An unsupervised acoustic description of fish schools and the seabed in three fishing regions within the Northern Demersal Scalefish Fishery (NDSF, Western Australia)
Gastauer, S and Scoulding, B and Parsons, M, An unsupervised acoustic description of fish schools and the seabed in three fishing regions within the Northern Demersal Scalefish Fishery (NDSF, Western Australia), Acoustics Australia, 45, (2) pp. 363-380. ISSN 0814-6039 (2017) [Refereed Article]
Fisheries acoustics is now a standard tool for monitoring marine organisms. Another use of active-acoustics
techniques is the potential to qualitatively describe fish school and seafloor characteristics or the distribution of fish density
hotspots. Here, we use a geostatistical approach to describe the distribution of acoustic density hotspots within three fishing
regions of the Northern Demersal Scalefish Fishery in Western Australia. This revealed a patchy distribution of hotspots within
the three regions, covering almost half of the total areas. Energetic, geometric and bathymetric descriptors of acoustically
identified fish schools were clustered using robust sparse k-means clustering with a Clest algorithm to determine the ideal
number of clusters. Identified clusters were mainly defined by the energetic component of the school. Seabed descriptors
considered were depth, roughness, first bottom length, maximum Sv, kurtosis, skewness and bottom rise time. The ideal
number of bottom clusters (maximisation rule with D-Index, Hubert Score and Weighted Sum of Squares), following the
majority rule, was three. Cluster 1 (mainly driven by depth) was the sole type present in Region 1, Cluster 2 (mainly driven
by roughness and maximum Sv) dominated Region 3, while Region 2 was split up almost equally between Cluster 2 and 3.
Detection of indicator species for the three seabed clusters revealed that the selected clusters could be related to biological
information. Goldband snapper and miscellaneous fish were indicators for Cluster 1; Cods, Lethrinids, Red Emperor and
other Lutjanids were linked with Cluster 2, while Rankin Cod and Triggerfish were indicators for Cluster 3.