Basic methods:
This experiment was designed to quantify the distribution and abundance of invasive lionfish and then determine whether the distribution and abundance of various native prey species is correlated with lionfish distribution and abundance. Eight reefs were selected and assigned low or high lionfish density. Discrete plots and/or transects were establish on the eight reefs and the local distribution of invasive lionfish and select prey species was monitored for ten weeks. Automated video cameras were also deployed on the reefs to capture the movement of fish across the reef. Behavioral observations were made on each of the high lionfish density reefs at dawn, midday, and dusk, to record lionfish movement and behavior on the reef. Habitat structure of the reef was measure along with rugosity in all the plots and transects.
Here is an example of one of the high lionfish reefs. The star represents the potential hotspot for lionfish presence. Right now the plots and transects are only representations of the actual spatial distribution.
These are examples of lionfish location on different surveys.
TO DO NEXT?:
For each parameter, list an explicit prediction from the hypothesis that lionfish live and forage mostly within hotspots on reefs. The way to envision a prediction is: “If the hypothesis is true, then…”. Example predictions:
(1) There should be a significant correlation between the rankings of plots within a reef based on distance from the hotspot (1-9) vs. based on mean distance to lionfish through time.
(2a) Lionfish should spend more time in plots close to the hotspot than in plots further away.
(2b) Lionfish paths of movement should be close to the hotspot.
Specific tasks for each example prediction:
(1) Run Kendall’s tau rank correlation analysis?? of plots within a reef based on distance to hotspot vs. mean distance to lionfish through time.
(2a) Calculate lionfish time per plot from time budgets.
(2b) Map lionfish paths of movement from time budgets (eventually analyze distance of path from hotspot).
I don’t think I need to/can use Arc to get this done. I have GPS points for the center of each reef, as well as measurements for the reefs (length, width, surface area, circumference etc).
I need to be able to calculate distances and creates paths of movement and then calculate distances traveled. It only needs to be related to within in reef scale. I am unfamiliar with any sort of programs that can do stuff like this, however I don’t think it would be to hard once I figure out which one to use.
Firstly, I have a couple clarifying questions: How are you collecting data on prey species? And has this data been collected, and if so what are the species? How were hotspots defined in your preliminary work? Do you have GIS point locations of Lionfish ranges?
If I can get these questions answered then I feel I can provide some constructive comments.
Responses to questions from Eric.
1/2. Data collected on prey species was done on SCUBA, and was collected last summer. I surveyed ~ 20 species of fish that have been shown to have high site fidelity, meaning once they settle on the reef they have a very small home range (sometimes <1m). Fish data was collected for each plot and transect for 10 weeks. Plots were ~2×2 m and transects ranged from 2×3 to 2×7 m.
3. Hotspots for lionfish were determined through initial surveys where I found locations on the reef with a high density of lionfish in a resting state. This would mean they were either settled on the reef, or tucked up underneath ledges or coral heads.
4. I dont have GIS points for the lionfish on the reef. All of my location points are based on visual surveys where I would mark locations on a map of the reef.
Hope this helps, and let me know if you have any more Q's.
Hi Alex,
Sounds like a complex project! Must have been fun collecting that data!
I wonder how you’ve settled on that yellow star being the hotspot for lionfish? Is this from pervious survey data? Is it possible that there are a couple hotspots distributed elsewhere in the reef? Seems like if there are other aggregation sites (to spawn?), this could affect the movement patterns of the individual fish. Maybe I’m missing something.
If you have GPS points through time for individual fish you could use tracking analyst in GIS to help construct paths and calculate path attributes. I did quite a bit of work with tracking analyst in GIS for my MSc – happy to help if you want.
Caren