In situ Target Strength versus Fork Length Relations of Trachurus japonicus Extracted from a Set of Acoustic and Corresponding Length Surveys Data

以最適搜尋法解析現場標物反射強度與真鯵尾叉長間之關係

張引(Yin Chang) ； 葉顯椏(Shean-Ya Yeh)

《臺灣水產學會刊》 30卷2期 (2003/06) Pp. 159-170

https://doi.org/10.29822/JFST.200306.0005

摘要

在以聲探回訊積分法估計魚類資源量時，係以標物反射強度與魚體尾叉長間之關係式為基礎，將聲探單位體積背景散亂反射強度轉換成為單位水體積內之魚類資源量。此關係式之正確與否，顯著影響以聲探回訊積分法估計資源量的結果。標物反射強度的測量可分為離境法與現場法兩大類，由於現場法所測得之標物反射強度較能反應環境與生物的自然狀況，相對上應能得到較佳的結果。近年來由於水中聲学科技的進步，已經可以於航測當時量得現場標物反射強度。但是現場標物反射強度在量測時，無法掌控被測魚體，常造成難以確認特定標物反射強度所對應之魚體尾叉長，進而導致難以利用迴歸法估算兩者之間的關係式。在本研究中，我們嘗試利用最適搜尋法，解析現場標物反射強度分佈與其所對應之魚體尾叉長分佈間的關係，進而求得兩者間之關係式。並且以民國八十四年七月，於台灣東北部海域大型圍網漁場，所收集到的㆒組現場標物反射強度分佈，與其所對應之圍網真鯵魚獲體長分佈為例，示範如何以最適搜尋法，估算現場標物反射強度(TS)與魚體尾叉長(FL)間之關係式。搜尋結果為：TS=112.7×log (FL)-205（尾叉長範圍介於17.8-24.6cm，單體魚標物反射強度測量值的標準差為3dB）。為了驗証最適搜尋法的結果，另外設計實驗在港內測量已知體長真鯵活體的標物反射強度，結果與前述最適搜尋法估算結果非常相近。

關鍵字

現場標物反射強度分佈 ； 體長頻度分佈 ； 真鯵

並列摘要

A constrained optimal searching method was developed in this study to estimate the logarithm-linear relations between in situ Target Strength (TS) and Fork Length (FL). This method needed only a set of properly matched data of two surveys, one on acoustic and a corresponding one on length. This paper demonstrated this method by coupling data of in situ TS survey by SIMRAD EK500 (38K Hz) and the length survey, which were carried out concurrently on Trachurus japonicus caught by purse seine vessels in the same waters off NE Taiwan in July 1995. The relationship between in situ TS and FL of T. japonicus obtained by the optimal searching method was: TS=112.7×log (FL)-205. The applicable range of FL for this species was from 17.8 cm to 24.6 cm, and the standard deviation of TS by individual fish was 3 dB. Experiments on hooked alive individual T. japonicus, of which the size for each fish was known, were also carried out and the observed mean TS of these known fish were f ell well in the relational prediction.

並列關鍵字

In situ Target Strength Distribution ； Fork Length Distribution ； Trachurus japonicus