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The abundance of anadromous salmon is partially determined by size-selective mortality during the early marine life phase. Consequently, identifying the growth patterns of juvenile salmon during this life phase is important in understanding the dynamics of salmon populations. We examined patterns of early marine growth in juvenile pink salmon Oncorhynchus gorbuscha released by four hatcheries in Prince William Sound (PWS), Alaska, and explored how these patterns related to marine survival. Since larger individuals are thought to experience reduced mortality, we partitioned the data into weight-based quartiles and compared growth rates (% body weight/d) of all fish, the largest fish (top 25%), and the smallest fish (bottom 25%). Sampling occurred during summer 1997–2004 in PWS, the inshore Gulf of Alaska (GOA), and the offshore GOA. Growth rates varied significantly among years and sampling locations; however, the growth rate patterns were markedly similar among size-groups and hatcheries. Growth rates tended to be high in 1997, 2002, and 2004 and lower in 1998, 2001, and 2003. Fish sampled in the offshore GOA typically had faster growth rates than those sampled elsewhere, although this was less pronounced for the largest fish. For all size-groups, the relationship between survival and growth rate was strongest for fish captured in the offshore GOA and weakest for those captured in PWS, indicating that the likelihood of survival is greater for juveniles that migrate offshore earlier. The strength of the growth rate—survival relationship for pink salmon captured in the offshore GOA was similar among all size-groups, suggesting that once fish migrate offshore they are less vulnerable to size-selective predation.

Recruitment for many marine fishes is believed to be determined at an early life history stage. Pacific herring (Clupea pallasi) spawn in the intertidal and shallow subtidal zones and have a demersal egg stage that is susceptible to egg removals during incubation. Data were collected by the Alaska Department of Fish and Game in four years in Prince William Sound, Alaska, to identify important factors contributing to egg removals. We constructed analysis of variance models based on physical and biological variables to determine which environmental factors control egg loss rates. The habitat variables examined at each study transect were depth, wave exposure, north-south location, substrate, vegetation, mean bird abundance, abundance of loose eggs, and fish predation. Depth of spawn was the primary factor determining egg loss. Cumulative time of air exposure over incubation was substituted into the model for depth. Using the model, the total estimated egg loss from spawning to hatching ranged from 67 to 100% with an average of 75% (SE = 3.3%) in 1995. Eggs were originally deposited from 4 to -6 m depth relative to mean low water. The majority of eggs that remained in the spawning beds to hatching were deposited from 1 to -4 m depth. Egg removals due to avian predation were probably responsible for extreme egg loss rates at shallow depths.

The abundance of anadromous salmon is partially determined by size-selective mortality during the early marine life phase. Consequently, identifying the growth patterns of juvenile salmon during this life phase is important in understanding the dynamics of salmon populations. We examined patterns of early marine growth in juvenile pink salmon Oncorhynchus gorbuscha released by four hatcheries in Prince William Sound (PWS), Alaska, and explored how these patterns related to marine survival. Since larger individuals are thought to experience reduced mortality, we partitioned the data into weight-based quartiles and compared growth rates (% body weight/d) of all fish, the largest fish (top 25%), and the smallest fish (bottom 25%). Sampling occurred during summer 1997-2004 in PWS, the inshore Gulf of Alaska (GOA), and the offshore GOA. Growth rates varied significantly among years and sampling locations; however, the growth rate patterns were markedly similar among size-groups and hatcheries. Growth rates tended to be high in 1997, 2002, and 2004 and lower in 1998, 2001, and 2003. Fish sampled in the offshore GOA typically had faster growth rates than those sampled elsewhere, although this was less pronounced for the largest fish. For all size-groups, the relationship between survival and growth rate was strongest for fish captured in the offshore GOA and weakest for those captured in PWS, indicating that the likelihood of survival is greater for juveniles that migrate offshore earlier. The strength of the growth rate-survival relationship for pink salmon captured in the offshore GOA was similar among all size-groups, suggesting that once fish migrate offshore they are less vulnerable to size-selective predation.

Feeding of larval walleye pollock was examined with respect to density and distribution of micro- and mesozooplanktonic prey (<500 μm) at 6 depths in the oceanic domain of the Bering Sea to determine if first-feeding larvae select among available prey and to assess their foraging environment in comparison to other locations where walleye pollock spawn. At 30 m depth, walleye pollock larvae and copepod nauplii occurred at maximum densities of 106.6 ind. 100 m−3 and 26.3 ind. l−1, respectively. First-feeding walleye pollock larvae (3.5 to 6.5 mm) fed exclusively on copepod nauplii and copepod eggs. Among copepod nauplii, larvae selected for Metridia sp. and Microcalanus sp. but against Oithona similis, even though the latter was the most abundant prey taxon in the study area. Of the nauplii ingested by larval walleye pollock, there was evidence of selection for larger nauplii within Metridia sp., Microcalanus sp., and O. similis. In addition, larvae preferred Stages III to V of calanoid nauplii. Larvae at 30 m depth had the highest incidence of feeding (97.5 %) and number of prey items (4.6 larva−1) ingested. Although the 30 m depth stratum provided best physical and foraging conditions, the overall low percentage of feeding larvae and low numbers of prey consumed suggest that foraging conditions for larval walleye pollock at the time of sampling were below saturation feeding levels.

Aurelia labiata medusae occurred in aggregations with hundreds to millions of jellyfish. The aggregations were widely distributed in inlets of Prince William Sound (PWS), Alaska. Aerial surveys of PWS in May to August in 1995, 1996, and 1997 showed marked interannual variation in the numbers of aggregations observed, from a minimum of 38 in 1997 to a maximum of 557 in 1996. Acoustic surveys showed that the aggregations extended from near-surface (0 to 5 m) to 15 m depth. Schools of young-of the-year walleye pollock Theragra chalcogramma were associated with A. labiata, both within and below the aggregations. All seine catches that contained juvenile pollock also contained jellyfish. Medusa swimming was analyzed from underwater videotapes in order to elucidate how aggregations might be formed and maintained. Medusae did not swim in circles in the aggregations. Medusae all swam vertically in the same direction, either up or down, in crowded parts of the aggregations, suggesting that they had become concentrated in flow features, like convergences, in the water column. Reduced swimming, due primarily to frequent collisions among medusae in the aggregations, also may have caused the medusae to become concentrated. The potential advantages of aggregation include increased fertilization success, retention near shore where planula settlement sites and zooplankton prey may be more abundant, retention in convergences where zooplankton are concentrated, and reduced predation.

Fish larvae were collected at 6 depths in Auke Bay, southeastern Alaska, USA, on 4 days in May and June 1987. On 3 dates samples were collected between 08:00 and 13:00 h, on the other date samples were collected every 4 h during 24 h. Vertical distributions of light, temperature, salinity, chlorophyll and copepod nauplii were also measured. Wind speed data were available from a nearby station. Smelt (Osmeridae) larvae, the most abundant larval fish taxon, migrated to the surface at midnight, whereas walleye pollock, flathead sole, rock sole, poacher (Agonidae) and northern smoothtongue moved deeper at dusk. During the day, most fish larvae were concentrated from 5 to 15 m, broadly overlapping the highest abundances of copepod nauplii, although poacher and northern smoothtongue were consistently deeper (15 to 25 m). Diurnally, smelt larvae were shallow (5 to 10 m), and pycnocline depth accounted for more variability in their mean depth than any other biotic or physical variable. Mean depths of the other 5 most abundant taxa were in the same rank order by depth in all 4 sets of daytime samples, and depth of isotherms below the pycnocline accounted for more variation in their mean depths than did any other variable. The diurnal depth distributions we observed apparently result from temperature preferences among marine larval fishes, with descent at dusk as the most common form of diel vertical migration.

Five species of rockfish (Sebastes spp.) were examined off southeast Alaska for Sarcotaces arcticus (Copepoda). Only Sebastes ciliatus was infected. Sarcotaces were compared to those found in 7 species of Sebastes collected off California and those from Molva dypterygia collected off Norway. As a result of these comparisons it is suggested that Sarcotaces komaii be synonymized with S. arcticus. It is possible that S. arcticus is synonymous with Sarcotaces verrucosus. Studies on aspects of the host-parasite relationship indicated that younger fish have a higher prevalence of infection and more multiple infections. There is no host-parasite size relationship. Seventy-five percent of the female parasites were associated with males, 85% had eggs and 10% nauplius larvae. Females ranged in size from 20 to 50 mm. Smaller specimens were represented by degenerated cysts. There was no indication of parasite-induced host mortality. The absence of infection in some species may be more a result of the hosts' natural history and geographic distribution than parasite specificity.