Geology topics

Michael F. O’Dea

Publications and source records attributed to Michael F. O’Dea.

4 recordsLinked to original sources

USGS2015

Evidence for episodic acidification effects on migrating Atlantic salmon Salmo salar smolts

Field studies were conducted to determine levels of gill aluminium as an index of acidification effects on migrating Atlantic salmon Salmo salar smolts in the north-eastern U.S.A. along mainstem river migration corridors in several major river basins. Smolts emigrating from the Connecticut River, where most (but not all) tributaries were well buffered, had low or undetectable levels of gill aluminium and high gill Na + /K + -ATPase (NKA) activity. In contrast, smolts emigrating from the upper Merrimack River basin where most tributaries are characterized by low pH and high inorganic aluminium had consistently elevated gill aluminium and lower gill NKA activity, which may explain the low adult return rates of S. salar stocked into the upper Merrimack catchment. In the Sheepscot, Narraguagus and Penobscot Rivers in Maine, river and year-specific effects on gill aluminium were detected that appeared to be driven by underlying geology and high spring discharge. The results indicate that episodic acidification is affecting S. salar smolts in poorly buffered streams in New England and may help explain variation in S. salar survival and abundance among rivers and among years, with implications for the conservation and recovery of S. salar in the north-eastern U.S.A. These results suggest that the physiological condition of outmigrating smolts may serve as a large-scale sentinel of landscape-level recovery of atmospheric pollution in this and other parts of the North Atlantic region.

Journal of Fish Biology↗

USGS2014

Migratory patterns of hatchery and stream-reared Atlantic salmon Salmo salar smolts in the Connecticut River, U.S.A.

The timing of downstream migration and detection rates of hatchery-reared Atlantic salmon Salmo salar smolts and stream-reared smolts (stocked 2 years earlier as fry) were examined in the Connecticut River (U.S.A.) using passive integrated transponder (PIT) tags implanted into fish and then detected at a downstream fish bypass collection facility at Turners Falls, MA (river length 192 km). In two successive years, hatchery-reared smolts were released in mid-April and early May at two sites: the West River (river length 241 km) or the Passumpsic (river length 450 km). Hatchery-reared smolts released higher in the catchment arrived 7 to 14 days later and had significantly lower detection rates than smolts stocked lower in the catchment. Hatchery-reared smolts released 3 weeks apart at the same location were detected downstream at similar times, indicating that early-release smolts had a lower average speed after release and longer residence time. The size and gill Na + /K + -ATPase (NKA) activity of smolts at the time of release were significantly greater for detected fish (those that survived and migrated) than for those that were not detected. Stream-reared pre-smolts (>11·5 cm) from four tributaries (length 261–551 km) were tagged in autumn and detected during smolt migration the following spring. Stream-reared smolts higher in the catchment arrived later and had significantly lower detection rates. The results indicate that both hatchery and stream-reared smolts from the upper catchment will arrive at the mouth of the river later and experience higher overall mortality than fish from lower reaches, and that both size and gill NKA activity are related to survival during downstream migration.

Connecticut, Massachusetts, Rhode Island, Vermont↗

USGS2013

Physiological and endocrine changes in Atlantic salmon smolts during hatchery rearing, downstream migration and ocean entry

Billions of hatchery salmon smolts are released annually in an attempt to mitigate anthropogenic impacts on freshwater habitats, often with limited success. Mortality of wild and hatchery fish is high during downstream and early ocean migration. To understand changes that occur during migration, we examined physiological and endocrine changes in Atlantic salmon (Salmo salar) smolts during hatchery rearing, downstream migration, and early ocean entry in two successive years. Gill Na + /K + -ATPase activity increased in the hatchery during spring, increased further after river release, and was slightly lower after recapture in the ocean. Plasma growth hormone levels increased in the hatchery, were higher in the river, and increased further in the ocean. Plasma IGF-I remained relatively constant in the hatchery, increased in the river, then decreased in the ocean. Plasma thyroid hormones were variable in the hatchery, but increased in both river- and ocean-captured smolts. Naturally reared fish had lower condition factor, gill NKA activity, and plasma thyroxine than hatchery fish in the river but were similar in the ocean. This novel data set provides a vital first step in understanding the role and norms of endocrine function in smolts and the metrics of successful marine entry.

Maine↗

USGS2012

Thresholds for short-term acid and aluminum impacts on Atlantic salmon smolts

Although the negative effects of acid and aluminum (Al) on smolt development have been known for some time, the thresholds for impact of short-term exposure of several days that may occur during episodic acidification have not been systematically examined. In order to determine the levels of acid and Al that impact juvenile Atlantic salmon, smolts and yolk-sac larvae were exposed to three pH levels (6.0, 5.7, and 5.3) and four added Al levels (0, 40, 80 and 175 μg/L total Al) for 48 h. Following this treatment, 10 smolts were sampled in freshwater and another 10 were subjected to a 24 h seawater challenge (35 ppt). Survival of yolk-sac larvae was > 96% in all acid and Al treatments. All smolts died within 48 h at pH 5.3, 175 μg L− 1 Al. There were some mortalities in freshwater at pH 5.3, 80 μg L− 1 Al and pH 5.7, 175 μg L− 1 Al, and further mortalities when these fish were transferred to seawater. Mortalities in these groups were associated with decreased plasma chloride in freshwater and higher plasma chloride in seawater, indicating that these smolts had lost seawater tolerance. Gill Na+/K+-ATPase (NKA) activity decreased at pH 5.7, 175 μg L− 1 Al in freshwater, and further decreases were observed at more moderate pH and Al exposures after transfer to seawater. Hematocrit and plasma glucose were the most sensitive physiological responses, increasing at all Al treatments at pH 5.7 and 5.3 in freshwater. There was no detectable increase in gill Al levels at pH 6.0 with added Al, whereas substantial increases in gill Al were observed in all added Al groups at pH 5.7 and 5.3. Our results demonstrate a critical interaction between acid and Al in their effects on smolts, and that episodic acidification events will negatively impact smolt survival in freshwater and after seawater entry.

Aquaculture↗