Tuesday, December 4, 2012

The Importance of Understanding Life Stage Duration


Did you know that it is currently not possible to accurately age a living turtle? Yet successful conservation of marine turtles relies on having the best possible understanding of habitat use and complete life history. Therefore, age-at-size estimates are used to construct population structure and abundance models for management (Crouse et al. 1987, Heppell et al. 2003). Hamann et al. (2010) identified the need to “develop methods to accurately age individual turtles, determine a population’s (or species’) mean age-at-maturity, and define age-based demography” as one of the top 20 global research priorities for marine turtle conservation and management. This report also concluded that researchers must identify the “parameters [that] influence the biogeography of sea turtles in the oceanic realm” and resolve the “demography of turtles in the oceanic stage, including the duration of the oceanic juvenile stages”.
Source: http://seaturtlefoundation.com/

Determining age of turtles and life stage-duration through my research will address this priority to improve the population ecology and conservation of sea turtles. In addition, each distinct life stage of marine turtles experiences different types and intensities of threats. For example, a small juvenile turtle living out in the open ocean is exposed to threats (i.e. large industrial fishing fleets, natural oceanic predators, ghost-fishing nets & etc.) that are very different from the types of threats that a much large turtle will be faced with while living in a coastal area or lagoon (i.e. boat traffic, coastal pollution, smaller scale fishing efforts & etc.).

Assessing the variability of these impacts at each stage and habitat is difficult when stage duration is uncertain, making it a challenge to prioritize and implement protection measures to mitigate these impacts. By more accurately determining the duration of each life stage (i.e. how many years a turtle is in each stage) the full impact of particular sources of mortality on the overall population can be prioritized and more effectively managed.

My research will uses skeletochronology- a method to age dead turtles, together with other emerging techniques to generate age-based demographic parameters, including stage duration, for two populations of marine turtles in the Pacific. This research will contribute important information to marine turtle managers by directly addressing two of the top research priorities identified for marine turtle conservation.

Next blog entry: Techniques used to address these questions - learn more about how skeletochronology and stable isotope analysis can determine the age and past locations of sea turtles. 


And if you have not already - please see the previous entry, "A call to help: Support Community Based Sea Turtle Conservation & UCSD Research" and watch the video to learn more about my research and how YOU can help out

Some images in video obtained under NMFS Permit #1591


References:

 
Avens, L., and L. R. Goshe. 2007. Comparative skeletochronological analysis of Kemp's ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) humeri and scleral ossicles. Marine Biology (Berlin) 152:1309-1317.
Bjorndal, K. A., A. B. Bolten, R. A. Bennett, E. R. Jacobson, T. J. Wronski, J. J. Valeski, and P. J. Eliazar. 1998. Age and growth in sea turtles: Limitations of skeletochronology for demographic studies. Copeia:23-30.
Casale, P., N. Conte, D. Freggi, C. Cioni, and R. Argano. 2011. Age and growth determination by skeletochronology in loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea. Scientia Marina 75:197-203.
Coles, W. C., J. A. Musick, and L. A. Williamson. 2001. Skeletochronology validation from an adult loggerhead (Caretta caretta). Copeia:240-242.
Crouse, D. T., L. B. Crowder, and H. Caswell. 1987. A STAGE-BASED POPULATION MODEL FOR LOGGERHEAD SEA TURTLES AND IMPLICATIONS FOR CONSERVATION. Ecology (Washington D C) 68:1412-1423.
Goshe, L. R., L. Avens, F. S. Scharf, and A. L. Southwood. 2010. Estimation of age at maturation and growth of Atlantic green turtles (Chelonia mydas) using skeletochronology. Marine Biology 157:1725-1740.
Hamann, M., M. H. Godfrey, J. A. Seminoff, K. Arthur, P. C. R. Barata, K. A. Bjorndal, A. B. Bolten, A. C. Broderick, L. M. Campbell, C. Carreras, P. Casale, M. Chaloupka, S. K. F. Chan, M. S. Coyne, L. B. Crowder, C. E. Diez, P. H. Dutton, S. P. Epperly, N. N. FitzSimmons, A. Formia, M. Girondot, G. C. Hays, I. J. Cheng, Y. Kaska, R. Lewison, J. A. Mortimer, W. J. Nichols, R. D. Reina, K. Shanker, J. R. Spotila, J. Tomas, B. P. Wallace, T. M. Work, J. Zbinden, and B. J. Godley. 2010. Global research priorities for sea turtles: informing management and conservation in the 21st century. Endangered Species Research 11:245-269.
Heppell, S. S., M. L. Snover, and L. B. Crowder. 2003. Sea turtle population ecology.
Parham, J. F., and G. R. Zug. 1997. Age and growth of loggerhead sea turtles (Caretta caretta) of coastal Georgia: An assessment of skeletochronological age-estimates. Bulletin of Marine Science 61:287-304.
Reich, K. J., K. A. Bjorndal, and A. B. Bolten. 2007. The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages. Biology Letters 3:712-714.
Snover, M. L., L. Avens, and A. A. Hohn. 2007a. Back-calculating length from skeletal growth marks in loggerhead sea turtles Caretta caretta. Endangered Species Research 3:95-104.
Snover, M. L., and A. A. Hohn. 2004. Validation and interpretation of annual skeletal marks in loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) sea turtles. Fishery Bulletin (Seattle) 102:682-692.
Snover, M. L., A. A. Hohn, L. B. Crowder, and S. S. Heppell. 2007b. Age and growth in Kemp's ridley sea turtles: evidence from mark-recapture and skeletochronology.
Snover, M. L., and A. G. J. Rhodin. 2008. Comparative ontogenetic and phylogenetic aspects of chelonian chondro-osseous growth and skeletochronology. Biology of Turtles:17-43.
Zug, G. R. 1985. Skeletochronological age estimates for Hawaiian green turtles. Marine Turtle Newsletter:9-10.
Zug, G. R., G. H. Balazs, and J. A. Wetherall. 1995. Growth in juvenile loggerhead sea turtles (Caretta caretta) in the North Pacific pelagic habitat. Copeia 1995:484-487.
Zug, G. R., G. H. Balazs, J. A. Wetherall, D. M. Parker, and S. K. K. Murakawa. 2002. Age and growth of Hawaiian green seaturtles (Chelonia mydas): an analysis based on skeletochronology. Fishery Bulletin 100:117-127.
Zug, G. R., M. Chaloupka, and G. H. Balazs. 2006. Age and growth in olive ridley seaturtles (Lepidochelys olivacea) from the north-central Pacific: a skeletochronological analysis. Marine Ecology-an Evolutionary Perspective 27:263-270.
Zug, G. R., and R. E. Glor. 1998. Estimates of age and growth in a population of green sea turtles (Chelonia mydas) from the Indian River lagoon system, Florida: a skeletochronological analysis. Canadian Journal of Zoology-Revue Canadienne De Zoologie 76:1497-1506.
Zug, G. R., H. J. Kalb, and S. J. Luzar. 1997. Age and growth in wild Kemp's ridley seaturtles Lepidochelys kempii from skeletochronological data. Biological Conservation 80:261-268.
Zug, G. R., A. H. Wynn, and C. Ruckdeschel. 1986. Age determination of loggerhead sea turtles, Caretta caretta, by incremental growth marks in the skeleton. Smithsonian Contributions to Zoology:i.


Wednesday, November 28, 2012

A call to help: Support Community Based Sea Turtle Conservation & UCSD Research


Hello friends of San Diego Sea Turtles,

I'm writing today to share with you a short video which I've put together in an effort to raise funds for the non-profit organization which is essential to my research I'm doing for my PhD at UCSD: Grupo Tortuguero de las Californias (GTC). For the past year, and for the next 4 years, members of GTC are actively collecting sea turtle samples for my research - and this is my effort to support the hard work they are doing in this partnership with me. Consider this a grassroots-D.I.Y. crowd-sourcing project!  (All the benefit - none of the overhead middleman costs!)

Grupo Tortuguero is based in Baja, Mexico and is part of The Ocean Foundation. GTC is a non-profit organization comprised of scientists, researchers, students, fishermen/women, and volunteers, and is pivotal to the success of my research.  While I work in the lab at UCSD and at NOAA in San Diego - my partners in Baja are monitoring beaches and lagoons and providing me with samples which I use to answer important conservation research questions. At the core, Grupo Tortuguero is a collective of citizen scientists and engaged community members - a truly remarkable example of community based conservation.

My fundraising goal is $3,000 - but if I were to dream big, I'd hope to raise $5,000 - and I do like to dream big! And the best part is, that all of the funds we raise go directly to Grupo Tortuguero.
 


(Some images obtained under NMFS Permit #1591)
  
I would be grateful if after you watch this short video - you might also share this note and the video with your own friends who might also like to pitch in. Please pass this on to other colleagues, friends and family. Contributions in any amount are greatly appreciated. 
 
"Never doubt that a small group 
of thoughtful, committed citizens 
can change the world; 
indeed, it's the only thing that ever has." 
- Margaret Mead

Please watch the below video to learn more about how you can help support this research.
Or you may view the video directly at YouTube:
http://www.youtube.com/watch?v=TzKIlN1ei78

To donate, visit: http://snipurl.com/humerus
   To help us track donations raised for this project, please comment "Humerus Project" in the "Other Purposes" box on the donate page.

All donations are tax deductible, and all donors will be acknowledged at my blog, San Diego Sea Turtles, at all research presentations, and in publications resulting from this research. (Simply make a note when you donate if you'd prefer your donation to remain anonymous.)

Thank you for your time and thank you for considering donating to this project.

Sincerely,

Cali

Cali (center) with Victor de la Toba (left) and Dr. Hoyt Peckham (right) at a key field site, Playa San Lazaro in Baja California Sur, Mexico. Peckham and de la Toba are just two of the many partners who will benefit from the funds raised for Grupo Tortuguero.

Tuesday, September 11, 2012

Two Marine Turtle Populations in the East Pacific

My research focuses on two populations of sea turtles found in the East Pacific, the East Pacific Green Sea Turtles (species: Chelonia mydas) and the North Pacific Loggerhead Sea Turtles (species: Caretta caretta). Here's a bit more information on these two populations which are the focus of my studies.


East Pacific Green Sea Turtles (Chelonia mydas)

The Mexican nesting stock of East Pacific green sea turtles is currently designated as endangered due to the decline in nesting in recent decades, as well as intense poaching and harvesting during the middle of the century. This stock of green turtles ranges from South America to southern California, but the vast majority are born on sandy beaches in southern Mexico, primarily in the state of Michoacán, before beginning their juvenile stage of life (see region shown in map below). 



The oceanic juvenile stage of East Pacific green turtles remains one of the least understood stages in the life history of this endangered species population. In the last decade, progress has been made on elucidating the lost years oceanic juvenile state of marine turtles (Reich et al. 2007, Arthur et al. 2008, Cardona et al. 2010, Snover et al. 2010). However, the duration of the juvenile stage of this endangered stock of green turtles remains to be known and is current research priority for the management of this slowly recovering population of turtles. 
 
This oceanic juvenile stage is currently estimated to last from two to five+ years, during which turtles feed opportunistically and omnivorously - eating what they can find - along ocean current boundaries. Eventually these juveniles are large enough settle into nearshore subtidal algae and seagrass ecosystems to feed and grow (Carr 1987, Reich et al. 2007). If they were to live in nearshore habitats too soon, they would be too small and would become prey to larger fish, birds and other common predators in coastal ecosystems. After growing even more in these nearshore habitats, turtles reach maturity, at around thirty years of age, and return to their nesting sites to breed approximately every three years. In between breeding times, the turtles migrate between nesting grounds and foraging areas in Mexico (both along the Pacific coast and in the Gulf of California) and some even live as far north as California, USA. Main foraging (or eating) grounds include bays and lagoons where green turtles eat several species of eelgrass, marine algae, and invertebrates like crabs and snails (Seminoff et al. 2002a, Lopez-Castro et al. 2010, Lemons et al. 2011)


Larger region, zoomed in area to the right -->
Region of East Pacific Green Turtles: San Diego shown to the north, nesting area in Michoacán in the south.

This population of green turtles is considered a regional management unit - meaning it has its own management plans and and protection. It was also once the target of a large turtle fishery that reached its peak in the 1970s. The fishery harvested turtle meat and eggs that were sold and consumed in large numbers. Due to this fishery, this once plentiful population of green turtles is currently a fraction of the size of what it once was (National Marine Fisheries Service 2007a). Cooperative efforts, including protective measures put in place in 1990 by the Mexican government, prevented further collapse of the green turtle population, and evidence of slow recovery continues to be observed (Koch et al. 2006). Despite international legal protection, impacts beyond poaching, such as fishing bycatch, boat strikes, development of nesting beaches, and development of coastal foraging areas, continue to threaten these sea turtles.


North Pacific Loggerhead Sea Turtles (Caretta caretta)

 In the Pacific, two genetically distinct stocks of loggerhead turtles have been identified (National Marine Fisheries Service 2007b). One in the South Pacific, which nests in and around Australia, and one in the North Pacific, which nests on multiple islands of Japan (Bowen et al. 1995). Both of the Pacific population stocks are currently designated as endangered due to the decline in nesting in recent decades (Kamezaki et al., 2003). In the North Pacific, over 40 nesting beaches are known and monitored, yet approximately 30-40% of this population’s nesting occurs at three main beaches on the small island of Yakushima at the southern end of Japan (Kamezaki et al., 2003). Hatchlings from these beaches, once they swim offshore, are moved north and then east by swimming with the Kuroshio Current and the North Pacific drift - eventually being guided toward the Central North Pacific (CNP), close to Hawaii. Immature loggerhead turtles have been found as fisheries bycatch in the CNP around the extended Hawaiian Islands. Satellite tracks of juvenile loggerheads show extended and concentrated foraging in the areas where currents help create highly productive waters (specifically near the Kuroshio Extension Bifurcation Region and the Transition Zone Chlorophyll Front) (Polovina et al. 2004, Polovina et al. 2006, Kobayashi et al. 2008). Eventually some of these turtles are guided by the California Current, and a large aggregation of loggerheads, estimated to be in the tens of thousands, forage off the coast of the Baja California Peninsula (BCP) (Lewison et al. 2004, Wallace et al. 2008, Peckham et al. 2011).


Loggerhead sea turtle. Image by author.
 Studies examining body size and stomach contents of fishery-bycaught and dead-stranded turtles show that turtles near Hawaii (CNP turtles) are smaller in size and foraged primarily on pelagic invertebrates and fish commonly associated with fisheries bycatch and bait. In contrast, turtles examined from the Baja region (BCP) were slightly larger in size, although still juveniles, and ate primarily pelagic red crabs (Pleuroncodes planipes) and fish associated with fishing operations (Peckham et al. 2011). Upon reaching maturity, adult loggerheads migrate back across the Pacific to return to the neritic waters of the Western Pacific where they remain to forage and breed for the rest of their lives (Resendiz et al. 1998, Nichols et al. 2000, Hatase et al. 2002, Hatase et al. 2004).

A primary threat to the North Pacific loggerheads in the East Pacific is the intense mortality associated with small-scale artisanal fisheries. Conservative estimates indicate that 1000+ individual loggerheads are killed per year (Peckham et al. 2007, Peckham et al. 2008) from bycatch related to BCP small-scale fisheries. Upwelling in the East Pacific creates productive waters that result in large amounts of biomass (plankton, fish & other animals) in a concentrated area. While the loggerheads in this area are foraging primarily on swarms of red crab, many types of fish also forage in these productive waters. The concentration of fish attracts local fishers to the same location, thereby contributing to high turtle-fishery interaction making this area a bycatch “hotspot” (Peckham et al. 2007, Wingfield et al. 2011)

The figure below is from Peckham et al., 2007 (click for access to full article and figures).
Notice the concentration of loggerhead turtles (red areas) in the vicinity of small-scale fishing efforts (white boat logos and outline).


In the past fifteen years, significant efforts have been made to engage local fishers and address the problem of this turtle hotspot. Gradually, fishing practices are being adjusted in order to reduce interactions with turtles and a protected area has been established (Lewison et al. 2011). Cooperative work by Grupo Tortuguero and their partners in communities throughout Baja and Pacific Mexico states have been addressing this issue of bycatch, as well as poaching and other threats to marine turtles and sea life through diverse community engagement programs. And while much has been learned about this population of loggerheads and their use of this productive yet dangerous East Pacific habitat, it remains unclear how long the juvenile loggerheads forage in this BCP hotspot region prior to migrating to the West Pacific. Understanding the duration of exposure to sources of high mortality is important information for population management (Hamann et al. 2010, Wallace et al. 2011).

My research will address these some of these unknowns related to habitat use and duration of different life stages of turtles of each of these two populations.

Me helping H. Peckham tag and measure a loggerhead in the "loggerhead hotspot" off of San Juanico, BCP, MEX




References:

Arthur, K. E., Boyle, M. C. and Limpus, C. J. (2008) 'Ontogenetic changes in diet and habitat use in green sea turtle (Chelonia mydas) life history', Marine Ecology Progress Series, 362, 303-311.

Bowen, B. W., Abreugrobois, F. A., Balazs, G. H., Kamezaki, N., Limpus, C. J. and Ferl, R. J. (1995) 'TRANS-PACIFIC MIGRATIONS OF THE LOGGERHEAD TURTLE (CARETTA-CARETTA) DEMONSTRATED WITH MITOCHONDRIAL-DNA MARKERS', Proceedings of the National Academy of Sciences of the United States of America, 92(9), 3731-3734.

Cardona, L., Campos, P., Levy, Y., Demetropoulos, A. and Margaritoulis, D. (2010) 'Asynchrony between dietary and nutritional shifts during the ontogeny of green turtles (Chelonia mydas) in the Mediterranean', Journal of Experimental Marine Biology and Ecology, 393(1-2), 83-89.

Carr, A. (1987) 'New perspectives on the pelagic stage of sea turtle development', Conservation Biology, 1(2), 103-121.

Hamann, M., Godfrey, M. H., Seminoff, J. A., Arthur, K., Barata, P. C. R., Bjorndal, K. A., Bolten, A. B., Broderick, A. C., Campbell, L. M., Carreras, C., Casale, P., Chaloupka, M., Chan, S. K. F., Coyne, M. S., Crowder, L. B., Diez, C. E., Dutton, P. H., Epperly, S. P., FitzSimmons, N. N., Formia, A., Girondot, M., Hays, G. C., Cheng, I. J., Kaska, Y., Lewison, R., Mortimer, J. A., Nichols, W. J., Reina, R. D., Shanker, K., Spotila, J. R., Tomas, J., Wallace, B. P., Work, T. M., Zbinden, J. and Godley, B. J. (2010) 'Global research priorities for sea turtles: informing management and conservation in the 21st century', Endangered Species Research, 11(3), 245-269.

Hatase, H., Takai, N., Matsuzawa, Y., Sakamoto, W., Omuta, K., Goto, K., Arai, N. and Fujiwara, T. (2002) 'Size-related differences in feeding habitat use of adult female loggerhead turtles Caretta caretta around Japan determined by stable isotope analyses and satellite telemetry', Marine Ecology-Progress Series, 233, 273-281.

Hatase, H., Matsuzawa, Y., Sato, K., Bando, T. and Goto, K. (2004) 'Remigration and growth of loggerhead turtles (Caretta caretta) nesting on Senri Beach in Minabe, Japan: life-history polymorphism in a sea turtle population', Marine Biology, 144(4), 807-811.

Kamezaki, N., et al. (2003) ‘Loggerhead Turtles Nesting in Japan’. Pages 210-217 in
Bolten, A.B. and B.E. Witherington (editors). Loggerhead Sea Turtles. Smithsonian Books, Washington D.C.

Kobayashi, D. R., Polovina, J. J., Parker, D. M., Kamezaki, N., Cheng, I. J., Uchida, I., Dutton, P. H. and Balazs, G. H. (2008) 'Pelagic habitat characterization of loggerhead sea turtles, Caretta caretta, in the North Pacific Ocean (1997-2006): Insights from satellite tag tracking and remotely sensed data', Journal of Experimental Marine Biology and Ecology, 356(1-2), 96-114.

Koch, V., Nichols, W. J., Peckham, H. and de la Toba, V. (2006) 'Estimates of sea turtle mortality from poaching and bycatch in Bahia Magdalena, Baja California Sur, Mexico', Biological Conservation, 128(3), 327-334.

Lemons, G., Lewison, R., Komoroske, L., Gaos, A., Lai, C.-T., Dutton, P., Eguchi, T., LeRoux, R. and Seminoff, J. A. (2011) 'Trophic ecology of green sea turtles in a highly urbanized bay: Insights from stable isotopes and mixing models', Journal of Experimental Marine Biology and Ecology, 405(1-2), 25-32.

Lewison, R. L., Freeman, S. A. and Crowder, L. B. (2004) 'Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles', Ecology Letters, 7(3), 221-231.

Lewison, R. L., Soykan, C. U., Cox, T., Peckham, H., Pilcher, N., LeBoeuf, N., McDonald, S., Moore, J., Safina, C. and Crowder, L. B. (2011) 'INGREDIENTS FOR ADDRESSING THE CHALLENGES OF FISHERIES BYCATCH', Bulletin of Marine Science, 87(2), 235-250.

Lopez-Castro, M. C., Koch, V., Mariscal-Loza, A. and Nichols, W. J. (2010) 'Long-term monitoring of black turtles Chelonia mydas at coastal foraging areas off the Baja California Peninsula', Endangered Species Research, 11(1), 35-45.

National Marine Fisheries Service 2007a, National Marine Fisheries Service 2007b,
Available online at: http://www.nmfs.noaa.gov/pr/species/turtles/

Nichols, W. J., Resendiz, A., Seminoff, J. A. and Resendiz, B. (2000) 'Transpacific migration of a loggerhead turtle monitored by satellite telemetry', Bulletin of Marine Science, 67(3), 937-947.

Peckham, S. H., Diaz, D. M., Walli, A., Ruiz, G., Crowder, L. B. and Nichols, W. J. (2007) 'Small-Scale Fisheries Bycatch Jeopardizes Endangered Pacific Loggerhead Turtles', Plos One, 2(10).

Peckham, S. H., Maldonado-Diaz, D., Koch, V., Mancini, A., Gaos, A., Tinker, M. T. and Nichols, W. J. (2008) 'High mortality of loggerhead turtles due to bycatch, human consumption and strandings at Baja California Sur, Mexico, 2003 to 2007', Endangered Species Research, 5(2-3), 171-183.

Peckham, S. H., Maldonado-Diaz, D., Tremblay, Y., Ochoa, R., Polovina, J., Balazs, G., Dutton, P. H. and Nichols, W. J. (2011) 'Demographic implications of alternative foraging strategies in juvenile loggerhead turtles Caretta caretta of the North Pacific Ocean', Marine Ecology-Progress Series, 425, 269-280.

Polovina, J. J., Balazs, G. H., Howell, E. A., Parker, D. M., Seki, M. P. and Dutton, P. H. (2004) 'Forage and migration habitat of loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) sea turtles in the central North Pacific Ocean', Fisheries Oceanography, 13(1), 36-51.

Polovina, J., Uchida, I., Balazs, G., Howell, E. A., Parker, D. and Dutton, P. (2006) 'The Kuroshio Extension Bifurcation Region: A pelagic hotspot for juvenile loggerhead sea turtles', Deep-Sea Research Part Ii-Topical Studies in Oceanography, 53(3-4), 326-339.

Reich, K. J., Bjorndal, K. A. and Bolten, A. B. (2007) 'The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages', Biology Letters, 3(6), 712-714.

Resendiz, A., Resendiz, B., Nichols, W. J., Seminoff, J. A. and Kamezaki, N. (1998) 'First confirmed east-west Transpacific movement of a loggerhead sea turtle, Caretta caretta, released in Baja California, Mexico', Pacific Science, 52(2), 151-153.

Seminoff, J. A., Resendiz, A. and Nichols, W. J. (2002a) 'Diet of East Pacific green turtles (Chelonia mydas) in the central Gulf of California, Mexico', Journal of Herpetology, 36(3), 447-453.

Snover, M. L., Hohn, A. A., Crowder, L. B. and Macko, S. A. (2010) 'Combining stable isotopes and skeletal growth marks to detect habitat shifts in juvenile loggerhead sea turtles Caretta caretta', Endangered Species Research, 13(1), 25-31.

Wallace, B. P., Heppell, S. S., Lewison, R. L., Kelez, S. and Crowder, L. B. (2008) 'Impacts of fisheries bycatch on loggerhead turtles worldwide inferred from reproductive value analyses', Journal of Applied Ecology, 45(4), 1076-1085.

Wallace, B. P., DiMatteo, A. D., Bolten, A. B., Chaloupka, M. Y., Hutchinson, B. J., Abreu-Grobois, F. A., Mortimer, J. A., Seminoff, J. A., Amorocho, D., Bjorndal, K. A., Bourjea, J., Bowen, B. W., Duenas, R. B., Casale, P., Choudhury, B. C., Costa, A., Dutton, P. H., Fallabrino, A., Finkbeiner, E. M., Girard, A., Girondot, M., Hamann, M., Hurley, B. J., Lopez-Mendilaharsu, M., Marcovaldi, M. A., Musick, J. A., Nel, R., Pilcher, N. J., Troeng, S., Witherington, B. and Mast, R. B. (2011) 'Global Conservation Priorities for Marine Turtles', Plos One, 6(9).

Wingfield, D. K., Hoyt Peckham, S., Foley, D. G., Palacios, D. M., Lavaniegos, B. E., Durazo, R., Nichols, W. J., Croll, D. A. and Bograd, S. J. (2011) 'The Making of a Productivity Hotspot in the Coastal Ocean', Plos One, 6(11).

Friday, July 13, 2012

The turtles' home is closer to getting a new look: Chula Vista Bayfront Master Plan moves forward

Long-time followers of this blog will recall that initial focus was on the sea turtles of San Diego - as representatives of the coastal and marine environment of the South San Diego Bay - and their interaction with the South Bay Power Plant (SBPP) now and into the future. Primarily, when this blog began, the SBPP was still operating, but it was understood that the plant would be shut down in the near future, and looking forward, the type of development which took place on the land surrounding and then-occupied by the SBPP could greatly impact the incredible and often under-valued environment - including the sea turtles of San Diego and their fellow marine and coastal critters and habitats.

Understanding and incorporating the philosophy that the maximum benefit - yes, even economic benefit - can be realized through a mutualistic approach to development where both the environment and the economy are given priority, was the perspective hoped for to be held by planners, developers, and all stakeholders involved in the Chula Vista Bayfront redevelopment.  Over the past 10 years, many groups, companies and public officials have been involved in the ongoing process, and it appears that a fairly good balance of economic opportunity and environmental value has been incorporated into this plan.

And just this month, the development plan, termed the "Chula Vista Bayfront Master Plan," has received approval by local agencies, groups and stakeholders and is awaiting approval by the California Coastal Commission as the next step in the process. This will likely take place this summer.

The Port of San Diego's website has a section devoted to the project, and another site dedicated to the CV Bayfront project is also available to those interested to learn more. The background section of this site has a link to the full Environmental Impact Statement, Fact and FAQ sheets, and helpful illustrative images of the plan which are shown below.

On initial glance, the plans look well conceived, largely due to the years of stakeholder involvement, and appear to provide good public access to the waterfront, and provide protection and buffer to much of the sensitive, beautiful, and valuable coastal environment - including the home of our San Diego sea turtles.

Continued involvement by concerned citizens and groups, and support by attentive representatives, will be necessary to make sure that responsible development and planning continues, so that our community will be able to gain the maximum amount of value from this wonderful resource in our collective backyard.


Image of South San Diego Bay natural resources - Google Earth, habitats from Port of San Diego, primary sea turtle monitoring site also marked. A second image is also below with the habitat overlay removed. Google Earth aerial images from 8/23/2010.




Image of Illustrative Land Use Plan - also available for download online.

Image of Ecological Resource Illustrative Plan - also available online.



Saturday, June 23, 2012

When the "lost years" end

Juvenile loggerhead sea turtle being rehabilitated. Photo by author.
Most species of sea turtles - all except flatbacks and leatherbacks - have an oceanic juvenile stage, called the "lost years" between the time they hatch to when the settle as juveniles in near shore, or neritic, habitats. And for a variety of reasons, the coastal waters where juvenile turtles eat and grow are usually not near the nesting beaches where they will breed as adults. And so, after several years, and for most species of sea turtles, decades, the juvenile turtles in neritic habitats become mature and initiate breeding migrations as part of their next stage in the life cycle (Heppell et al. 2003)

Given the large body size reached by this stage in the life cycle, mortality due to natural predation is quite low. That is, these turtles are now too large for most ocean predators to be a real threat. And  turtles have been shown to be highly adapted physiologically to survive environmental fluxes (food availability, water temperature, storms and etc.) by employing various strategies including reserving resources, slowing metabolic processes, entering hibernation-like torpor states, survival within this stage should be quite high (Felger et al. 1976, Heppell et al. 2003). However, survivability during both the juvenile and adult neritic stage of life is largely dependent on exposure to anthropogenic impacts – especially fishing (intentional and incidental take) and pollution (Crouse et al. 1987). This will be a focused on more later.

During breeding migrations, both male and female turtles from multiple foraging grounds migrate and converge on breeding areas near the same beach where they hatched out decades earlier! This is called their "natal beach". Mating occurs in the water near the nesting beaches, and also during migrations – which is one way turtles are thought to increase gene flow among nesting groups. And while variation among species and populations exists, individuals from most species do not breed every year. Instead, female turtles migrate and nest in two to three year cycles, and this is based on tagging and tracking of female turtles. There is still much to be learned about the breeding and behavior of adult male turtles, who are harder to tag and study since they never come ashore the way that the females do to lay their nests. 

Sea turtle nest and female turtle tracks - see the V-shape tracks. Photo by author.
A nesting female sea turtle lay a single nest, or clutch, consisting of 40-100 eggs (depending on species), at each nesting event. Nesting typically occurs during the night. Females may lay multiple clutches during the 1-3 month-long nesting season, and each clutch of eggs has typically been fertilized by more than one male, which is another way to enhancing genetic diversity and maximizing survivability and fitness of offspring (Stewart and Dutton 2011, Hamann et al. 2003). Upon completion of laying the final clutch of eggs, the female turtles, as well as the males who have been gathered offshore, migrate back to their foraging grounds, leaving the nests and the developing hatchlings alone on the beach. 

In 40-60 days (again, depending on species, location, and other environmental factors), the hatchlings will emerge from the nest and begin their own journey through the life cycle. 


Conservatively, a female turtle may start nesting when she is thirty years old, and may continue nesting for 30 to 60 years; therefore, a reproductively mature female who has survived to sexual maturity has a very high reproductive value (Crouse et al. 1987, Heppell et al. 2003). That is to say, a full grown female turtle is very valuable to the continued existence of that sea turtle population.

A handful of nesting site studies range longer than 30 years, including Tortuguero in Costa Rico, Hawaii in the USA, and Michoacán in Mexico, and our understanding of sea turtle reproductive and life expectancy is still in progress. This is also further complicated by the lack of technique to determine the age of a turtle. The age of living sea turtles is still a great unknown. Captive-raised turtles have been known to live for nearly 30+ years (Schwartz 1997, Snover et al. 2007b), but we know turtles live much longer than that. The age of a sea turtle can be estimated based on its size, and after a sea turtle has died, a method called skeletochronology can also estimate age. Skeletochronology is similar to the process used to age trees by cross-section (dendrology) and marine mammals by tooth cross-section (Zug 1985, Zug et al. 1986)

Green sea turtle foraging (eating) in the Caribbean. Photo by author.
Yet to this day, there is no way to accurately age a living wild sea turtle, as a result, age-at-size estimates are most commonly used to study life history and to construct population structure and abundance models (Crouse et al. 1987, Heppell et al. 2003). In 1986, George Zug and colleagues described the process of skeletochronology for sea turtles, and since then, multiple studies have been conduced describing growth and age information for several marine turtle populations using this technique. 

Studies include green turtles Chelonia mydas, in Hawaii (Zug 1985, Zug et al. 2002), and the Caribbean/Atlantic (Goshe et al. 2010, Zug and Glor 1998, Bjorndal et al. 1998), loggerheads Caretta caretta in Gulf of Mexico/Atlantic (Zug et al. 1986, Coles et al. 2001, Snover and Hohn 2004, Snover et al. 2007a, Parham and Zug 1997), and the Mediterranean (Casale et al. 2011) and in the Pacific (Zug et al. 1995), for Kemp’s ridleys Lepidochelys kempii in the Gulf of Mexico (Avens and Goshe 2007, Snover and Hohn 2004, Snover et al. 2007b, Zug et al. 1997), leatherbacks Dermochelys coriacea in the Atlantic (Snover and Rhodin 2008) and olive ridley’s Lepidochelys olivacea in the Pacific (Zug et al. 2006). Similarly, Reich compared skeletochronology of loggerheads and green turtles together with layers of scute material (layers of the sea turtle's shell, or carapace) of green turtles to estimate age at settlement for green turtles in the Atlantic (Reich et al. 2007)

Skeletochronology will be one of two primary techniques I will use for my research, and is what I've been learning all about during my time here in North Carolina.



References:


Avens L, Goshe LR. 2007. Comparative skeletochronological analysis of Kemp's ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) humeri and scleral ossicles. Marine Biology (Berlin) 152(6):1309-1317.
Bjorndal KA, Bolten AB, Bennett RA, Jacobson ER, Wronski TJ, Valeski JJ, Eliazar PJ. 1998. Age and growth in sea turtles: Limitations of skeletochronology for demographic studies. Copeia(1):23-30.
Casale P, Conte N, Freggi D, Cioni C, Argano R. 2011. Age and growth determination by skeletochronology in loggerhead sea turtles (Caretta caretta) from the Mediterranean Sea. Scientia Marina 75(1):197-203.
Coles WC, Musick JA, Williamson LA. 2001. Skeletochronology validation from an adult loggerhead (Caretta caretta). Copeia(1):240-242.
Crouse DT, Crowder LB, Caswell H. 1987. A STAGE-BASED POPULATION MODEL FOR LOGGERHEAD SEA TURTLES AND IMPLICATIONS FOR CONSERVATION. Ecology (Washington D C) 68(5):1412-1423.
Felger RS, Cliffton K, Regal PJ. 1976. WINTER DORMANCY IN SEA TURTLES - INDEPENDENT DISCOVERY AND EXPLOITATION IN GULF OF CALIFORNIA BY 2 LOCAL CULTURES. Science 191(4224):283-285.
Goshe LR, Avens L, Scharf FS, Southwood AL. 2010. Estimation of age at maturation and growth of Atlantic green turtles (Chelonia mydas) using skeletochronology. Marine Biology 157(8):1725-1740.
Hamann M, Limpus CJ, Owens DW. 2003. Reproductive cycles of males and females. The biology of sea turtles. Volume II.:135-161.
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Parham JF, Zug GR. 1997. Age and growth of loggerhead sea turtles (Caretta caretta) of coastal Georgia: An assessment of skeletochronological age-estimates. Bulletin of Marine Science 61(2):287-304.
Reich KJ, Bjorndal KA, Bolten AB. 2007. The 'lost years' of green turtles: using stable isotopes to study cryptic lifestages. Biology Letters 3(6):712-714.
Schwartz FJ. 1997. Growth, maturity, and reproduction of a long-term captive male loggerhead sea turtle, Caretta caretta (Chelonia, Reptilia), in North Carolina. Journal of the Elisha Mitchell Scientific Society 113(3):143-148.
Snover ML, Avens L, Hohn AA. 2007a. Back-calculating length from skeletal growth marks in loggerhead sea turtles Caretta caretta. Endangered Species Research 3(1):95-104.
Snover ML, Hohn AA. 2004. Validation and interpretation of annual skeletal marks in loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) sea turtles. Fishery Bulletin (Seattle) 102(4):682-692.
Snover ML, Hohn AA, Crowder LB, Heppell SS. 2007b. Age and growth in Kemp's ridley sea turtles: evidence from mark-recapture and skeletochronology.
Snover ML, Rhodin AGJ. 2008. Comparative ontogenetic and phylogenetic aspects of chelonian chondro-osseous growth and skeletochronology. Biology of Turtles:17-43.
Stewart KR, Dutton PH. 2011. Paternal genotype reconstruction reveals multiple paternity and sex ratios in a breeding population of leatherback turtles (Dermochelys coriacea). Conservation Genetics 12(4):1101-1113.
Zug GR. 1985. Skeletochronological age estimates for Hawaiian green turtles. Marine Turtle Newsletter:9-10.
Zug GR, Balazs GH, Wetherall JA. 1995. Growth in juvenile loggerhead sea turtles (Caretta caretta) in the North Pacific pelagic habitat. Copeia 1995(2):484-487.
Zug GR, Balazs GH, Wetherall JA, Parker DM, Murakawa SKK. 2002. Age and growth of Hawaiian green seaturtles (Chelonia mydas): an analysis based on skeletochronology. Fishery Bulletin 100(1):117-127.
Zug GR, Chaloupka M, Balazs GH. 2006. Age and growth in olive ridley seaturtles (Lepidochelys olivacea) from the north-central Pacific: a skeletochronological analysis. Marine Ecology-an Evolutionary Perspective 27(3):263-270.
Zug GR, Glor RE. 1998. Estimates of age and growth in a population of green sea turtles (Chelonia mydas) from the Indian River lagoon system, Florida: a skeletochronological analysis. Canadian Journal of Zoology-Revue Canadienne De Zoologie 76(8):1497-1506.
Zug GR, Kalb HJ, Luzar SJ. 1997. Age and growth in wild Kemp's ridley seaturtles Lepidochelys kempii from skeletochronological data. Biological Conservation 80(3):261-268.
Zug GR, Wynn AH, Ruckdeschel C. 1986. Age determination of loggerhead sea turtles, Caretta caretta, by incremental growth marks in the skeleton. Smithsonian Contributions to Zoology:i.