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Subject: Re: Best methods to describe artisanal fisheries?
From: Trevor Kenchington <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Tue, 3 Jun 2014 17:10:35 -0300

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An interesting challenge!

Any kind of statistical analysis would require you to determine which  
units (individual vessel days, perhaps?) are replicates of other such  
units. ANOVA would require that you bin the data in some way. Do not  
rush those steps. You may learn as much about the fisheries from  
thinking about how to arrange the data as from the analyses that  
follow. Indeed, the analyses could all too easily return results that  
are merely artifacts of the way that the data were arranged and hence  
getting the right arrangement could be critical.

Twenty years ago, I worked on a data set that was a lot smaller (some  
200 boats) but more detailed (being based on interview data) than  
yours likely is. One thing that quickly became evident was that the  
200 captains followed about 150 different annual cycles -- quite  
deliberately so, as (outside of the local lobster seasons, which  
encouraged everyone to do much the same as his neighbours for several  
weeks) most men consciously chose to spread themselves across the  
available fishing opportunities by specializing differently from  
everyone else. The concept of a "replicate" became very shaky.

I'd recommend a lot of exploratory, descriptive analysis, before  
moving to hard number crunching.

Also: Fish catches are a consequence of fishing effort (as well as  
the availability of fish biomass to harvest) and fishing effort is,  
ultimately, a product of human decisions. As a sometime biologist, I  
find it all too easy to analyze catch data as though it was the  
outcome of some sort of bio-economic process but, in reality, it is  
mostly a result of the choices of the most behaviourally-complex of  
all species: Homo sapiens. The one saving grace is that we can talk  
to the decision-makers and so come to an understanding of their  
choices without the sort of manipulative experiments needed when  
working with other species -- experiments that would be both too  
expensive (because of the behavioural complexity) and unethical if  
attempted with fishermen. In short and if you have not already done  
so: Discuss your data and your analyses with the subjects of your  
study. They may well help you define the questions to be asked of the  
data, as well as aiding interpretation of your analytical results.

Trevor Kenchington

On 3-Jun-14, at 2:30 PM, Grant Adams wrote:

>> <>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>
> <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><  <><
> I am assisting a South American research institute. After working on a
> commercial species catalog and noticing the lack of published local  
> fisheries data
> I have convinced my colleagues to publish. We are going to start  
> with a 10 year
> data set of daily artisanal landings (kg) including; date, vessel,  
> gear, species,
> and fishing grounds.
> Currently we are thinking of describing the seasonal and  
> interannual/long term
> trends of all pelagic and coastal artisanal fishery operations  
> using ANOVA and
> multivariate regression.
> We are looking for the best way to diffuse this information;  
> analysis, focus, etc.
> Any advice would be great!
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