1. No category

REPRODUCTIVE POTENTIAL OF
EASTERN BERING SEA TANNER
CRAB
Laura Stichert, Joel Webb, and Doug Pengilly
Alaska Department of Fish and Game, Division of Commercial Fisheries
Measuring Reproductive Potential
Motivation

Do refined indices of female reproductive potential
alter perceptions of stock renewal processes?
Tanner Crab,
Chionoecetes bairdi
Ashton Photography
www.lastfrontier.org
Motivation


Fishery open for only six of past eighteen years;
historic harvest exceeded 10,000 mt
Spawning stock biomass appropriate for exploited
species with complex reproductive biology?
 impact
estimation of biological reference points
 alter perceptions of stock productivity

Extensive data available on variation in egg
clutch size (volume) from assessment surveys
Life History
Shell Condition
Reproductive
status
Approximate
years postmaturity
Immature
Newshell
(SC2)
Oldshell
(SC3)
Very Oldshell
(SC4-5)
Primiparous
Young Multiparous
Old Multiparous
≤~ 1yr.
~2-4 yr.
4+ yr.
Clutch Fullness Index
Orensanz et al. 2005
Objectives



Evaluate effectiveness of CFI as an indicator of
differences in fecundity
Estimate size-fecundity relationships by CFI and
develop an index of stock egg production
Examine association among egg production and
indices of mature male and female abundance
Methods


414 females of collected by CFI class in the EBS
during US NMFS eastern Bering Sea trawl surveys
from 2005-2010
Fecundity (dry weight) and clutch volume estimated
and clutch fullness index assigned for each female
Clutch Fullness Index
400,000
Fecundity
300,000
200,000
100,000
0
50
70
90
110
Carapace Width (mm)
ANCOVA; R2=0.87
130
Fecundity by CFI
Model-adjusted Mean Fecundity
(+/- 95% CI)
200,000
e
150,000
d
c
100,000
b
50,000
a
0
CF2
CF3
CF4
CF5
Tukey HSD; p<0.05
CF6
Maximum clutch volume
Population CFI Variability
% of Female Abundnace
100%
75%
≥CF5
50%
≤ CF4
25%
0%
1994
1998
2002
2006
2010
2014
EPI Estimation
Egg Clutch Fullness
400,000
Fecundity
300,000
𝑛
200,000
𝑛
𝐸𝑃𝐼𝑡 =
100,000
𝐴𝐼𝑖,𝑗,𝑡 𝐹𝑗,𝑘
𝑖
0
50
70
90
110
Carapace Width (mm)
130
𝑗
Egg Production Index
1.20E+13
Egg Production Index
1.00E+13
8.00E+12
CF6
CF5
CF4
CF3
CF2
6.00E+12
4.00E+12
2.00E+12
0.00E+00
1994
1998
2002
2006
2010
2014
Male and Female RP
Pearson Correlation
MF
MF
MM
LM
MM
0.51 (0.08, 0.77)
LM
EPI
0.26 (-0.20, 0.63) 0.95 (0.87, 0.98)
0.73 (0.43, 0.89)
0.56 (0.17, 0.80)
0.43 (-0.01, 0.73)
EPI
First differenced time-series and alpha adjusted by Bonferroni correction
Conclusions




CFI is a robust index of differences in fecundity
Differences in maximum clutch volume between
studies… shifting baselines may be problematic
Variation in egg production index is strongly
associated with mature female abundance – less so
with males.
Identifying biological covariates including mating
dynamics associated with low CFI could clarify the
impact of exploitation on mating success
Acknowledgements




Funding from ADF&G and NOAA grants
Kirsten MacTavish
NMFS EBS Crab and Groundfish survey
All those who have worked on the ADF&G
reproductive potential of female Chionoecetes crabs
long term study in Kodiak and Juneau.