Species Only (SO) surveys are sometimes submitted along with SA surveys. SA surveys record only the presence of the species with no abundance information. On the survey form, the Species Only category in the Survey Type section is filled in and the Single category is used to indicate the presence of the species. A single SO survey may span multiple dives (or even an entire dive trip). It's primary use is to list species that were sighted outside of dives where SA surveys were taken. These surveys help to fill in the distribution data for species but contribute nothing to the survey bottom time or to the Sighting Frequency or Density calculations. For species that are included on a report only because they appeared in a SO survey, the %SF and Den columns are filled in with the text "----SO----".
This weighted density average is calculated as:
(S * 1) + (F * 2) + (M * 3) + (A * 4) Den = ------------------------------------------------- (Number of surveys in which species was observed)This number indicates which abundance category the species was most often recorded in when it was recorded. For example, Den=2.2 would be reflective of a species that was most often recorded in category 2 (Few) but since the density index is greater than 2, there were some abundances recorded for this species in the other, larger abundance categories (either category 3 or 4). The density index should be used as a density guide. In this survey method, area is not rigorously controlled. It should also be kept in mind that the density (Den) parameter is reflective of sighting distributions in the four different abundance categories (S, F, M, and A) and different distributions of sightings in each abundance category could potentially give similar values of Den.
The %SF parameter is calculated as:
S + F + M + A (for each species) %SF = 100 * -------------------------------- (Number of surveys)By simultaneously examining the sighting frequency (%SF) and density index (Den), data summaries can be interpreted for fish species. The Den and %SF scores could be multiplied to provide a measure of species abundance which includes zero observations.
The following table shows an example of how to interpret summary information at the species level.
Den | %SF | Explanation |
---|---|---|
HIGH Den >3.0 |
HIGH %SF >50 |
Species is often observed and observed at high densities.
Species is seen > 50% of the time and when it is seen the abundance
category most often recorded is M or A. Species examples: bicolor damselfish, blue chromis, brown chromis |
HIGH Den >3.0 |
LOW %SF <50 |
Species is not often seen, but when it is seen, it is observed at
high densities. Species is seen < 50% of the time and when it is seen
the abundance category most often recorded is M or A. Species examples: silversides/herrings, garden eel |
LOW Den <3.0 |
HIGH %SF >50 | Species is often observed, but always
at low densities. Species is seen > 50% of the time and when it is seen
the abundance category most often recorded is F or S. Species examples: trumpetfish, rock beauty, foureye butterflyfish |
LOW Den <3.0 |
LOW %SF <50 |
Species is not often observed and when it is observed, it is at very low
densities. Species is seen < 50% of the time and when it is seen the
abundance category most often recorded is F or S.
Species examples: green moray, saucereye porgy, spotted scorpionfish |
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