Seasonal Estimates of Fish Biomass and Length Distributions Using Acoustics and Traditional Nets to Identify Estuarine Habitat Preferences in Barataria Bay, Louisiana

Abstract

We conducted hydroacoustic, gill‐net, and push trawl surveys to quantify changes in habitat‐specific fish size and biomass in shallow (<2‐m) estuarine waters of Barataria Bay, Louisiana, in order to evaluate essential fish habitat. Surveys were conducted monthly between June 2003 and May 2004 among regions located along a north—south salinity gradient. The fish length distributions derived from the gill‐net and push trawl catches showed moderate concordance with the measured target strength distributions, indicating that our integrated approach more effectively characterized the fish community than using only a single gear type would have. Acoustic estimates showed that biomass was highest during fall (mean ± SE; 2.30 ± 0.27 g/m3) and next highest in spring (1.49 ± 0.20 g/m3), with relatively low biomass during summer (0.70 ± 0.14 g/m3) and winter (0.86 ± 0.14 g/m3); pelagic fish biomass from nets was low during winter (53.9 ± 14.9 grams per unit effort [gpue]) but relatively high in fall (846.1 ± 207.2 gpue), spring (774.3 ± 175.5 gpue), and summer (620.3 ± 140.7 gpue). Oyster habitat supported a greater biomass of pelagic fish (acoustic survey: 1.54 ± 0.15 g/m3; gill‐net survey: 467.3 ± 81.0 gpue) than soft‐bottom habitat (acoustic: 0.94 ± 0.11 g/m3; gill‐net: 315.2 ± 54.8 gpue). Among regions, the greatest biomass of pelagic fish was observed at polyhaline stations (acoustic: 1.78 ± 0.19 g/m3; gill‐net: 654.3 ± 136.5 gpue), followed by mesohaline (acoustic: 1.18 ± 0.15 g/m3; gill‐net: 378.5 ± 79.1 gpue) and oligohaline stations (acoustic: 0.82 ± 0.12 g/m3; gill‐net: 228.3 ± 50.2 gpue). Gill‐net biomass was linearly related to the acoustic biomass estimates of small pelagic fish. The complementary, multigear approach proved to be useful in evaluating habitat use and may be particularly helpful in identifying and monitoring ecosystem reference points to evaluate change and in standardizing ecosystem‐based assessment approaches.

Relationship between horizontal hydroacoustic stock estimates and gillnet catches of surface-oriented fish in shallow Lake Balaton (Hungary)

“…In accordance with other studies (Hansson and Rudstam, 1995;Boswell et al, 2010;Dennerline et al, 2012), we found that gillnet catches hardly correlated with fish density estimates obtained from an acoustic survey, which is the most widely suggested complementary tool to improve and calibrate gillnet data. Pure acoustics-derived density estimates accounted for <8.8% of the variation in the gillnetting NPUE data, but they contributed insignificantly to regression models describing BPUE.…”

“…In contrary to the above hypothesis, but in accordance with the observations of Hansson and Rudstam (1995), we did not identify a significant temperature effect in gillnet catches. Corresponding to other observations (Mehner and Schulz, 2002;Boswell et al, 2007Boswell et al, , 2010, size distribution and median size estimates obtained from gillnetting and acoustics differed. It is well known that gillnetting is a highly size selective gear, and in general, it underestimates the presence of small fish (Hamley, 1975;Olin and Malinen, 2003;Prechalová et al, 2009).…”

“…Moreover, gillnetting is a highly destructive tool, causing high mortality in captured fish, and therefore, any methodological development encouraging reduced gillnet use would be favourable (see also Winfield et al, 2009). Because of the problems associated with gillnet sampling, the complementary use of hydroacoustics has widely been suggested (Hansson and Rudstam, 1995;Mehner and Schulz, 2002;Mous et al, 2004;Guillard and Vergès, 2007;Winfield et al, 2009;Boswell et al, 2010). Hydroacoustics is an effective tool for assessing total abundance, size distribution and habitat usage of fish, but with the exception of special situations, it does not provide species-specific information (but see Elliott and Fletcher, 2001;Winfield et al, 2009).…”

“…Hydroacoustics is an effective tool for assessing total abundance, size distribution and habitat usage of fish, but with the exception of special situations, it does not provide species-specific information (but see Elliott and Fletcher, 2001;Winfield et al, 2009). The existence of a positive correlation between acoustics-derived abundance estimates and gillnet CPUE values seems to be ordinary, however its strength varies strongly, and often, it is weak (Hansson and Rudstam, 1995;Mehner and Schulz, 2002;Tátrai et al, 2008;Boswell et al, 2010;Dennerline et al, 2012). Since the catching efficiency of gillnetting varies due to environmental and technical factors, a comparison of data between different gears should consider these variables.…”

Do fish and blue-green algae blooms coexist in space and time?

“…Data were stored in a computer and later processed by the Sonar 5 Pro software (Balk and Lindem 2008). The areal sound backscattering coefficient Sa (m 2 ha −1 ) (MacLennan et al, 2002) was considered as a proxy of fish biomass (Simmonds and MacLennan 2005;Boswell et al, 2010). The volume numerical fish density estimates were carried out using the echo integration method (Sv/TS scaling) (Balk and Lindem 2008).…”