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- Piccolo, John, et al.
(author)
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Feeding intensity, diet, and survival in relation to body size of juvenile pink salmon
- 2009
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Conference paper (peer-reviewed)abstract
- Variations in body size and growth rates in a cohort of juvenile fish can lead to differences in the feeding ecology of different sized conspecifics, thus, increasing differential survival in the cohort. Consequently, identifying the relationships between body size, feeding ecology, and survival is important in understanding mortality of juvenile fishes during the early marine life phase. We used feeding intensity, diet composition, and growth rate data collected from juvenile pink salmon (Oncorhynchus gorbuscha) to investigate how feeding ecology differs between large and small conspecifics and how the growth rates of large and small individuals influences overall marine survivorship. The sampling occurred from 1997-2004 and encompassed three marine habitats in the northern Gulf of Alaska. Feeding intensity did not significantly differ between large and small individuals across all habitats. Diet composition varied more among years and habitats than between large and small individuals. Within a year and habitat the diet composition of large and small conspecifics differed more in offshore waters than the near shore habitats with larger pink salmon eating more fish and less large copepods than smaller conspecifics. Growth positively related to marine survival in all habitats. The growth of fish sampled in offshore habitats related stronger to survival than the growth of fish in the near shore habitats. Within the offshore waters, the growth rates of larger individuals better explained marine survival than the growth of smaller conspecifics. These results suggest that diet composition does differ between small and large conspecifics on small temporal and spatial scales, which may allow larger individuals to exploit bigger and more energy rich prey, resulting in increase survival of larger fish.
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- Piccolo, John, et al.
(author)
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Seasonal distribution and size of juvenile pink salmon in the Gulf of Alaska: relating ocean habitat use to growth and survival
- 2007
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Conference paper (peer-reviewed)abstract
- Each year millions of wild and hatchery juvenile pink salmon enter the waters of Prince William Sound (PWS) in the northern Gulf of Alaska. By mid summer, they begin to migrate out of PWS, first into the Alaska Coastal Current (ACC), and then into Shelf waters, where they forage and grow prior to migrating offshore in the fall. Differences in feeding and growth conditions among PWS, ACC, and Shelf habitats are likely to affect growth during the first summer, and ultimately cohort survival. In July-September of 2001-2004, we collected juvenile pink salmon with a surface trawl in PWS, ACC and Shelf habitats, to determine their seasonal distribution, diet, and growth. In July of all years, catch per unit effort was relatively high in PWS and ACC habits, and low in the Shelf habitat. By August and September this pattern had reversed, with most fish being caught in the Shelf habitat. Fish from year classes that subsequently showed higher adult survivals (2002 and 2004) were larger, and they tended to migrate into Shelf habitats earlier than did those with lower adult survivals (2001 and 2003). Using thermal mark recovery of PWS hatchery cohorts, we compared the size of known-age fish in the different habitats. In three of four years, hatchery fish of the same age were significantly larger in Shelf habitats than they were in ACC or PWS habitats. In general, hatchery cohorts that had larger juveniles in late summer had higher adult survivals, but there was considerable variation in this trend both among hatcheries and among years
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