Jungle fishing adventures in French Guiana

Hot work fishing in the jungle

by Bill Beaumont,
GWCT Senior Fisheries Scientist

French Guiana (FG) is an overseas department and region of France located on the northeast Atlantic coast of South America. It borders Brazil to the south, and Suriname to the west.

The country has a very low population density of only 3 inhabitants per km2, with half of the population living in the metropolitan area of Cayenne, its capital. The country is the largest (by area) overseas department of France. As an overseas region, it is inside the European Union, and its official currency is the euro.

As the country is an overseas department of France the authorities are examining the status of the rivers and fish with regard to the Water Framework Directive that applies to Europe and calls for all rivers to achieve good or excellent status. Many of the rivers in FG are very low conductivity (that is they do not conduct electricity very well) this makes sampling with electric fishing difficult.

Dense jungle and amazing trees

Therefore fish sampling in FG has historically been carried out by using Rotenone to poison the fish in small creeks. Electric fishing has been tried but the method has not been very successful (Allard et al. 2014). However, the use of Rotenone is now subject to review by the French authorities and is likely to be banned due to the lethal effects.
 
Due to the links between GWCT and the French INRA scientists arising from the MORFISH project (who are also involved with fish research in FG) I was asked to review the methods used by Allard et al. (2014).

I found that whilst their equipment was moderately successful at 50 uS.cm-1, at lower conductivity fishing efficiency declined. I carried out some theoretical calculations to determine the power settings that would be needed to improve catch rate at the lower conductivities (Power Transfer Theory calculations) and found that in order to keep the same (50 S.cm-1 water) capture efficiency in 20 uS.cm-1 water, the output voltage would need to be increased to 1061 V DC.

These settings are beyond the capabilities of the equipment used by the FG researchers. However, I have had success in fishing low conductivity streams in UK using pulsed DC at voltages between 500 and 600 volts and have access to equipment that will fish up to 990 volts.
 
In order to demonstrate fishing using pulsed DC electric fishing methods I joined a small team of  five researchers from both Hydreco-Guyane and INRA in FG between 3rd to 9th June. We were based in the Hydreco-Guyane field research station at Petit Saut, where there is a large hydro-electric dam producing 116 MW of power. Creating the dam inundated 3,500,000 Hectares of forest and the research station has been set up to monitor the on-going impacts of the dam on the ecology of the area.



Home for four days

Accommodation was basic (tin roof and no walls, but did have a kitchen area, showers and electricity). Sleeping arrangements were hammocks slung in the single main room. The good thing about this arrangement was hearing the howler monkey chorus on the first morning, the bad was that the rain on the tin roof was deafening for much of the visit. Another downside was wearing chest waders, thick rubber gloves and a 15 Kg backpack electric fishing machine in 30 degree heat and 95% humidity!

Suitable sites in the forest were identified and enclosed with stop nets. We then carried out a 3-catch depletion population estimate of the reaches using electric fishing, followed by using rotenone to capture any remaining fish.

Most of the fish within the reach were small (<10 cm) and this often made seeing them in the slightly turbid water difficult. At some of the sites we were also working on the limits of the equipment (using 990 volts, 100 Hz pulsed DC). Estimates of the population by electric fishing were not very accurate (about 50 % of the ‘true’ population).

Exotic - but small fish

At another, smaller and slightly more conductive, site the total population (electric fishing population estimate + additional fish sampled by Rotenone) was within the estimate from the electric fishing data. The number of different species caught by electric fishing (which is the metric used to assess site status) was very good when compared with the total species caught by both methods.

At the largest site we fished, electric fishing caught 20 species and the Rotenone added two more (all this in just 25m of river!). At another site the electric fishing caught more species than the Rotenone including a species that is rarely caught by Rotenone.

Conclusions of using electric fishing methods were that it showed promise as a non-lethal method of assessing fish species composition in the low conductivity waters present in the area. In addition, in smaller streams above 20-25 uS.cm-1 it could provide population estimates of fish numbers.

For the future, I am going to explore ways in which the method can be refined for the difficult conditions in the streams and hope to return to further test the method. If the method does prove effective it will have implications for fish sampling in other low conductivity areas of South America (and elsewhere) where electric fishing is currently considered not feasible.

References: Allard et al. (2014). Fisheries Management and Ecology, 21, 234–243

A visit to the (Welsh) river Dee fish trap

by Stephen Greogry - sgregory@gwct.org.uk

Anton Ibbotson and Stephen Gregory of project Morfish recently paid a visit to the Cyfoeth Naturiol Cymru/Natural Resources Wales fish trapping facility on the river Dee in Chester.

Ian Davidson and Rich Cove kindly gave us a guided tour and showed us the fantastic facility in action.

The schematic below shows the trap which is located at the tidal limit. Ian and Rich are currently catching good numbers of both salmon and trout in the Dee.

 



The potential benefits of catching returning spawning fish are obvious to Anton and I. With the fish in your hand you're able to measure length and weight precisely and take biological material such as scales and fin clips.

 

We currently use a passive monitoring system for spawners meaning we detect the returns on either the adult counter or the PIT tag system. By having biological data on the returning spawners we would be able to investigate changes in the condition over time, allowing us to investigate possible drivers of stock sizes over time.

 

One last photo - Anton Ibbotson chasing fish around the trap floor:

 

Working towards a standard salmon stock monitoring programme

The GWCT's Stephen Gregory recently presented a talk on the recommendations for monitoring and modelling of salmon populations based on the shared experiences of scientific researchers working on Project Morfish.

The slides are below. Please contact Stephen on sgregory@gwct.org.uk for more information.

View Towards a standard salmon stock monitoring programme and other presentations by sgregory.

IFM smolt monitoring workshop

The Institute for Fisheries Management (IFM) with the Scottish Fishery Co-ordination Centre (SFCC) held a workshop on smolt monitoring on the 14th May 2014.

Details of the workshop can be found here.

Sadly, no-one from the GWCT Fisheries group or the INRA Ecology and Ecosystem Health unit could attend because we were all involved with our own long-term monitoring programmes.

Nevertheless, we did prepare and send this informative MorFish poster:

Trout Life History Project - An Update

Acoustic tracking of trout smolts

The near shore migration behaviour of post-smolt sea trout potentially impacts their life history choices. Parameters that may be affected by migration choices of post-smolts are growth rate, fecundity and timing of first spawning migration.

Vemco VR2W receiver

Acoustic tags were chosen to study post-smolt migration behaviour in the near shore environment. Unlike radio tags and PIT tags, acoustic tags actively transmit signals that can be heard effectively in the marine environment.

We chose to use V6 tags made by Vemco, the world’s leading manufacture developer of acoustic technology for fish tracking. The V6 tag is 6 mm in diameter, 16 mm long, weighs 1 gr and has a detection range of approximately 200 metres.

On the 26th of March 10 Vemco WR2W receivers were deployed throughout Poole Harbour. The receivers (listening stations) were deployed strategically to record movement both into and out of Poole Harbour as well as potential feeding areas (see Map 1 below for location of the receivers in Poole Harbour).


Map 1: Location of WR2W receivers in Poole Harbour, the area shaded red represents
approximate detection range of the receivers. Click image to enlarge.

In addition to the receivers monitoring movement in the harbour, receivers were deployed in the River Frome at Bindon Mill, East Stoke, and at the tidal limit by the bypass around Wareham (see Map 2 below for position of in-river receivers). These in-river receivers were deployed to monitor post tagging in-river loss rate and freshwater migration speed.

Map 2: Location of East Burton eel rack (yellow dot) and WR2W receivers
in the River Frome (red dots). Click image to enlarge.

Capture and tagging of trout smolts

We acquired 50 V6 tags for the 2014 smolt run and another 50 tags for the 2015 smolt run.



Trapping trout smolts on the Eel Rack at East Burton

Tagging of the trout smolts is done at the eel rack at East Burton, 8 km up-stream of East Stoke. The eel rack at East Burton represents a piece of cultural history as it was made many decades ago to trap down-stream migrating silver eels for commercial purposes.

The eel rack at East Burton has been restored and is now an excellent tool for GWCT to intercept down-stream migrating fish in a fish friendly manner. Click here to see a video clip of an eel rack in operation on the River Test.

The capture and tagging at the eel rack commenced on the 28th of March and was carried out at night time as this is the time when the majority of smolts migrate. The trout smolts were captured, anaesthetised, measured, weighed, scales taken, PIT and acoustic tag inserted, moved to a recovery tank and released when fully recovered (see pictures below for tagging process).

The last of the 2014 tags were deployed on the 23rd of April.

Trout smolt on measure board with acoustic and PIT tags

Insertion of acoustic tag

Trout post-surgery

Tracking of tagged trout smolts

By 21st of Aril 70% of the tagged trout had been recorded entering the tidal section of the river. The battery life of the acoustic tags is 105 days from the day they are deployed. This battery life of the acoustic tags will give us an excellent window into the migration behaviour of the tagged post-smolts in the near shore area.

However, as the battery in the acoustic tags will run out before their first spawning migration we also fitted the smolts with PIT tags. The PIT tags will enable us to record returning adults on our PIT readers at East Stoke and Bindon Mill.

GWCT Fisheries Research

To find out more about the GWCT's fisheries work please click here and to find out more about our trout research please click here.

2013 Salmon research report now available online

Our 2013 salmon research report has been published and is now available to download as a PDF.

The abstract from the report is below:

2013 was the 41st year of the salmon counter’s operation at East Stoke. It was an extremely good year for the juvenile phases of salmon with high numbers of every life stage being recorded. For the adults it was very poor. Parr numbers in the river in September 2012 were very good: the third highest since 2002 and the number of autumn migrant parr that went past East Stoke was high: the second highest we have recorded. The spring monitoring of smolts was excellent and, at over 13,000, was over twice the number recorded in 2012.

On the adult count, equipment failure meant that some data that we normally collect on salmon movement was lost. For this reason we have added an efficiency estimate to the collected data to give an estimated nett upstream count of 343 fish.

This is the lowest number ever recorded on the counter. Adult numbers calculated from PIT tag returns give an estimate very similar to this (383) so we are confident that the numbers were low. This low number of adults is also in agreement with our prediction last year about low numbers of grilse returning this year.

The collaboration with the Poole Harbour netsman continues with only one sea trout caught, tagged and released in 2013.

Our research (with Cefas) on the effect of using rotary screw traps to assess salmon smolt numbers was completed and results will be analysed and written up as soon as possible. The research on the medium and long-term effect of Archimedes screw turbines on salmon smolts and eels also got underway using the facility at Bindon Abbey.

Our current Passive Integrated Transponder (PIT) tag detection equipment is getting very fragile and the manufacturer is no longer supplying new equipment. After reviewing available options we have found sponsorship and funding to replace the readers with new ‘state of the art’ equipment. The new detectors will be better able to withstand the high river flows we have recently experienced and installation should take place this summer.

Mean annual discharge (up to December) was above average, however, the mean monthly discharge in January 2014 was the highest ever recorded for that month.

Finally we are continuing to work with our French colleagues at INRA in Rennes, France, on the Monitoring for Migratory Fish (MorFish) project which will compare data to give us a better understanding of the changes in our populations of migratory fish.

Professor Nick Sotherton
Director of Research, Advisory & Education

Download GWCT 2013 Salmon research report >

Webcam installed at our Salmon & Trout Research Centre

We've recently hooked up with Farson Digital Watercams who have installed a webcam at our Salmon & Trout Research Centre on the River Frome.

As well as watching a live feed from the centre you can also view photos showing recent river heights and conditions.

Go to webcam >