## Sea Turtles are Eating our Plastic; Networks help tell us Where

I am a large follower of the iflscience Facebook page.  Recently, there has been a post about how “more than half of sea turtles have eaten plastic” which is based on the study cited below.  This is an extremely large number of sea turtles that are mistaking plastic for food.  While following-up on this article, I realized that a lot of the information they used in the study could have been maintained as a sort of graph.  They collected data about drifting debris, turtle distribution, turtle deaths, and the likelihood that a turtle will ingest plastic.  Firstly, the data about drifting ocean debris was maintained as a set of probability matrices.  The values in the  matrices represented the probability that debris in that sector of the ocean would end up in the other grid 2 months later.  This could easily be interpreted as a sort of directed and weighted graph.  Each of the grid locations (aka matrix locations) would be a node.  An edge would exist from node i and another node j if there is a positive value in the matrix at (i,j).  The weight of that edge would represent the likelihood that debris in sector i travels to sector j.  In this study, the information was best represented in a matrix simply because they multiplied the matrix by a “vector of plastic concentrations” to track the movement of plastics around the ocean.

Other information that the study maintained was about where the turtles were located during different parts of the year called an RMU.  These locations differed by species.  You could represent this information as a graph for each species by creating nodes out of different map locations and connecting the locations that the species usually inhabits.  Essentially, when this location graph is laid over the graph for debris circulation, researchers can see where turtles are most at risk of ingesting plastics.  The outcome of this study is the knowledge that up to 52% of sea turtles have ingested plastics and that this tread will likely increase until we do something about it.

This study is important because it opened the eyes of a lot of people to see how detrimental plastics can be in the ocean and how they are affecting the sea turtle population.  The main connection to networks from this article is that there are hidden networks and graphs in all of these pieces of data.  It is important for us to recognize that graphs can be useful ways to interpret and represent data.  Graphs exist in the color coated maps where the nodes are the locations and the color is the strength of a tie.  They also exist in the movement of debris from one location to another.  Overlaying graphs can give us insight into how two pieces of society/nature interact and where we should be focusing our efforts  to get the best results.  Networks allow us to analyze connections that we never knew we had to worry about… that is we didn’t know until a gruesome video of a turtle and a straw went viral.

Source:
http://www.iflscience.com/plants-and-animals/52-world-s-sea-turtles-have-eaten-plastic
http://onlinelibrary.wiley.com/doi/10.1111/gcb.13078/full#gcb13078-fig-0001
For straw reference: http://www.iflscience.com/plants-and-animals/sea-turtle-12cm-plastic-straw-stuck-her-nose