Atlantic Fisheries Research Document 1996/007

Incorporating ecosystem information into the Fisheries Assessment Process: Can we develop a quantitative "Plankton Index"?

By W.G. Harrison; D.D. Sameoto

Abstract

The incorporation of environmental data into the fisheries assessment process is now a priority within DFO. During the 1995 FOC meeting, plankton (both phytoplankton and zooplankton) data was added to the list of environmental properties for consideration. At that meeting, we identified both archived (e.g. CPR) and future (e.g. satellite ocean colour data) data sources that would be useful. The next step (and the subject of this paper) is to begin to explore more specifically if and how we can incorporate this information into the assessment process.

Our approach is to identify and exploit properties of the plankton which, based on established ecosystem principles, are most likely to reveal cause-effect relationships between prey (plankton) and predator (fish larvae). Our first cut at this is based on Cushing's "Match-mismatch Hypothesis" in which the timing, magnitude and duration of the phytoplankton seasonal cycle influences the survival of fish larvae and, in turn, recruitment and stock variability.

We have "parameterizedî the phytoplankton growth cycles using two gaussian distributions (one for the spring and one for the fall bloom) which yield the relevant ecosystem properties of phase, magnitude and duration. Our test datasets are the CPR data from the NW Atlantic (1961-1994) and the 1979 CZCS ocean colour satellite data on primary production. The mathematical representation of the growth cycle and the resulting parameters are promising and, with regard to the CPR data, show some interesting changes in the relative magnitude and duration of the spring blooms between the early 60's and the present. A similar analysis is planned for the CPR zooplankton data.

It is anticipated that these plankton "parameters" alone may not be adequate in the assessment process. Therefore, we have speculated on a procedure in which we might "scale" or "rank" the parameters based on their observed environment range in order to come up with a quantitative "Plankton Index", analogous to the "Fire Hazard Index". This is presented more as a starting point for discussion than for implementation at this point.

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