Robust statistical modelling of hawksbill sea turtle growth rates (southern Great Barrier Reef)

Abstract

ABSTRACT. Growth rates recorded between 1974 and 1991 for 44 immature hawksbill sea turtles in the southern Great Barrier Reef foraging grounds were modelled using nonparametric regression methods. The implicit sampling design in this long-term mark-recapture program was mixed longitudinal and included growth records for both female and male hawksbills ranging between 39 and 85 cm CCL (curved carapace length). Distinct sex-speclfic growth patterns were found, with immature female hawksbills growing at ca 0.5 cm yf' faster than male immature hawksbills at all recorded sizes. The mean-size specific growth rate function for females was nonmonotonic, rising rapidly from recruitment size (> 35 cm CCL) to a maximum growth rate of 2.2 cm yr-l at 60 cm CCL before declining to negligible growth approaching sexual maturity at a size 280 cm CCL. The mean-size specific growth rate function for males was also nonmonotonic, rising from the same recruitment size to a maximum growth rate of 1.7 cm yr-' at 60 cm CCL before declining to negligible growth approaching sexual maturity 280 cm CCL. No significant inter-annual variation in growth rates was found but the data set was too small to be conclusive. Size-specific growth rates were slower than observed for stocks from western Atlantic-Caribbean waters. Juvenile hawksbill growth spurts around 60 cm CCL, sex-specific growth and slow size-specific growth rates are distinct growth characteristics for immature hawksbill sea turtles resident in southern Great Barrier Reef waters.

Kemp's Ridley Sea Turtle Saga and Setback: Novel Analyses of Cumulative Hatchlings Released and Time-Lagged Annual Nests in Tamaulipas, Mexico

“…Hawksbill sea turtles exhibit slow growth rates although they are known to vary within and among populations from a low of 0.4-1.2 in (1-3 cm) per year measured in the Indo-Pacific (Chaloupka and Limpus 1997;Mortimer et al 2003;Mortimer et al 2002;Whiting 2000) to a high of 2 in (5 cm) or more per year measured at some sites in the Caribbean (Díez and Dam 2002;León and Díez 1999). Differences in growth rates are likely due to differences in diet and/or density of sea turtles at foraging sites and overall time spent foraging (Bjorndal and Bolten 2000;Chaloupka et al 2004).…”

Habitat effect on hawksbill turtle growth rates on feeding grounds at Mona and Monito Islands, Puerto Rico

“…Other habitat properties were not examined in these studies. Chaloupka & Limpus (1997) present growth curves based on data collected for 44 immature hawksbill turtles of the southern Great Barrier Reef. Growth rates in these Australian hawksbills exhibit a non-monotonic pattern, rising from 1.0 to 1.5 cm yr -1 at 40 cm SCL, peaking at 2.2 cm yr -1 (females) and 1.7 cm yr -1 (males) at 55 cm SCL, then gradually descending to negligible growth (reported curved carapace lengths converted to SCL using Table 1 in Limpus 1992).…”

“…Partly in response to such difficulties, recent studies of marine turtle growth have used sophisticated, generalized additive modelling (GAM) approaches to determine growth curves and examine contributing factors, such as sex and year effects (e.g. Chaloupka & Limpus 1997, Bjorndal et al 2000. An important objective of these (and our) studies is to obtain representative growth curves (e.g.…”

“…Overall, immature hawksbills of the southern Great Barrier Reef grow much slower than their counterparts in the Caribbean. Chaloupka & Limpus (1997) did not consider habitat effect on growth, though it is likely that a vast area such as the southern Great Barrier Reef encompasses a range of hawksbill habitats.…”

“…We are aware of only 3 published studies reporting the measurements taken of a size-able number (n > 10) of foraging ground hawksbills. Chaloupka & Limpus (1997) modelled growth rates measured in 44 immature turtles of the southern Great Barrier Reef; León & Diez (1999) reported growth rates for 37 juveniles in the Dominican Republic; and Boulon (1994) gave growth rates for 13 immatures in the US Virgin Islands. In this paper, we present growth data obtained from 1992 to 2000, from 197 hawksbill turtles at study sites along the shores of Mona and Monito Islands, Puerto Rico.…”