Changes in food web dynamics and ocean productivity over the past 4500 years are investigated using stable isotope analysis of nitrogen and carbon in collagen from animal bones preserved in coastal arche - ological middens on Sanak Island, along the eastern edge of the Aleutian archipelgo. Samples included Steller sea lions, Harbor seals, Northern fur seals, sea otters, Pacific cod and sockeye salmon. Sea otters had the high - est δ 13 C ( −11.9 ± 0.7‰) and lowest δ 15 N values (14.5 ± 1.4‰), Northern fur seals had the lowest δ 13 C values (−13.6 ± 1.4‰), and Steller sea lions had the highest δ 15 N values (18.4 ± 1.4‰) of the marine mammals. Cod isotope values were consistent with those of demersal organisms from near shore habitats ( −12.5 ± 0.9‰ δ 13 C, 16.1 ± 1.4‰ δ 15 N), while salmon values were consistent with those of organisms existing in an open ocean habi - C, corrected for the oceanic Suess Effect, of modern specimens of all species (except Northern fur seals) were sig - nificantly lower than prehistoric animals. Several hypotheses are explored to explain these differences includ ing a reduction in productivity during the twentieth century in this region of the Gulf of Alaska. If true, this sug gests that North Pacific climate regimes experienced during the twentieth century may not be good analogs of North Pacific marine ecosystems during the late Holocene.

http://web.corral.tacc.utexas.edu/UAF/arctos/2011_03_15/Misarti_etal_2009_Changes_in_northeast_Pacific_marine_ecosystems_over_the_last_4500_years.pdf

Changes in northeast Pacific marine ecosystems over the last 4500 years: evidence from stable isotope analysis of bone collagen from archeological middens

A method that links acoustic mapping data to underwater video observations of seafloor substrate is described for use in defining fish habitat. Three study areas in the Aleutian Islands were acoustically mapped using sidescan and multibeam sonar. The sidescan sonar data were used to compute average reflectivity (hardness) and seafloor complexity. The multibeam depth data were used to determine local slope, rugosity (seafloor roughness) and relative height. Underwater video was collected from three to four transects in each of the three study areas. The underwater video was used to classify the seafloor into nine observed primary and secondary substrate classes. A statistical relationship between the observed (video) and the remotely sensed (acoustic) seafloor characteristics was estimated using a classification tree. The best classification tree utilized rugosity, reflectivity and complexity data and produced misclassification rates of less than 25% overall. Mean grain size of sediment samples was not strongly related to the acoustic data. Error rates were highest for those substrate classes with the smallest number of data points. The results highlight the need for adequate sample sizes and coverage of all potential substrate types when groundtruthing acoustic maps.

A bottom-up methodology for integrating underwater video and acoustic mapping for seafloor substrate classification

The 1800-km-long Aleutian Archipelago is a breeding area for more than 10 million seabirds of 26 species. We evaluated the distribution of breeding colonies of 24 common breeding species in relationship to ocean passes of two sizes, availability of nesting habitat and the distribution of introduced predatory mammals. Further, we evaluated population trends and reproductive rates to amplify information about distribution. We compared distributions and demographic parameters based on proposed differences in marine habitats in the eastern, central and western Aleutians. Samalga Pass did not appear to be a break point for breeding seabird distribution as is suggested for oceanographic characteristics and other species groups by papers in this volume. Factors affecting distribution varied with foraging and nesting strategies of various species groups. The three largest breeding aggregations of seabirds in the Aleutians (Buldir, Chagulak and Kiska) all have relatively high species diversity and are located next to large passes. However, when other predictors were considered, proximity to medium or large passes was important mainly for surface-feeding piscivores. The extent of nesting habitat apparently does not limit the distribution of surface- or burrow-nesting species (including planktivores and piscivores). Instead, the distribution of these species probably has been shaped by introduced mammals. Nesting habitat for ledge- and crevice-nesting species is more limited than for surface and burrow nesters but is still fairly widespread. Ledge- and crevice-nesting species are less susceptible to fox predation than are surface and burrow nesters. These species may have been reduced by predation but were not extirpated.

Distribution patterns and population trends of breeding seabirds in the Aleutian Islands

The majority of survival analyses focus on temporal scales. Consequently, there is a limited understanding of how species survival varies over space and, ultimately, how spatial variability in the environment affects the temporal dynamics of species abundance. Using data from the Barents Sea, we study the spatiotemporal variability of the juvenile Atlantic cod (Gadus morhua) survival. We develop an index of spatial survival based on changes of juvenile cod distribution through their first winter of life (from age-0 to age-1) and study its variability in relation to biotic and abiotic factors. Over the 25 years analyzed (1980–2004), we found that, once the effect of passive drift due to dominant currents is accounted for, the area where age-0 cod survival was lowest coincided with the area of highest abundance of older cod. Within this critical region, the survival of age-0 cod was negatively affected by its own abundance, by that of older cod, and by bottom depth. Furthermore, during cold years, age-0 cod survival increased in the eastern and coldest portion of the examined area, which was typically avoided by older conspecifics. Based on these results we propose that within the examined area top-down mechanisms and predation-driven density dependence can strongly affect the spatial pattern of age-0 cod survival. Climate-related variables can also influence the spatial survival of age-0 cod by affecting their distribution and that of their predators. Results from these and similar studies, focusing on the spatial variability of survival rates, can be used to characterize species habitat quality of marine renewable resources.

/pdf/spatial-anatomy-of-species-survival-effects-of-predation-and-2vl98ggsr5.pdf

Spatial anatomy of species survival : Effects of predation and climate-driven environmental variability

Ecosystem management requires information to determine and mitigate adverse impacts of fishing on all ecosystem components. Deep-sea coral and sponge ecosystems often co-occur with fishing activities, and there is considerable research documenting the vulnerability and slow recovery of deep-sea coral and sponge communities to damage. The objective of the present analysis was to construct models that could predict the distribution, abundance and diversity of deep sea corals and sponges in the Aleutian Islands. Generalized additive models were constructed based on bottom trawl survey data collected from 1991 to 2011 and tested on data from 2012. The results showed that deep-sea coral and sponge distributions were strongly influenced by the maximum tidal currents at bottom trawl locations, possibly indicative of reduced sedimentation or increased food-delivery processes near the seafloor in areas of moderate to high current. Depth and location were also important factors affecting the distribution of deep-sea sponges and corals. The analysis resulted in acceptable models of presence or absence for all taxonomic groups and similar fits when models were applied to test data. The best-fitting models of abundance explained between 20 and 25% of the deviance in the abundance data. Current management protects ~50% of the coral and sponge habitat in the Aleutian Islands at depths to 500 m. The models constructed here will allow managers to evaluate ecological versus economic benefits between protecting coral and sponge habitat and allowing commercial fishing by examining the effect of spatial closures on the amount of coral and sponge habitat that is protected.

https://www.int-res.com/articles/meps2014/503/m503p157.pdf

Predictive models of coral and sponge distribution, abundance and diversity in bottom trawl surveys of the Aleutian Islands, Alaska

The goals of this research were to investigate geographic patterns in the Aleutian Island region’s demersal ichthyofauna and to determine whether they reflected the physical and biological oceanographic patterns documented by other authors in this volume. The analyses were structured according to the level of organization: at the community level, patterns in species occurrence and community structure were investigated; at the population level, distribution and abundance were examined; at the individual level, food habits and growth were studied. There were stepchanges in species occurrence, diversity, population distribution and food habits at Samalga Pass and at sites farther west. These longitudinal trends indicated physical and biological variation along the length of the Aleutian Islands chain; however, depth-related patterns were as common as longitudinal patterns in demersal fish distribution. In addition, high catches of patchily distributed species occurred in areas expected to be biological ‘hot spots’ because of increased productivity and prey availability. These patterns suggest linkages between demersal fish ecology and the biophysical processes described by other authors in this volume and indicate that inter-disciplinary research is needed to elucidate the underlying mechanisms.

Geographic patterns in the demersal ichthyofauna of the Aleutian Islands

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Geographic patterns in the demersal ichthyofauna of the Aleutian Islands