Using Hydroacoustics to Spatially Quantify Productive Capacity in Freshwater Ecosystems

Using Hydroacoustics to Spatially Quantify Productive Capacity in Freshwater Ecosystems

A Thesis Proposal Submitted by Riley Pollom in Partial Fulfillment of the Requirements for the

Master’s of Science Degree in Biology at Memorial University of Newfoundland

Advisor: Dr. George A. Rose – Director, Centre for Fisheries Ecosystems Research

(Fisheries and Marine Institute of Memorial University)

Committee: Dr. Daniel Boisclair – Professor, Département de Sciences Biologiques

(Université de Montréal); Scientific Director, NSERC HydroNet Strategic Network

Dr. Rodolphe DeVillers – Professor, Department of Geography (Memorial University)

Statement of Purpose

It is the purpose of this MSc. thesis to determine hydroacoustic methods to evaluate

the productive capacity of fish habitats in freshwater lakes and reservoirs in Manitoba, and

to discover how this productive capacity varies over space within and between natural and

reservoir systems. This research is part of NSERC’s HydroNet research program

(Smokorowski et al. 2011).

Introduction

Freshwater ecosystems of the world provide people with a vast amount of

ecosystem services that are vital to our survival and well-being (Brauman et al. 2007). One

of the most salient services provided by these ecosystems is the production of fish for

human consumption and recreation. Increasingly, freshwater systems and the services

they provide - including fish productivity - are under threat from multiple stressors

(Ormerod et al. 2010). One of the major ways in which the productive capacity of fish

habitats (i.e. the total production of all stock during the time they spend any part of their

life history in that habitat; Minns 1997) is altered is through the creation and operation of

hydropower facilities (Rosenberg et al. 1997).

In Canada there is a federal mandate to protect fish habitat and productive capacity

through a ‘no net loss’ approach (DFO 1986), however it remains prohibitively challenging

to measure such capacity in the field (Randall and Minns 2002; Smokorowski et al. 2011).

Challenges include the need for long-term monitoring and the necessary measurement of

multiple ecosystem components such as plankton production and interactions among

trophic levels. Even when such comprehensive studies are undertaken, they can lead to

ecosystem disturbances and fish mortality that can contradict the ultimate goals of the

project (Argent and Kimmel 2005).

Hydroacoustics offer a substantial contribution to the amelioration of the challenges

for assessing aquatic production. The technology allows researchers to study multiple

facets of ecosystems including fish, plankton, macrophytes, and bathymetry relatively

quickly over large areas and with minimal impact to the studied environment (Simmonds

and MacLennan 2005). Hydroacoustics have long been used in marine environments for

studying fish (e.g. Trout et al. 1952; Tungate 1956; Robichaud and Rose 2002), and have

more recently been applied to the study of freshwater environments in northern Europe

(e.g. Mehner et al. 2007; Godlewska et al. 2009), the Pacific Northwest (e.g. Ransom et al.

1998; Scheuerell and Schindler 2004), and the Laurentian Great Lakes (Rudstam et al.

2009).

Although hydroacoustics have traditionally been used only for fish surveys,

scientists studying smaller planktonic organisms have recently adopted the technology.

Euphasiid shrimp (Amakasu and Furusawa 2006), smaller-bodied zooplankton

(Georgakarakos and Kitsiou 2008), and even phytoplankton (Selivanovsky et al. 1996)

have been assessed using hydroacoustics. This versatility of the technology allows for a

comprehensive examination of pelagic aquatic ecosystems at relatively low cost in terms of

both man-hours and subject mortality.

Another advantage of hydroacoustics is the spatial resolution of the data collected.

Integrated GPS and a high ping rate (the number of sound waves sent per unit time)

provide data for analysis at various spatial scales, including across an entire lake as well as

at meso- and microscale habitat patches. This presents the opportunity to appreciate

pattern and process at multiple levels, and to understand the aquatic ecosystem more fully

(Rose and Leggett 1990; Levin 1992).

One of the major potential drawbacks of using hydroacoustics is the difficulty

associated with species identification (Horne 2000). The echograms produced through the

use of hydroacoustic devices effectively depict the body size of an organism (as a function

of target strength, or TS), but it is very challenging to be confident in the actual

identification of fish species, and the possibility of identifying plankton is even more

remote. Body size has been seen, however, as fundamental to the ecology of individuals for

many decades (Elton 1927). Recent literature strongly suggests that the binomial species

classification of organisms may not be as crucial as body size data when studying structure

and function in ecosystems, especially in aquatic environments (Kerr and Dickie 2001;

Hildrew et al. 2007; Belgrano and Reiss 2011).

The theoretical foundations for using organismal body size as a primary avenue for

understanding ecosystems are found in the close linkages between this trait, metabolism,

and energy flux through ecological communities (Woodward et al. 2005). It has even been

suggested that the concepts surrounding body size lie at the heart of a unified theory of

ecology as a discipline (Allen and Hoekstra 1993; Brown et al. 2004).

Body size shows a consistent relationship to metabolic rate across all ecosystems at

the individual level, resulting in strong implications in terms of resource allocation (Brown

et al. 2007; Yvon-durocher et al. 2011). Aquatic ecosystems in particular have provided

evidence to support this theory of size structure, owing largely to the gape-limitation that

only permits efficient feeding for a certain predator-prey body size ratio (Jennings et al.

2001). Body size is thus robustly indicative of the ecology of individuals and the flux of

energy through an ecosystem (White et al. 2007), and can accurately reveal patterns in the

productive capacity of fish habitat at multiple scales.

It is the overarching goal of the present study to use hydroacoustic methods

(combined with a limited amount of traditional sampling techniques for groundtruthing) to

first spatially quantify fish productivity in Lac du Bonnet and Lake Manigotagan, Manitoba,

and then to analyze how this productivity relates to other functional characteristics of the

ecosystem, namely the distribution of organisms at lower trophic levels. Finally, individual

size distributions (ISDs – i.e. a histogram of log10Abundance vs. log10Body Size, sensu White

et al. 2007) will be used to determine how resources are divided across body size classes

within each ecosystem.

Methods

Study Sites

Hydroacoustic surveys will be conducted over two summers on one natural lake

(Lake Manigotagan) and one reservoir (Lac du Bonnet), both of which are a part of the

Winnipeg River system in southeastern Manitoba. The much smaller Lake Manigotagan is

located at 50° 52’N 95° 37W in Nopiming Provincial Park. It is a naturally formed,

undammed lake, and the only human settlements on it are a modest fishing lodge and some

small cabins. Lac du Bonnet is located at 50° 22’N 95° 55’W. It is a reservoir which is

dammed at both ends and is highly developed, with many large summer homes,

campgrounds, and a small town on its banks. Each system has a maximum depth of

approximately 30 metres, and summer surface temperature is approximately 22°C.

Both Lac du Bonnet and Lake Manigotagan lie over the Canadian Shield in the

transition zone between aspen parkland and boreal forest, and can be classified as

mesotrophic. Each is characterized by larger fish such as walleye (Sander vitreus), sauger

(Sander canadensis), northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis)

and burbot (Lota lota), as well as smaller cisco (Coregonus spp.) and shiners (Notropis spp.)

(Stewart and Watkinson 2004; personal observation August 2011).

Hydroacoustic Surveys

Acoustic surveys will be performed in July and August of 2011 and 2012 in both

systems. Parallel straight-line transects will be run along the short axis of the basin getting

as close to the shoreline as possible in order to cover the most ground. Space between

transects will be one nautical mile for Lac du Bonnet and 500m for Lake Manigotagan, with

vessel speeds of 6kts and 4kts, respectively. Areas with high densities of fish targets will be

adaptively sampled with increased transect frequency to capture more variability.

A BioSonics splitbeam DTX echosounder will be used with 200kHz, 430kHz and

1000kHz transducers mounted on a 17’ Boston Whaler. The vessel will have a foam-cored

hull and a four-stroke engine, and will use battery power to reduce noise interference. The

transducers will be deployed on an aluminum arm between 40 and 50cm below the water

surface. Transducers will be calibrated using well-established standard methods (Foote

1982). All acoustic data will be georeferenced with an integrated GPS and collected using

Visual Acquisition Software version 6.0.2 (BioSonics Inc., Seattle, WA, USA). Acoustic fish

target signals will be ground-truthed haphazardly using a combination of gill-netting and

line fishing at sites that are identified as having high fish densities or unique acoustic fish

signal.

Target Strength Experiments

In situ target strength experiments will be performed in order to quantify the

relationship between target strength and body size for the more important species in the

study sites. Fish of a known size will be enclosed in a mesh bag beneath the transducers for

a period of time to record target strength. An underwater camera will be used to help

quantify any deviations in target strength due to fish movement (Gauthier and Rose 2001).

This technique may also shed light on what some of the species that are actually observed

with the hydroacoustics, furthering our understanding of how the ecosystems are

structured.

Plankton Sampling

Plankton sampling to ground-truth acoustic signals will occur haphazardly at sites

with interesting or unrecognized signals (collected with the 1000kHz transducer), with

enough replication to ensure each signal type is consistently identifiable. Vertical tows will

take place with an 80µm plankton net. Zooplankton will be counted, measured and

identified in the lab. A fluorometer will be used to systematically measure chlorophyll a

levels in the water as a proxy for phytoplankton densities. Maps portraying both

zooplankton and phytoplankton distributions will be created using ArcGIS 10 Software

(ESRI Inc., Redlands, CA, USA).

Fish Tagging

During the summer of 2012 several individual fish will be tagged and tracked with

the Vemco VRAP acoustic telemetry system (Amirix Systems Inc., Halifax, NS, Canada) in

order to determine the movement patterns of fish within each system.

Data Analysis

All acoustic data will be edited and analyzed using Echoview version 5.0 (Myriax

Inc., Hobart, TAS, Australia). All noise in the data, including that arising from air bubbles or

wave action will be removed prior to analysis, and bottom lines will be corrected in all data

files. Abundance and biomass estimates of fish will be analyzed, while only biomass

estimates of plankton will be looked at due to logistical difficulties associated with

obtaining count data. Spatial data will be analyzed using intrinsic geostatistical methods

(Rivoirard et al. 2000) with ArcGIS 10 (ESRI).

Potential Results

The results from the first portion of the study will be largely descriptive in nature,

and will lead into the more biologically interesting topics addressed later on. Echograms

(see Figure 4) will be used to create fish and plankton distribution maps for Lac du Bonnet

and Lake Manigotagan. GIS will be used in order to visualize general patterns in

productivity that occur in each system. Biomass estimates will be performed on both fish

and plankton to determine relative abundances and to visualize the system from a ‘bird’s-

eye view’. At this point it may become apparent that fish are avoiding the vessel in

shallower areas, or that different portions of the lake or reservoir are supporting more

biomass. Variability in the biomass estimates from the acoustic surveys may prove to be

quite high. Repetition of surveys will hopefully deal with this problem effectively. In

addition, the fish and/or plankton may display variability in habitat selection, failing to

reveal a particular pattern.

Geostatistical analysis has the potential to reveal different patterns at different

scales in terms of the correlation between fish and plankton biomass. On a small scale, it

may be apparent that fish are not closely associated with food sources, while at a larger

scale they may be more closely linked (i.e. smaller fish or plankton avoid predators, but

predators are always close enough to food sources to access them when necessary). It may

be possible to recognize that fish are associated with a particular plankton species or body

type. Differences between day and night surveys due to diel migrations will become

evident as well.

In terms of the body size analysis, it can be predicted that a hierarchical trophic

pyramid will be exposed, one in which organisms with a much larger body size are much

less abundant and/or make up less biomass in the ecosystem due to metabolic scaling and

differences in energy use and availability. Predicted values for the relationship between

abundance and body mass can be calculated using the equation

Log Abundance = log a + b log Mass ,

where a is a coefficient different for each group, and b (the slope of the regression line) is

approximately equal to -¾ (Boudreau and Dickie 1987). Observed data may deviate from

this as organisms can experience influences that affect their numbers outside of the body

mass – metabolism – energy flux framework, including competition from fish or other

species that are transient in the system, and obtaining resources from outside the system.

In addition, patterns may only be observable at certain scales, and the estimate of body size

used in this case may not capture everything (Hildrew et al. 2007a).

In conclusion, this thesis should provide a general understanding of how the

structure of the aquatic community can be described and analyzed using hydroacoustics.

Patterns of organism distribution will be better understood in both freshwater systems,

and the role of body size on the partitioning and movement of energy throughout the

ecosystem will be exposed. In general the project will help to better understand the

productive capacity of fish habitats and how to assess it. This will lead to further

knowledge about the impacts of hydropower projects on aquatic ecosystems.

Figures

Figure 1. Photo of study site at Lake Manigotagan, Manitoba.

Figure 2. Photo of study site at Lac du Bonnet, Manitoba.

Figure 3. Photo of the deployment system for the acoustic transducers. The arm swings down into the water, orienting the transducer faces toward the lake bottom.

Figure 4. 200 kHz echogram displaying bathymetry, plankton and fish targets in Lake Manigotagan, Manitoba. Hotter colours represent stronger sound wave backscatter detection by the transducer. The lake bottom is the large yellow-green band. Light blue fish targets are visible, and dark purple flecks represent plankton signal, evidently beginning at the thermocline or about eight metres depth. Maximum depth is approximately 25m.

Timetable and Milestones

Milestone Description Timeframe

Acoustic TrainingAttend workshops in Seattle to learn hydroacoustics basics, how to use BioSonics DTX system, how to use Echoview software program.

January 2011

MED-A1 Complete Marine Emergency Duties course January 2011

Research Aboard the RV Celtic Explorer

Taking part in cod acoustic and trawl surveys with other CFER members aboard the RV Celtic Explorer

February 2011

SVOPComplete Transport Canada's Small Vessel Operator's Proficiency course

April 2011

First Field SeasonComplete multiple acoustic surveys of both Lake Manigotagan and Lac du Bonnet; Collect first set of plankton data; Perform some gillnetting to groundtruth acoustic fish signals.

July & August 2011

Course Work

Complete MSc. coursework at MUN including Biology 7220: Model-based Statistics in Biology; Biology 7000: Graduate Core Seminar; and Fisheries Resource Management 6009: Overview of World Fisheries.

September-December 2011

Research ProposalComplete comprehensive research proposal for peer review and editing.

November 21st, 2011

Research Proposal SeminarPresent proposal to Biology 7000 classmates and instructors for critiquing.

November 28th, 2011

Departmental Research Proposal Seminar

Present proposal to MUN Biology Department. December 5th, 2011

Data Editing and AnalysisEdit and analyze data using Echoview. Map plankton and fish distributions using ArcGIS. Perform geostatistical analyses. Preliminary thesis preparations.

January-May 2012

Research Aboard the RV Celtic Explorer

Taking part in cod acoustic and trawl surveys with other CFER members aboard the RV Celtic Explorer

May 2012

Second Field Season

Complete multiple acoustic surveys of both Lake Manigotagan and Lac du Bonnet; Collect more comprehensive plankton data; Perform gillnetting to groundtruth acoustic fish signals; Use VRAP telemetry system to track several fish species in each system; Perform in situ target strength experiments to relate target strength to fish body size.

July & August 2012

Data Editing and AnalysisEdit and analyze data using Echoview. Map plankton and fish distributions using ArcGIS. Perform geostatistical analyses.

September-November 2012

Submit First Draft of Thesis

December 2012

Thesis RevisionsJanuary-February

2012Convocation June 2013

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