Tuesday, June 14, 2016

Smalltooth Sawfish Population Collapse and Plans for Recovery, by Logan McElroy

Smalltooth Sawfish (Pristis pectinata) are a species of concern that have been in decline for some time now, and much of it has to do with human activities in their home range.   After being placed on the Endangered Species list in 2003, and being listed as “critically endangered” by the IUCN, there have been a number of recovery plans established in order to protect the species (NMFS 2009).  The smalltooth sawfish  is a cartilaginous marine fish in the Class Chondrichthyes and suborder Elasmobranchii (NMFS 2009).  They are known to be one of the most critically endangered fish in the entire world, with most of the species being concentrated around the waters of southwestern Florida (Chapman et al. 2011).  The current levels of smalltooth sawfish is thought to be less than 5% of its historic abundance (NMFS 2009).  Despite these widespread declines that have occurred, some studies show, such as the one by Chapman et al. in 2011, that smalltooth sawfish populations have still been able to retain a high level of genetic diversity (Chapman et al. 2011).  Statistics such as these provide some optimism as to the species potential to be recovered, if the right steps are taken.  Recovery, as defined by the National Marine Fisheries Service in their Smalltooth Sawfish Recovery Plan (2009), involves initially downlisting (changing ESA status from endangered to threatened) and ultimately delisting the species.   According to the NMFS (2009), this would involve preventing human-caused mortality, protection of habitats, and reoccupation of areas from which the fish was extirpated.  
Smalltooth Sawfish (Pristis pectinata)

Smalltooth sawfish are a tropical marine elasmobranch that often utilizes estuaries as a part of their habitat (NMFS 2009).  They have been found to tend to stay in coastal waters, spending most of their time in shallow areas (Carlson et al. 2014).  This tendency could maybe explain their historic frequent encounters with humans, and possibly why they have been affected so much by human development and fishing activities.  Their name comes from their saw-like rostrum, with transverse teeth on both sides (NMFS 2009).  The range of the smalltooth sawfish has become highly restricted, contributing to the population collapse.  Their range was once thought to extend all the way up the eastern coast of the United States to New York, but now their range is restricted to the southwestern waters of Florida (NMFS 2009).  They have also been found to live near some of the islands of the Bahamas (Guttridge et al. 2015).   
Distribution of reported encounters with smalltooth sawfish along the US coast, 1998 to 2008 (Wiley and Simpfendorfer 2010)
Declines in smalltooth sawfish populations can be attributed to a number of factors, most of them being anthropogenic causes.  The drastic declines in sawfish populations have been attributed mostly to being bycatch in commercial and recreational fisheries and to the depletion of suitable habitat (NMFS 2009).  As stated before, the main reason for the smalltooth sawfish’s decline is by bycatch.  According to Seitz and Poulakis (2006), one of the main reasons for the decline of the species is mortality caused from bycatch in net fisheries.  Their low rates of population increase coupled with their high catchability (often caused by their rostra being tangled in nets) has contributed to their decline (Dulvy et al. 2016).  The Recovery Plan by NMFS (2009) also states that their slow reproductive rates are a limiting factor in their overall recovery, so it could take a very long time for any sort of positive change in population numbers to become evident.  Recovery, or stage where managers could delist the species, would require that there be strict adherence to regulations protecting smalltooth sawfish from harm, as well as protecting their critical habitats. 

Because of this decline, many plans have been put in place in attempt to recover the smalltooth sawfish.  Some of the data used to direct the study of related to smalltooth sawfish was done through examining the records of public encounters with the fish (Wiley and Simpendorfer 2010).  Wiley and Simpendorfer found in their study that most of the bigger fish were located towards the center of the sawfish’s range in southern Florida, as well as that most fish were observed in estuarine and nearshore habitat.  It was also found by Wiley and Simpendorfer that most of the smaller fish were found in shallower waters.  Many studies on smalltooth sawfish reference these data that were collected via voluntary encounter reports by the public, as they found some important habitat information.  Norton et al. (2012) states that protection of critical habitat would be an important step in smalltooth sawfish recovery, especially in the protection of nursery areas for juvenile sawfish.   

There is a lot to be done if the smalltooth sawfish is to be delisted, let alone just downlisted to simply “endangered” by the IUCN or to “threatened” on the endangered species list.  According to the National Marine Fisheries Service’s Smalltooth Sawfish Recovery Plan, this will involve programs to educate the public, establishment of guidelines for safely releasing sawfish, and laws at the state and federal level (NMFS 2009).  Carlson and Simpfendorfer (2015) state that, optimistically, smalltooth sawfish can be recovered only if fishing-related mortality is kept to an absolute minimum.  As Seitz and Poulakis (2006) point out, many of the reasons for declines, such as pollution and direct harm by humans, can be decreased if the public becomes more educated on the topic of smalltooth sawfish.  It seems that this goal of education could maybe be reached, considering all of the voluntary public involvement that was used to generate much of the data used in many studies.  It is also important to note the need for sound management involving development in areas where smalltooth sawfish were known to live.  But with increasing populations, and so much development in areas where smalltooth sawfish historically thrived, this may not be likely.  For example, the areas in which the sawfish have nurseries should be considered in decisions relating to freshwater withdrawals and development on the coasts such as changing the shoreline (Poulakis et al. 2012).  If all of these things are achieved, it is quite possible that the smalltooth sawfish can be recovered, but whether all of these things can happen together for the benefit of the sawfish is yet to be seen.  

Carlson, J. K., Gulak, S. J. B., Simpfendorfer, C. A., Grubbs, R. D., Romine, J. G., & Burgess, G. H. (2014). Movement patterns and habitat use of smalltooth sawfish, Pristis pectinata, determined using pop-up satellite archival tags. Aquatic Conservation-Marine and Freshwater Ecosystems, 24(1), 104-117. doi: 10.1002/aqc.2382
Carlson, J. K., & Simpfendorfer, C. A. (2015). Recovery potential of smalltooth sawfish, Pristis pectinata, in the United States determined using population viability models. Aquatic Conservation-Marine and Freshwater Ecosystems, 25(2), 187-200. doi: 10.1002/aqc.2434
Chapman, D. D., Simpfendorfer, C. A., Wiley, T. R., Poulakis, G. R., Curtis, C., Tringali, M., . . . Feldheim, K. A. (2011). Genetic Diversity Despite Population Collapse in a Critically Endangered Marine Fish: The Smalltooth Sawfish (Pristis pectinata). Journal of Heredity, 102(6), 643-652. doi: 10.1093/jhered/esr098
Dulvy, N. K., Davidson, L. N. K., Kyne, P. M., Simpfendorfer, C. A., Harrison, L. R., Carlson, J. K., & Fordham, S. V. (2016). Ghosts of the coast: global extinction risk and conservation of sawfishes. Aquatic Conservation-Marine and Freshwater Ecosystems, 26(1), 134-153. doi: 10.1002/aqc.2525
Guttridge, T. L., Gulak, S. J. B., Franks, B. R., Carlson, J. K., Gruber, S. H., Gledhill, K. S., . . . Grubbs, R. D. (2015). Occurrence and habitat use of the critically endangered smalltooth sawfish Pristis pectinata in the Bahamas. Journal of Fish Biology, 87(6), 1322-1341. doi: 10.1111/jfb.12825
National Marine Fisheries Service. 2009. Recovery Plan for Smalltooth Sawfish (Pristis pectinata). Prepared by the Smalltooth Sawfish Recovery Team for the National Marine Fisheries Service, Silver Spring, Maryland.
Norton, S. L., Wiley, T. R., Carlson, J. K., Frick, A. L., Poulakis, G. R., & Simpfendorfer, C. A. (2012). Designating Critical Habitat for Juvenile Endangered Smalltooth Sawfish in the United States. Marine and Coastal Fisheries, 4(1), 473-480. doi: 10.1080/19425120.2012.676606
Poulakis, G. R., Stevens, P. W., Timmers, A. A., Stafford, C. J., & Simpfendorfer, C. A. (2013). Movements of juvenile endangered smalltooth sawfish, Pristis pectinata, in an estuarine river system: use of non-main-stem river habitats and lagged responses to freshwater inflow-related changes. Environmental Biology of Fishes, 96(6), 763-778. doi: 10.1007/s10641-012-0070-x
Seitz, J. C., & Poulakis, G. R. (2006). Anthropogenic effects on the smalltooth sawfish (Pristis pectinata) in the United States. Marine Pollution Bulletin, 52(11), 1533-1540. doi: 10.1016/j.marpolbul.2006.07.016
Wiley, T. R., Simpfendorfer, C. A. (2010).  Using public encounter data to direct recovery efforts for the endangered smalltooth sawfish Pristis pectinata.  Endangered Species Research 12(1). 179-191.

1 comment:

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