Impact of exceptional growth rates on estimations of life-stage duration in Hawaiian green sea turtles

Skk Murakawa,Ml Snover

doi:10.3354/esr00885

Abstract

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 35:181-193 (2018) - DOI: https://doi.org/10.3354/esr00885 Impact of exceptional growth rates on estimations of life-stage duration in Hawaiian green sea turtles Shawn K. K. Murakawa1,*, Melissa L. Snover2 1NOAA Fisheries, Pacific Islands Fisheries Science Center, 1845 Wasp Boulevard, Building 176, Honolulu, Hawaii 96818, USA 2Population Ecology Services, PO Box 3673, Pago Pago, American Samoa 96799, USA *Corresponding author: shawn.murakawa@noaa.gov ABSTRACT: The Hawaiian green sea turtle Chelonia mydas population has steadily increased since its protection under the US Endangered Species Act of 1978. However, an understanding of their recovery status is stymied by lack of certainty regarding the population age structure. Based on the observed slow growth rates of juveniles, current assessments place age at first reproduction in Hawaiian green sea turtles at 35-40 yr, although a recent study suggests 23 yr for this population. It is possible that somatic growth dynamics such as growth spurts have been missed by traditional mark-recapture studies. Skeletochronology provides annual longitudinal data on growth rates of marine turtles, allowing for the detection of rare but potentially important growth spurts. The present study uses skeletochronology to estimate growth rates and detect the frequency of growth spurts in 30-90 cm straight carapace length (SCL) Hawaiian green sea turtles. We found that growth spurts occurred throughout the life span, but peaked for males from 50 to 59.9 cm SCL and for females from 70 to 79.9 cm SCL. The growth rates were binned into 10 cm SCL size class bins, and 4 methods were used to estimate the mean growth rate for each bin. We found that mean growth rates overestimated life-stage durations for each of the methods, although the expectation of the lognormal distribution gave the least biased results. Our study suggests that infrequent growth spurts are not represented in mean growth rate statistics but that these spurts likely result in faster lifetime growth rates and lower age at first reproduction than has been estimated using traditional methods. KEY WORDS: Chelonia mydas · Age at first reproduction · Growth spurts · Humeri · Skeletochronology Full text in pdf format PreviousCite this article as: Murakawa SKK, Snover ML (2018) Impact of exceptional growth rates on estimations of life-stage duration in Hawaiian green sea turtles. Endang Species Res 35:181-193. https://doi.org/10.3354/esr00885 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 35. Online publication date: April 27, 2018 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2018 Inter-Research.

Highlights

Green sea turtles Chelonia mydas are found globally throughout tropical, subtropical, and temperate oceans
Our study suggests that infrequent growth spurts are not represented in mean growth rate statistics but that these spurts likely result in faster lifetime growth rates and lower age at first reproduction than has been estimated using traditional methods
We demonstrate that while some methods are more accurate than others, all of the methods used overestimated the time to grow when more than 10 cm of carapace length growth is being estimated

Summary

Introduction

Green sea turtles Chelonia mydas are found globally throughout tropical, subtropical, and temperate oceans. The Hawaiian green sea turtle is one of the most extensively monitored nesting populations (Balazs & Chaloupka 2006), the diverse geographic habitats make a comprehensive understanding of growth rates and age at first reproduction difficult. Managing this protected DPS is challenging because there is uncertainty in the data on lifestage durations and age at first reproduction, which are critical for modeling sea turtle populations (Heppell et al 2003). Growth rate (and its variation) in sea turtles is an important demographic parameter, and is crucial to understanding age at first reproduction and the variability in that age, leading to a better understanding of population dynamics for recovery and conservation (Heppell et al 2003, Avens & Snover 2013)

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