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Female reproductive potential of eastern Bering
Sea snow crab (Chionoecetes opilio)
Laura M. Slater1,3, Joel B. Webb2, Gordon Kruse3, Franz J. Mueter3, Bernard
Sainte-Marie4, Ginny L. Eckert3, and Douglas Pengilly1
1Alaska Department of Fish and Game, Commercial Fisheries Division, Kodiak, AK, USA. 2Alaska Department of Fish and Game, Commercial Fisheries Division, Juneau, AK, USA.
3University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Juneau, AK, USA. 4Department of Fisheries and Oceans, Maurice Lamontagne Institute, Mont-Joli, QC, Canada.
Motivation
• EBS snow crab is a
federally managed stock.
• FMP approved in 1989.
• The FMP establishes a
State/Federal
cooperative
management regime that
defers crab management
to the State of Alaska
with Federal oversight.
Motivation
Figure modified from Pengilly et al. (2014).
Data compiled from NMFS Fisheries Statistics Division:
www.st.nmfs.noaa.gov/st1/commercial/landings/gc_runc.html.
Commercial
Harvest
EBS snow
crab have
contributed ~¼
of the biomass
of crabs
commercially
harvested in
the U.S. over
the past three
decades
Motivation
How does large-male exploitation influence
female reproductive potential and stock productivity?
Mature male biomass
used as an index of
reproductive potential
in stock assessment
Ashton Photography
www.lastfrontier.org
Goals
• Develop an index of female reproductive potential
that reflects stock mating dynamics
• Analyze spatiotemporal trends in female sperm
reserves to inform functional relationships among
female reproductive potential, maternal
characteristics, and the availability of male mates
• Assess the impact of the fishery’s harvest of only
large males on the reproductive output by females
• Compare new indices with the biomass proxy for
stock productive capacity currently used in
management
Approach
Evaluate Fecundity
• Factors that effect
variability in egg
production
• Clutch fullness index
over survey time series
Evaluate Female
Sperm Reserves
• Male availably for
mating and direct
measure of contribution
to female reproductive
success
• Spatiotemporal
variability
Approach
Shell
Condition
Newshell
(SC2)
Oldshell
(SC3)
Very Oldshell
(SC4-5)
Reproductive
status Immature Primiparous
Multiparous
(Primiparous) Multiparous
Approximate
years post-
maturity
≤~ 1yr. ~2-4 yr. 4+ yr.
Female Reproductive Stage
Approach
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A
AAAA AAAAAAAA AAAA
AAAAAA AAAA
Z-05
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A-06A-05
A-04A-03
A-02
160°W165°W170°W175°W180°
60°N
58°N
56°N
54°N
Depth (m)
0 - 50
50 - 100
100 - 150
> 150
E Stations
A Corner Stations
Study Area: Annual NOAA AFSC EBS shelf trawl survey
Approach
• Sperm
• Eggs
• Maternal characteristics and condition
Sample Processing: Dissect Crabs
Approach
Sample Processing: Sperm Storage
• Wet weight and counts
2nd count
Results
In Press. Canadian Journal of Fisheries and Aquatic Sciences.
Results
Clutch Fullness Index
Results
Robust size-fecundity relationship by clutch fullness
0 1 2 3 4 5 6 7 8 9
Series1
Series2
Series3
Series4
Series5
0
25,000
50,000
75,000
100,000
40 55 70 85
Fec
un
dit
y
Carapace Width (mm)
CFI 2
CFI 3
CFI 4
CFI 5
CFI 6
Linear mixed model, R2=0.80
Results
SC2 SC3
SC4 SC5
Increased variability and decreased output over
reproductive stage (age)
Results
Indices of Reproductive Potential
Conclusions
Egg Production
• clutch fullness index is a robust index of
egg production
• Demography (age & proportion abundance
by age) impacts population egg output
• Egg production index is proportional to
mature female abundance
• Proportion of population on biennial cycle
important but difficult to estimate
Results
2010. Biology and Management of Exploited Crab Populations under
Climate Change.
Results
• Most (92% of
3,781) snow
crab examined
had clutches
with mostly
viable eggs
• Restricted to
eggs with
noticeable
embryonic
development
Results
• Scale established for Atlantic Ocean snow crab
• Low SL where most of population is distributed
• Similar trends by reproductive stage
Primiparous Multiparous
Results
Size declines with latitude across all years
Results
SL also declines with latitude across all years
Results
SL increases with female size
Results
However, when examined at a station level
2012
Results
However, when examined at a station level
2013
Conclusions
Sperm Reserves
• no evidence of current sperm limitation
• re-mating is necessary and occurs
frequently
• lack of buffer against sperm limitation
• persistent spatial trends
Future Directions
Needs and New Opportunities
• Biennial reproduction – difficult to model,
paucity of empirical data
• Relationship with sex ratio (quantity and
quality of males)
• Relationship with temperature
• Genetics of paternity
Many Helping Hands
Pilot Study • Kirsten MacTavish (formerly ADF&G, now IPHC)
Project Management • ADF&G: Nat Nichols, Natura Richardson
Sample Collection – NOAA EBS Survey • ADF&G, NOAA, UAS survey participants, especially: Meg
Inokuma, Mike Knutson, Natura Richardson
Logistics & Sample Transport • ADF&G Kodiak and Dutch Harbor staff, NOAA Kodiak Lab staff,
UniSea
Live Crab Stewardship & Sample Processing • ADF&G in Kodiak and Juneau, especially: Kayla Bevaart, Jassalyn
Bradbury, Leslie Curran, Tara Fritzinger, Meg Inokuma, Sarah
Johnson, Thomas Kinsley, Mike Knutson, Nina Leacock, Natura
Richardson, Andrew Olsen
Funding
• ADF&G, including Bristol Bay Red King Crab Test Fishery
• National Oceanographic and Atmospheric Administration Grants
• North Pacific Research Board (Project #714)
Any Questions?
Laura.Slater@alaska.gov
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