Sawfish, and crocodiles, and mosquitoes! Oh my! The adventures of Team Sawfish

Sweltering heat, mosquitoes, angry crocodiles and swarms of flies characterise the typical late dry season (September-November) in northern Western Australia. And it’s here that we at Team Sawfish have found ourselves for the past 13 years, as we continue our research on several species of sawfish. This past October, Dr Ruth Leeney of Protect Africa’s Sawfishes and Dr Barbara Wueringer of James Cook University decided to brave these conditions as they joined our team during our month long expedition on the Fitzroy River. 

Map of Fitzroy River (blue line) in northern Western Australia.
Map source: Google Earth

The goal of our adventure was to investigate how barriers, such as dams, may impact the movements and health of the largetooth sawfish (aka freshwater sawfish) (Pristis pristis). Fish like the largetooth sawfish that live part of their life in freshwater are more likely to be influenced by human caused disturbances (e.g. dams, mines, pollution) than their marine relatives.

The Camballin Barrage, a small weir on the Fitzroy River used for irrigation of
cattle and crops. Photo: Jeff Whitty

This work was part of an ongoing project that involves several rivers throughout Western Australia, where sawfish are known to occur. The Fitzroy River itself is an ideal site for this study. This river is one of the largest known nurseries of the largetooth sawfish. In addition, the Fitzroy River has several barriers of various sizes, including a weir (a type of dam often used for irrigation) and several road crossings. 

While a lot of our trip was spent avoiding swarms of mosquitoes and checking for crocodiles, we also managed to sample numerous pools located between the mouth of the Fitzroy River and 380 km (236 miles) upstream from the river mouth. From these pools we captured seven different sawfish. This is fewer fish than we typically see, and was largely due to the lack of captures of young of the year (YOY; fish pupped within the year). The number of YOY that we captured earlier in the year was also relatively low, which suggests this may have been a poor year for these newborns.

Myroodah Crossing, a low-relief road crossing on the Fitzroy River.
Photo: Jeff Whitty

The sawfish we did capture were 2-3+ years old (juveniles) but still averaged a length of 205 cm (6.7 feet)! In addition, the majority of these fish were recaptures of those that we had previously tagged with individually numbered Rototags (i.e. cattle ear tags). Two of these sawfish were initially tagged as YOY (i.e. 2-3 years ago). Long-term recaptures like these are rare, but allow us to gather some important information on the distribution, movements and growth of this species. Although we can collect some of this vital information during the few months of the year that we are in the field, we also rely on local and visiting fishers to report their encounters, which we are very appreciative of (see instructions below on how to report an encounter with a sawfish). 

We also tagged sawfish with small acoustic tags. These tags transmit a unique acoustic signal that can be detected and logged by receivers, which we installed throughout the river. Data from downloaded receivers can tell us when a particular sawfish was near a receiver, and what water temperature and depth the sawfish was in. This data will help us to understand sawfish movements and how they are impacted by dams.

Release of a largetooth sawfish (Pristis pristis) in the Fitzroy River.
Photo: Jeff Whitty

As well as capturing the largetooth sawfish, we had hoped and expected to find the smaller dwarf sawfish (Pristis clavata), which we have been monitoring over the last few years. Although the largetooth sawfish is the only sawfish that lives in freshwater for long periods of time, the dwarf sawfish, which lives in marine and estuarine environments, is attracted to the tidally influenced estuarine pools of the Fitzroy River in the late dry season, when these pools become more salty (around 35 ppt; similar to the ocean). During this period, we primarily find dwarf sawfish in the estuarine pools as the majority of the largetooth sawfish appear to leave the area. It is also this time of year and area that we find large and angry estuarine crocodiles. This year however, we were surprised to only find a couple largetooth sawfish and a number of crocodiles, which made sure we knew they were present. 

After a month in the sweltering heat our food supplies, energy levels and time ran out. As we left the sawfish and the river behind, our team agreed that in spite of a few minor setbacks that our trip was a success. We were able to tag a few new sawfish and collected some important recapture data. This will help us to better understand these threatened sawfish and inevitably help to advance conservation efforts for these fishes.

Although, we had to finally part ways with our esteemed and much appreciated colleagues, we had enjoyed the time spent with them and the memories of fly bites, tasty porridge, not so tasty tree sap and most importantly, the sawfish.

Pictured is the October 2014 Team Sawfish field crew. Missing are Dr David 
Morgan and James Keleher. Photo: Ruth Leeney

To report a sawfish captured in Western Australia or for more information about Team Sawfish please visit www.freshwaterfishgroup.com. 

If you encounter a tagged or untagged sawfish outside of Western Australia please visit the Sawfish Consveration Society at www.sawfishconservationsociety.org, or the International Sawfish Encounter Database at www.flmnh.ufl.edu/fish/sharks/sawfish/sawfishdatabase.html.

This research was funded by Chevron Australia and was made possible by the Western Australia Marine Science Institute.