[R-sig-Geo] Bycatch event as ppp?

GodinA godina at dal.ca
Sun Sep 18 13:36:36 CEST 2011

My mistake, I avoided using the word 'bycatch' to not get into the
definition, but I am actually looking at bycatch events, in other words,
where the presence or absence of nontarget species i.e., shark/skate in the
catch is recorded as a single point for a specific fishing location.
Following Gardner et al. (2008), I would like to test the null hypothesis
that marks (shark/skate captures) are distributed randomly within the non-
random spatial distribution of events (fishing locations). They used a
permutation test, whereby under a series of simulations, the marks were
randomly assigned to event locations (i.e., permuted) to create a series of
distributions that represent complete spatial randomness conditioned upon
the location of the fishing events. I just verified if Gardner et al. (2008)
had all points or 100 percent at-sea observer data, but they didn't (between
3-5%), with the exception of 2 years (100%). In a sense this is their
complete set of point process. However what will be described/model will
undeniably be only what has been observed and potentially far from
describing overall clusters of bycatch events within fishing locations.

Anyone who worked or have experience with fishery data on this mail list is
welcome to join the discussion. 

I am looking for advices on how I (or if I should pursue the idea) can model
bycatch data with point process. Essentially, I know that fishing locations
are not randomly located in space, but I would like to take a similar
approach then Gardner et al. (2008) and compare the known bycatch capture
locations with a simulated set of bycatch captures, which are randomly
located within the known fishing locations. I am using at-sea observer data
(best data available), which often is only 5-15% of all fishing locations,
but this varies over the years, fishery, and regions. I have 15 years of
data (1995-2010).
It doesn't seem that obvious that I can model bycatch event with point
process. I would love to hear people experience, comments, advices, and/or

Thank you very much for your time,

Gardner B, Sullivan PJ, Morreale SJ, Epperly SP. Spatial and temporal
statistical analysis of bycatch data: patterns of sea turtle bycatch in the
North Atlantic. Canadian Journal of Fisheries and Aquatic Sciences
2008;65(11):2461-2470. Available from:

Aurelie Cosandey-Godin
Ph.D. Candidate, Department of Biology
Industrial Graduate Fellow, WWF-Canada

Dalhousie University | Biology Dept. |Halifax, NS, Canada 
Email: godina at dal.ca | Web: wormlab.biology.dal.ca
Want to learn more about sharks in Atlantic Canada? Visit ShARCC! www.atlanticsharks.org
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