Stock Assessment of Connecticut River Shad: Examination of Fishing and Predation Effects on the Recent Stock Decline



Download 0.5 Mb.
Page4/9
Date31.03.2018
Size0.5 Mb.
#44219
1   2   3   4   5   6   7   8   9



Table 3. Parameter estimates and equilibrium overfishing thresholds (Fmsy, Nmsy) for Connecticut River shad derived from the Gompertz external production model. The model was fitted to the LTS Robust regression model. The standard error (SE) is given for each parameter estimate (a, b), as well as the coefficient of determination (r2). Overfishing thresholds (Fmsy, Nmsy) are presented with 80% CI.

LTS Robust Regression Model
Parameter Mean SE P

a 3.611 1.00 < 0.0004


b -0.507 0.144 < 0.0004
r2 0.58

Overfishing Thresholds

________________________________________________________________________

Threshold Mean 80% Confidence Limit



________________________________________________________________________
Fmsy 0.51 0.32 – 0.69
Fcoll 1.38 0.87 – 1.88
Nmsy 456,000 fish 288,000 – 621,000 fish
________________________________________________________________________


Table 4. Coastwide striped bass abundance from tagging (Strip*1000), coastwide striped bass abundance from VPA (Strip2*1000), striped bass index from LIS (Stripls), bass index from the river (Stripriv), estimated bass population size in the river (Striprv*1000) and American shad prerecruit mortality (Z0)- note that all of the above estimates are for 72cm+ striped bass except for the LIS estimates (Stripls).




Year


Strip

Strip2

Stripls

Stripriv

Striprv

Z0

1981

1300

215







63.70




1982

1395

218







68.36




1983

1619

253







79.33

0.102

1984

1734

271

0.02




84.97

0.498

1985

1498

234

0.00




73.40

1.069

1986

1734

271

0.00




84.97

0.392

1987

1210

357

0.05




59.29

0.861

1988

2849

348

0.04




139.60

1.064

1989

3827

501

0.06




187.52

0.597

1990

2075

997

0.16




101.68

0.924

1991

1844

1278

0.15




90.36

1.205

1992

1994

1840

0.22




97.71

1.000

1993

2486

2022

0.27

11

121.81

1.966

1994

4027

2373

0.30

44

197.32

2.998

1995

3486

2832

0.59

13

170.81

2.922

1996

5201

3129

0.63

86

254.85

2.657

1997

4893

3606

0.85

142

239.76

2.866

1998

3877

4120

0.97

110

189.97

3.093

1999

4256

4072

1.10

59

208.54

3.169

2000

8280

4592

0.84

198

405.72

2.331

2001

9907

5960

0.61

126

485.44

2.136

2002

13066

6621

1.30

113

640.23

2.280

2003

13672

6056

0.87

162

669.93

2.501

2004

17099

6712

0.56

203

837.85

2.765

2005

21102

6923

1.17




1034.00

3.110



Table 5. Population estimate and 95% confidence limits (CI) of striped bass in the Connecticut River from April through June, 1994 based on the Petersen mark-recapture method (Savoy 1995). Note that this table was taken from Savoy and Crecco (2004).

-----------------------------------------------------------------
Statistic Estimate or Number
-----------------------------------------------------------------

Number Tagged (M) 346 1/

Number Recaptured (R) 26 2/

Recreational Catch in River (C) 30,610 3/

Population Estimate (P) 407,300

95% Confidence Limits 269,400 to 604,100 4/

1/ Marked fish were reduced by 50% (from 692 tagged fish to 346 fish) to reflect a combination of factors including tag loss, tag-induced mortality and migration of tagged fish from the River to LIS.
2/ Number of recaptures increased to reflect a 60% (from 16 recaptures to 26 recaptures) reporting rate.
3/ Striped bass recreational catch in the Connecticut River was taken from the MRFSS and information in the 1994 Volunteer Angler Survey.
4/ 95% confidence limits were based on a Poisson distribution of recaptures (Appendix 2, Ricker 1975).

Table 6. Results of striped bass dietary studies in the Connecticut River during 2005 and 2006 conducted by Mr. Justin Davis as part of his Doctoral dissertation. The dietary data (234 stomach samples) are expressed as the percentage of river herring and shad biomass in the stomachs of striped bass distributed by 10 cm length groups.

Striped Bass
Size class (cm) % biomass river herring % biomass shad
------------------------------------------------------------------------------------------------------------
< 30 0 0
30 – 39 0.8 0
40 – 49 1.7 0
50 – 59 2.5 3.7
60 – 69 18.3 5.9
70 – 79 41.1 6.3
80 – 89 34.4 8.3
90 – 99 9.2 45.5
> 100 5.8 82.4

Table 7. Parameter estimates and approximate equilibrium overfishing thresholds for Connecticut River shad derived from the Steele-Henderson production model with predation effects. The Steele-Henderson production model (equation 6) with striped bass predation effects was fitted by least squares iterative re-weighting with lognormal error using data for 1981-2005. The standard error (SE) is given for each parameter such as the intrinsic rate of shad population increase (r), shad carrying capacity (K in numbers), striped bass per capita consumption (c), and shad stock size at which striped bass satiation (A) takes place. The coefficient of determination (r2) is also shown. Averaged long-term overfishing thresholds (avFmsy, avFcoll, avBmsy) with 95% CI are also shown below.

Iterative Re-weighting Least Squares

Parameter Mean SE

________________________________________________________________________
r 0.59 0.09
K 1,396,000 fish 210,611 fish
c 0.88 0.21


Download 0.5 Mb.

Share with your friends:
1   2   3   4   5   6   7   8   9




The database is protected by copyright ©ininet.org 2024
send message

    Main page