Sea Turtles, Volunteers and Visitors

Sea Turtle Conservation Program: October Update

We’ve completed another month of the sea turtle conservation program on the Osa Peninsula, Costa Rica and we’re getting close to the end of the nesting season. After 4 months of tireless work by our field coordinators, field assistants and volunteers, we have registered a total of 1233 sea turtle nests, between Piro and Carate (Fig. 1). As I mentioned earlier, for logistical reasons, we cannot gather daily information from all beaches and visits to Rio Oro beach have been very limited, so this number of sea turtle nests should be considered a minimum; i.e., the actual number of sea turtle nests on these beaches is higher than reported here.

Figure 1. Total nests registered, according to month, beach and species. CM: Chelonia mydas agassizii, DC: Demochelys coriacea, EL: Eretmochelys imbricata, LO: Lepidochelys olivacea

Of these 1233 recorded nests, we know that at least 242 (20%) were predated. Of predated nests, 43% were by humans, while the remaining 57% were predated by dogs, pigs, crabs and other animals. We can reasonably estimate that approximately 10,600 eggs have been illegally removed between Piro and Carate for human consumption (assuming that each nest had 100 eggs and they were all taken).

If we focus on the Olive Ridley sea turtles (Lepidochelys olivacea), the most common sea turtle species on the Osa Peninsula, not taking into account the Rio Oro data, as the data that we have doesn’t appear to be representative of the real situation, we can see that during the 2010 season, Carate beach is where we find the greatest amount of illegal harvesting of eggs (Fig 2). Throughout the season, more than 50% of reported predation is caused by humans, a situation that hasn’t occurred on Piro and Pejeperro beaches.

Figure 2. Percentage of Olive Ridley sea turtle nests predated by humans and other animals according to month and beach.

Remember that you can help us save sea turtles that visit the southern part of the Osa Peninsula in several ways: 1) tell others about our project and the importance of protecting sea turtles, 2) by volunteering with sea turtles or 3) by making a donation to support our sea turtle program or the other conservation work that Friends of the Osa does on the Osa Peninsula.

Science and Research, Sea Turtles

Sea Turtle Conservation Program Piro-Carate: August Update

Last month I shared with you the total data for in situ nests, nest predation and false crawls for the month of July, and mentioned that these data were not adjusted for sampling effort. By sampling effort, I mean the amount of time and / or distance that was invested on each beach to get the data. For example, we monitor 2 km of Piro beach and 4.5 km of Pejeperro beach.  So, it isn’t the same to walk Piro beach and find two turtles as it is to walk Pejeperro beach and find two turtles – the distances covered are very different.  To compare these two values, we must express them in proportion to the distance traveled, i.e. density of turtles per kilometer. In this case, that would be: Piro: 2 / 2 = 1 and Pejeperro: 2 / 4.5 = 0.44.

Sea Turtle Conservation Results through August 2010

Figure 1. Density of sea turtle visits during the months of July and August on the beaches of Piro-Carate, Osa Peninsula 2010.

By calculating the July and August data in this way, taking the sampling effort on each beach into account, we get the results shown in Figure 1. As you can see, Rio Oro is the beach with the highest density of in situ nests, nest predation and false crawls, followed by Pejeperro. From this graph, we can also see that the density of depredated nests on Rio Oro beach is very similar to the density of in situ nests, which is obviously worrying. In the coming days, I will conduct a preliminary analysis of predation in conjunction with Courtney Thomas, one of our assistants, who is using her participation in this project as part of her studies at Evergreen State College.

I would also like to take advantage of this note to thank Mr. Eliecer Villalta and Mr. Geinor Barquero, from MINAET’s Department of Control and Protection, for their support in recent weeks. Their presence, along with other peers in the area, had an immediate effect in reducing poaching of turtle eggs. I hope we can continue to coordinate this type of support throughout the rest of the season.

Remember that you can help us to protect sea turtles that visit the southern part of the Osa Peninsula in several ways: 1) telling others about our project and the importance of protecting sea turtles, 2) participating in our sea turtle volunteer program and 3) by making a donation to help fund the continuation of the Sea Turtle Conservation Program.