ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on April 24, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):1012-1020; doi:10.1093/icesjms/fsn065
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Side-aspect target-strength measurements of bay anchovy (Anchoa mitchilli) and Gulf menhaden (Brevoortia patronus) derived from ex situ experiments
1 Department of Oceanography and Coastal Sciences, School of the Coast and Environment, Louisiana State University, Baton Rouge, LA 70803, USA
2 Louisiana Sea Grant College Program, Louisiana State University, Baton Rouge, LA 70803, USA
Correspondence to K. M. Boswell: tel: +1 225 578 9390; fax: +1 225 578 6513; e-mail: kboswe1{at}lsu.edu.
Boswell, K. M., and Wilson, C. A. 2008. Side-aspect target strength measurements of bay anchovy (Anchoa mitchilli) and Gulf menhaden (Brevoortia patronus) derived from ex situ experiments. – ICES Journal of Marine Science, 65: 1012–1020.Acoustic target strengths (TSs) of bay anchovy [Anchoa mitchilli, 4.7–6.1 cm TL (total length)] and Gulf menhaden (Brevoortia patronus, 5.1–7.7 cm TL) were measured at 420 kHz during side-aspect, ex situ experiments. TS–TL relationships were derived at aspect for tethered individuals, and TS distributions were compared with those of free-swimming fish. Linear models relating TS and TL were fitted to data at two levels of pulse duration (0.1 and 0.4 ms) for both side aspect and all horizontal aspects of each species, and for pooled data from both species. At a pulse duration of 0.4 ms, the side-aspect TS–TL relationships were anchovy: TSlateral = 19.5 log10 TLcm – 62.4; menhaden: TSlateral = 26.1 log10 Lcm – 65.6; pooled: TSlateral = 32 log10 TLcm – 70.9. For all horizontal-aspect orientations (0–180° in the horizontal) the best-fit TS–TL relationships were anchovy: TSall = 20 log10 TLcm– 65.4; menhaden: TSall = 20 log10 TLcm – 64.8; pooled: TSall = 20 log10 TLcm– 65. However, the "fit" for all angles was consistently low. Predicted TS comparisons with side-aspect models presented by earlier authors suggested biases in the estimated TL. Additionally, relationships between TS and wet weight (W) were derived for each species. Variation in TS by pulse-duration level suggests the potential for the use of this factor as a time-dependent variable by which to separate echoes from bay anchovy and Gulf menhaden.
Keywords: anchovy, menhaden, pulse duration, side aspect, target strength
Received 16 August 2007; accepted 28 February 2008; advance access publication 24 April 2008.
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