Environmental Influences on the Spatial Ecology of Juvenile Smalltooth Sawfish (Pristis pectinata): Results from Acoustic Monitoring

PLOS ONE, Feb 2011

To aid recovery efforts of smalltooth sawfish (Pristis pectinata) populations in U.S. waters a research project was developed to assess how changes in environmental conditions within estuarine areas affected the presence, movements, and activity space of this endangered species. Forty juvenile P. pectinata were fitted with acoustic tags and monitored within the lower 27 km of the Caloosahatchee River estuary, Florida, between 2005 and 2007. Sawfish were monitored within the study site from 1 to 473 days, and the number of consecutive days present ranged from 1 to 125. Residency index values for individuals varied considerably, with annual means highest in 2005 (0.95) and lowest in 2007 (0.73) when several P. pectinata moved upriver beyond detection range during drier conditions. Mean daily activity space was 1.42 km of river distance. The distance between 30-minute centers of activity was typically <0.1 km, suggesting limited movement over short time scales. Salinity electivity analysis demonstrated an affinity for salinities between 18 and at least 24 psu, suggesting movements are likely made in part, to remain within this range. Thus, freshwater flow from Lake Okeechobee (and its effect on salinity) affects the location of individuals within the estuary, although it remains unclear whether or not these movements are threatening recovery.

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Environmental Influences on the Spatial Ecology of Juvenile Smalltooth Sawfish (Pristis pectinata): Results from Acoustic Monitoring

et al. (2011) Environmental Influences on the Spatial Ecology of Juvenile Smalltooth Sawfish (Pristis pectinata): Results from Acoustic Monitoring. PLoS ONE 6(2): e16918. doi:10.1371/journal.pone.0016918 Environmental Influences on the Spatial Ecology of Juvenile Smalltooth Sawfish (Pristis pectinata ): Results from Acoustic Monitoring Colin A. Simpfendorfer 0 Beau G. Yeiser 0 Tonya R. Wiley 0 Gregg R. Poulakis 0 Philip W. Stevens 0 Michelle R. Heupel 0 Brian Gratwicke, Smithsonian's National Zoological Park, United States of America 0 1 Center for Shark Research, Mote Marine Laboratory, Sarasota, Florida, United States of America, 2 Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Charlotte Harbor Field Laboratory , Port Charlotte, Florida , United States of America To aid recovery efforts of smalltooth sawfish (Pristis pectinata) populations in U.S. waters a research project was developed to assess how changes in environmental conditions within estuarine areas affected the presence, movements, and activity space of this endangered species. Forty juvenile P. pectinata were fitted with acoustic tags and monitored within the lower 27 km of the Caloosahatchee River estuary, Florida, between 2005 and 2007. Sawfish were monitored within the study site from 1 to 473 days, and the number of consecutive days present ranged from 1 to 125. Residency index values for individuals varied considerably, with annual means highest in 2005 (0.95) and lowest in 2007 (0.73) when several P. pectinata moved upriver beyond detection range during drier conditions. Mean daily activity space was 1.42 km of river distance. The distance between 30-minute centers of activity was typically ,0.1 km, suggesting limited movement over short time scales. Salinity electivity analysis demonstrated an affinity for salinities between 18 and at least 24 psu, suggesting movements are likely made in part, to remain within this range. Thus, freshwater flow from Lake Okeechobee (and its effect on salinity) affects the location of individuals within the estuary, although it remains unclear whether or not these movements are threatening recovery. - Funding: Financial support was provided by NOAA Fisheries Office of Protected Resources, South Florida Water Management District, National Fish and Wildlife Foundation, National Geographic Committee for Research and Exploration, The Disney Wildlife Conservation Fund, and the Florida Fish and Wildlife Conservation Commission. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Environmental influences on the spatial ecology of elasmobranchs have been poorly investigated. The effect of seasonal temperature changes on the broad-scale distribution of species has been widely reported [1], although the mechanisms and specific tolerances have rarely been investigated [2,3]. Research has revealed that salinity plays an important role in the movement and distribution of nearshore and estuarine species [4]. Bull sharks (Carcharhinus leucas) are able to tolerate a wide range of salinities [5], but young juveniles have recently been shown to move so they remain at salinity levels between 7 psu and 20 psu [6,7,8]. Heithaus et al. [9] also demonstrated that for bull sharks in some estuarine habitats dissolved oxygen levels can influence movements and distribution more than salinity. Other nearshore species that have been shown to have movements affected by salinity include bonnetheads (Sphyrna tiburo) [10], sandbar sharks (Carcharhinus plumbeus) [11], and bat rays (Myliobatis californica) [12]. Given the importance of salinity, changes in freshwater flow regimes into estuaries as a result of climate change or water management practices will affect populations by potentially changing their distributions. The sawfishes (Family Pristidae) were once common inhabitants of tropical and subtropical inshore, estuarine, and freshwater areas world-wide [13]. However, pressure from fishing and habitat loss have led to population declines [14] and all species are currently Critically Endangered on the IUCN Red List (see www.redlist.org); and some species are protected under national endangered species legislation. The smalltooth sawfish (Pristis pectinata) was listed as Endangered by the United States National Marine Fisheries Service (NMFS) and protected by the Endangered Species Act in 2003. Although once prevalent throughout Florida and commonly encountered from Texas to North Carolina, P. pectinata currently occurs mostly in south and southwest Florida [15,16,17]. It grows to over 500 cm STL (stretched total length) after being born in estuarine and nearshore areas at sizes between 69 and 81 cm STL [18]. One of the objectives of the recovery plan for P. pectinata is to protect or restore habitats for the juveniles that occur in (...truncated)


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Colin A. Simpfendorfer, Beau G. Yeiser, Tonya R. Wiley, Gregg R. Poulakis, Philip W. Stevens, Michelle R. Heupel. Environmental Influences on the Spatial Ecology of Juvenile Smalltooth Sawfish (Pristis pectinata): Results from Acoustic Monitoring, PLOS ONE, 2011, Volume 6, Issue 2, DOI: 10.1371/journal.pone.0016918