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Figure 1. A map of Australia, showing New South Wales shaded in black.

Predicted foraging areas for hawksbill turtles on the east coast of Australia extend from Torres Strait at 9°S in the north to at least Moreton Bay at 27°S (Limpus 2008). In Moreton Bay, hawksbill turtles were captured throughout the year including during all winter months. Recapture intervals indicated a local long-term residency. The same was expected for the numerous hawksbill turtles that live on the rocky reef habitat immediately to the south in Northern NSW (Limpus 2008). Records of hawksbill turtle sightings beyond this predicted habitat, as far south as Tasmania, were recorded as early as 1971 (Green 1971).

Further studies described wildlife species in NSW waters (Ganassin 2005), which outlined the predicted abundance and distribution of marine turtles (Cogger 2000). These later studies included new data collated by the NSW Atlas of Wildlife, which at the time of development did not include the hawksbill turtle stranding information provided in this report. Further, a 2007 review of existing datasets for the marine environment of Northern NSW identified multiple data deficiencies for marine turtles in NSW (Rule 2007). A survey of threatened and protected species published in 2010 did not target turtles, and subsequently gathered limited data on these reptiles across NSW (Smith 2010). Only green turtles and one loggerhead turtle were identified during that limited study. Recent studies indicate that dichotomies in foraging area strategies do exist for adult hawksbill turtles in the eastern Pacific, with some individuals using inshore mangrove estuaries and, to a lesser extent, others using open-coast rock and coral reefs (Gaos et al. 2012).

Regardless of the lack of in-water surveys in NSW, the reports listed above confirmed the presence of, and identified and described threats to marine turtles in this state. Also, reports of impacts due to threats such as shark-meshing associated with the catch of potentially dangerous sharks indicate that marine turtle bycatch in NSW represents a small but consistent non-target species; others include sharks, dolphins, rays and finfish (Krogh 1996).

In nearby South East Queensland, hawksbill turtle populations at Heron Island on the Southern Great Barrier Reef (Limpus 1992) skew in size class toward 40 cm curved carapace length (CCL). A recruitment size to the reef of 35 CCL cm was determined, which is the size class that strands in NSW most frequently. The study at Heron Island was the geographically closest survey of hawksbill turtles to the current study area of NSW.

This work provides the first review and analysis of hawksbill turtle stranding data reported to the NSW state government between 1996 and 2013. These data were collected from government field staff and supporting agencies. A suite of basic information is gathered for each stranding event including date, location, species, CCL, and head width. This report analyzes an extract of that central database relating to the hawksbill turtle (Eretmochelys imbricata) and to some extent the green turtle (Chelonia mydas).

During the study period three marine turtle rehabilitation centers operated under an NSW National Parks and Wildlife Service license to rescue and rehabilitate sick, injured or orphaned fauna. The turtles in this study were reported injured or ill by members of the public, government staff and in some cases, commercial fisherman. Live animals were transported to one of the three rehabilitation centers. All centers carried out standard practices for the collection of biometric details when and where possible. In some cases for deceased turtles, data were not available due to geographic isolation of the event, limited resources to respond, unskilled responders or severe decomposition of the turtle.

Measurement methods followed those defined in Flint et al. (2009). Midline CCL measurements were taken using a flexible fiberglass tape measure (± 0.1cm). Any large barnacles on the carapace likely to interfere with measurement were removed. The CCL measurement (cm) of hawksbill turtles (n = 139) and green turtles (n = 42) were categorized into size classes at 5-cm intervals between 20 cm and 95 cm. Average CCL was determined over categories of time by year (fixed factor) and by total average over the study period totaling 15 years from 1996 to 2011. Head width measurements were taken using stainless steel vernier slide calipers (± 0.01 cm). Head width (n = 116) measurements (cm) were compared against the CCL (cm) of the same sample to identify the relationship between the two measures.

Global Positioning System (GPS) coordinates recorded for stranding events were mapped using ArcGIS10. Coordinates were categorized by whole degrees (e.g., 28°, 29°, etc.) and frequency of hawksbill turtle stranding events (n = 173) were analyzed within each degree from -28°S to -36°S, resulting in nine latitudinal categories extending from Tweed Heads to Eden. Records were reclassified by date according to Austral seasonal categories. Summer (Dec-Feb), Autumn (Mar-May), Winter (Jun-Aug) and Spring (Sept-Nov).

A total of 181 confirmed hawksbill turtle stranding events were recorded in the central government database between 1996 and 2011. Forty-two records did not provide a CCL, and 61 records did not provide a head width. Other outliers (n = 3) containing entry errors identified by comparing recorded head width and CCL were eliminated. A total of 139 records contained CCL data.

The CCL of stranded hawksbill turtles between 1996 and 2011 ranged from 23.0 cm to 96.0 cm. The CCL analysis showed a normal distribution around a smaller size class (Fig. 2). The average CCL was 40.1 cm ± 9.5 cm (n = 139). A total of 116 hawksbill records recorded both CCL and head width. A positive relationship with CCL was expected and observed as the growth rates of carapace and skull are closely related in subadult marine turtles (Bell 2012). The CCL of stranded green turtles in 2011 ranged from 6.9 cm to 99.0 cm. The average CCL was 43.5 cm ± 15.9 (n = 42).

Figure 2. Frequency of CCL size classes represented by stranded hawksbill turtles from 1996 to 2011 (n = 136) with standard error.

Figure 3. Latitudinal spread of hawksbill turtle stranding events in New South Wales (n = 173) between 1996 and 2011.

The analysis of the number of hawksbill turtle stranding events by latitude showed that within NSW waters, hawksbill turtles stranded more frequently toward the north of the state between the years 1996 and 2011 (Fig. 3).

Stranding results show a steady upward trend until 2011 (Fig. 4) when a significant increase in strandings was reported particularly in the latter half of that year. Forty percent of the recorded hawksbill turtle strandings since 1996 occurred in the spring and summer of 2011. The stranding rate then appeared to return to previously observed levels in 2012 and 2013. During the 15-year study period (1996 -2011), 79% of hawksbills stranded between September and January, in Austral spring and summer (Fig. 5).

Figure 4. Frequency of hawksbill turtle stranding events in NSW between 1996 and 2011 (n = 226).

Figure 5. Frequency of hawksbill turtle stranding events between 1996 and 2011 by season (n = 139).

By running a linear regression model of CCL by event date for stranded hawksbills in NSW, we confirmed that average turtle size did not significantly vary from year to year between 2001 and 2011 (residual standard error = 9.575, df = 127; multiple R² = 0.07282, F = 0.9067, df = 11 and 127, p = 0.5361).

There were some discrepancies found in some records in the central database. There are many resource issues relating to quality data acquisition including the logistics of responding to strandings, minimum skill level required to identify turtles in the field and human error in data entry. Recommendations for improving collaborative data strategies are made at the end of this report. The geographic location data that were recorded were reliable but not always accurate. In some cases geographic coordinates were estimated if only a beach name was given in the original report. This error in exact location of some events may be up to 5 km, however, the error is restricted to the parameters of a long, geographically slender, beach environment. Of 173 records used for location, 83 records were recorded and the rest were estimated using maps from interpretation of written notes.

A comprehensive review of Australian hawksbill turtle population dynamics (Limpus 2008) noted the average size of hawksbill turtles that had recently recruited to the inshore reef habitat from the pelagic environment was 36.3 cm CCL. We found that most hawksbills stranded in NSW were subadults and the same size as new recruits to coral reefs. In a study of growth rates for hawksbills in the southern Great Barrier Reef (Chaloupka 1997) there were a limited number of individuals in size classes <35 cm and >60 cm, which closely reflects the size range of stranded hawksbills in this study. It was also earlier inferred that the lack of adult hawksbills indicated a developmental migration to northern Australian waters (Limpus 1992), which may explain why only a small number of hawksbill turtles with CCL >60 cm have been recorded in NSW. It appeared that healthy hawksbill turtles recruit from the pelagic environment to commence residency on south Queensland Reefs at about 5-7 years of age. It was concluded that there is not a single size at which these turtles recruit to inshore residency but rather a spread of sizes encompassing approximately 10 cm in carapace length (Limpus 2008).
A similar pattern in size frequency was also seen in a study of stranded green, hawksbill and loggerhead turtles at Caribbean Panama and Bermuda study sites, in the context of ontogenetic shifts (Meylan et al. 2011) which were first proposed by Carr (1956). In Caribbean Panama and Bermuda there was a peak in the size distribution for stranded hawksbill and green turtles in the smallest size classes (20 - 25 cm SCL for hawksbills; 25 - 30 cm SCL for greens). These data suggested an increased rate of mortality during the transition between life stages, between the epipelagic and benthic developmental stages (Meylan 2011). In an analogous situation sea snakes were also found to be more likely to die when they moved away from their usual home range (Bonnett et al. 1999). Tag return data from Meylan et al. (2011) suggest that this may be a dangerous time for turtles, and protection of subadults as they move into adult foraging ranges could be a productive objective of policy change for effective marine turtle conservation (Meylan 2011)

It may be concluded that the subadult age class in the population of hawksbill turtles stranding in NSW may represent individuals failing to successfully complete the ontogenetic shift from pelagic waters to neritic inshore waters of eastern Australia and this aspect warrants further study.

In the 12 months leading up to the 2011 peak hawksbill turtle stranding event, the east coast of Australia had been subjected to a series of extreme weather events including cyclones and floods. As a result, it was estimated by experts at the Australian Sea Turtle Health Workshop held in Townsville in 2012 that 80% of available seagrass habitat along the Queensland coastline had been significantly disturbed. Consequently, an increased number of marine turtles and dugong were reported stranded and presenting symptoms concurrent with starving. A total of 72 hawksbill turtles with average CCL of ~30 cm stranded within one month on the northern New South Wales coastline during the November 2011 event, all presenting with chronic emaciation and no evidence of other trauma or disease. The impact of extreme weather events was one explanation for the high frequency of marine turtle strandings both in NSW and Queensland during that time. Habitat loss caused by turbidity and wave action is just one consequence of extreme weather events.

We found that hawksbill turtle strandings increased in spring and summer months (September to February); several factors may have contributed to this seasonal pattern. A slight increase in the frequency of stranding events between 34°S and 35°S likely represents a catching effect where reported strandings were influenced by an increase in human population throughout the Sydney basin. There were also more recreational beach-goers during the summer holiday period (December and January). However, marine turtle strandings in North America also follow a seasonal regime that is predictable from physical oceanography and mimicked by drift bottle experiments (Hart et al. 2006). There appeared to be a predictable pattern of strandings-favorable seasons and strandings-unfavorable seasons, regardless of whether turtles or bottles were the stranded objects (Hart et al. 2006).

The strength and seasonal variation of the East Australian Current correlated with seasonal peaks in hawksbill turtle stranding events in NSW. This would most certainly be a significant contributing factor to the movement of debilitated hawksbill turtles to the NSW coastline that was observed during the summer months in the study period. The increase in strandings closer to urban centers may also be associated with an increase in pollutant runoff, which could adversely affect habitat quality. Itinerant or transient marine turtles are now thought to exhibit both residency and site fidelity at some sites (Meylan 2011), highlighting the need for ongoing monitoring.

The conservation and management of marine vertebrates that cross jurisdictional borders, including marine turtles that migrate both annually and throughout various life phases, is complex. As a signatory to the Migratory Species Convention it is incumbent on the Australian State and Federal Government to undertake measures to protect and conserve migratory species if and when they occur within their jurisdiction.

It is recommended that training and assistance is provided to participating organizations to ensure that the turtle stranding data collection process is:

Reviewing hawksbill turtle stranding event data has increased our understanding of trends and influencing factors in marine turtle stranding events in NSW. The interpretation provides future research a baseline of information and possible explanations of patterns of variance that may contribute to the management of threatened turtle species in NSW.

Threats to the welfare of protected turtle species in NSW and reef habitat include commercial trawling operations, recreational crab pots, shark-nets, the construction of approved fishing-related boating facilities, driving through or anchoring in seagrasses (Ganassin 2005) and block-and-tackle moorings that can damage habitat. Plastic ingestion was also recorded in multiple individuals raising concerns about waste management across the entire south Pacific region.
Despite the scarcity of funding for research, the labor-intensive nature of in-water sampling in particular, and the need for sustained focus in the field due to the slow growing long lived life history characteristics of these turtles (Prince 2012), it is vital to the conservation of marine turtles in the South Pacific to understand the full scope of habitat use and threats to their survival throughout all phases of their life history within the region.

Acknowledgements. With thanks to James Cook University, Mark Hamman, Mariana Fuentes, Richard Rowe & Glen Connolly. Thanks also to the NSW State Government, particularly the staff in the Office of Environment and Heritage and the volunteers at the Marine Turtle Rehabilitation Centre at Australian Seabird Rescue Inc. in Ballina. Also Keith, Finn and Rhonda and a hat tip to Lance Ferris.

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