Ecological commonalities among pelagic fishes: comparison of freshwater ciscoes and marine herring and sprat

Systematic comparisons of the ecology between functionally similar fish species from freshwater and marine aquatic systems are surprisingly rare. Here, we discuss commonalities and differences in evolutionary history, population genetics, reproduction and life history, ecological interactions, behavioural ecology and physiological ecology of temperate and Arctic freshwater coregonids (vendace and ciscoes, Coregonus spp.) and marine clupeids (herring, Clupea harengus, and sprat, Sprattus sprattus). We further elucidate potential effects of climate warming on these groups of fish based on the ecological features of coregonids and clupeids documented in the previous parts of the review. These freshwater and marine fishes share a surprisingly high number of similarities. Both groups are relatively short-lived, pelagic planktivorous fishes. The genetic differentiation of local populations is weak and seems to be in part correlated to an astonishing variability of spawning times. The discrete thermal window of each species influences habitat use, diel vertical migrations and supposedly also life history variations. Complex life cycles and preference for cool or cold water make all species vulnerable to the effects of global warming. It is suggested that future research on the functional interdependence between spawning time, life history characteristics, thermal windows and genetic differentiation may profit from a systematic comparison of the patterns found in either coregonids or clupeids

Water chemistry and its effects on the physiology and survival of Atlantic salmon \u3ci\u3eSalmo salar\u3c/i\u3e smolts

The physiological effects of episodic pH fluctuations on Atlantic salmon Salmo salar smolts in eastern Maine, U.S.A., were investigated. During this study, S. salar smolts were exposed to ambient stream-water chemistry conditions at nine sites in four catchments for 3 and 6 day intervals during the spring S. salar smolt migration period. Plasma chloride, plasma glucose, gill aluminium and gill Na+- and K+-ATPase levels in S. salar smolts were assessed in relation to ambient stream-water chemistry during this migration period. Changes in both plasma chloride and plasma glucose levels of S. salar smolts were strongly correlated with stream pH, and S. salar smolt mortality occurred in one study site with ambient stream pH between 5·6 and 5·8 during the study period. The findings from this study suggest that physiological effects on S. salar smolts are strongly correlated with stream pH and that in rivers and streams with low dissolved organic carbon (DOC) concentrations the threshold for physiological effects and mortality probably occurs at a higher pH and shorter exposure period than in rivers with higher DOC. Additionally, whenever an acidification event in which pH drops below 5·9 coincides with S. salar smolt migration in eastern Maine rivers, there is potential for a significant reduction in plasma ions of S. salar smolts

Coarse woody habitat and glacial lake fisheries in the Midwestern United States: knowns, unknowns, and an experiment to advance our knowledge

Coarse woody habitat and glacial lake fisheries in the Midwestern United States: knowns, unknowns, and experiment to advance our knowledge. Lake Reserv Manage. 35:382–395. Coarse woody habitat (CWH) additions have increased in popularity in glacial lakes (i.e. kettle lakes) of the Midwestern United States. However, most enhancements have not been treated as deliberate experiments to test for fish and aquatic ecosystem responses. Whole-lake CWH removal studies have shown reductions in fish growth rates, declines in forage fish abundance, and behavioral changes. Whole-lake CWH addition studies have shown improved reproductive output of certain fishes, increased availability and diversity of prey available to fishes, and influenced behavior and habitat use. Key uncertainties identified in previous CWH addition studies include: (1) Does CWH increase fish production? (2) Does CWH influence certain fish species differently? (3) Does CWH influence fish populations in larger lakes than previously studied? (4) Does CWH influence fish populations over longer periods of time? In 2015, we began a whole-lake CWH addition experiment on a northern Wisconsin lake aimed to address these uncertainties. Sanford Lake maintains a low productivity fish community and supports fishes not generally studied before in the context of CWH. Fish population dynamic/behavior and aquatic ecosystem response variables will be monitored, and tree drop CWH additions are slated for 3 phases over 20 yr. We introduce the Sanford Lake experiment and provide recommendations for expectations and the implementation of CWH additions in inland glacial lakes. Given the reliance of north-temperate inland glacial lake fisheries on allocthonous sources of energy and negative influences of lakeshore residential development on CWH, we hypothesize that CWH addition may contribute to maintaining or enhancing fish production