Paper: Howell, E. A., A. Hoover, S. R. Benson, H. Bailey, J. J. Polovina, J. A. Seminoff, and P. H. Dutton. 2015. Enhancing the TurtleWatch product for leatherback sea turtles, a dynamic habitat model for ecosystem-based management. Fisheries Oceanography 24:57-68. DOI: 10.1111/fog.12092
Everybody loves sea turtles, right? I know I do. Last Saturday was even World Turtle Day (not that that specifically applied to sea turtles, but they are included). Sea turtles are among the ocean’s charismatic megafauna. They play important roles in many habitats: grazers in seagrass beds, nutrient deposition in beach/dune habitats, and consumers of jellyfish, to name a few. They are also culturally important to many coastal peoples, some of which historically or currently harvest the eggs or adults themselves for their meat or carapaces (shells). They are also frequently depicted in art and have increasingly become the basis for ecotourism, including trips to protect sea turtle nest sites.
These conservation efforts exist because, unfortunately, sea turtle populations are threatened or endangered worldwide due to anthropogenic activities including coastal development, oil spills, encounters with marine debris such as plastic bags, and interactions with fishing gear. The latter is called bycatch, the unintentional harvest of non-target organisms when fishing. Fisheries are important in supplying food rich in protein to many human populations and as a major source of economic income. But, unfortunately, sometimes non-target organisms are captured and killed as a result of fishing activities.
The following case study describes an attempt at ecosystem-based management to balance the needs of humans and maintain biodiversity and sustainable resources. It also presents an example of dynamic management (a strategy in which the area managed moves as the target species does) for migratory species, such as sea turtles.
The Case of the Hawaiian Longline Fisheries
In Hawai’i, swordfish are harvested using pelagic longlines (Fig. 3). These types of fisheries have a problem with sea turtle and shark bycatch. As a result, these fisheries are regulated with a hard-cap. If the fishery exceeds the limit (or cap) for bycatch of an endangered species (for example 16 leatherback sea turtles), the fishery is closed for the rest of the year. Therefore, it is to the benefit of fishermen to avoid these species so they can continue fishing throughout the year.
A Possible Solution
But how to accomplish that? Well, NOAA came up with one possible way: TurtleWatch! Version 1 was designed by NOAA to minimize fisheries interactions with loggerhead sea turtles. Just look at that pretty and intuitive map below that TurtleWatch provides fishermen to help them avoid turtles (Fig. 4)! The program incorporated previous work that had determined that loggerheads were most often caught in the longline gear in the first quarter of the year in areas where sea surface temperatures were below 18.5° C and then modified (version 1.5) to specify the range between 17.5° C and 18.5° C. (Fig. 4). The first version of TurtleWatch was successful in shifting fishery behavior, encouraging fishermen to focus their efforts during different times of year and in areas not likely to overlap with loggerheads. This shift unfortunately may have increased the interactions between the fishery and leatherback sea turtles.
Therefore, we now have TurtleWatch version 2! The program was upgraded with data from fisheries, such as catch per unit effort—the number of target organisms, in this case swordfish, caught per “unit effort”, in this case defined as the number of hooks deployed—and bycatch from the fishermen’s reports and NOAA’s observer program, as well as from satellite tagging. Researchers found that leatherbacks migrating westward moved within waters with an SST range between 22.5° and 23.5°C, while those migrating east either used that same range or the range of 16.5° and 17.5°C. They also learned that catch per unit effort of the swordfish is, in some cases, actually lower where the turtles are most likely to occur. For example, catch per unit effort is lower east of the 140° W longitude line while leatherback occurrence is higher. Therefore, fishermen can both maximize their catch per unit effort and avoid turtle bycatch by remaining west of there.
Given the data, the new and improved TurtleWatch program produces a daily map just like previous versions with real-time ocean current and SST, but showing where both loggerhead and leatherback sea turtles are most likely to be. The program indicates where fishermen should focus their harvesting based on 2 rules: 1) a static boundary in which fishing occurs only west of 140° W and 2) a dynamic boundary to avoid fishing in SST ranges of 17-18.5°C and 22.5-23.5°C (Fig. 5). Pretty straightforward and useful, right?!?!
Innovation is going to be important in finding solutions to our world’s problems. TurtleWatch is a very cool program that makes it easier for fishermen to avoid sea turtle bycatch that is detrimental to their fishery and their source of income. It is also a great example of dynamic management for migratory species, a field that will likely gain more attention and traction. I think this project describes one way in which technological innovation can benefit both endangered species and humans, reminding us that those two ends are not mutually exclusive! I personally would love to see more programs like this and hope it is successful!
Share Your Thoughts: What do you think of this program? Should/Could this type of technology be applied to other endangered species or spread to other regions of the world?
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I am a graduate of the University of Notre Dame (B.S.) and the University of Rhode Island (M.S.). I now work in southwest Florida, contributing to the management of an estuary. I am fascinated by the wonders of nature, the land-sea interface, ecology and human disturbance (and solutions!). On a personal level, I am a chocoholic, love to travel and be outside, and relax by reading or spending time with my emotionally needy dogs!