# Integrating Beach Monitoring and Satellite Telemetry to Estimate Loggerhead Clutch Frequency in Brazil

## TL;DR

Researchers combined beach monitoring and satellite tracking to better estimate how often loggerhead sea turtles nest in Brazil, finding that previous methods underestimated nesting frequency.

## Contribution

The study introduces an integrated approach using satellite telemetry with beach monitoring to improve clutch frequency estimates for loggerhead turtles.

## Key findings

- Satellite tracking revealed that females nest more frequently than estimated by beach monitoring alone.
- The average clutch frequency increased from 3.9 to 5.6 nests per female when satellite data was included.
- Relying solely on beach monitoring overestimates the number of breeding females.

## Abstract

Although conservation status varies among species, most sea turtle species are globally threatened. Estimating their population size is challenging because only adult females come ashore to nest during the breeding season. Knowing how many females nest each year is essential for understanding population trends and guiding effective conservation measures. Sea turtle nesting female abundance is often derived from nest counts and clutch frequency (CF). However, CF based on nighttime patrols alone can be inaccurate, as some nesting events are often missed or occur outside surveyed areas. In the current study, we combined traditional nighttime beach monitoring with satellite tracking of loggerhead turtles nesting in Bahia, Brazil, to improve the accuracy of CF estimates. Satellite tracking data allowed estimation of nesting events missed during beach patrols, indicating that females lay more nests per season than previously estimated. Consequently, earlier assessments based only on beach monitoring may have overestimated the number of breeding females. This integrated approach provides a more reliable estimate of reproductive parameters, which are extremely important for population abundance assessments of loggerhead turtles in Brazil.

Accurate clutch-frequency estimates are essential for assessing population abundance and reproductive output in sea turtles. Traditional nighttime beach-monitoring approaches, however, often underestimate clutch frequency by missing nesting events occurring outside patrolled beaches. Here, we integrated long-term beach monitoring (2009–2016) with satellite telemetry to estimate the clutch frequency of loggerhead turtles (Caretta caretta) nesting at Praia do Forte, Bahia, Brazil. A total of 593 females were identified along a 5 km monitored beach segment, and transient individuals represented 42.4% ± 3.9 SD of seasonal records. A 2-year remigration interval was the most frequent. The observed clutch frequency (OCF) averaged 3.1 ± 1.2 SD clutches per female, while the estimated clutch frequency based on beach monitoring alone (ECF_BM) averaged 3.9 ± 1.5 SD. For the subset of satellite-tracked females (n = 12), integration of residency length derived from telemetry increased the estimate to 5.6 ± 0.7 SD clutches per female (ECF_BMST). Statistical comparisons confirmed significant differences among estimation methods. These findings align with previous studies, demonstrating that clutch frequency is substantially underestimated when relying solely on beach monitoring. Incorporating satellite telemetry, therefore, provides a more accurate assessment of reproductive output and has important implications for population modelling and the conservation of loggerhead turtles in Brazil.