ACOUSTIC BACKSCATTERING BY HAWAIIAN LUTJANID SNAPPERS 夏威夷鯛科聲波探測之研究I. TARGET STRENGTH AND SWIMBLADDER CHARACTERISTICS 單體標物反射強度與泳鰾特性

Kelly J. Benoit-Bird and Whitlow W. L. Au

Reporter :曾綺停

2003 Acoustical Society of America Pages: 2757–2766

Introduction

The most commercially important bottomfish, are the primary species of concern in Hawaiian.

About these deepwater fish and their habitat is very little known.

Need for detailed acoustic backscattering data for targeted species.

Red snapper

Long-tailed red snapper

Pink snapper

Brighma’s snapper

Von Siebold’s snapper

Blue-striped snapper

Objective

The first objective was to obtain controlled measurements of acoustic backscatter strength from all aspects of these fish, particularly the two depleted species and the pink snapper, which is the most commercially valuable species.

The second was to measure the shape, size, and orientation of the swimbladders of the same fish.

Objective three was to assess how acoustic backscattering strength was related to the swimbladder measures and other physiological characters such as length, biovolume, and wet weight.

本文精華資料蒐集採樣泳鰾與 TS之間理論關係

聲學背景分析方法 TS實驗流程及技術

結果分析

Methods

anestsetizedacclimated

transported

Kept alive

captured

文字

A. BackscatterFrequency range of 60 100 150 200 kHz

B. SwimbladdersPreserving

swimbladders to slit the fish ventral side, and inject Plaster of Paris

X rays after frozen, maeasured dorsal and lateral aspect

measured length, total length, displacement volume, and wet weight

over-anesthetization using 2 mL of 2-phenoxy-ethanol

per 10L of seawater

Red snapper

Long-tailed red snapper

Pink snapper

Brighma’s snapper

Von Siebold’s snapper

Blue-striped snapper

C. Data analysis

First, the maximum measured TS was compared to the TS of the fish predicted by modeling the swimbladder as a prolate spheroid.The second model predictstarget strength of the fish by modeling the swimbladder as a sphere with a volume equivalent to that measured from the plaster cast of the swimbladder.

(Furusawa,1988)

(Urick,1983)

Results1.Swimbladders

Red snapper

Long-tailed red snapper

Pink snapper

Brighma’s snapper

Von Siebold’s snapper

Blue-striped snapper

Results2.Target strength

The angle at which the maximum dorsal-aspect target strength was measured had a nearly one-to-one relationship with the angle of the swimbladder relative to the dorsal aspect of the fish, regardless of species

• Pink snapperTS=20.6*㏒ (FSL)-55.1, r2=0.85• Red snapperTS=13.7*㏒ (FSL)-46.4, r2=0.54• Longtailed red snapperTS=12.6*㏒ (FSL)-42.9, r2=0.80

• Pink snapperTS=26.2*㏒ (FSL)-63.5, r2=0.85• Red snapperTS=47.2*㏒ (FSL)-98.3, r2=0.81• Longtailed red snapperTS=28.9*㏒ (FSL)-68.8, r2=0.81

.

Variancevalues increased from 13 to 49 dB with increasing frequency 0.1 to 11 dB

Red snapper

Long-tailed red snapper

Pink snapper

Red snapper

Long-tailed red snapper

Pink snapper

Red snapper

Long-tailed red snapper

Pink snapper

lower

Red snapper

Long-tailed red snapper

Pink snapper

Results3.ModelsAbout both the dorsal and lateral aspects of the fish are the most important for utilizing these measures in a field study.The target strength over this range of angles had a range of 8 to 12 dB in the tilt plane, 2.5 to 7 dB in the roll plane, and 4 to 6 dB in the lateral plane.

Red snapper wet weight (g)=22983*sigma(m2)-18.39 (r2=0.82 P<0.05)Long-tailed red snapper wet weight(g)=24631*sigma(m2)-527.55 (r2=0.71 P<0.05)red snapper wet weight(g)=12665*sigma(m2)-122.91 (r2=0.77 P<0.05)

Discussion

The differences in volume between fish aregreater within each genus than between them.

Target strengths, both lateral and dorsal,of all three target species were correlated with standardlength.

Variance in target strength within individuals aboutthe lateral axis was also high.

This could permit a conversion ofacoustic scattering to snapper species biomass, even if specificspecies identification were not possible.