy is consumed thus less oxygen is required. There is a significant difference of energy usage between 10°C and 3°C. Turtles deliberately seek out the colder water to reduce their metabolic rate thus energy usage and hence oxygen use. This is particularly important for the pond dwellers, it will be remembered that up north winters can last many months so any energy saved can be reserved for the first days of spring. In addition in anoxic conditions glycogen is used significantly faster so lactic acid is produced faster. These animals actively seek out the coldest water with the highest oxygen content for overwintering. Stories are often told about turtles moving about under the ice, now we have a reason.
- As in humans, the effects of oxygen deprivation are similar but of course turtles have 10 times our capability. Lack of oxygen or glycogen impairs brain activity significantly that's why pilots need oxygen masks at high altitudes. The burn of glycogen without oxygen forms lactic acid in the blood and body fluids. In marathon runners this contributes to seizing up the muscles and is called acidosis. Acidosis will kill a turtle in extreme cases. It can be seen that a riverine turtle caught in an anoxic pond as a result of freezing and is unable to get to the surface air easily is seriously at risk. This happens in the wild surprisingly often and many Northern US states have procedures to prevent such winter kill.
- Many turtles, in particular the pond turtles, have the ability to utilise the calcium carbonate (CaCo3) within the shell. Their shell is about 40% of body mass and its calcium is used to buffer the lactic acid in the blood and raise the pH thus reducing the effect of acidosis. In addition the shell can sequester some of the acid and store it for disposal when oxygen becomes available again after the winter thaw.
- The build up of lactic acid can take days or weeks depending on the temperature and the level of anoxia in the water. The lactic acid in the blood and in the shell can take equally long to dispose of once conditions are better in spring. The calcium used must also be replaced so for females about to produce eggs this is a particularly hard time.
I hope I have shown that to go into hibernation a turtles physical condition is so important. All aspects of the body contribute to the survival strategy. Animals raised in glass prisons that have not developed properly may well not have the right tools to survive winter.
Habitat
In the wild turtles select their own place for habitation and hibernation. Females will remember where they were born and hence remember a potential nesting site, then over the years they will learn of locations that prove suitable for feeding and hibernation. Much of their knowledge is instinctive and mistakes of choice are paid for with their lives.
Read any of David Carrols books - his accounts of turtle migration as the seasons change are very telling. He talks of migration in spring to vernal ponds where there is plenty of easy food such as tadpoles. He talks of migration to breeding areas and of migration to other areas as food availability changes. In the wild they have to hunt for their food and learn where to find it with the seasons; in the domestic pond this will not be an issue, but their willingness to travel and explore will be. The garden must be secure as they are great climbers.
When winter comes they will not have a choice of location for the big sleep and the pond keeper must provide suitable hibernation conditions appropriate to the animal type kept. It will invariably be a riverine type.
From my understanding the riverine animals do take care that they have good oxygenated water but they also have to deal with water level changes. In the UK we think floods, however in northern USA the depth of winter brings months of freezing temps often less than -100c for weeks and weeks. Rain does not fall; snow does, several feet in fact. This acts as an insulator from the severe weather above the water. The temperatures in the water will be the same as we would find in the UK. During the winter period the water levels often drop and air gaps develop between water and ice.
Animals do hide themselves away as some predators still go about their business even in winter. David Caroll tells of turtles that have been found by otters with varying degrees of damage - its distressing reading.
The spring brings on the thaw and with that flooded rivers, animals then seek more sheltered waters.
Last year was a nightmare for many of us that hibernated turtles outside. Whilst my pond dwellers all did well generally, my riverine species were hit very hard. The ice stayed for nearly a month and as I don't have any pump system the inevitable anoxic conditions overcame some of my animals - mostly the big Slider females.
So finally the habitat too plays a part in the ability for the turtles to survive outside in the UK.
In conclusion
There is no doubt that most of the commonly imported North American turtles can survive in outdoor ponds in the UK. This is confirmed by the many thousands that have survived since the original Ninja craze over 20 years ago. With luck many have found suitable food and hibernation conditions.
It is regrettable that the turtles have been lumbered with a reputation of being killers of UK fauna. These omnivores will take insects and other invertebrates but they are too slow to catch a fish or even a young bird. They will take easy protein so dead animals will be eaten. If seen eating carrion they will of course be labeled as the killer.
I have many turtles outdoors in my ponds I have never seen one catch a fish; I have seen them catch tadpoles and newts. However at the end of spring I always still have masses of little frogs hopping about and I have all three species of newts in my ponds.
I think the domestic pond can be a good way of reducing the numbers of animals released into the wild ponds provided it is secured to prevent escape.
So what do they need?
As we have read turtles have many complex needs and just placing them in a pond does not mean it will be suitable. It is an assumption commonly made.
Turtles are ectothermic and need heat (infrared) from sunlight to raise their metabolic level in order to move and digest food. They need sunlight (ultra-violet B) to help manage and produce vitamins, the two sunlight qualities go hand in hand. Without sunlight they will simply not survive. Their pond therefore needs a basking area that has full sunlight for good parts of the day but especially around midday. That basking area should be private so they are not scared into the water frequently and a bit of wind shade will help too. They should be able to get into their area easily.
The pond should not be too deep, say less than 2 feet. This depth allows sunlight to penetrate allowing plant oxygen generation. It also helps to reduce build the up of anoxic water layers by water circulation due to wind.
The pond should have sloping sides so that animals can move about and get to the surface easily if they are cold stiff or in trouble through acidosis.
The pond should have as many oxygenating plants as possible. If snow falls, clear it off the ice above the plants and allow the sunlight back in.
I shall be using an aerator this year to add movement to the water. In USA with waters under anoxic threat, the State wildlife Rangers strap outboard motors to jetty pylons and really circulate the water.
References
If you want to read more get these two books first.
- The Year of the Turtle – David Carroll
- Life in a shell - Donald Jackson