Nancy J. Brown-Peterson, Robert T. Leaf and Michael J. Andres

Department of Coastal Sciences, University of Southern Mississippi, Ocean Springs, MS

From: Gulf States Marine Fisheries Commission

Gulf Menhaden FisheryOne of the largest fisheries, by volume, in USA

Currently 4 reduction factories operating along Gulf CoastHighly regulated fishery; extends from third week of April through November 1

0

100

200

300

400

500

600

700

0

200

400

600

800

1000

1200

Vessel ton weeks x 1000

Met

ric to

ns x

100

0

Year

Gulf menhaden landings (thou. of metric tons)Nominal fishing effort (thou. of vessel-ton-weeks)

Gulf Menhaden fishery is not overfished and not undergoing overfishing (2015 Gulf Menhaden Regional Management Plan)

14.6% of total population removed annually in fishery (Vaughan et al. 2007)

User group conflicts: recreational fishers fear harvest negatively impacts forage base of popular game fish

Stock assessments based on reproductive data from 1960’s-1970’s (Suttkus and Sundararaj 1961; Coombs 1969; Lewis and Roithmayr 1981)

Background—Gulf Menhaden Stock

Photo from Sanibel Sea School

Objectives

• Describe reproductive biology• Size at maturity• Gonadal development and spawning seasonality• Fecundity and spawning frequency

Photo credit: healthygulf.org

Sampling Methods

Samples obtained from Omega Moss Point MS reduction plant August-October, April-June (fisheries dependent)

Samples obtained from LDWF January – March (fisheries independent)

No samples November and December

Many samples from October – March were frozen; impacts histological analysis

Menhaden boats fishing (credit: Mike Andres) From www.undercurrentnews.com

0%10%20%30%40%50%60%70%80%90%

100%

0 50 100 150 200 250

Mat

urity

Fork Length (FL, mm)

L50 = 137.2 mm FL

Female

0%10%20%30%40%50%60%70%80%90%

100%

0 50 100 150 200 250M

atur

ity

Fork Length (FL, mm)

L50 = 140.8 mm FL

Male

Size at Sexual Maturity

No previous data on size at sexual maturity—assumed 125 – 150 mm FL Age-size relationship suggests sexual maturity occurs late Age 1

(during second autumn of life, assuming January 1 birthdate)

Spawning Seasonality—GSI Values

Female GSI elevated mid-October through mid-MarchMale GSI elevated mid-October through early March

High male GSI valuesCorresponds to reported spawning seasonality

Spawning Seasonality--Histology

Month

15Aug15Sep

1Oct15Oct

15Jan1Feb

1Mar15Mar

15Apr15May

1Jun

Rep

rodu

ctiv

e Ph

ase

(% T

otal

)

0

20

40

60

80

100

120

Imm EDev Dev SC AS Rgs Rgn

Month

15Aug15Sep

1Oct15Oct

15Jan1Feb

1Mar15Mar

15Apr15May

1Jun

Rep

rodu

ctiv

e Ph

ase

(% T

otal

)

0

20

40

60

80

100

120

Imm EDev Dev SC Rgs Rgn

Female Male

Females spawning capable/actively spawning early October – mid MarchMales spawning capable mid September – mid March

5+ month spawning season in Gulf of Mexico

Asynchronous oocyte development, batch spawners

October spawning frequency, based on presence of POF—7.3 daysIndividual female has potential for 25 spawns during reproductive season

Spawning Capable Female Gulf Menhaden

28 October 2014; 177 mm FL 6 October 2014; 171 mm FL

OM

Vtg3Vtg2

CA

POF

Vtg3

Vtg1

CA

Oocyte Diameter (µm)100 200 300 400 500 600 700

Freq

uenc

y

0

20

40

60

80

100

120

140

Oocyte Diameter (µm)100 200 300 400 500 600 700

Freq

uenc

y0

20

40

60

80

100

120

140

October 31186 mm FL

March 18165 mm FL

Oocyte Frequency Distribution of Secondary Growth Oocytes

Gulf Menhaden have determinate fecunditySupported by high GSI values

Recruit all oocytes into vitellogenesis prior to spawning season

Batch Fecundity

Significant relationship between fecundity and fish lengthOlder, larger fish have greater fecundity

Log10 FL (mm)

2.20 2.22 2.24 2.26 2.28 2.30 2.32

Log 10

Bat

ch F

ecun

dity

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

r2 = 0.306p = 0.040logBF = 5.104*(logFL) - 7.468

Mean RBF of 108 ± 19.6 eggs/g fishMean Batch Fecundity of 156 g fish: 16,848 ± 3,065 eggs

Potential Annual Fecundity in 5.5 month spawning season: 387,735Previous annual fecundity estimates: 37,100 – 151,00 (Lewis and Roithmayr 1981)

log10 FL (mm)2.20 2.22 2.24 2.26 2.28 2.30 2.32

log 10

Rel

ativ

e Ba

tch

Fecu

ndity

1.4

1.6

1.8

2.0

2.2

2.4

2.6

r2= 0.116p = 0.233

Relative Batch Fecundity

Length-specific Annual Egg Production

Lewis and Rothmayr 1981

Current Study

Egg production estimates used in most recent stock assessment represent an ~10x reduction from current estimate for all lengths examined

Summary

• Male and female 50% sexual maturity 137-140 mm FL; Age 1• Spawning occurs early October through mid March• Asynchronous oocyte development with determinant

fecundity• Spawning frequency every 7 days• Batch fecundity increases with fish size, age• Batch fecundity 16,848 eggs; annual fecundity 387,735• Fecundity and egg production estimates much higher than

current data used for stock assessments

Acknowledgments

• Sample Collections• Kenny Hebert, Omega Protein• Thu Bui, LSU Extension• Chloe Dean, LA Department of Wildlife and Fisheries

• Sample Processing• Cody Jones, David Dippold, USM

• Landings Data• Steve VanderKooy, Gulf States Marine Fisheries Commission

• Funding• NOAA/NMFS CRP Project NA14NMF4540064