以高頻聲學技術進行底棲魚類生物量與行為評估

High-Frequency Acoustic Techniques for Assessment of Benthic Fishery Abundance and Behavior

A point stationary acoustic-based surveying system was proposed to fulfill the necessities of benthic fishery abundance assessment. The surveying system can be split into two major and inter-dependent components, i.e., image acquisition and image processing. The first part comprises a high-frequency, mechanically scanned imaging sonar (MSIS) with bottom-fixed, side-looking working configuration. Major modules of the proposed image processing procedure included: stationary objects subtraction, region and textural feature extraction, unsupervised classification, fish target identification and quantification. For the specific case study conducted in a deep water fishpond, it is evident that individual and school fish could be detected by image frames collected at a randomly selected point with range setting at 5 m. Within an observation period of over an hour where 56 consecutive image frames were collected, both relative abundance of total fish target and prominent fish schools fluctuated with time. This phenomenon could be correlated with the erratic and milling behavior of the milk fish (Chanos chanos) in the pond. The proposed system represented a practical tool in acquiring image frames with sufficient spatial and temporal resolution as well as in detecting and quantifying fish target with limited human intervention for characterizing relative abundance and behavior patterns of fish.

本研究在於探討水下固定式聲學探測技術於底棲魚類數量評估之應用，所提出之探測系統包含二個密切關連的模組：影像收集單元與影像處理單元。其中影像收集單元包含一組海床固定式與側向觀測之高頻機械掃描式影像聲納；影像處理單元之組件包含：靜態物件去除、區域與組織特徵擷取、非監督式分類與魚隻目標物辨識與資料量化等。此探測系統於深水虱目魚塭進行之現場實際驗證顯示：在掃描半徑為5m的參數設定下，可有效進行魚隻與魚群之偵測。在超過一小時之連續探測過程中，共收集56組聲納影像，其中魚隻總數與主要魚群數量隨時間有明顯的變化，此現像與虱目魚之不規則與成群迴游的運動習性相穩合。本研究所提出之探測系統，在影像資訊收集上具有足夠之時間與空間解析度，在魚類數量與行為等資訊的判讀部分可滿足非人為介入的需求，對於水下與底棲魚類資源的探測，尤其是台灣附近海域人工魚礁聚魚效果之評估，具有實質效益。