woensdag 17 juni 2009
These fish are young Ide and the picture on top shows a young Asp that has a more pointed head, a bigger mouth and pointed fins. I presume they are about four weeks old because on May 8. I caught an Ide that was producing eggs when pressure was applied to the abdomen.
It is pretty hard to be certain about the species on these small fish, so I caught a few of the thousands along the banks to let them grow a little bigger. Thus far it seems to be mostly Ide and some Asp (Aspius aspius).
The Asp is an exotic species native to the Danube area where it is getting rarer. In the larger Dutch rivers the Asp is one of the most abundant species now. More and more species from the Danube area are colonizing the Rhine river system and quite a few are becoming dominant species. Recently there are a lot of species from the gobio family.
I am kind of big so the fish tend to look small when I am posing with them. The barbels here can reach nice sizes though this on was 55 cm, but many fisherman have personal bests from 80 till 89 cm's. There are a lot of barbel sites now in the Netherlands full of pictures and tips how to catch these beauties.
It was more difficult to catch a barbel then expected. Anyway I am glad I finally caught one. This one I caught together with some strong river bream.
The relevant cybertracker windows are there and it shows the tracker wasn't very accurate, probably because of the long time interval between readings. At a two minute interval Cybertracker closes down and starts up the pda every time a reading is taken, at the expense of the accuracy. This can be corrected by constraining the accuracy of the readings.
Here is the report of a a one hour reptile survey at a place nearby. Not too many sightings, but good to get the broader picture. I have been walking letting cybertracker take a GPS reading every 20 seconds which are the small dots on the map. The graphs and maps are based on a query for the date I was surveying, selecting only the reptile sightings.
I added a picture view, displaying the picture I took of the lizzard that is in the active sighting.
There is also an efficiency graph showing I covered a distance of 1 km in one hour doing three sighings, which is not particularly good (takes time to take a picture of course, and lizards are easily scared away by quick movements.).
The map shows there is a preference for the western side of the field. Ecologically this can be explained by the great variation in the terrain there because there are some pits dug out and some piles of dead branches. The woods nearby give shelter to the dominant and cold and wet western winds that prevail in this country, while it is still far enough from the trees to receive the sunlight. The map itself is from Microsofts Virtual Earth which is integrated with Cybertracker.
In the far west there is a pond that is home to frog eating grass snakes, but this time I didn't spot any, but I have been walking around a bit there according to the tracker.
With Cybertracker a South African based application initiated by Louis Liebenberg and progammed by Justin Steventon ( http://www.cybertracker.org/) I am keeping track of the species I encounter and I am also using a similar program called WnPda which is connected to the waarneming.nl database ( http://www.waarneming.nl ).
The difference between the two is that Cybertracker is a data capture tool that is completely customizable by the user. Wnpda is a data capture tool developed by Alex Kwak here in the Netherlands to capture field data without the need of pencil and paper and with a mobile internet connection it is even possible to access google maps and upload the data in the field.
The proliferation of GPS tools have brought great possibilities even for moderate prizes. I am using an ipaq 6915 that is also a great scheduler and mobile phone, which I bought for 70 euro here on the second hand market.
What we are seeing on the screen here are patterns of small dots called tracks and big dots which are representing the sightings. The tracks are automatically taken readings of the postion of the data capturer. In this case the fishing was static, but for the data capture of amphibians and reptiles it is a great tool, because it allows for data analysis of the effort (distance covered and time spent). For that kind of surveys the GPS data are more valuable too, because reptiles are seldom evenly dispersed and it is hard to get the map data right in the field when there are not many terrain features and even harder to accurately remember where a particular sighting was. Because of the ease of capture with a pda also the more commons species will be recorded accurately and completely which can provide valuable data on ecological changes.
Fish sightings also have their difficulties in capturing often there are a lot of individuals of not always expected species and also there is a great variation in lenghth. I put in some filters so the typical riverine species pop up when you are fishing in a river and so forth.
On the top right there is a window displaying the query, which is a part of a database defined by certain constraints, in this case the species has to be a "Witvingrondel" (White finned gudgeon).
As you can see I am using Picasa for the handling of the pictures and even for the postings of this blog. It is a great tool for handling pictures and it has about everything I wish except for a hierarchy in the tagging of pictures. For example I would like to tag this picture as a "white finned gudgeon", but I would like it to be automatically tagged then as a cyprinid, a teleost etc.
This can be done in Lightroom, but lately I haven't been using that much because the lightroom databases get very slow when containing too many pictures. It is however possible to use Lightroom for tagging the pictures, making a new database every 6 months or so and Picasa can use the tags in a search later. The georeferencing tools of picasa are great. It is possible to tag pictures later when you are home using Google Earth button.
It is also possible when using the Waarneming.nl tool or cybertracker to tag the pictures automatically with programs like JetPhotoStudio comparing the time of the track point with that of the time the picture was taken. In this manner it is possible to feed the program with a gps track (gpx format) and with a picture folder. The pictures will then get a georeference tag that adds the Longitude and the Latitude to the Exif of the picture. (The Exif is a part of the jpeg file containing all kinds of data varying from time and date the picturee was taken,camera data to copyright, contact address etc.) (http://www.jetphotosoft.com/web/manual/gps_win.html )
Using cybertracker this is pretty hard to do and requirers a script to change the relevant data table into a gpx file. On the other hand Cybertracker allows you to use a touch screen pda with GPS and camera directly to add a picture to a sighting.
Here the same fish, freshly caught without any discernable black spots and markings. Due to stress and environmental conditions most fish will change their color pretty quickly. Especialy the black chromatophores will respond quickly to stress and changing conditions.
The fish that nobody ever noticed? Anglers love to catch fish, but most of them are more intererested in size and quantity then what they have just caught. This species has probably always been indigenous here, but due to its likeness to Gobio gobio it has never been noticed as being a different kind of fish. Actually I caught the first documented one in this country in 2004, alerted by the publications of Freyhof about findings in the Rhine River system in 1998.
Anyway this year they seem to be blooming in our major rivers because my friend caught about twelve of them near Wageningen 20 km downstream and I caught three specimen. Determination of cyprinids and fish is not an easy thing which can be demonstrated comparing this picture with the other one of the same fish freshly caught. In the other picture no black spotting can be seen due to the action of chromatophores concentrating the black pigment into tiny dots. After keeping the fish in a glass jar in the shade the spots became very obvious, just as the nice markings along the lateral line. Most typical of this fish is its habitat, right in the middle of big rivers on sandy bottoms contrary to Gobio gobio which prefers smaller waters and less current.