Improving conservation planning for an endangered sawfish using data from acoustic telemetry

Understanding the movement and habitat use patterns of threatened species is essential to effective conservation\ud planning. Modern tracking techniques such as active tracking and passive acoustic monitoring can be useful tools in elucidating this information for aquatic species. To aid in the development of conservation strategies for juvenile critically endangered smalltooth sawfish (Pristis pectinata) their fine scale movements and habitat use in southwest Florida were studied using a combination of these techniques. Between 2002 and 2006 a total of 12 individuals were actively tracked for periods of up to 24 h to provide\ud detailed habitat use and movement parameters (distance moved, speed, and linearity). Smaller individuals\ud (<100 cm stretched total length (STL)) had the smallest home ranges, low linearity of movement and had a preference for very shallow mud banks. Juveniles >100 cm STL demonstrated larger home ranges, preference for shallow mud or and sand banks, and remained close to mangrove shorelines. Tide was found to be the main factor influencing movement on short time scales. Sawfish <150 cm STL spend the majority of their time in water <50 cm, while larger juveniles spend most of their time in water 50–100 cm deep. From 2003 to 2007 a total of 22 individuals were fitted with acoustic tags for long-term monitoring. Juveniles >130 cm had high levels of site fidelity for specific nursery areas for periods up to almost 3 months, but the smaller juveniles had relatively short site fidelity to specific locations. The use of a combination of tracking and monitoring techniques provided an expanded range of information by generating both short and long term data on habitat use. The data demonstrated that the conservation of shallow mud and sand banks, and mangrove shorelines will benefit the recovery of these endangered elasmobranchs

Effects of biofouling on performance of moored data logging acoustic receivers

Biofouling on scientific equipment deployed in marine and estuarine environments can have implications for equipment performance, and the type and amount of data collected. We examined the effects of biofouling on the performance of data logging acoustic receivers deployed in shallow coastal waters off Florida. Five treatment types of receivers were examined including old and new versions of VR2 (Vemco Ltd) receivers with complete, partial, or no antifouling paint. Receivers were deployed for 2 mo, and acoustic signal detection rates examined. All receivers had some extent of biofouling during the course of the study, and performance was variable among treatment types. Old version receivers did not perform as well as new version receivers in all cases, and significant differences were apparent in detection rate and receiver performance metrics. Reductions in receiver performance over time occurred for most treatments and were likely due to settlement of biofouling organisms including barnacles, annelids, tunicates, and ascidians. Biofouling appeared to affect receiver performance over time and should be taken into account in acoustic telemetry studies

Long-term presence and movement patterns of juvenile bull\ud sharks, Carcharhinus leucas, in an estuarine river system

Elasmobranchs living in rivers and estuaries may be highly susceptible to environmental and anthropogenic changes to coastal habitats. To address this, patterns of movement of 67 juvenile bull sharks (Carcharhinus leucas) were examined in the Caloosahatchee River between 2003 and 2006 using an array of 25 acoustic receivers. Individuals were monitored for periods of 1–460 days with most present for periods of weeks to months. Individuals utilised the entire monitored section of the river (∼27 km) and also moved upriver beyond the extent of the acoustic array. Daily activity spaces of individuals ranged from 0 to 14 km with most <5 km. Monthly mean home ranges were 0.9–5.6 km and although home-range sizes were consistent through time, location of individuals within the river changed through time. Individuals moved upstream during the day and downstream at night and this pattern persisted across years. Based on data collected from depth transmitters in 2006, individuals swam closer to the surface at night and remained in deeper water during the day, suggesting further diurnal patterns in habitat use. Long-term consistent use of this habitat by young C. leucas suggests this population is highly dependent on the Caloosahatchee River as a nursery area

Environmental influences on the spatial ecology of juvenile smalltooth sawfish (Pristis pectinata): results from acoustic monitoring

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