Showing papers by "National Marine Fisheries Service published in 2006"
TL;DR: Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production, but it is shown that these ecosystems are shifting away from these characteristics.
Abstract: Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean.
855 citations
TL;DR: In this article, spatial and temporal patterns are discussed using maps of surface temperature, salinity, and nutrients (phosphate, silicate, nitrate and nitrite), and thermocline and mixed layer parameters.
634 citations
TL;DR: Evidence is presented from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species, and this remains true after accounting for life-history effects, abundance, ecological traits and phylogeny.
Abstract: The separation of the effects of environmental variability from the impacts of fishing has been elusive, but is essential for sound fisheries management. We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments. Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment. Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species. This remains true after accounting for life-history effects, abundance, ecological traits and phylogeny. The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure, which reduces the capacity of populations to buffer environmental events. Therefore, to avoid collapse, fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure. The double jeopardy of fishing to potentially deplete stock sizes and, more immediately, to amplify the peaks and valleys of population variability, calls for a precautionary management approach.
572 citations
TL;DR: In this paper, the authors discuss some of the problems associated with the use of cpue data and some methods to assess and provide management advice about fish populations that can help overcome these problems, including integrated stock assessment models, management strategy evaluation and adaptive management.
Abstract: Despite being one of the most common pieces of information used in assessing the status of fish stocks, relative abundance indices based on catch per unit effort (cpue) data are notoriously problematic. Raw cpue is seldom proportional to abundance over a whole exploitation history and an entire geographic range, because numerous factors affect catch rates. One of the most commonly applied fisheries analyses is standardization of cpue data to remove the effect of factors that bias cpue as an index of abundance. Even if cpue is standardized appropriately, the resulting index of relative abundance, in isolation, provides limited information for management advice or about the effect of fishing. In addition, cpue data generally cannot provide information needed to assess and manage communities or ecosystems. We discuss some of the problems associated with the use of cpue data and some methods to assess and provide management advice about fish populations that can help overcome these problems, including integrated stock assessment models, management strategy evaluation, and adaptive management. We also discuss the inappropriateness of using cpue data to evaluate the status of communities. We use tuna stocks in the Pacific Ocean as examples.
494 citations
TL;DR: In this paper, a high-resolution physical-biological model for the U.S. east coast continental shelf and adjacent deep ocean was developed to estimate nitrogen fluxes in the shelf area of the Middle Atlantic Bight (MAB).
Abstract: [1] The biogeochemistry of continental shelf systems plays an important role in the global elemental cycling of nitrogen and carbon, but remains poorly quantified. We have developed a high-resolution physical-biological model for the U.S. east coast continental shelf and adjacent deep ocean that is nested within a basin-wide North Atlantic circulation model in order to estimate nitrogen fluxes in the shelf area of the Middle Atlantic Bight (MAB). Our biological model is a relatively simple representation of nitrogen cycling processes in the water column and organic matter remineralization at the water-sediment interface that explicitly accounts for sediment denitrification. Climatological and regionally integrated means of nitrate, ammonium, and surface chlorophyll are compared with its model equivalents and were found to agree within 1 standard deviation. We also present regional means of primary production and denitrification, and statistical measures of chlorophyll pattern variability. A nitrogen budget for the MAB shows that the sediment denitrification flux is quantitatively important in determining the availability of fixed nitrogen and shelf primary production (it was found to remove 90% of all the nitrogen entering the MAB). Extrapolation of nitrogen fluxes estimated for the MAB to the North Atlantic basin suggests that shelf denitrification removes 2.3 � 10 12 mol N annually; this estimate exceeds estimates of N2 fixation by up to an order of magnitude. Our results emphasize the importance of representing shelf processes in biogeochemical models.
379 citations
TL;DR: This work builds on the nursery concept by developing a framework for evaluating juvenile habitats based on their overall contribution to adult populations, and introduces the concept of Effective Juvenile Habitat (EJH) to refer to habitats that make a greater than average overall contributionto adult populations.
Abstract: Much recent attention has been focused on juvenile fish and invertebrate habitat use, particularly defining and identifying marine nurseries. The most significant advancement in this area has been the development of a standardized framework for assessing the relative importance of juvenile habitats and classifying the most productive as nurseries. Within this framework, a marine nursery is defined as a juvenile habitat for a particular species that contributes a greater than average number of individuals to the adult population on a per-unit-area basis, as compared to other habitats used by juveniles. While the nursery definition and framework provides a powerful approach to identifying habitats for conservation and restoration efforts, it can omit habitats that have a small per-unit-area contribution to adult populations, but may be essential for sustaining adult populations. Here we build on the nursery concept by developing a framework for evaluating juvenile habitats based on their overall contribution to adult populations, and introduce the concept of Effective Juvenile Habitat (EJH) to refer to habitats that make a greater than average overall contribution to adult populations.
365 citations
TL;DR: The depth distributions of marlin and sailfish monitored with electronic tags and average dissolved oxygen and temperature profiles show that this cold hypoxic environment constitutes a lower habitat boundary in the ETP, but not in the western North Atlantic (WNA), where DO is not limiting.
Abstract: Large areas of cold hypoxic water occur as distinct strata in the eastern tropical Pacific (ETP) and Atlantic oceans as a result of high productivity initiated by intense nutrient upwelling. We show that this stratum restricts the depth distribution of tropical pelagic marlins, sailfish, and tunas by compressing the acceptable physical habitat into a narrow surface layer. This layer extends downward to a variable boundary defined by a shallow thermocline, often at 25 m, above a barrier of cold hypoxic water. The depth distributions of marlin and sailfish monitored with electronic tags and average dissolved oxygen (DO) and temperature profiles show that this cold hypoxic environment constitutes a lower habitat boundary in the ETP, but not in the western North Atlantic (WNA), where DO is not limiting. Eastern Pacific and eastern Atlantic sailfish are larger than those in WNA, where the hypoxic zone is much deeper or absent. Larger sizes may reflect enhanced foraging opportunities afforded by the closer proximity of predator and prey in compressed habitat, as well as by the higher productivity. The shallow band of acceptable habitat restricts these fishes to a very narrow surface layer and makes them more vulnerable to over-exploitation by surface gears. Predictably, the long-term landings of tropical pelagic tunas from areas of habitat compression have been far greater than in surrounding areas. Many tropical pelagic species in the Atlantic Ocean are currently either fully exploited or overfished and their future status could be quite sensitive to increased fishing pressures, particularly in areas of habitat compression.
338 citations
TL;DR: Water quality criteria for aquaculture systems have typically considered parameters such as temperature, dissolved oxygen, total gas pressure, ammonia, and nitrite as mentioned in this paper, but these criteria may not be appropriate for a single species and life stage, especially in commercial applications.
296 citations
TL;DR: Though much has been made of the detrimental effects of El Nino events on apex predators, more research is needed to understand the magnitude, and even direction, of these effects on seabirds and cetaceans in space and time.
280 citations
TL;DR: In this article, the authors proposed a model to predict channel patterns in forested mountain river systems of the Pacific Northwest, USA, and found that the predicted spatial distribution of channel patterns reflects a downstream decline in channel slope, which is likely correlated with a declining ratio of bed load to suspended load.
243 citations
TL;DR: Stable 13C and 15N analysis on white shark vertebrae demonstrated that incremental analysis of isotopes along the radius of a vertebral centrum produces a chronological record of dietary information, allowing for reconstruction of an individual's trophic history.
Abstract: We conducted stable 13C and 15N analysis on white shark vertebrae and demonstrated that incremental analysis of isotopes along the radius of a vertebral centrum produces a chronological record of dietary information, allowing for reconstruction of an individual's trophic history. Isotopic data showed significant enrichments in 15N with increasing sampling distance from the centrum center, indicating a correlation between body size and trophic level. Additionally, isotopic values verified two distinct ontogenetic trophic shifts in the white shark: one following parturition, marking a dietary switch from yolk to fish; and one at a total length of >341 cm, representing a known diet shift from fish to marine mammals. Retrospective trophic-level reconstruction using vertebral tissue will have broad applications in future studies on the ecology of threatened, endangered, or extinct species to determine life-long feeding patterns, which would be impossible through other methods.
TL;DR: It is argued that sexual recruitment is more prevalent in the eastern range of A. palmata than the west, and that these geographic differences in the contribution of reproductive modes to population structure may be related to habitat characteristics.
Abstract: Species that build the physical structure of ecosystems often reproduce clonally, both in terrestrial (e.g., grasses, trees) and marine (e.g., corals, seagrasses) environments. The degree of clonality may vary over a species' range in accordance with the relative success of sexual and asexual recruitment. High genotypic (clonal) diversity of structural species may promote the species diversity and resilience of ecosystems in the face of environmental extremes. Conversely, low genotypic diversity may indicate an asexual strategy to maintain resources and genetic variation during population decline. Here, we use microsatellite markers to assess geographic variation in clonality in the coral Acropora palmata sampled from 26 reefs in eight regions spanning its tropical western Atlantic range (n ¼ 751). Caribbean-wide, the ratio (6SD) of genets (Ng) to sampled ramets (N) was 0.51 6 0.28. Within reefs (30-70 m) and among reefs (10-100 km) within regions, clonal structure varied from being predominantly asexual (Ng/N approaching 0) to purely sexual (Ng/N ¼ 1). However, two genetically isolated regions (western and eastern Caribbean) differed in clonal structure: genotypically depauperate populations (Ng/N ¼ 0.43 6 0.31) with lower densities (0.13 6 0.08 colonies/m 2 ) characterized the western region, while denser (0.30 6 0.21 colonies/m 2 ), genotypically rich stands (Ng/N ¼ 0.64 6 0.17) typified the eastern Caribbean. Genotypic richness (standardized to sample size; Ng/N) and genotypic diversity (Go/Ge) were negatively related to colony density within each province (r 2 ¼ 0.49-0.66, P , 0.001), indicating that dense stands have higher rates of asexual recruitment than less dense populations. Asexual recruitment was not correlated with large- scale disturbance history or abundance of large colonies (potential fragment sources) but was negatively correlated with shelf area (r 2 ¼ 0.57, P , 0.01). We argue that sexual recruitment is more prevalent in the eastern range of A. palmata than the west, and that these geographic differences in the contribution of reproductive modes to population structure may be related to habitat characteristics. The two populations of the threatened A. palmata differ fundamentally in reproductive character and may respond differently to environmental change.
TL;DR: In this article, a global biogeochemical model with an explicit representation of mesozooplankton (PISCES) is presented, and a sensitivity study is performed to analyze the impact of uncertainty in the flux rates.
Abstract: Mesozooplankton are significant consumers of phytoplankton, and have a significant impact on the oceanic biogeochemical cycles of carbon and other elements. Their contribution to vertical particle flux is much larger than that of microzooplankton, yet most global biogeochemical models have lumped these two plankton functional types together. In this paper we bring together several newly available data syntheses on observed mesozooplankton concentration and the biogeochemical fluxes they mediate, and perform data synthesis on flux rates for which no synthesis was available. We update the equations of a global biogeochemical model with an explicit representation of mesozooplankton (PISCES). We use the rate measurements to constrain the parameters of mesozooplankton, and evaluate the model results with our independent synthesis of mesozooplankton concentration measurements. We also perform a sensitivity study to analyze the impact of uncertainty in the flux rates. The standard model run was parameterized on the basis of the data synthesis of flux rates. The results of mesozooplankton concentration in the standard run are slightly lower than the independent databases of observed mesozooplankton concentrations, but not significantly. This shows that structuring and parameterizing biogeochemical models on the basis of observations without tuning is a strategy that works. The sensitivity study showed that by using a maximum grazing rate of mesozooplankton that is only 30% higher than the poorly constrained fit to the observations, the model mesozooplankton concentration gets closer to the observations, but mesozooplankton grazing becomes higher than what is currently accounted for. This is an indication that food selection by mesozooplankton is not sufficiently quantified at present. Despite the amount of effort that is represented by the data syntheses of all relevant processes, the good results that were obtained for mesozooplankton indicate that this effort needs to be applied to all components of marine biogeochemistry. The development of ecosystem models that better represent key plankton groups and that are more closely based on observations should lead to better understanding and quantification of the feedbacks between marine ecosystems and climate.
TL;DR: In this article, the authors analyzed relationships between annual hydrograph patterns and life history traits (spawn timing, age at spawning and body size) of Puget Sound Chinook salmon (Oncorhynchus tshawytscha) to identify environmental indicators of current and historic diversity.
TL;DR: In this article, the authors combined existing inventories of barriers to adult fish passage in the Willamette and Lower Columbia River basins and identified 1,491 anthropogenic barriers to fish passage blocking 14,931 km of streams.
Abstract: Large portions of watersheds and streams are lost to anadromous fishes because of anthropogenic barriers to migration. The loss of these streams and rivers has shifted the distribution of accessible habitat, often reducing the diversity of accessible habitat and the quantity of high-quality habitat. We combined existing inventories of barriers to adult fish passage in the Willamette and Lower Columbia River basins and identified 1,491 anthropogenic barriers to fish passage blocking 14,931 km of streams. We quantified and compared the stream quality, land cover, and physical characteristics of lost versus currently accessible habitat by watershed, assessed the effect of barriers on the variability of accessible habitats, and investigated potential impacts of habitat reduction on endangered or threatened salmonid populations. The majority of the study watersheds have lost more than 40% of total fish stream habitat. Overall, 40% of the streams with spawning gradients suitable for steelhead (anadromo...
TL;DR: The first in situ exploration of Aleutian Island coral habitat was completed in 2002 to determine the distribution of corals, examine fine-scale associations between targeted fish species and corals and investigate the interaction between the areas diverse fisheries and coral habitat as discussed by the authors.
Abstract: The first in situ exploration of Aleutian Island coral habitat was completed in 2002 to determine the distribution of corals, to examine fine-scale associations between targeted fish species and corals, and to investigate the interaction between the areas’ diverse fisheries and coral habitat. Corals, mostly gorgonians and hydrocorals, were present on all 25 seafloor transects and at depths between 27 and 363 m, but were most abundant between 100 and 200 m depth. Mean coral abundance (1.23 colonies m−2) far exceeded that reported for other high-latitude ecosystems and high-density coral gardens (3.85 colonies m−2) were observed at seven locations. Slope and offshore pinnacle habitats characterized by exposed bedrock, boulders, and cobbles generally supported the highest abundances of coral and fish. Overall, 85% of the economically important fish species observed on transects were associated with corals and other emergent epifauna. Disturbance to the seafloor from bottom-contact fishing gear was evident on 88% of the transects, and approximately 39% of the total area of the seafloor observed had been disturbed. Since cold-water corals appear to be a ubiquitous feature of seafloor habitats in the Aleutian Islands, fisheries managers face clear challenges integrating coral conservation into an ecosystem approach to fisheries management.
TL;DR: The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef.
Abstract: Whale sharks (Rhincodon typus Smith) aggregate seasonally (March–June) to feed in coastal waters off Ningaloo Reef, Western Australia. Pop-up archival tags were attached to 19 individuals (total lengths 4.5–11.0 m) at this location in early May of 2003 and 2004 to examine their horizontal and vertical movements. The long-term movement patterns of six whale sharks were documented, all of which travelled northeast into the Indian Ocean after departing Ningaloo Reef. They used both inshore and offshore habitats and made extensive vertical movements, occasionally to a depth of at least 980 m. Frequent up-and-down movements, diel vertical migration, and crepuscular descents were evident in the depth records. The sharks experienced ambient temperatures ranging between 4.2 and 28.7°C and encountered gradients of up to 20.8°C on dives.
TL;DR: In this paper, the authors assess the design and use of catch-quota balancing mechanisms for multispecies fisheries and find that a combination of incentives and limits on use rates for the mechanisms provide sufficient flexibility to the quota owner without the fishery manager incurring excessive levels of overexploitation risk.
TL;DR: It is found that fall stream flow is the best predictor of average survival across all populations, and stream width and stream temperature are identified as key habitat factors that shape the responses of individual populations to climate.
Abstract: Summary
1
We explored differential population responses to climate in 18 populations of threatened spring–summer Chinook salmon Onchorynchus tshawytscha in the Salmon River basin, Idaho.
2
Using data from a long-term mark–release–recapture study of juvenile survival, we found that fall stream flow is the best predictor of average survival across all populations.
3
To determine whether all populations responded similarly to climate, we used a cluster analysis to group populations that had similar annual fluctuations in survival. The populations grouped into four clusters, and different environmental factors were important for different clusters.
4
Survival in two of the clusters was negatively correlated with summer temperature, and survival in the other two clusters was positively correlated with minimum fall stream flow, which in turn depends on snow pack from the previous winter.
5
Using classification and regression tree analysis, we identified stream width and stream temperature as key habitat factors that shape the responses of individual populations to climate.
6
Climate change will likely have different impacts on different populations within this metapopulation, and recognizing this diversity is important for accurately assessing risks.
TL;DR: A mark-recapture-based model is developed that uses the observed distribution to relax the assumption of zero correlation between detection probabilities implicit in the mark-Recapture model and demonstrates its usefulness in coping with unmodeled heterogeneity using data from an aerial survey of crabeater seals in the Antarctic.
Abstract: Mark-recapture models applied to double-observer distance sampling data neglect the information on relative detectability of objects contained in the distribution of observed distances. A difference between the observed distribution and that predicted by the mark-recapture model is symptomatic of a failure of the assumption of zero correlation between detection probabilities implicit in the mark-recapture model. We develop a mark-recapture-based model that uses the observed distribution to relax this assumption to zero correlation at only one distance. We demonstrate its usefulness in coping with unmodeled heterogeneity using data from an aerial survey of crabeater seals in the Antarctic.
TL;DR: In this article, the authors used generalized linear models (GLMs) and generalized additive models (GAMs) to explain the percentage of longline shoaling as a function of predicted catenary depth and environmental effects.
TL;DR: It is shown that liver tissue turned over significantly faster than muscle tissue suggesting the potential for a multiple tissue stable isotope approach to study movement and trophic position over different time scales; metabolism contributed significantly to isotopic turnover for both liver and muscle.
Abstract: Nitrogen stable isotopes are frequently used in ecological studies to estimate trophic position and determine movement patterns. Knowledge of tissue-specific turnover and nitrogen discrimination for the study organisms is important for accurate interpretation of isotopic data. We measured delta15 N turnover in liver and muscle tissue in juvenile mummichogs, Fundulus heteroclitus, following a laboratory diet switch. Liver tissue turned over significantly faster than muscle tissue suggesting the potential for a multiple tissue stable isotope approach to study movement and trophic position over different time scales; metabolism contributed significantly to isotopic turnover for both liver and muscle. Nitrogen diet-tissue discrimination was estimated at between 0.0 and 1.2 per thousand for liver and -1.0 and 0.2 per thousand for muscle. This is the first experiment to demonstrate a significant variation in delta15 N turnover between liver and muscle tissues in a fish species.
TL;DR: It is revealed that juvenile green turtles occupy stable home ranges along the nearshore worm-rock reefs of Southeast Florida, during the summer and fall, and which habitats are used by them will assist conservation managers in their global effort to protect this endangered species.
Abstract: Many animals, including sea turtles, alter their movements and home range in relation to the particular type and quality of the habitat occupied. When sufficient resources are available, individuals may develop affinities to specific areas for activities, such as foraging and (or) resting. In the case of green sea turtles (Chelonia mydas L.), after a number of years in the open ocean, juveniles recruit to shallow-water developmental habitats where they occupy distinct home ranges as they feed and grow to maturity. Our goal was to study the habitat use and home range movements of juvenile green turtles along a shallow, worm-rock reef tract in Palm Beach, Florida. Six turtles, measuring from 27.9 to 48.1 cm in straight carapace length and from 7.2 to 12.6 kg in mass, were tracked via ultrasonic telemetry from August to November 2003. Upon capture, each turtle’s esophagus was flushed via lavage to determine recently ingested foods. In addition, four turtles were recaptured and fitted with a time-depth recorder to study dive patterns. Home range areas measured with 100% minimum convex polygon and 95% fixed kernel estimators varied from 0.69 to 5.05 km2 (mean=2.38±1.78 km2) and 0.73 to 4.89 km2 (mean=2.09±1.80 km2), respectively. Home ranges and core areas of turtles were largely restricted to the reef tract itself, and showed considerable overlap between food and shelter sites. The mean number of dives during daylight hours (0600–1800 hours) was 84±5.0 dives, while the mean during night hours (1800–0600 hours) was 39±3.0 dives. Dives during the day were shallower (mean=3.20±1.26 m) than dives at night (mean=5.59±0.09 m). All six turtles were found to have a mixed diet of similar macroalgae and sponge fragments. Our results reveal that juvenile green turtles occupy stable home ranges along the nearshore worm-rock reefs of Southeast Florida, during the summer and fall. Determining which habitats are used by green turtles will assist conservation managers in their global effort to protect this endangered species.
TL;DR: In this paper, a structural bioeconomic model of a coastal recreational fishery was developed and applied to estimate the value of water quality changes for the Atlantic Coast summer flounder fishery, which predicts that improving water quality conditions in Maryland's coastal bays alone would have relatively small impacts on the fishery as a whole.
TL;DR: Formulation and fitting of a hidden process model are demonstrated for Sacramento River winter-run chinook salmon and its role in animal population dynamics is demonstrated.
Abstract: Hidden process models are a conceptually useful and practical way to simultaneously account for process variation in animal population dynamics and measurement errors in observations and estimates made on the population. Process variation, which can be both demographic and environmental, is modeled by linking a series of stochastic and deterministic subprocesses that characterize processes such as birth, survival, maturation, and movement. Observations of the population can be modeled as functions of true abundance with realistic probability distributions to describe observation or estimation error. Computer-intensive procedures, such as sequential Monte Carlo methods or Markov chain Monte Carlo, condition on the observed data to yield estimates of both the underlying true population abundances and the unknown population dynamics parameters. Formulation and fitting of a hidden process model are demonstrated for Sacramento River winter-run chinook salmon (Oncorhynchus tshawytsha).
TL;DR: It is suggested that this method, when coupled with projectile biopsy procedures, can be used to assess the pregnancy status of free-ranging cetaceans and thus provide a new tool to determine pregnancy rates of wild populations.
Abstract: We quantified progesterone in 110 blubber samples from dolphins of known reproductive status in order to test the accuracy of a method to determine pregnancy status in wild cetaceans. The samples were collected from fishery-bycaught delphinids of three species (Delphinus delphis, Lissodelphis borealis, and Lagenorhynchus obliquidens). We ascertained that blubber progesterone concentrations could clearly distinguish pregnant D. delphis (range 132–415 ng/g, mean 261 ng/g) from non-pregnant mature and immature ones (range 0.92–48.2 ng/g, mean 15.2 ng/g). We found similar dramatic differences in L. borealis and L. obliquidens. These results were insensitive to various blubber sampling depths and anatomical sampling locations on the body, suggesting relative homogeneity of progesterone levels throughout the blubber. However, no trend was found in blubber progesterone concentration with fetal length, indicating that although blubber progesterone appears to distinguish pregnancy status, it is unlikely to differentiate pregnancy stage. Based on the findings presented here we suggest that this method, when coupled with projectile biopsy procedures, can be used to assess the pregnancy status of free-ranging cetaceans and thus provide a new tool to determine pregnancy rates of wild populations.
TL;DR: The zone most strongly affected extended from northern California to southern British Columbia, where zooplankton biomass was low from spring through autumn, community composition showed reduced dominance by northern origin taxa, and life cycles of some species shifted to earlier in the year.
Abstract: [1] Zooplankton in the California Current had large anomalies in biomass and composition in 2005. The zone most strongly affected extended from northern California to southern British Columbia, where zooplankton biomass was low from spring through autumn, community composition showed reduced dominance by northern origin taxa, and life cycles of some species shifted to earlier in the year. Although similar anomalies have previously been observed over the entire California Current system during strong El Nino events, the 2005 zooplankton anomalies were more localized, initiated by a combination of very warm temperatures (since early 2003), plus weak and late upwelling, and low phytoplankton productivity in spring and early summer of 2005. However, the zooplankton anomalies persisted longer: through the remainder of 2005 and into 2006.
TL;DR: Sensitivity analyses suggest that future emphasis should be placed on collecting time-series of diet composition data for marine mammals, large pelagic fish, and seab birds, with additional monitoring focused on the abundance of seabirds and daily rations of all groups.
Abstract: Overholtz, W. J. and Link, J. S. 2007. Consumption impacts by marine mammals, fish, and seabirds on the Gulf of Maine-Georges Bank Atlantic herring (Clupea harengus) complex during the years 1977-2002. ICES Journal of Marine Science, 64: 83-96.A comprehensive study of the impact of predation during the years 1977-2002 on the Gulf of Maine-Georges Bank herring complex is presented. An uncertainty approach was used to model input variables such as predator stock size, daily ration, and diet composition. Statistical distributions were constructed on the basis of available data, producing informative and uninformative inputs for estimating herring consumption within an uncertainty framework. Consumption of herring by predators tracked herring abundance closely during the study period, as this important prey species recovered following an almost complete collapse during the late 1960s and 1970s. Annual consumption of Atlantic herring by four groups of predators, demersal fish, marine mammals, large pelagic fish, and seabirds, averaged just 58 000 t in the late 1970s, increased to 123 000 t between 1986 and 1989, 290 000 t between 1990 and 1994, and 310 000 t during the years 1998-2002. Demersal fish consumed the largest proportion of this total, followed by marine mammals, large pelagic fish, and seabirds. Sensitivity analyses suggest that future emphasis should be placed on collecting time-series of diet composition data for marine mammals, large pelagic fish, and seabirds, with additional monitoring focused on the abundance of seabirds and daily rations of all groups.
TL;DR: A "mechanistic" PVA of threatened Chinook salmon is developed in which the density-dependent parameter associated with freshwater recruitment was consistently the most important, regardless of viability measure, suggesting that increasing juvenile carrying capacity is important for recovery.
Abstract: The viability of populations is influenced by driving forces such as density dependence and climate variability, but most population viability analyses (PVAs) ignore these factors because of data limitations Additionally, simplified PVAs produce limited measures of population viability such as annual population growth rate (λ) or extinction risk Here we developed a "mechanistic" PVA of threatened Chinook salmon (Oncorhynchus tshawytscha) in which, based on 40 years of detailed data, we related freshwater recruitment of juveniles to density of spawners, and third-year survival in the ocean to monthly indices of broad-scale ocean and climate conditions Including climate variability in the model produced important effects: estimated population viability was very sensitive to assumptions of future climate conditions and the autocorrelation contained in the climate signal increased mean population abundance while increasing probability of quasi extinction Because of the presence of density dependence in the model, however, we could not distinguish among alternative climate scenarios through mean λ values, emphasizing the importance of considering multiple measures to elucidate population viability Our sensitivity analyses demonstrated that the importance of particular parameters varied across models and depended on which viability measure was the response variable The density-dependent parameter associated with freshwater recruitment was consistently the most important, regardless of viability measure, suggesting that increasing juvenile carrying capacity is important for recovery
TL;DR: The response of pelagic nekton to these anomalous conditions was widespread and included onshore and poleward displacement of taxa to new geographic areas, population changes within the normal range, and reduced productivity of early life stages based on larval and juvenile surveys.
Abstract: [1] Although the California Current has undergone substantial environmental shifts in the past few decades, the summer of 2005 exhibited highly anomalous conditions relative to all previous recorded summers in terms of late initiation of upwelling and the resulting elevated surface temperatures and depressed productivity through July. The response of pelagic nekton to these anomalous conditions was widespread and included onshore and poleward displacement of taxa to new geographic areas, population changes within the normal range, and reduced productivity of early life stages based on larval and juvenile surveys. Some nekton exhibited anomalous distributions in 2004. Many ecologically important species were affected. The response of the nektonic community off California was greater than during El Nino conditions.