Browsing College of Fisheries and Ocean Sciences (CFOS) by Subject "snow crab"
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Defining genetic population structure and historical connectivity of snow crab (Chionoecetes opilio)The snow crab (Chionoecetes opilio) is a valuable commercial resource within the Bering Sea, as well as other areas in the North Pacific and Atlantic Oceans. Large populations are known to exist within the Chukchi and Beaufort Seas, including recently discovered commercial sized individuals (Beaufort). However, genetic connectivity throughout these regions has not been examined until now. Based on seven polymorphic microsatellite loci, relatively low population genetic structuring occurs throughout the Alaskan region (Gst = 0.001). This homogeneity is likely due to long-distance larval dispersal, adult migrations, and a possible recent population expansion following the last glacial maximum. Furthermore, meta-population analysis was conducted for Alaskan and Northwest Atlantic stocks. Although significant genetic divergence characterizes the West Greenland stock in relation to all other populations, low divergence (Gst = 0.005) was found between Atlantic Canada crabs and those from the Alaska region. Larval dispersal between regions is highly unlikely due to the transit distance. Therefore, low divergence is likely the result of a recent population expansion into the Northwest Atlantic <5000 years ago.
Effects of climate variability and fishing on gadid-crustacean interactions in subarctic ecosystemsSnow crab (Chionoecetes opilio) are a vital economic and biotic resource to many subarctic ecosystems. Their abundance varies greatly, but what causes large changes in production and early life survival is unknown. My overall goal is to improve our understanding of snow crab population dynamics during early life history stages. Chapter 1 provides background information on subarctic ecosystems, addresses possible mechanisms of population control and potential drivers of variability, describes snow crab life history, and reviews recent population trends in snow crab and their major cod predators. Chapter 2 details a regression study examining the effects of snow crab spawning stock biomass, environmental conditions, and Pacific cod (Gadus macrocephalus) or Atlantic cod (Gadus morhua) biomass on snow crab recruitment. This study compares three ecosystems: the eastern Bering Sea, the Newfoundland-Labrador Shelf, and the southern Gulf of St. Lawrence. Cold ocean conditions during early life history were associated with increased snow crab recruitment or recruitment indices in all three ecosystems. However, there was no consistent observed effect of spawning stock biomass or gadid predation on subsequent recruitment. The dominant role of environmental conditions in driving snow crab recruitment highlights the importance of an ecosystem-based management approach for these stocks.
Evaluating potential age structures for three Alaska crustacean speciesBanding patterns are observed in calcified structures of red king crab (Paralithodes camtschaticus), snowcrab (Chionoecetes opilio), and spot shrimp (Pandalus platyceros). Recent research supports an age determination method based on these banding patterns; however, processing methodologies for these structures have not been established. Further, species-specific evidence is needed to determine whether these patterns indicate actual age or growth. The objectives of this thesis are to: (1) describe optimal species-specific methods for producing and evaluating band counts for red king crab, snow crab, and spot shrimp; and (2) use differences in shell condition to test whether band counts indicate age for snow crab. For each species, we comprehensively thin-sectioned structures, evaluated each section for banding pattern presence (readability), and developed band count criteria. To address objective 1, we used generalized additive models to describe readability across structures to find the location that optimizes the production of readable sections. For objective 2, we used a one-way ANOVA to compare band count and endocuticle measurements among shell conditions in snow crab. Results indicated preferred structures, locations, section orientation, and thickness. Results also indicated that there is no relationship between band count and shell condition for terminally molted snow crab. These results describe optimal methods for processing crustacean structures and suggest that the potential age structures may not continue to produce bands after terminal molt in the case of snow crab. Further evaluation is needed to validate potential age relationships and the use of this technique for age estimation.