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Acoustic and in situ measurements of freshwater amphipods (Jesogammarus annandalei) in Lake Biwa. Japan
Author(s) -
Trevorrow Mark V.,
Tanaka Yuji
Publication year - 1997
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1997.42.1.0121
Subject(s) - diel vertical migration , nocturnal , thermocline , amphipoda , scattering , population , radius , crustacean , oceanography , geology , biology , physics , ecology , optics , demography , computer security , sociology , computer science
During a 23‐d study of Lake Biwa, Japan (starting 23 August 1993), multifrequency inverted echo‐sounder measurements of nocturnal scattering layers in the meta‐ and epilimnion were performed at a single location. Direct samples from within this scattering layer indicated that it was composed of Jesogammarus annandalei (Crustacea: Amphipoda), with mean adult length of 8.3 mm and population densities from 4 to 50 per m 3 . Estimates of the scattering cross‐section for individual amphipods were extracted from echo‐amplitude probability distributions combined with volume scattering strength from a 198‐kHz sonar. Total scattering cross‐sections for adult amphipods at 88, 118, and 198 kHz were estimated as 4.3±0.9 × 10 −8 m 2 , 8.7±1.2 × 10 −8 m 2 , and 2.8±0.5 × 10 −7 m 2 . These cross‐section measurements were found to be consistent with a fluid cylinder acoustic scattering model with a 1.2‐mm radius and a 9.6‐mm length. The acoustically derived population densities, sizes, and length‐to‐radius ratio were consistent with in situ amphipod samples. The amphipods exhibited a clear nocturnal migration into the lower thermocline, concentrating at depths of 15–25 m beginning after sunset (near 1830 hours local time) each day. Population densities (10‐min averaged) showed maxima of 10–30 per m 3 near 2000 hours, with densities decreasing rapidly toward midnight and disappearing by approximately 0430 hours.