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Sea turtles have existed since the time of the dinosaurs, and have had millions of years to adapt to their environment. However, they have had just a few decades to come to terms with mass coastal development, plastic waste, light pollution, beach tourism and deep sea fishing, and unsurprisingly, their numbers have plummeted.

Combine this with the poaching of adult turtles and their eggs for food, with their shells used to make highly valuable tortoiseshell, and it is no wonder that six of the seven species of sea turtle are now classified as vulnerable, endangered or critically endangered.

Conservation organisations work around the globe to protect sea turtles, focusing on the beaches where they lay and hatch their eggs. Where nests are considered to be particularly at risk, the eggs may be transferred to a new part of the beach, known as a hatchery.

Volunteering at or visiting a hatchery while on holiday certainly sounds like a worthy cause. However, online travel company Responsible Travel has investigated the ethics of hatcheries - and it turns out that not all are as beneficial to turtles as they may seem. Here are five questions to ask to ensure the hatchery you're visiting is genuinely helping, not harming, the turtles.

1. Do they use tanks?

Some hatcheries place the hatchlings in tanks for a couple of days in order to 'headstart' them, before releasing them once they are a little stronger. However, swimming can exhaust the hatchlings before they've reached the sea and food sources, and the tanks are breeding grounds for diseases and bacteria, which can then be transmitted to wild turtles.

Worse still, some turtles are kept in tanks for weeks or even months, with tourists paying to hold them and take photos. Perhaps conservation is not the tanks' main purpose...

2. Do they buy eggs from poachers?

In many countries, sea turtle eggs are on the menu. To prevent this, some hatcheries buy the eggs from poachers at higher rates than those offered by local restaurants. Unsurprisingly, this leads to more eggs being dug up, as their value increases.

3. Is there an expert on site?

Running a hatchery is far more complex than just burying eggs and releasing hatchlings. The incubation temperature affects the sex of the hatchlings; diseases can be transmitted if gloves are not worn; dry sand dehydrates eggs; compacted sand starves them of oxygen; moving the eggs too long after laying can rupture the membranes inside... in short, this is no business for amateurs. A qualified expert must oversee the hatchery.

4. Can they prove they are successful?

Unless detailed records are kept about the number of nesting turtles, eggs and hatchlings, there is no real way to know if a hatchery is having a genuinely beneficial impact on sea turtle populations. Good intentions alone do not guarantee good results.

5. How else are they conserving turtles?

Hatcheries should never be the end goal of sea turtle conservation. The theft of eggs is one of the biggest threats to their survival, so working with local communities and schools to raise awareness is essential.

Coastal development must be deterred, light pollution reduced, tourists should be warned to avoid nests, and shorelines cleared of harmful plastic waste.

And there are plenty of ways for people to contribute while on a volunteering holiday - such as carrying out beach patrols, monitoring nesting turtles and deterring predators from attacking hatchlings. If all these efforts paid off, of course, the hatchery wouldn't even be needed in the first place. And this is the real marker of a hatchery's success.