Using Bioenergetics Models to Estimate Predation Rates · Using Bioenergetics Models to Estimate...

Using Bioenergetics Models to Using Bioenergetics Models to Estimate Predation RatesEstimate Predation Rates

Kyle J. HartmanKyle J. Hartman

West Virginia UniversityWest Virginia University

Wildlife & Fisheries Resources Wildlife & Fisheries Resources ProgramProgram

OutlineOutline

1)1) Background on bioenergetics.Background on bioenergetics.

2)2) Model requirements.Model requirements.

3)3) Predation case studies.Predation case studies.

4)4) Strengths and weaknesses.Strengths and weaknesses.

Bioenergetics principlesBioenergetics principles

Based on the 1Based on the 1stst Law of Thermodynamics.Law of Thermodynamics.

Energy cannot be created or destroyed…Energy cannot be created or destroyed…

Balanced Energy EquationBalanced Energy Equation

Balanced Energy EquationBalanced Energy Equation

Balanced Energy EquationBalanced Energy Equation

Balanced Energy EquationBalanced Energy Equation

The “Wisconsin” ModelThe “Wisconsin” Model

Jim Jim KitchellKitchell et al. 1974 and 1977.et al. 1974 and 1977.Convenient computer software (v. 3.0 1997).Convenient computer software (v. 3.0 1997).

Framework used to estimate predation by Great Framework used to estimate predation by Great Lakes Lakes salmonidssalmonids, prey fish, lamprey, walleye, , prey fish, lamprey, walleye, etc.etc.

Used to estimate predation by striped bass and Used to estimate predation by striped bass and other Atlantic coast predators.other Atlantic coast predators.

Basic model requirementsBasic model requirements

1.1. Measures of growth of average Measures of growth of average individual.individual.

2.2. Water temperatures occupied by fish.Water temperatures occupied by fish.3.3. Diet composition (mass).Diet composition (mass).4.4. Energy content of predator and prey.Energy content of predator and prey.5.5. Population parameters (N, Z, I & E) Population parameters (N, Z, I & E) –– if if

applying to populations.applying to populations.

Coastal Striped Bass Case StudyCoastal Striped Bass Case Study

R2 = 0.6191

R2

= 0.76890

1000200030004000

50006000700080009000

0 10 20 30 40 50

Age 1-7 Striped Bass (millions)

Men

hade

n (m

illio

ns)

MH LandingsAge-0 MH VPA

In the midIn the mid--Atlantic Atlantic –– Concern that burgeoning striped Concern that burgeoning striped bass pops were influencing Atlantic menhaden bass pops were influencing Atlantic menhaden

populations.populations.

Atlantic menhaden are important in Atlantic menhaden are important in regional diets (Walters et al. 2003)regional diets (Walters et al. 2003)

CBDEL

0

50

100

150

200

250

300

Spring Summer Fall Winter

Men

hade

n co

ntrib

utio

n (%

) 601-1183 mm

451-600 mm

150-450 mm

Chesapeake Bay & Delaware Bay

Atlantic menhaden are important in Atlantic menhaden are important in regional diets (Walters et al. 2003)regional diets (Walters et al. 2003)

NCARO all sizes

0

10

20

30

40

50

60

70

80

90

100

Spring Summer Fall Winter

Men

hade

n co

ntri

butio

n (%

)

North Carolina

Several model analyses to evaluate Several model analyses to evaluate predation by striped bass in predation by striped bass in

Chesapeake BayChesapeake BayStep 1.Step 1. Estimating increases in SB predatory Estimating increases in SB predatory demand demand

(1982(1982--2001).2001).

Step 2.Step 2. Comparing Chesapeake Bay predatory Comparing Chesapeake Bay predatory demand (1991 vs. 2002) and evaluating demand (1991 vs. 2002) and evaluating importance of menhaden vs. alternate prey in importance of menhaden vs. alternate prey in “fattening” period.“fattening” period.

Step 3. Step 3. Timing and magnitude of SB use of MH.Timing and magnitude of SB use of MH.

Step 4.Step 4. Evaluating management actions upon Evaluating management actions upon predatory demand. predatory demand.

CoastwideCoastwide Bioenergetics Modeling Bioenergetics Modeling MethodsMethods

Modeled coast wide Modeled coast wide poplspopls. . 19821982--2001, ages 12001, ages 1--10.10.

Used the Hartman & Brandt Used the Hartman & Brandt (1995) BM and energy (1995) BM and energy densities.densities.

ASMFC (2003) mortality ASMFC (2003) mortality estimates.estimates.

Water temperatures from Water temperatures from coastal area (Hartman 2003).coastal area (Hartman 2003).

CoastwideCoastwide Population Population ConsumptionConsumption

0

20

40

60

80

100

120

140

160

180

1982 1988 1992 1995 1998 1999 2000 2001

Con

sum

ptio

n (1

000

mt)

age-10

age-9

age-8

age-7

age-6

age-5

age-4

age-3

age-2

age-1

Coastal Predatory Demand increasedCoastal Predatory Demand increased

Population level consumption increased Population level consumption increased 265% from 1982 to 1988.265% from 1982 to 1988.

Consumption increased 227% from 1988 Consumption increased 227% from 1988 to 1992.to 1992.

Population ConsumptionPopulation Consumption

Peaked in 2001 (155,500 t)Peaked in 2001 (155,500 t)

88--fold increase from 1982 fold increase from 1982 –– 1995.1995.

SB consuming up to 57% of menhaden SB consuming up to 57% of menhaden harvested per year (261,000 to 413,000 t ). harvested per year (261,000 to 413,000 t ).

Management approaches to reduce Management approaches to reduce Predatory DemandPredatory Demand

Management OptionsManagement OptionsResultsResults

Changing ageChanging age--atat--entry (AE) and fishing entry (AE) and fishing mortality (by increments of 0.10) had mortality (by increments of 0.10) had similar impacts on PD.similar impacts on PD.

Moving AE from ageMoving AE from age--5 to age5 to age--4 reduced 4 reduced PD 17% at intermediate F.PD 17% at intermediate F.

Similar declines by increasing F from 0.25 Similar declines by increasing F from 0.25 to 0.35.to 0.35.

Strengths & WeaknessesStrengths & Weaknesses

Strengths or PlusesStrengths or Pluses

Models have been validated for many species.Models have been validated for many species.

Model already exists for striped bass.Model already exists for striped bass.

Much of the siteMuch of the site--specific data needs may already specific data needs may already be available:be available:–– TemperatureTemperature

–– DietsDiets

–– Growth?Growth?

–– Population parameters?Population parameters?

Weaknesses or MinusesWeaknesses or Minuses

Models are only as good as the inputs Models are only as good as the inputs and assumptions.and assumptions.

Most BM applications assume closed Most BM applications assume closed systems.systems.

Final thoughtsFinal thoughts

BMs have commonly been linked to more BMs have commonly been linked to more complex / dynamic models to address complex / dynamic models to address complex questions.complex questions.

E.g. E.g. IBMsIBMs, spatial models, etc., spatial models, etc.

SB select strongly for clupeid fishes.

Prey Selectivity in Albemarle Sound, NC

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Menhaden Alosa yellow perch Menidia

Perc

ent p

ositi

ve s

elec

tivity

Age-1Age-2Age-3+

N = 8 - 33

** MH not selected for only in earliest samples (late May) for age-2, 3+; tended to be selected for May thru July for age-1 SB.