Catalina Vásquez Carrillo
Characterization of Juvenile Habitats for the Green Sea Turtle at La Guajira, Colombia: A Connectivity Boundary Region in the Caribbean
1. Project goals
The long term goal of the project was to ecologically characterize habitats for the green sea turtle, Chelonia mydas in La Guajira, Colombia, a likely connectivity boundary region of the species in the Caribbean basin.
The Short term goal of this project was to characterize the aggregation of sea turtles in Bahia Hondita, La Guajira, Colombia. The project aimed to determine whether or not juvenile turtles are present in the area and if they remain there for long periods of time. Also, the project aimed to identify the population in the Atlantic basin from which these sea turtles are originating by performing a genetic mixed stock analysis.
2. Audience Reached and community involvement
This project was able to reach a diverse audience while activities were performed. During the month of August, 2015, sea turtle population surveying activities performed in this project required the participation of around twenty-five people from different backgrounds, including twenty-three Wayuu indigenous men in Bahia Hondita and two natural scientists from Colombia. Several participant men were fishers and were reached because they are part of a local group of sea turtle conservation stewards and have consequently been trained for scientific data collection, animal handling and other activities related to sea turtle research and conservation. While they perform regular fishing activities, these fishers commonly bycatch sea turtles. As one part of their conservation activities, they collect several data on by-caught turtles. These sea turtle conservationist fishers were willing to provide the data they had on sea turtles to this project for its analysis. In addition, project participants were hired and trained as field assistants for two weeks to perform sea turtle surveying activities that contributed to this project. Other Wayuu men were involved as renters of motor boats or facilitators.
Additionally, this project reached an audience of Colombian scientists and natural marine resources managers. Biologist Luis Merizalde, from the NGO Conservation International, actively participated in activities related to the deployment of a satellite tag on a juvenile turtle to track its trajectory and habitat use. He was informed about the main findings of this activity. Marine biologist Carmen Lucia Noriega from Universidad Tadeo Lozano was reached to provide advising and training in satellite telemetry and was brought to the project area to perform these activities. From this association with Noriega, a research collaboration was built with the sea turtle conservation program she works in at Mundo Marino Aquarium and Tadeo Lozano Univesity in Santa Marta, Colombia, lead by Dr. Aminta Jauregui.
Methods used and main findings in this project were communicated to a large audience of natural sciences students both within and outside the University of Miami in Coral Gables, FL (UM). Around forty-four undergraduate students of UM were reached through the Biology department seminar series in November 2015. Also, about forty already or soon-to-be graduate students and twenty-two faculty members were reached through the Biology Symposium in January 2016 at UM and the Bouchet conference on Diversity and Graduate Education held at University of Yale, New Haven, Ct on April, 2016.
Finally, the project reached a gross majority of the community of Bahia Hondita including more than ninety children from grades 1st to 5th from one of the elementary schools in Bahia Hondita. The children were involved for two class periods in the release of a sea turtle who had been tagged with a satellite telemeter as part of one of the main activities related to this project.
3. Major approaches and results
a. The aggregation of sea turtles in Bahia Hondita is comprised of juvenile-stage individuals
Green sea turtles were surveyed along the ocean side of Bahia Hondita bay in La Guajira using fishing entanglement nets for two weeks as part of the conservation steward group’s activities. Nets were deployed in the same fashion and in the same areas that fishers used to fish for sea turtles. Nets were placed at depths from 1-10 m at four sites. The areas of net placement were usually spots with rocks and “jimoura” the Wayuu word for sea weed which is used to describe both seagrass and algae. A total of four green sea turtles were surveyed directly by the survey team. In addition, data on eleven sea turtles that were captured accidentally by fishers in Bahia Hondita while performing daily fishing activities during year 2015 were included in this analysis.
For all turtles, the straight carapace length and width (SCL, SCW) were measured with metal calipers. Captured sea turtles were tagged with a unique, metal ID tag. The majority of green sea turtles in the study area, encompassing the nearshore shallow waters of the Bahia Hondita bay are in the juvenile stage, ranging in size between 27- 62 cm SCL .
Some environmental conditions in 2015 may have affected the presence of turtles in the project study area. In spite of the high surveying effort, a low number of turtles were surveyed; contrary to observations made by the surveyors and the conservation stewards in the previous year at the same surveying areas. The difference in the presence of sea turtles in Bahia Hondita between years, specifically the decrease in the amount of turtles in 2015 deserves attention.
The developmental habitat (DH) hypothesis states that juvenile green sea turtles tend to remain in the same areas for years. However, in Bahia Hondita, turtles were not found in the same survey areas they had been surveyed in the previous year. The variation in the amount of turtles in the area may be related to the variation in oceanographic conditions from year to year. Bahia Hondita’s ocean side is within an open and highly connected system, and is probably a boundary system for oceanic currents. It is also located within the Southern Caribbean Upwelling System, a highly productive system, in which productivity (food availability) depends on the dynamics of oceanographic phenomena such as upwelling. The productivity in the area may vary among years and turtles may be responding to this variation by moving in to and out of other areas within the system, taking advantage of its openness. These hypotheses need to be tested, and to do this, surveying the sea turtle population next year is recommended. A window for collaboration was open from the project interaction with local scientists in Colombia to continue surveying this population as well as explore new areas where juvenile turtles may be aggregating within the Guajira oceanographic system. Collaboration on the writing of a proposal to the field exploratory grants of National Geographic and the American Philosophical Society in January of 2016 was built with Noriega and other Colombian scientists after the analysis of the results of this project.
b. Juvenile turtles stay at given areas or “hotspots”
One juvenile C. mydas (42 cm SCL) who had been captured accidentally during fishing practices in Bahia Hondita was chosen to have its position tracked using satellite telemetry. A SPOT6 satellite telemetry tag (Wildlife Computers inc.) of 72 x 56 x 22 mm dimensions was placed on the turtle on the 9th of August 2015 (Figure 4) was proided by the University of Miami, I support to the activities related to this project. The tag was attached using a 2-phase, fast dry epoxy. The juvenile sea turtle named “Iwa” was tracked 24-hours, seven days per week after its release, outside the bay, on the same day of tag deployment. Location data was analyzed using STAT software (www.seaturtle.org) and displayed in a map using ArcGIS 10.2 (Esri 2016). A spatial hotspot analysis was performed using the hotspot analysis tool, taking into account the frequency of transmission in each area visited by the animal and embracing an error of 0.05.
Iwa traveled for thirty-seven days, close the shore at depths no deeper than 20 m, against the prevailing current. The total distance traveled was 29 km straight line in the eastern direction bordering the coastline of the peninsula and then south towards the Gulf of Venezuela. The turtle stopped at multiple spots, however there was one spot where the turtle remained the longest (twenty days) called Chimare. The amount spent in this spot was significantly higher than in any other, indicating that this site was a “hotspot” for this juvenile.
c. Genetic Analyses of the juvenile sea turtle stock
A total of nine turtles were included in the genetic analysis. A small skin sample was removed from the back flipper of individual turtles using sterile 3 mm diameter biopsy punches. Total genomic DNA was extracted from the samples using a salting out and organic solvents method (Qiagen, 2016). The control region of extracted mtDNA was amplified by PCR and sequenced using Sanger sequencing, following standard protocols for sea turtles as in Naro-Maciel (2007) at the molecular core of University of Miami. Sequences were visualized and edited using Geneious 6 software (Drummond et al., 2012).
All samples yielded abundant DNA and amplified the desired control region gene. However, DNA sequences were not of the expected length and/or quality and did not match known control region sequence. Therefore, these sequences could not be used in the analysis to determine haplotypes or to match these haplotypes to the ones from candidate populations of origin in the Atlantic basin. These results were replicated in a second trial including a sea turtle DNA sample from 2014 as a control. This sample provided the expected sequence, therefore, there were no errors in the laboratory procedures of this genetic analysis but the quality of the DNA of 2015 samples was poor. Tissue samples from sea turtles surveyed in this project were kept in 70% ethanol solution, however, the field conditions in the area are very extreme (e.g. heat) and storage until lab processing took a long time, therefore tissue quality was compromised. This drawback could not be overcome in the laboratory.
4. Conclusions and Recommendations
Through this project, a broad audience of local sea turtle conservationists and scientists in Colombia as well as the student community at University of Miami and Yale University were reached. The project benefited a group of conservation stewards by providing active training and engagement in project related activities such as sea turtle and habitat surveying.
Activities performed in this project could not have been done without the collaboration of the local group of conservation stewards and fishermen of Bahia Hondita who also kindly provided data on their sea turtle by-catch during fishing activities and the fishing grounds where turtles are observed.
Sea turtles found in Bahia Hondita during 2015 either by active surveying or during fishing practices were all juveniles (below the AAM threshold). This finding corresponded with expectations due to the depth and position of surveyed areas.
Even though a high effort and collaboration in sea turtle surveys was undertaken, it was not possible to recover the expected amount of sea turtles based on observations from previous years, thus, juvenile sea turtles may not have been present in the area during 2015. It is hypothesized that there is variation in the use of this area by sea turtles. It is recommended to perform the same surveys in the next year to see if this is true and to monitor environmental oceanographic factors that may correlate to this variation.
It is recommended to increase the quality of reagents for genetic sampling storage and minimize the time of sample storage to decrease the effects of the harsh environmental conditions in the project field location.