mathgeek..Big Lake or Grand Isle

[MathGeek]

Originally Posted by Coppertone

Thank you for your words Mathgeek. I'm sorry if it came across wrong...I wasn't intending to doubt any differences in sizes or health, but rather what causes any differences in sizes or health. What were the constituents involved in the "contaminated" areas of Calcasieu?

Having done some research work in this area, my personal opinion is that it's really hard to nail down any true cause/effect "ideas" because of the thousands and thousands and thousands of variables that affect the health of an estuary and its biological population.

I agree, ascribing causality for observations (why fish are thinner or fatter in a given area or year) is harder to do with cetainty than observing what is happening (fish as one location or year are fatter than at another location or year).

However, with sufficient data one can say whether the data tends to support or fails to support a given hypothesis. Suppose one has a hypothesis that the oil spill negatively impacted important food sources in a specified area. If the fish were thinner in that area (compared with pervious years or the long term LA average), then the hypothesis would be supported (but not proven). If the fish were fatter or the same in the area, then the hypothesis would be disproven.

There are a number of hypotheses regarding the declining fish condition in the Calcasieu estuary. These hypotheses are not mutually exclusive, but if one is hypothesized to be the primary or most important cause, then it is possible that data exists or could be gathered to support or refute it.

For example, consider the hypothesis that the overharvesting of oysters is the primary cause of the decline of fish condition. This hypothesis would be supported by the following observations:

1. Species more heavily dependent on benthic food sources (bottom feeders) would likely be more impacted than species less dependent on benthic food sources.
2. Species that feed directly on oysters would be strongly impacted.
3. The decline of fish condition would be correlated in time (coincident or shortly after) a significant increase in oyster harvesting.
4. Other data or bioindicators showing that the oyster population is decreasing.

This hypothesis would be refuted by the following observations:

1. The species showing the greatest loss of condition factor are not heavily dependent on benthic food sources.
2. The greatest decline in fish condition occurred before significant increases in oyster harvesting.
3. Other data or bioindicators showing that the oyster population is actually increasing.

This kind of logic cannot really prove which of the competing hypothesis is the primary cause, but applied to all of the hypotheses, it might be possible to suggest which hypothesis (or hypotheses) are more likely to identify the causal factor(s).