Wild Chinook salmon productivity is negatively related to seal density and not related to hatchery releases in the Pacific Northwest

Predation risk and competition among conspecifics significantly affect survival of juvenile salmon, but are rarely incorporated into models that predict recruitment in salmon populations. Using densities of harbour seals (Phoca vitulina) and numbers of hatchery-released Chinook salmon (Oncorhynchus tshawytscha) smolts as covariates in spatially structured Bayesian hierarchical stock–recruitment models, we found significant negative correlations between seal densities and productivity of Chinook salmon for 14 of 20 wild Chinook populations in the Pacific Northwest. Changes in numbers of seals since the 1970s were associated with a 74% decrease (95% CI: −85%, −64%) in maximum sustainable yield in Chinook stocks. In contrast, hatchery releases were significantly correlated with Chinook productivity in only one of 20 populations. Our findings are consistent with recent research on predator diets and bioenergetics modeling that suggest there is a relationship between harbour seal predation on juvenile Chinook and reduced marine survival in parts of the eastern Pacific. Forecasting, assessment, and recovery efforts for salmon populations of high conservation concern should thus consider including biotic factors, particularly predator–prey interactions.

Temperature regimes, growth, and food consumption for female and male adult walleye in Lake Huron and Lake Erie: a bioenergetics analysis

Bioenergetics modeling was used to assess the relative importance of food availability and water temperature in determining walleye (Sander vitreus) growth. Temperature regimes experienced by both female and male adult walleye in three basins of Lake Huron and in Lake Erie were determined by use of surgically implanted temperature loggers and acoustic telemetry. Temperatures experienced by walleye were higher in Lake Erie than in Lake Huron. Walleye from Lake Erie grew at nearly double the rate of walleye from Lake Huron, and mass at age for adult females averaged about 50% greater than that for adult males in both lakes. Food consumption rate for an average adult walleye in Lake Erie was nearly twice as high as that in Lake Huron. Interbasin and interlake variability in temperature regimes accounted for a moderate degree of variability in walleye growth. We concluded that the driver for faster growth in Lake Erie compared with Lake Huron was higher food availability in Lake Erie compared with Lake Huron. The sex difference in temperature regimes explained 15% of the sex difference in Lake Erie walleye growth.

Black Bass Diversity: Multidisciplinary Science for Conservation

<em>Abstract.</em>—Largemouth Bass <em>Micropterus salmoides</em> is typically thought of as a freshwater species, but populations occur in oligohaline portions of estuaries throughout the U.S. Atlantic and Gulf of Mexico coasts, often with popular fisheries. These coastal populations must deal with the physiological stresses associated with salinity variation and may be isolated from inland freshwater populations, increasing the potential for differentiation. To understand factors important to the ecology and management of these coastal populations, we quantified individual- and population-level parameters for Largemouth Bass across a natural salinity gradient in the Mobile-Tensaw River delta in southwestern Alabama during 2002–2009 (including population demographics, feeding ecology, movement, recruitment, and bioenergetics processes). Combining traditional mark–recapture and telemetry techniques with otolith microchemical analyses, we demonstrated that Largemouth Bass of all ages moved very little, even in response to increasing salinity (up to 15‰) in downstream areas. Large individuals were rare in our sampling across both fresh and brackish habitats (only 7 out of 9,530 individuals were >2.27 kg), and fish body condition increased downstream with increasing marine influence. Growth responses for fish across the estuary were more complex, varying with both fish age and salinity. Faster growth was observed in the brackish, downstream areas for fish ≤age 2, while growth of older fish was faster in freshwater upstream sites. Using bioenergetics modeling, we demonstrated that a complex combination of spatial variation in water temperature, prey energetic content, and metabolic cost of salinity was responsible for age-specific spatial variation in growth. Preliminary genetic analysis suggests that these coastal Largemouth Bass may differ genetically from inland fish. Coastal Largemouth Bass populations face a number of potential conservation concerns, and their management will require different approaches compared to their inland counterparts, including different goals and expectations, likely even requiring consideration as unique stocks.