Using Light to Reduce Sea Turtle Bycatch

By Emma Schillerstrom, SRC intern

We often hear about light pollution as a threat to sea turtle nesting success and hatchling survival. Artificial light near beaches discourages females from nesting, disorients hatchlings toward landing sites where they cannot survive, and can even increase the activity of predators that target their offspring (Silva et al., 2017) (Information About Sea Turtles: Threats from Artificial Lighting, n.d.). However, light may not be all bad for sea turtles. It could help them if employed as a method of bycatch reduction.

Bycatch, or the incidental capture of non-target species when fishing, is a threat to many marine animals (Henry, n.d.). Electric and magnetic devices have been studied as potential strategies to deter sharks from fishing equipment. They work by overstimulating their ampullae of Lorenzini – a sensory organ of jelly-filled pores which detect electrical impulses. Similarly, studies suggest fishers and managers may use light to protect sea turtles from fishing efforts.

Image of a sea turtle caught in fishery netting (Doug Helton, NOAA/NOS/ORR/ERD, Public domain, via Wikimedia Commons).

Bycatch reduction efforts for sea turtles have primarily focused on longlines and bottom trawls rather than set gillnets (Virgili, Vasapollo, & Lucchetti, 2018). TEDs, or turtle excluder devices, consist of a metal grid attached to trawl nets to physically block sea turtles from being able to enter the net, and NOAA has required them since 1987 for use by shrimp fisheries in the Gulf of Mexico and South Atlantic (Southeast Fisheries Science Center, 2019). While TEDs have been modified and improved over time, a similar device does not exist for gillnets.

Image of a turtle excluder device (William B. Folsom, NMFS (US National Oceanic and Atmospheric Administration), Public domain, via Wikimedia Commons)


Drawing of a bottom set gillnet set-up (Joseph William Collins, Public domain, via Wikimedia Commons)

Using acoustic devices is not an effective strategy because sea turtle hearing is not sensitive enough for them to be selectively warded off (Virgili, Vasapollo, & Lucchetti, 2018). Visual deterrence, however, is much more promising since they rely heavily on visual cues for hunting, and bright light can be overstimulating (Virgili, Vasapollo, & Lucchetti, 2018). Chemical light sticks and LED lights have been tested in several studies and were found to be effective (Virgili, Vasapollo, & Lucchetti, 2018). Green, loggerhead, and leatherback sea turtles are sensitive to light in the ultraviolet (UV) range, whereas many commercially coveted fish are not (Wang, Barkan, Fisler, Godinez-Reyes, & Swimmer, 2013). UV-LED lamps are generally more expensive but have a longer life and greater light intensity, perhaps further lending to increased efficacy (Virgili, Vasapollo, & Lucchetti, 2018).

In a 2017 study, researchers at the CN-ISMAR Institute of Marine Sciences in Italy tested the ability of UV light to reduce loggerhead turtle bycatch in gillnets employed in the Mediterranean Sea (Virgili, Vasapollo, & Lucchetti, 2018). They modified nets by lining them with UV lamps spaced five and ten meters apart. By equipping some nets with lights and some without, they could compare the effectiveness of illumination for bycatch reduction through a measure called catch per unit effort, or CPUE. In this case, the catches were measured by weight or by the number of individuals, and the unit of fishing effort was standardized to be 1000 meters of net sitting underwater for 12 hours.

The addition of lamps led to a 100% decrease in bycatch. Sixteen loggerhead turtles were caught in control nets, while none were caught in the UV-lit nets. In this study, about 31% of the bycatch turtles were found dead, but in general, the mortality rate of sea turtles caught by gillnets may be as high as over 60% (Virgili, Vasapollo, & Lucchetti, 2018). All turtles caught were in nets at least 400 meters away from the illuminated nets. Between the control and illuminated nets, there was no significant difference in the CPUE in terms of the number or weight of animals caught once the bycaught turtles were excluded.

There was no observable effect of illumination on target catch efficiency, composition, or size of individuals (Virgili, Vasapollo, & Lucchetti, 2018). These findings suggest that the light did not affect the capture of target species, meaning fishery productivity should not be impacted by the addition of lamps to their nets. Based on optimized lamp spacing of 15 meters and an average net size of 300 meters, the cost of implementing this bycatch reduction device (BRD) would be around $6087 USD for an Italian vessel (Virgili, Vasapollo, & Lucchetti, 2018). A study in the Adriatic Sea in 2018 corroborated the effectiveness of this set-up, producing a 100% reduction in bycatch with two turtles caught in control nets among a mix of 20 illuminated and unaltered nets (Lucchetti, Bargione, Petetta, Vasapo, & Virgili, 2019).

In a 2013 study, researchers worked with volunteer commercial fisherman of a bottom-set gillnet fishery in Mexico (Wang, Barkan, Fisler, Godinez-Reyes, & Swimmer, 2013). They attached UV LEDs every five meters and turned them on in a subset of the nets. Fishery operations were carried out as usual. During the expedition, 332 green turtles were caught, with 209 caught in the control nets and 123 caught in the experimental nets, corresponding to a 39.7% reduction in the mean catch rate of the turtles. The scientists found no significant difference in target fish catch rates or the mean value per unit effort (VPUE) – bycatch profit – between the control and experimental nets (Wang, Barkan, Fisler, Godinez-Reyes, & Swimmer, 2013). The LEDs cost around $2 USD each, but a cost estimate for the whole fishery was not provided (Nuwer, 2013).

An alternate study conducted in northern Peru also tested green turtle bycatch reduction in gillnets (Ortiz et al., 2016). The CPUE of the turtles went down by 63.9% when illumination was added to the nets. Instead of UV light, they used standard LEDs, and the estimated costs for this set-up were 34 USD per turtle or 9200 USD for a whole gillnet fishery in Sechura Bay (Ortiz et al., 2016).

The current aim should be to optimize this bycatch reduction method by finding a balance between effectiveness and cost – in terms of device cost and any potential reductions in fishery catch – for realistic implementation. Currently, a great barrier to implementing light-based BRDs in fisheries appears to be their financial cost. However, TED use is nationally enforced offers hope that the regulated use of other bycatch reduction devices is possible and hopefully on the horizon.


Works Cited

Henry, L. (n.d.). What is bycatch? Understanding and Preventing Fishing Bycatch. (n.d.). Retrieved March 29, 2021, from 

Information about sea turtles: Threats from artificial lighting. (n.d.). Retrieved March 29, 2021, from 

Keledjian, A., Brogan, G., Lowell, B., Warrenchuk, J., Enticknap, B., Chester, G., . . . Cano-Stocco, D. (2014). Wasted Catch: Unsolved Problems In US Fisheries. Oceana.

Lucchetti, A., Bargione, G., Petetta, A., Vasapo, C., & Virgili, M. (2019). Reducing Sea Turtle Bycatch in the Mediterranean Mixed Demersal Fisheries. Frontiers in Marine Science.

Nuwer, R. (2013, November 1). Ultraviolet Illumination Warns Sea Turtles away from Fishing Nets. Retrieved from Scientific American.

Ortiz, N., Mangel, J. C., Wang, J., Alfaro-Shigueto, J., Pingo, S., Jimenez, A., . . . Godley, B. J. (2016). Reducing green turtle bycatch in small-scale fisheries using illuminated gillnets: the cost of saving a sea turtle. Marine Ecology Progress Series, 251-259.

Silva, E., Marcob, A., Graça, J. d., Pérez, H., Abella, E., Patino-Martinez, J., . . . Almeidaa, C. (2017). Light pollution affects the nesting behavior of loggerhead turtles and predation risk of nests and hatchlings. Journal of Photochemistry and Photobiology B: Biology, 240-249.

Southeast Fisheries Science Center. (2019, June 4). History of Turtle Excluder Devices. Retrieved from National Oceanic and Atmospheric Administration.

Virgili, M., Vasapollo, C., & Lucchetti, A. (2018). Can ultraviolet illumination reduce sea turtle bycatch in Mediterranean set net fisheries? Fisheries Research, 1-7.

Wang, J., Barkan, J., Fisler, S., Godinez-Reyes, C., & Swimmer, Y. (2013). Developing ultraviolet illumination of gillnets as a method to reduce sea turtle bycatch. Biology Letters.

A Multi-Faceted and Comprehensive Approach to Understanding San Diego Bay’s Green Turtle Populations and their Origin

By: Casey Dresbach, SRC Intern

Green turtles (Chelonia mydas) have called the South San Diego Bay home since the 1850s  (National Oceanic and Atmospheric Administration (NOAA) Fisheries , 2014). Their origin however remains a mystery. There are beliefs that commercial fishermen of the mid 17th century harvested the species in Mexican waters and brought them back to San Diego Bay (National Oceanic and Atmospheric Administration (NOAA) Fisheries , 2014). Yet upon transit, many believe the turtles may have escaped and perhaps justify the presence of Chelonia mydas population in San Diego Bay today. San Diego Bay, California has been documented as one of the northern-most foraging areas for green turtles in the eastern Pacific (Figure 2). (Dutton, LeRoux, LaCasella, Seminoff, Eguchi, & Dutton, 2018)

Figure 1. Green Sea Turtle. (Caption: Green Sea Turtle, Chelonia mydas.) (Wikimedia Commons, 2010)

Figure 2. Green Sea Turtle Nesting Sites and Foraging Site. (Caption: Nesting sites (circles) of Green Sea Turtle, Chelonia mydas as well as foraging site in the northern part of San Diego Bay.) (Dutton, LeRoux, LaCasella, Seminoff, Eguchi, & Dutton, 2018)

Turtles are marine reptiles whose life history includes a terrestrial component for reproduction, where females lay their eggs on tropical or sub-tropical beaches (Miller 1997). Green turtles in the eastern Pacific Ocean continue to face threats posed by human imprint. Some of these include habitat destruction, incidental capture in commercial fisheries, and often illegal harvesting (National Oceanic and Atmospheric Administration (NOAA) Fisheries , 2014). Green turtles are listed on the IUCN as an endangered species (Dutton, LeRoux, LaCasella, Seminoff, Eguchi, & Dutton, 2018). Hence, many recent studies aim to understand their geographical patterns, how and why they end up in certain regions, to ultimately engage in comprehensive measures of conservation. The greatest threat posed to this species among several other marine and terrestrial animals is in fact the contribution of industrialization. In a 2010 study by (Eguchi, Tomoharu & Seminoff, Jeffrey & A. LeRoux, Robin & H. Dutton, Peter & L. Dutton, Donna), the abundance and survival rates of green turtles in an urban environment was examined. The coexistence of humans and an endangered species was analyzed specifically because of the turtles’ proximity to warm effluent from a power plant nearby. With 99 capture sessions between 1990-2009, 96 turtles were caught. Researchers constructed design-mark-recapture models to estimate abundance and recapture rates. This work provided both the first survival rate and abundance estimates for a green turtle foraging population in industrialized San Diego Bay (Eguchi, Tomoharu et. al 2010).

In 2018, a study was conducted to reveal the origin of the green turtle population in San Diego Bay. In aiming to understand population structure and migration patterns, researchers used a combination of genetics and satellite telemetry to identify the nesting stock origin of Chelonia mydas foraging in San Diego Bay (Dutton, LeRoux, LaCasella, Seminoff, Eguchi, & Dutton, 2018). They examined the stock origin of green turtle foraging aggregation in San Diego using segregated pieces of mtDNA (770 bp) from 121 green turtles captured in San Diego and then compared them to nesting populations across the greater Pacific. Mixed stock analysis was conducted to look at where all these green turtles had originated. This provided indication that the San Diego Bay foraging population originates from eastern Pacific nesting sites, primarily the Revillagigedo Archipelago and the coast of Michoacán, Mexico (Dutton, LeRoux, LaCasella, Seminoff, Eguchi, & Dutton, 2018). Further evaluation of current life history hypotheses was enhanced with the satellite tagging of 3 female green turtles in the San Diego foraging ground (FG) to track migration patterns. After 364 days, one had nested at Socorro Island in Revillagigedo and returned to San Diego Bay and another was tracked nesting at Tres Marias Islands near the Mexican mainland coast. Of critical importance was that all three returned back to San Diego Bay. These findings locate green turtle populations from Revillagigedo Islands and Michoacán as well as the Tres Marias Islands. Their findings supported the mixed stock analysis indication of where the San Diego foraging population originates. With more insight and accumulation of data such as these, heightened conservation efforts in areas such as the Tres Marias Islands, Revillagigedo Islands, and Michoacán can be done.

Further research needs to be conducted to better understand the migration patterns and selection of FG in lieu of the threats posed by the human imprint. Despite scientific efforts, the general public can have a major influence on further conservation of the species. Public outreach and engagement is a multifaceted tool that informs those both inside and outside of scientific communities and often simultaneously establishes a personal connection to an area of concern. Pairing an unfamiliar subject matter with something recognizable will not only incite curiosity but also serve better when trying to relay conservation messages to a wider audience. For example, when a child is introduced to a topic of subject matter in a way that is familiar to them through art or a game, he or she is more likely to engage (See Figure 3). With that personalization comes a greater likelihood that an individual or set of individuals will pursue that newfound connection further. Especially when the matter, such as polluting by the coast, will affect their and those of generations to come. With urbanization on the rise and industrialization seeping further into coastal habitats marine and terrestrial life are suffering at that expense. Disseminating knowledge about how the human imprint is and will continue to deteriorate ecosystems worldwide is crucial to inciting behavioral changes.

Figure 3. Sea Turtle outreach at the San Diego International Airport JPEG aligned in text to the left. (Caption: Public outreach and engagement is crucial to bridging the gap between the informed and the uninformed. The engagement of students is critically important as they become the next generation and future voices of change).

Work Cited:

Dutton, P. H., LeRoux, R. A., LaCasella, E. L., Seminoff, J. A., Eguchi, T., & Dutton, D. L. (2018, November 8). Genetic analysis and satellite tracking reveal origin of the green turtles in San Diego Bay . Marine Biology .

Eguchi, Tomoharu & Seminoff, Jeffrey & A. LeRoux, Robin & H. Dutton, Peter & L. Dutton, Donna. (2010). Abundance and survival rates of green turtles in an urban environment: Coexistence of humans and an endangered species. Marine Biology. 157. 1869-1877. 10.1007/s00227-010-1458-9.

Miller JD (1997) Reproduction in sea turtles. In: Musick JA, Lutz PL (eds) Biology of sea turtles. CRC Press, Boca Raton, pp. 51–82

National Oceanic and Atmospheric Administration (NOAA) Fisheries . (2014, December 24). Green Sea Turtle Research at San Diego Bay. Retrieved from NOAA Fisheries :

NOAA. (n.d.). San Diego Bay Sea Turtles. (P. Dutton, Producer) Retrieved from National Oceanic and Atmospheric Administration (NOAA) Fisheries:

Senko J, López-Castro MC, Koch V, Nichols WC (2010) Immature East Pacific green turtles (Chelonia mydas) use multiple foraging areas off the Pacific coast of Baja California Sur, Mexico: first evidence from mark-recapture data. Pac Sci 64 (1):125–130.

Wikimedia Commons. (2010, May 10). Green turtle swimming over coral reefs in Kona. Retrieved from Wikimedia Commons:

Epibionts and Sea Turtles

By Grant Voirol, SRC intern

Sea turtles are notoriously difficult to study due to their large size and highly migratory behavior. However, a new technique is being utilized to help shed light on their habitat use and migration patterns. When looking at a sea turtle, oftentimes you are not just looking at a sea turtle. What you are looking at is an extensive community of micro and macro organisms that participate in complex interactions (Caine, EA 1986). Attached to the surface of the turtle’s shell are a wide variety of organisms that spend their entire lives traveling the seas with their turtle captain. These organisms, known as epibionts, are each a small piece of the puzzle that can be used to give us a more complete picture of the movement preferences of many species of sea turtles.

By Jun V Lao  [CC BY-SA 4.0 (], via Wikimedia Commons

Epibionts on sea turtles come from a variety of taxa and can range widely in size. Algae, tiny crustaceans, and barnacles of different species can be found on all seven different types of sea turtles and exert a wide range of effects. Barnacles growing on the turtle’s carapace might increase the drag felt my the turtle, making it expend more energy to more through the water but also provide it with camouflage while it rests on the ocean floor. Additionally, other epibionts may feed off of the parasitic epibionts benefitting the turtle (Robinson et al. 2017).

While describing the community structure of these hitchhikers is interesting, we can gain other useful information from them as well. By using just one species, the flotsam crab Planes major, a small crab ranging from 1-2 cm, scientists were able to gain better understanding into the amount of time different turtle species spent near the surface (Pfaller et al., 2014). Using three turtle species, loggerhead, green, and olive ridley, the study found that each species holds significantly different amounts of crabs on their backs. This suggests that the turtles are using their habitats in different ways. The flotsam crab is generally found in surface waters where it makes its home on (as its name implies) flotsam, drifting through the ocean. Therefore, green turtles, which were found to have a very low frequency of flotsam crab on their shell, most likely don’t spend much time at surface waters but mostly stay near the bottom to forage. Similarly, olive ridleys and loggerheads, which were found to have a high frequency of flotsam crab, most likely spend much of their time near the surface (Pfaller et al. 2014).

But this study was conducted using turtles from multiple different areas, what if that had a factor in the results? Another recent study proved that this most likely is not the case. Testing three species of turtles, green, olive ridley, and leatherback, from one nesting location in Costa Rica and using multiple different species of epibionts, it was concluded that each species of turtle does have its own unique community of epibionts (Robinson et al. 2017). All turtles sampled in the study came from the same beach yet exhibited large differences in epibiont diversity.  Leatherbacks, which forage far into the open ocean, were found to have much lower epibiont diversity than the other two species. This makes sense, as the environment that they spend most of their time in is largely uniform. Olive ridleys and green turtles, which occupy varying habitats of the open ocean as well as coastal waters, were found to have an increased level of epibiont diversity. Furthermore, certain epibionts were only found on one species of turtle (Robinson et al. 2017).

Barnacles encrusted on a sea turtle By U.S. Fish and Wildlife Service Southeast Region (Barnacles on Carapace Uploaded by AlbertHerring) [CC BY 2.0 ( or Public domain], via Wikimedia Commons

All of this gives credence to the use of epibionts for habitat and migratory use. Sea turtles use such large habitats, that it is difficult and expensive to attach satellite trackers to large numbers of them. Epibionts can be used as miniature tags, showing us where a turtle has been. Say an epibiont that is only found in a certain area is found on the back of turtle, then we know that the turtle has visited that area recently. This is important for fisheries management. One of the main causes of turtle mortality is from bycatch, when fishing boats catch nontarget species and they die in the process (Wallace et al. 2011). Now that we can gain more and more information about their migratory habits, we are better able to identify hotspots that turtles are likely to visit in their travels and properly protect them. We can also now do this affordably, as no tags need to be used. With this new technique we can help to better protect sea turtles with the help of these little creatures.


Caine E.A. (1986). “Carapace epibionts of nesting loggerhead sea turtles: Atlantic coast of U.S.A.” Journal of Experimental Marine Biology and Ecology, 95, 15-26.

Pfaller, J. B., Alfaro-Shigueto, J., Balazs, G. H., Ishihara, T., Kopitsky, K., Mangel, J. C., … Bjorndal, K. A. (2014). “Hitchhikers reveal cryptic host behavior: New insights from the association between Planes major and sea turtles in the Pacific Ocean.” Marine Biology, 161(9), 2167–2178.

Robinson, N. J., Lazo-Wasem, E. A., Paladino, F. V., Zardus, J. D., & Pinou, T. (2017). “Assortative epibiosis of leatherback, olive ridley and green sea turtles in the Eastern Tropical Pacific.” Journal of the Marine Biological Association of the United Kingdom, 97(6), 1233–1240.

Wallace, B. P., C. Y. Kot, A. D. DiMatteo, T. Lee, L. B. Crowder, and R. L. Lewison. (2013). “Impacts of fisheries bycatch on marine turtle populations worldwide: toward conservation and research priorities.” Ecosphere 4(3), 1-49.

Climate Change effects on sea turtles

By Molly Rickles, SRC intern

Climate change has become an increasing threat to species across the planet. With hotter average temperatures and less predictable weather patterns, humans have undeniably influenced the global climate. The effects of a changing climate are translated to the ocean, where warmer sea surface temperature and rising sea level can alter the marine ecosystem on many levels. These changes can decrease biodiversity and alter the balance of marine ecosystems (Fuentes et al. 2010). These far-reaching effects have extreme consequences for marine life, but some species are impacted more than others. Sea turtles are heavily affected by climate change because of their wide range of habitats (Butt et al. 2016). Since sea turtles lay eggs on beaches but spend their lives in the ocean, they are affected by climate change on both fronts. In addition, climate change may affect survival of juvenile sea turtles, decreasing adult population numbers. Since sea turtles can be widely affected by the far-reaching effects of climate change, it is necessary to implement measures of protection for them. There are ongoing research projects to determine how climate change directly impacts sea turtles and what the best policy options are to combat these effects. This is important because there is little information on how to protect these species from the effects of climate change.

In A, the mean air temperature is shown (black points) against the mean sand temperature (white points) to show how the temperature fluctuates throughout the year. In B, the proportion of nesting by loggerhead turtles for 2005, 2007, 2008, 2009. (Source: Perez, E. A., Marco, A., Martins, S., & Hawkes, L. (2016). Is this what a climate change-resilient population of marine turtles looks like? Biological Conservation, 193, 124-132. doi:10.1016/j.biocon.2015.11.023)

Over the past forty years, sea level has risen at an average of 2mm each year (Butt et al. 2010). This is an alarming statistic especially for low-lying and coastal areas. This is also bad news for sea turtles, which lay their eggs on beaches, which have already been affected by rising sea levels. Beaches are at a high risk for flooding from sea level rise, and when this does occur, the sea turtle eggs are washed away or swamped (Perez et al. 2016). This is especially devastating for endangered species of turtles such as the Hawksbill Turtle or the Australian Loggerhead Turtle, whose numbers are already low and cannot afford a sharp decrease in reproductive output (Butt et al. 2016).

Another major threat to sea turtles is rising sea surface temperature. One of the major effects of climate change is an increase in air temperature, which correlates to an increase in sea surface temperature. This excess thermal stress has especially hard consequences for reptiles, who are exothermic animals that rely on outside temperature to regulate their internal temperature (Perez et al. 2016). An increased sea surface temperature creates a more stressful environment for the sea turtles, but the increased sand temperature has proven to be even more harmful. Since sea turtles lay eggs on beaches, the hotter sand leads to less ideal conditions for laying eggs, which leads to decreased reproductive output. In addition, the sex of the embryos is partially determined by the outside temperature. In this case, a warmer environment leads to a higher percentage of females. It has been estimated that a 2°C increase will lead to a 99.86% female hatching rate (Butt et al. 2016). This, of course, will lead to a very lopsided sex ratio within sea turtle populations, further decreasing the reproductive output and population size.

The image shows all of the nesting sites identified in Australia. This shows that sea turtles have a wide range of habitats. This is beneficial because it allows policy makers to protect certain beaches where sea turtles are known to use for nesting. (Source: Butt, N., Whiting, S., & Dethmers, K. (2016). Identifying future sea turtle conservation areas under climate change. Biological Conservation, 204, 189-196. doi:10.1016/j.biocon.2016.10.012)

All of these threats to sea turtles could have devastating effects on their populations. Decreases in sea turtle populations have already been observed, and most sea turtle species are already on the endangered species list. Due to the fact that sea turtles are dealing with a multitude of threats, it becomes increasingly difficult to find management techniques to combat these issues (Fuentes et al. 2010). Some of the more straightforward strategies deal with the sea turtle’s habitat on land, since it is easier to manage beaches than the open ocean. Since sea turtles rely on certain beaches for nesting, it is possible to protect these areas to preserve the nesting habitat (Fuentes et al. 2010). This has already been implemented in many coastal areas, where nesting sites are blocked off from public use. In addition, many coastal areas have regulations to control nighttime lighting near nesting beaches so the sea turtle hatchlings have a better chance of making it to the ocean. By protecting these important nesting areas, sea turtles will continue to be able to lay eggs safely, and more hatchlings will survive to adulthood. This will lead to an increase in sea turtle population, thus preventing their numbers from decreasing even more rapidly.

In addition to managing habitat on land, it is also important to protect sea turtles in the ocean. One way to do this is to implement marine protected areas in important habitats for the turtles, such as areas where their young mature. However, the main issue affecting sea turtles is climate change, and this must be dealt with at a larger scale. To reduce the overall impact of climate change not only on sea turtles, but every other species, it is necessary to reduce the emissions of greenhouse gases and create a more sustainable way of life. There have already been steps made towards this goal, including the Paris Climate Accord, along with numerous clean air emission standards, but it is not enough. Stricter environmental regulations and environmental conservation education will help reach a more sustainable life, as well as protect sea turtles along with a multitude of other species


Fuentes, M., & Cinner, J. (2010). Using expert opinion to prioritize impacts of climate change on sea turtles’ nesting grounds. Journal of Environmental Management, 91(12), 2511-2518. doi:10.1016/j.jenvman.2010.07.013

Butt, N., Whiting, S., & Dethmers, K. (2016). Identifying future sea turtle conservation areas under climate change. Biological Conservation, 204, 189-196. doi:10.1016/j.biocon.2016.10.012

Perez, E. A., Marco, A., Martins, S., & Hawkes, L. (2016). Is this what a climate change-resilient population of marine turtles looks like? Biological Conservation, 193, 124-132. doi:10.1016/j.biocon.2015.11.023

Shark tagging with Empowered Youth

by Alison Enchelmeier, RJD student

On Saturday morning I headed over to Crandon Marina. As I drove down the causeway, the weather promised a great day with not a cloud in the sky. Our guests for the day were a brand new group, Empowered Youth, and several family members of graduating interns. With our gear loaded onto the boat and everyone excited for tagging we headed out to the Belzona wreck.

On the trip out, Jake explained what we would be doing and how our guests would be helping us with our research. We set our lines east of the wreck. Initially, some of our guests were a bit shy, but with a little encouragement they were soon pulling lines alongside us.

A student pulls in a drumline to check for a shark

A student pulls in a drumline to check for a shark

After letting the lines soak for an hour, we returned to pull lines. Early on in the day we caught our first shark. As line 3 was pulled up, something tugged on the line. With a shout of “Shark on!” the boat became a flurry of activity as the RJD team prepared to bring the shark to the boat. As the line was pulled in we predicted what we caught, the consensus being a nurse shark. We were pleasantly surprised when a 204 cm (~6.6 ft) sandbar shark came to the surface.

The students were prepared as they helped us work up the shark, bursting with excitement as they got to feel the sandpaper like skin of the shark and take measurements. Any fear of the shark disappeared as the shark remained calm during the whole procedure. Moments like these just highlight how important it is to give people first hand experience with sharks to help dispel the stigma against them. After the quick workup the shark was released, swimming down into the ocean until we could no longer see it. The first shark set the tone for the day as our guest’s infectious enthusiasm grew.


RJD intern Hanover draws blood from a shark’s caudal vein

RJD intern Hanover draws blood from a shark’s caudal vein

More sharks were soon to follow as we caught four more sharks, all in the same set. Our second shark was a nurse, followed by a blacktip. At only 126 cm (~4.1ft) it was one of the smallest sharks I’d seen while working on the boat! After that we caught two more nurse sharks. One popped off the hook just before we managed to get it onto the platform while the last nurse was a whopping 258 cm (~8.4 feet)! We continued to pull and set 20 more lines but we didn’t catch any more sharks that day. Even so, our guests remained enthusiastic, asking questions and pulling up drumlines like pros. While we caught no more sharks on our drumlines we managed to see a sea turtle resting at the surface.

An unexpected treat, a sea turtle!

An unexpected treat, a sea turtle!

In all this was a great trip with a wonderful group. Thank you to Empowered Youth for being such a great group and good luck to our graduating interns!

Impact of Costa Rican Longline Fishery on its Bycatch Species

by Fiona Graham, RJD Graduate Student and Intern

Bycatch, the incidental catch of non-target species, tends to be high when using non-discriminatory fishing methods, such as longlining. Longline fisheries, such as that of Costa Rica, generally target mahi mahi and silky sharks, however data collected by an observer program shows that a large percentage of their catch is olive ridley turtles and non-target shark species. These longlines literally consist of long lines of baited hooks that stretch for miles and soak in the water for hours. Unfortunately, fisheries bycatch is one of the primary reasons for population declines in sharks, rays and sea turtles.  This is due to their life history characteristics, such as long lifespans, late age of maturity, and few offspring, that make them inherently sensitive to these high rates of mortality.

In a recent paper describing the impact of the Costa Rican longline fishery on its bycatch species, authors Derek Dapp et al. examine the catch numbers, capture locations, seasonality and body size of non-target sharks, sting rays, bony fish and olive ridley turtles. The paper uses data from the fishery observer program from 1999 to 2010 where observations were conducted onboard six medium scale vessels out of a Costa Rican fleet of 350 vessels. One troubling, but not so surprising result of their analysis found that the olive ridley turtle was the second most abundant species captured by the fishery. Two of the six major beach nesting aggregations for olive ridleys in the world are in Costa Rica, and populations at these two main nesting beaches have declined since the 1980s. Based on (most likely an underestimate) of the number of olive ridleys caught by the fishery – 290,500 a year – the impact of the Costa Rican longline fishery on olive ridleys needs to be greatly reduced.

Olive ridley sea turtle (photo: Wikimedia Commons).

Olive ridley sea turtle (photo: Wikimedia Commons).

Large numbers of sharks and rays are also caught as bycatch by the longline fishery, where rays are thrown back overboard and sharks are retained for their fins, meat, or as bait. Notably, the authors were able to identify a blacktip nursery near the Osa Peninsula due to the presence of high catch rates of juvenile blacktip sharks during the spring and summer months.

Catch per 1000 hooks on longlines for blacktip sharks, indicating the presence of a nursery ground near the Osa Peninsula (figure: Dapp et al. 2013).

Catch per 1000 hooks on longlines for blacktip sharks, indicating the presence of a nursery ground near the Osa Peninsula (figure: Dapp et al. 2013).

As well as affecting blacktip sharks, the authors found that the fishery affected the other two species of shark that they examined, silky sharks and pelagic thresher sharks. They concluded that there is a clear need for more effective management of the Costa Rican fishery.

While this is an obvious conclusion to be made here based on the data available, the specific management protocol and how that management is put into place and enforced is a more complicated discussion. In this recent paper, Dapp et al. criticize many fisheries biologists for believing that the only acceptable methods of reducing bycatch are those that do not inconvenience fisherman or reduce their target catch substantially. They conclude that the only solution is through reduction of fishing effort through creation of marine protected areas or time area closures. They also suggest placing observers on at least 50% of medium and larger fishing vessels to acquire more data on fishing methods and bycatch and to educate fishermen to improve their techniques and to release bycatch species alive.

Finding “The Lost Year” Sea Turtles: The potential threats and conservation implications

by Ashley Hill,
Marine conservation student

Open ocean habitats are innately difficult to access. As a result, the majority of research on sea turtles is restricted to beach and coastal areas. However, there is a time span of several years from when hatchlings venture offshore to when the larger, juvenile turtles return to coastal waters. It is thought individuals of this life stage must live in the open ocean, but the lack of concrete, direct evidence has led to the term “the lost years” (Carr et al. 1978). The majority of the open ocean is desert like, with vast areas of minimal amounts of food or shelter. Oceanic processes push water together to form areas of convergence. These areas typically contain higher levels of plankton and therefore a higher abundance of other organisms that take advantage of the increased food source. In the Atlantic, Caribbean and Gulf of Mexico, convergence areas are often traced by lines of a branching, floating alga called Sargassum (Thiel and Gutow 2005, Butler et al 1983). Each individual clump of Sargassum is less than 80cm, but mats spanning hundreds of meters wide and tens of thousands of meters long can be formed in convergence areas (Butler et al 1983). In a way, these Sargassum drift communities can provide an oasis of nourishment and shelter for an assortment of organisms, including sea turtles.

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Incidental captures of sea turtles in the driftnet and longline fisheries in northwestern Morocco

By Ana Zangroniz, Marine Conservation Student

One important issue in marine conservation lies with the preservation of a healthy sea turtle population. Of the seven species (Leatherback, Green, Loggerhead, Hawksbill, Olive Ridley, Kemps Ridley, and Flatback), six are endangered or threatened. Besides the fact that these creatures are visually stunning, they play a crucial role in marine ecosystems, which can directly affect human beings and our livelihoods. For example, green sea turtles feed on seagrass. This grazing keeps seagrass beds healthy, helping maintain critical habitats for many life stages of scallops and mollusks that humans depend upon as a food source (Carroll et al. 2012, Nizinski 2007). Additionally, when female sea turtles come ashore to lay their eggs, beach ecosystems are enriched, as turtle eggs are a significant source of nutrients for plant life (Vander Zanden et al. 2012).

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