Estimating Gulf of Maine zooplankton distributions using multiple frequency acoustic, video and environmental data

Abstract

This thesis develops methods useful for estimating zooplankton distributions in the field by combining acoustic models and an integrated set of field data. The accnracy of existing models for fluid-like and elastic-shelled animals is determined by analysis of scattering data from individual aninials in a laboratory tank. Results indicate that simple two-ray scattering rnodels are accurate and allow predictions of size or orientation of an animal to be made for certain animal orientations. A model for gas-bearing zooplankton is compared with in sit'l multiple frequency acoustic measurements from siphonophores. Estimates of the numerical density of these animals are made using echo integration data from a scientific echo-sounder. Multiple frequency acoustic scattering data from a survey of an internal wave are analyzed to determine the contributions from biologieal and physical sources. Net tow data provide information about biological scatterers while temperature and salinity profiles are used with a theoretical model to predict contributions from physical sources. Results indicate that scattering from physical sources is comparable to that from biological sources in certain regions and that spectra may be used to distinguish these sources. Improved estimates of biomass from acoustic scatteriug data were made by accounting for the scattering contributions from physical sources. This is the first work to quantify the scattering contributions from biological and physical sources of scattering in a field study. It is better to fail in originality than to succeed in iniitation. He who has never failed somewhere, that man cannot be great. If it be said that continual snccess is proof that a man wisely knows his powers, it is only to be added that, in that ease, he knows them to be smaIL Hennan MelvilleDon't believe the hype. That ¡nade the school a place of decent order vVhere books were read and sums were proven true And paper maps t.hat showed t.he land and water vVere held up as the real wide world to you. Always, he kept his eyes upon his books:And now he has grown to be a man fellow .II' classmates are an exceptional group of people, not to mention they're all wicked srnart.From the initial pot-lucks to the defense parties, it's been a fantastic group of people t.o have as my peers.Ann P. was always up for a "date". Liz K. survived 10 hours in a ear with me and didn't have to be institutionalized. Sheri \V. never tackled me too hard while playing rugby. Brenda J. attended Lollapalooza 5 with me. Nicole P. survived with me during our thesis writing. i'ike A. reminded me you're never too old to have fun. 'rom i'd., Lou StL., and l'like B. were the original members of VomeletLe. Suzie \V.enthusiasm for school was a contrast to mine. Fellow NRQ members ,Albert and i'ak, made the last 6 months of school very survivable. Doc Reddy made the best brunclics I've ever eaten, taught me many acronyms, was a co-founder of PNF and rescued me after my kayak was attacked a rogue buoy.

Distributions of physonect siphonulae in the Gulf of Maine and their potential as important sources of acoustic scattering

“…This observation of constant pneumatophore volume, combined with the assumption of an ideal gas at constant temperature (T), implies that the density of the gas increases in an amount proportional to the increase in the water pressure (ideal gas law: p pneumatophore V = nRT, which is equivalent to p pneumatophore = ρ pneumatophore RT, where R = universal gas constant = MR, and R is the gas constant for air). Thus, the density contrast between the pneumatophore gas and the surrounding water at depth z was estimated by g = g 0 (1 + 0.1z), where g 0 = 0.0012 is the density contrast between the pneumatophore and the surrounding water at the surface (Warren 2001). Although the pneumatophore is filled with CO, the properties of air were used as an approximation.…”

“…With the additional assumption that the sound speed variation of the water is small as a function of depth, it can be concluded that, to first order, the variation in the sound speed contrast, h, with depth is small. Consequently, h was taken to be constant throughout the water column, using a value of 0.22 (again, for air) taken from Warren (2001).…”

Computational imaging and automated identification for aqueous environments

“…The three biggest problems for sonar are that most plankton is small and soft and thus does not e¢ ciently re ‡ect sound, models can only account for general categories of plankton, and the exact sonic properties of the water need to be know to account for changes in the observed signal. The consensus is that sonar may give rough estimates of biomass in certain populations, but is not a suitable tool for determining species or genus, especially for scales less than a millimeter [121], [172], [413], [421].…”

“…Non-contact methods for in situ measurements revolve around optical and sonic methods. Sonar is unfortunately not able to identify species and has size limits based on the wavelength, so that while it can penetrate further in an aqueous environment, it does not o¤er the detail needed for species-level biological studies [172], [413], [421]. Optical approaches have the best chance at achieving species-speci…c measurements coupled with Tradeo¤ between lateral resolution and depth of …eld.…”

Comparison of acoustic and net sampling systems to determine patterns in zooplankton distribution

“…There is a clear advantage in using zooplankton sampling methods which return distribution information on the same spatial and temporal scale as physical measurements. Multifrequency acoustic methods are a promising, and increasingly popular, approach to estimate zooplankton distribution and biomass patterns [ Greenlaw , 1979; Holliday and Pieper , 1980; Wiebe et al , 1996; Holliday et al , 1998; Warren , 2001; Holliday et al , 2003]. These instruments provide scientists with the ability to rapidly map distributions of scatterers at high spatial resolution without disturbing the observed organisms.…”