Model Simplifications/assumptions 1.Spatial dynamics Snow and red king crab distributions shifted to north after 1976/77. Snow crab migrated to southwest, deep waters when they grow older; males go to deeper waters than females: Good: few females and juvenile males on fishing ground. Bad: not sure these older males move back to mate with females or not. Males and females may spatially distribute unevenly during mating time. Only spatial consideration in the model is bipartite mating, so this model simplification could be biased toward higher harvest rates

Model Simplifications/assumptions 2.No male/female size difference consideration for snow crab: All other crab stocks modeled by ADF&G have cut-off size for mature males. Median mature males are 38 mm larger than median mature females for snow crab, so the issue may not matter much. This model simplification could slightly be biased toward higher harvest rates

Model Simplifications/assumptions 3.No stored sperm for Tanner and snow females (-). 4.No biennial spawning of female snow crab (in terms of need of males for mating each year) (-). 5.Extremely low natural mortality (-). 6.Assuming low productivity (higher Tau values) of S-R curves (-). 7.No consideration of mating competition for males (or only strong males can mate) (-). 8.High handling mortality rate for snow crab (-). 9.Much lower mating ratios than observed in labs (-). Above model simplifications/assumptions could be biased toward lower (conservative) harvest rates

What do egg clutch data mean? For red king crab:  Females need mating for extruding eggs (McMullen 1969, per. comm. with Drs. Brad Stevens and Tom Shirley).  Some females may extrude unfertilized egg clutches without mating if there are mature males near them, but when males:females ratio is very high, up to 72% of mature females without egg clutches (McMullen and Yoshihara 1969). So, some egg clutches may not be 100% fertilized, and % of barren females may be an indicator of lack of males for mating.

Mature harvest rates At survey time: 75-81: : : 0.16 (mostly 0.2) 94-95: : 0.13 ( ) Bristol Bay Red king crab

What do egg clutch data mean? For Bristol Bay red king crab:  About 0-20% of newshell mature females were barren before 1994, and few barren females occurred under the current harvest rates.  The current mature male harvest rates for retained crab are 10%-15% at the survey time, or 11%-16% at the beginning of the fishing season. With a 20% bycatch mortality rate, total mature male harvest rates range from 13% to 19% at the beginning of the fishing season.  Legal male harvest rates are about 50% to 100% higher than mature male harvest rate, or about 38% or lower based on the current mature harvest rates.

What do egg clutch data mean? For EBS snow crab:  All females can extrude egg clutches and hold them for at least 5 months in the absence of males, and about 20% of the females have full clutches of unfertilized eggs (Rugolo’s lab study).  Are barren females due to lack of males or their own problems? Logically, it may be their own problems.  Senescence may be the cause (Ernst, Orensanz & Armstrong 2005)  Snow crab egg clutch data may not be very useful to answer the question: lack or not lack of males for mating.

EBS snow crab: Reduced fecundity occurred primarily to very old mature females

EBS snow crab: post-terminal molt vs barren females Periods with high proportions of barren females correspond to the periods with very old mature females

One hypothesis is that because fishing occurred primarily in the south (south of 58.5 degree N), barren females in the south is due to lack of males caused by fishing. This hypothesis contradicts with the available data: 1.There were a lot more of old shell mature males to mate with females in the south than in the north ( degree N).

One hypothesis is that because fishing occurred primarily in the south (south of 58.5 degree N), barren females in the south is due to lack of males caused by fishing. This hypothesis contradicts with the available data: 2.There are no consistent difference of egg clutch fullness between north and south. The hypothesis was generated by using two years ( ) of data. There were very small sample sizes for newshell females in the south for some years, so the data are not shown here.

One hypothesis is that because fishing occurred primarily in the south (south of 58.5 degree N), barren females in the south is due to lack of males caused by fishing. This hypothesis contradicts with the available data: 3.Highest proportions of barren females occurred in the north, not south. There were very small sample sizes for newshell females in the south for some years, so the data are not shown here.

Summary of snow crab egg clutch Egg clutch data may be difficult to interpret Reduced fecundity/barren females are highly correlated to senescence There are no supports for the hypothesis that reduced fecundity/barren females in the south were caused by lack of males due to fishing Preliminary results of egg fertilization study: 52 out of 54 mature females sampled during 2005 summer survey carried fertilized eggs, and remaining two cannot be decided (Kirsten Gravel) ADF&G will continue to study egg fertilization rates, hopefully working with U.of AK and NMFS

Female Snow Crab