This week began in earnest when I caught a shocking number of invasive green crabs at the Coos History Museum and at Isthmus Slough. Over a single twenty four hour trapping period I trapped over 300 crabs between these two sites. This would have been overwhelming for me to process all on my lonesome back in the lab but I had some awesome volunteers who were willing to sit in the lab with me for two hours weighing crabs.
When I get this many crabs in one session it’s important to stay organized (a skill I am still developing). I separate out crabs I catch into two buckets - one bucket for green crabs that are caught in newer model fish traps, another for green crabs caught in older model traps. I label each bucket with flagging tape in order to keep the crabs straight, though especially when I first started I tended to mess up the order of my buckets. By now my crab sorting skills have improved and these sorts of mistakes are a lot less frequent. The more astute observer will observe a sneaky third bucket, this one is just for stakes and bait containers.
I’ve worked a lot this week to study the difference between the catch efficiency of the older and newer crab traps. One would assume this operation to be straightforward: take the average number of crabs I catch in each trap type and see which one has a higher average. Interestingly being able to determine if there is a difference in how many crabs each trap catches is turning out to be a much more complex operation. Variables such as the site where I set out the traps and when the traps were deployed also need to be taken into account as these will impact the average number of crabs I catch in each trap. For example I could observe that over time the number of crabs I catch in the new traps could slowly increase as they age and more resemble the more worn older traps. Simply taking and comparing the average of these two traps wouldn’t really capture this variability.
As a result of this thinking I have once more turned to statistical software which has the power to take these variables into account. I’ll spare you the nitty gritty details, but my first tentative result is that the new traps catch fewer green crabs than the old traps. I’m not really sure why yet, that will be a problem to figure out next season by making some careful modifications to the traps and running some tests.
I’m a rising junior at the University of Pennsylvania studying ecology and evolutionary biology. When I’m not doing science I love doing pretty much anything outdoors. I’m an avid backpacker, runner, paddler and rockclimber. Finally I love to read fiction in pretty much any form.