Breeding Periodicity for Male Sea Turtles, Operational Sex Ratios, and Implications in the Face of Climate Change

Abstract

Species that have temperature-dependent sex determination (TSD) often produce highly skewed offspring sex ratios contrary to long-standing theoretical predictions. This ecological enigma has provoked concern that climate change may induce the production of single-sex generations and hence lead to population extirpation. All species of sea turtles exhibit TSD, many are already endangered, and most already produce sex ratios skewed to the sex produced at warmer temperatures (females). We tracked male loggerhead turtles (Caretta caretta) from Zakynthos, Greece, throughout the entire interval between successive breeding seasons and identified individuals on their breeding grounds, using photoidentification, to determine breeding periodicity and operational sex ratios. Males returned to breed at least twice as frequently as females. We estimated that the hatchling sex ratio of 70:30 female to male for this rookery will translate into an overall operational sex ratio (OSR) (i.e., ratio of total number of males vs females breeding each year) of close to 50:50 female to male. We followed three male turtles for between 10 and 12 months during which time they all traveled back to the breeding grounds. Flipper tagging revealed the proportion of females returning to nest after intervals of 1, 2, 3, and 4 years were 0.21, 0.38, 0.29, and 0.12, respectively (mean interval 2.3 years). A further nine male turtles were tracked for short periods to determine their departure date from the breeding grounds. These departure dates were combined with a photoidentification data set of 165 individuals identified on in-water transect surveys at the start of the breeding season to develop a statistical model of the population dynamics. This model produced a maximum likelihood estimate that males visit the breeding site 2.6 times more often than females (95%CI 2.1, 3.1), which was consistent with the data from satellite tracking and flipper tagging. Increased frequency of male breeding will help ameliorate female-biased hatchling sex ratios. Combined with the ability of males to fertilize the eggs of many females and for females to store sperm to fertilize many clutches, our results imply that effects of climate change on the viability of sea turtle populations are likely to be less acute than previously suspected.

Informing Marine Protected Area Designation and Management for Nesting Olive Ridley Sea Turtles Using Satellite Tracking

“…We know very little about male olive ridley turtle movement in general and also in this area and they could also be at risk from fishing and boat strikes if they aggregate in the area to breed. Coastal waters could be even more of a conservation concern if the males are shown to utilize coastal waters such as zone 2, as has been demonstrated in other regions (James et al, 2005;Shaver et al, 2005;Hays et al, 2010), but this is entirely unknown in Gabon. Additionally, we are lacking data on the seasonality of males in the region.…”

“…Red List Status might be improving for some species (Balazs and Chaloupka, 2004;Dutton et al, 2005;Simpfendorfer and Dulvy, 2017), highlighting that improved knowledge can lead to better management and conservation outcomes. Nonetheless, threats are highest where species aggregate such as to breed or forage (Edgar et al, 2008;Hays et al, 2010) and where species and humans frequently overlap; for marine species this is often in coastal zones . Quantifying specific threats can be difficult due to limited data, largely because of the feasibility of collection, but quantitative data is necessary to undertake comprehensive assessments and quantify impacts on marine vertebrates.…”

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…Some of the turtles foraging in the northern Adriatic displayed seasonal migrations moving towards lower latitudes during the winter months (Zbinden et al 2011). In a few cases, turtles were tracked for long enough to reconstruct also their movements back to the breeding areas (Zbinden et al 2008;Hays et al 2010b;Schofield et al 2010a). This revealed valuable details of the poorly known pre-breeding migratory phenology of Mediterranean loggerheads.…”

“…Only groups of ≥ 10 animals released from the same site are considered, while releases of single individuals (Table I) turtles, having so far been shown in only a few turtles tracked from Zakynthos (Zbinden et al 2008;Hays et al 2010b;Schofield et al 2013). For example, a female tracked by Zbinden et al (2008) stayed on the move for the 189 days of tracking while visiting various areas of the Adriatic and Ionian sea, apparently without heading towards a specific destination (but slowing down its movement rate while in the Northern Adriatic) (Figure 2).…”

Pre-nesting Movements of Leatherback Sea Turtles, Dermochelys coriacea, in the Western Atlantic

“…For pelagic species such as most sea turtles, telemetry has provided insight into otherwise enigmatic oceanic movements and residency areas. Advancing telemetry methods have aided in the investigation of mating behavior for populations of loggerhead (Henwood, 1987;Hays et al, 2010;Schofield et al, 2010), green (Balazs and Ellis, 2000), and Kemp's ridley turtles (Shaver et al, 2005).…”