|Star acoustic surveys of localized fish aggregations|
Doonan, I.J.; Bull, B.; Coombs, R.F. (2003). Star acoustic surveys of localized fish aggregations. ICES J. Mar. Sci./J. Cons. int. Explor. Mer 60: 132-146
In: ICES Journal of Marine Science. Academic Press: London. ISSN 1054-3139, more
|Authors|| || Top |
- Doonan, I.J.
- Bull, B.
- Coombs, R.F.
‘‘Stars’’ are an alternative design for acoustically acoustically surveying isolated fish aggregations in which transects cross at a centre point over an aggregation to form a star or wheel-spoke pattern. The method was devised particularly for aggregations of orange roughy (Hoplostethus altanticus Collett) to cope with the practical difficulties of manoeuvring a vessel towing a transducer over a small, dense school of fish. Several methods of analysing star patterns were considered including kriging and a method that ignored the spatial arrangement of the transects. However, simulations of roughy aggregations showed that the best approach was to transform from Cartesian to polar coordinates and then use standard statistical methods (polar method). The polar method was robust to shifts in the transect centre off the aggregation centre and aggregation movement in a random way. Variance estimation was best with a polar version of transitive kriging. Stars using the polar method were also better than the usual parallel transect design when transect numbers were low but the results were similar when six or more transects were used. However, in all the cases considered parallel transects consistently overestimated the variance. We conclude that star transects offer a robust and effective way of estimating the biomass of small, localized aggregations of fish that minimizes vessel time, and yields good precision.