Saving the swimming dead

This is Saltwater Science's first guest post, written by historical ecologists Loren McClenachan, assistant professor at Colby College, and Ruth Thurstan, postdoctoral scholar at the University of Queensland.

Conservation biologists who study widely distributed but rare species face the challenge of designing conservation policies while lacking basic information about their distribution and abundance. Sawfish are geographically widespread, once occurring in 90 countries, but are now so rare that sightings off certain coastlines may occur only every 15-20 years. As reported in Aquatic Conservation¹, Nicholas Dulvy and other members of the IUCN Shark Specialist Group analyzed more than 8000 observations of sawfish across two centuries to document long-term change and determine present conservation status, which they linked to specific management actions.

Scientists should know a lot about sawfish. Their large size, unique toothed rostra (used to stun and kill prey), and coastal distribution have ensured high levels of human interaction throughout history. Individuals are frequently entangled in fishing nets and lines, their rostra have been dried and sold as curios, and they are the subjects of art, from ancient Roman mosaics to 20^th century Panamanian folk art. But as recently as 2013, taxonomists revised the sawfish family, Pristidae, to include just five species, instead of seven as previously identified².

Sawfish are highly extinction prone. The IUCN team compiled biological data for all five species, detailing ways in which their biology is more similar to large mammals than most fish. At more than seven meters, the largest sawfish species are among the biggest chondrichthyans (sharks and rays), smaller only than the massive basking and whale sharks. Individuals live more than 50 years and give birth to a small number of pups, making them slow to replace themselves. They inhabit nearshore, highly threatened environments like mangroves where their characteristic rostra make them extremely susceptible to entanglement in fishing gears. Finally, individuals have been targeted for high value body parts shipped around the world, including fins for Asian soup, rostra for curios in North America and Europe, and teeth for cockfighting spurs in South America.

Substantial declines have already occurred. The team summarized the largest collection of known encounter records to date-more than 8000 reported sightings of sawfish between the years 1791 and 2011-to complete the first analysis of global sawfish distribution through time. The result is a stunning 80% loss of historical range, with 43 countries that have lost one or more species. These steep declines were previously masked by a lack of capacity to assemble fragmented records over such large spatial and temporal scales, a shortfall first recognized more than a decade ago. George Burgess of the Florida Museum of Natural History created the International Sawfish Encounter Database³ for citizens to report contemporary sightings and compile historical records of past encounters. That this crowd-sourced information-which includes descriptive observations over more than two centuries-became the backbone of this global conservation assessment can be credited to the rise of a new research approach over the last decade. Beginning in the 1990s, marine scientists pointed to the need for novel historical data to fill critical data shortfalls^4,5. Subsequently, a wave of new historical ecology research has swept across the conservation landscape, providing legitimacy to masses of previously unused data, and facilitating conservation of widespread and data-poor species like sawfishes.

Together with the long-term declines made clear by this research are the insidious uncertainties surrounding sawfishes' current status. Fifty-six countries have at least one species documented as ‘presence uncertain,' which implies undetected local and regional extinctions. Undetected extinctions are frequent in marine environments, particularly where data are sparse and difficult to collect. In previous research, Dulvy and colleagues⁶ estimated that the average lag time between the last sighting of an organism and the reported date of extinction was more than 50 years. For slowly reproducing species like sawfish, extinctions may be already inevitable, a phenomenon known as extinction debt. Because of their inability to reproduce fast enough, adults exist effectively as the ‘swimming dead'⁷. Finally, from the broader perspective of ecosystems, crumbling of species diversity also may go undetected. The IUCN team explain that two, three or even four sawfish species historically inhabited the same environments, but these areas of co-existence - where functional redundancy exists - are now few. Consequently, while we may know little about their ecosystem role, whatever it was is now highly diminished.

Lest the sawfish story begin to sound hopeless, it is also apparent that depletion to low levels is not irreversible. In 2003, the United States listed Smalltooth Sawfish as ‘Endangered' under the Endangered Species Act (ESA). The population is small-reduced by 95% to only a couple of thousand individuals-but since protection has been increasing by approximately 5% annually⁸. The International Sawfish Encounter Database also originated as part of the US ESA process, facilitating both this latest global assessment and steps towards conservation around the world. In stark contrast, populations of largetooth sawfish in Lake Nicaragua collapsed after a directed fishery caught approximately 100,000 individuals in five years. Coupled with plans to break ground on a new canal directly through Lake Nicaragua this December⁹, the chance of recovering this unique freshwater population is slim. This geographical patchiness in conservation outcomes highlights an insidious problem: marine species with large ranges face greater risk, particularly when these ranges encompass multiple countries where coordinated action is lacking^10,11.

The publication of this paper and the Global Sawfish Conservation Strategy corresponds with several global events that may improve conservation for these species. Sawfish are the only chondrichthyan currently listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), which bans the international commercial trade of all sawfish species. Furthermore, in November 2014, member states of the Convention on the Conservation of Migratory Species of Wild Animals have an opportunity to protect all five species of sawfish, which have been highlighted for inclusion in Appendices I and II. These listings would obligate member states to coordinate their management and work together to conserve sawfish, providing a platform for global-scale protection and strengthening the current trade bans that are in force through CITES. Recovery of rare and vulnerable species is possible, and it is time to protect the world's sawfish populations, lest these iconic creatures join the ranks of the forever lost.

References

¹Dulvy, N. K., Davidson, L. N., Kyne, P. M., Simpfendorfer, C. A., Harrison, L. R., Carlson, J. K., & Fordham, S. V. (in press; 2014). Ghosts of the coast: global extinction risk and conservation of sawfishes. Aquatic Conservation: Marine and Freshwater Ecosystems.

²Faria, V. V., McDavitt, M. T., Charvet, P., Wiley, T. R., Simpfendorfer, C. A., & Naylor, G. J. (2013). Species delineation and global population structure of Critically Endangered sawfishes (Pristidae). Zoological Journal of the Linnean Society, 167(1), 136-164.

³International Sawfish Encounter Database, Florida Museum of Natural History; available at http://www.flmnh.ufl.edu/fish/sharks/sawfish/sawfishdatabase.html

⁴Pauly, D. (1995). Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology & Evolution, 10(10), 430.

⁵Jackson, J. B. C., et al. (2001). Historical overfishing and the recent collapse of coastal ecosystems. Science, 293(5530), 629-637.

⁶Dulvy, N. K., Sadovy, Y., & Reynolds, J. D. (2003). Extinction vulnerability in marine populations. Fish and fisheries, 4(1), 25-64.

⁷ Kuussaari, M., et al. (2009). Extinction debt: a challenge for biodiversity conservation. Trends in Ecology & Evolution, 24(10), 564-571.

⁸Carlson, J.K, Osborne, J. Relative abundance of smalltooth sawfih (Pristis pectinata) based on the Everglades National Park Creel Survey. NOAA Technical Memorandum NMFS-SEFSC-626 (2012).

⁹Meyer, A., & Huete-Perez, J. A. (2014). Conservation: Nicaragua Canal could wreak environmental ruin. Nature, 506(7488), 287-289.

¹⁰ Pimm, S. L., et al. (2014). The biodiversity of species and their rates of extinction, distribution, and protection. Science, 344(6187), 1246752.

¹¹Dulvy, N. K., et al. (2014). Extinction risk and conservation of the world's sharks and rays. Elife, 3.