Two of my colleagues and I have collected trawl catch data from 2006 - 2012. During this time we noticed an unusual phenomena that sea urchins were absent during the initial period (2006 - 2008) and a rapid increase in the sea urchin (Temnopleurus toreumaticus) population between 2009 - 2011. It later decreased during 2012. Note that sea urchins occurred only during March and April and sometimes in May. Further, when we recorded bulk of sea urchin, other demersal fauna showed much less abundance. What could be the reason for this interesting trend? I Have attached one of the photos taken during sampling period.
DO you know if there is a main predator for this urchins in the area? with longer dataset you could see a population cycle emerge, potentially. Then one can ask whether food shortages or predator pressure is the main force behind fluctuation of sea urchin fluctuations?
"So I want to know what could be the reason this interesting trend?"
trawling was carried out in the same spots?
Zsolt Torok There were fixed stations. And we took trawl hauls in regular intervals from all stations. I am trying write paper on it, But I could not add proper discussion part. So I am here to ask suggestions
Dear, Danial, Thanks for your interest. As you suggested major predators of the sea urchin and fluctuation in their population could influence sea urchin trend. As I know sea otters are the potential predators of sea urchin, but here in Goa neither any information available on sea otters nor we have observed. However, we recorded occurrence of sea urchin in stomachs of sciaenid fishes. I want to know weather temperature, or ocean acidification could be the reason? Or its regular ecological phenomena where succession of one community takes place of others..?
Kindly discuss.
I think zsolt has a good point, you would need to rule out possibility of major impact of trawling/exploitation?
As for water temperature and acidification, I am not very knowledgable in Marine ecosystems that much, but the do you know if there are available data on that type of metrics in you ecosystem area? you could try to explore if there is a link through more statistial analyses.
Mr. Salimi, I have taken the physical and chemical parameters, but could not carryout the pollution assesment.
Mahabaleshwar Hegde: "There were fixed stations. And we took trawl hauls in regular intervals from all stations."
two more questions:
1). what is the surface of a control-plot?
and
2). what were You doing with the urchins collected from the respective control-plots?
p.s. control plot = a surface where trawling was performed...
Mr. Torok , Surface was sandy habitat. and I am sorry I did not understood your second question.
Mahabaleshwar Hegde: "Surface was sandy habitat"
Good for you!
But I mean: how many hectares? O square meters/kilometers?
Mahabaleshwar Hegde: "I did not understood your second question"
I was interested in the following detail: if You released the collected specimens exactly inside the perimeter where they where collected?
Mr. Zsolt Torok, Yes we did release them back to the water, but not at the first two times, becz I was curious to know how many species and etc I collected as many as specimens I could. But during the later stage care was taken to drop them back when they are alive and only taken few samples for size class study. We informed other fishermen also try to avoid trawling in that control-plot or put then back to sea.
OK, but how many hectares or square km have You cleaned (of urchins... and all other species belonging to marine epibenthos)?
Oh no Mr. Torok, Ok you mean to say that I have cleaned the entire ecosystem? It was survey experiment where we use to operate trawl net once in every month. Otherwise more than 200 commercial trawlers, operate around the same fishing ground everyday. If your above comment says that we the survey researcher destroyed the benthic habitat I don't find logic in that.
Mahabaleshwar Hegde: "you mean to say that I have cleaned the entire ecosystem?"
for You "control-plot" means "ecosystem"?
Ya that is the part of the same ecosystem..
"but how many hectares or square km have You cleaned"
you mean taking samples means cleaning control plot..?
Any how I don't see these view points are not going any where useful...
I am sorry if I was not able to understand your point of view. But you should know if you take one trawl in the month you cannot ask any one that how much acres did you clean..?
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