Aquatic Invasive Species Change Ecosystem Services from the World�s Largest Wild Sockeye Salmon Fisheries in Alaska

This study combines a multi-method approach to structured expert judgment with market valuation to forecast fisheries damages from introduced invasive species. The method is applied to a case study of Alaska�s first submersed aquatic invasive plant, Elodea spp., threatening Alaska�s salmon fisheries. Assuming that Elodea spp. remains unmanaged, estimated mean damages to commercial sockeye fisheries aggregated across Alaska amount to a potential $159 million annually with a 5$577 million annually ($2015 USD). The associated mean loss of natural capital amounts to$5.1 billion cumulatively over the next 100 years reaching $400 million after 10 years. Results from the expert elicitation indicate that there is a 35% chance of positive net benefits associated with the believed positive effects of Elodea spp. on sockeye salmon (Oncorhynchus nerka). Despite the potential for positive net gains, the magnitude of the most probable damage estimate may justify substantial investment in keeping productive freshwater systems free of aquatic invasive species. The damage estimate for Alaska is significantly larger than similar estimates in the Great Lakes where ecosystems are already impaired by multiple aquatic invasive species, underscoring the value of keeping functioning ecosystems with global market value productive. This study is the first to estimate ecosystem service loss associated with introduction of an aquatic invasive species to freshwater habitat that supports the world�s most valuable wild sockeye salmon fisheries. Important policy implications related to natural resource management and efficient allocation of scarce resources are discusse

Aquatic Invasive Species Change Ecosystem Services from the World\u27s Largest Wild Sockeye Salmon Fisheries in Alaska

This study combines a multi-method approach to structured expert judgment with market valuation to forecast fisheries damages from introduced invasive species. The method is applied to a case study of Alaska’s first submersed aquatic invasive plant, Elodea spp., threatening Alaska’s salmon fisheries. Assuming that Elodea spp. remains unmanaged, estimated mean damages to commercial sockeye fisheries aggregated across Alaska amount to a potential $159 million annually with a 5$577 million annually ($2015 USD). The associated mean loss of natural capital amounts to$5.1 billion cumulatively over the next 100 years reaching $400 million after 10 years. Results from the expert elicitation indicate that there is a 35% chance of positive net benefits associated with the believed positive effects of Elodea spp. on sockeye salmon (Oncorhynchus nerka). Despite the potential for positive net gains, the magnitude of the most probable damage estimate may justify substantial investment in keeping productive freshwater systems free of aquatic invasive species. The damage estimate for Alaska is significantly larger than similar estimates in the Great Lakes where ecosystems are already impaired by multiple aquatic invasive species, underscoring the value of keeping functioning ecosystems with global market value productive. This study is the first to estimate ecosystem service loss associated with introduction of an aquatic invasive species to freshwater habitat that supports the world’s most valuable wild sockeye salmon fisheries. Important policy implications related to natural resource management and efficient allocation of scarce resources are discusse

Early marine growth in relation to marine-stage survival rates for Alaska sockeye salmon (Oncorhynchus nerka)

We tested the hypothesis that larger juvenile sockeye salmon (Oncorhynchus nerka) in Bristol Bay, Alaska, have higher marine-stage survival rates than smaller juvenile salmon. We used scales from returning adults (33 years of data) and trawl samples of juveniles (n= 3572) collected along the eastern Bering Sea shelf during August through September 2000−02. The size of juvenile sockeye salmon mirrored indices of their marine-stage survival rate (e.g., smaller fish had lower indices of marine-stage survival rate). However, there was no relationship between the size of sockeye salmon after their first year at sea, as estimated from archived scales, and brood-year survival size was relatively uniform over the time series, possibly indicating size-selective mortality on smaller individuals during their marine residence. Variation in size, relative abundance, and marine-stage survival rate of juvenile sockeye salmon is likely related to ocean conditions affecting their early marine migratory pathways along the eastern Bering Sea shelf

Long-Term Outlook for Salmon Returns to Alaska

With the exception of some western Alaska stocks, Alaska's salmon populations are numerically healthy. However, even fisheries on abundant stocks are suffering economically due to sharp declines in the value of the catch. The abundance of Alaskan salmon stocks has fluctuated greatly, both in modern times and prehistorically. These fluctuations are thought to be caused by multi-decadal changes in environmental conditions over large areas that affect many other species as well as salmon. Forecasts of salmon returns are not very reliable, and the potential for significant improvement in their accuracy is low in the short term. A viable fishing industry must be able to adapt to dramatic, persistent, and unanticipated changes in harvest levels. Nonetheless, Alaska's salmon stocks should continue to produce healthy harvests for the foreseeable future, barring significant damage to their habitat either via local activities or global warming

Bilateral asymmetry, sexual dimorphism, and nematode parasites in mature male sockeye salmon Oncorhynchus nerka

The extent of bilateral asymmetry of 3 10 mature male sockeye salmon (Oncorhynchus nerka) from 6 Alaskan populations was determined to investigate the relationship between fluctuating asymmetry in paired morphological characters and physical traits (body size and shape) that seem to signal male quality. There was marked variation within and among populations in body size and morphology (e.g., body depth), but no differences in the overall level of asymmetry were detected among the populations, nor between the two systems investigated (lakes Aleknagik and Iliamna). The counts or measurements of a number of the traits evaluated for asymmetry varied among populations, but most differences were attributable to population-specific variation in body size. The six populations exhibited marked similarities in the patterns of asymmetry. Three paired characters (length of pectoral fins, number of branchiostegals, and number of teeth) were directionally asymmetric, indicating a genetic basis for asymmetry rather than an environmental influence. Two other paired characters (ventral fin length and number of enlarged teeth) were bilaterally variable but not correlated with any attribute of male quality. Based on the low variation between the different populations in level of asymmetry, we conclude that either stress does not influence asymmetry levels in sockeye salmon or that these populations are under similarly low levels of stress. We also explored the relationship between biomass of a nematode parasite (Philonema oncorhynchi) and asymmetry. The weight of parasites was related to fluctuating asymmetry in the ventral fin length but was not related to fluctuating asymmetry in number of large teet

A longitudinal study of Steller sea lion natality rates in the Gulf of Alaska with comparisons to census data.

Steller sea lion (Eumetopias jubatus) numbers in the Western Distinct Population Segment are beginning to recover following the dramatic decline that began in the 1970s and ended around the turn of the century. Low female reproductive rates (natality) may have contributed to the decline and remain an issue of concern for this population. During the 2000s we found high natality among Steller sea lions in the Gulf of Alaska indicating a healthy population. This study extends these previous estimates over an additional three years and tests for interannual variations and long-term trends. We further examine the proportions of pups to adult females observed on the rookery and nearby haulouts during the birthing season to assess whether census data can be used to estimate natality. Open robust design multistate models were built and tested using Program MARK to estimate survival, resighting, and state transition probabilities in addition to other parameters dependent on whether or not a female gave birth in the previous year. Natality was estimated at 70% with some evidence of interannual variation but a long-term increasing or decreasing trend was not supported by the data. Bootstrap and regression comparisons of census data with natality estimates revealed no correlation between the two methods suggesting that census data are not an appropriate proxy for natality in this species. Longitudinal studies of individual animals are an appropriate method for estimating vital rates in species with variable detection over time such as the Steller sea lion. This work indicates that natality remains high in this region and is consistent with a population in recovery

Risk Analysis of Plausible Incidental Exploitation Rates for the Pacific Sleeper Shark, a Data-Poor Species in the Gulf of Alaska

<p>Monte Carlo simulation was used to investigate the sustainability of incidental exploitation rates (<i>U</i>) for Pacific Sleeper Sharks <i>Somniosus pacificus</i> in the Gulf of Alaska (GOA) under status quo management. Monte Carlo simulations were implemented with a standard, length-based, age-structured model that was evaluated with forward projection. Given the paucity of relevant data, we investigated the sensitivity of simulation results to a range of assumptions about key model parameters by using 24 alternative model configurations, each simulated 1,000 times. The risk analysis results were most sensitive to Pacific Sleeper Shark <i>U</i>-values. The aggregate fraction of simulations ending in an overfished condition increased from 0% under the low-<i>U</i> scenario to 59% under the high-<i>U</i> scenario. Risk analysis results were also sensitive to the assumed shape of the length-based selectivity curve (asymptotic or dome shaped) but were less sensitive to the range of assumptions about other key model parameters, including maximum age and stock productivity. These results indicate that a priority for Pacific Sleeper Shark management is to reduce the uncertainty in <i>U</i>. This major uncertainty will be decreased by an observer program that is now in place to monitor the historically unobserved GOA Pacific Halibut <i>Hippoglossus stenolepis</i> fishery, which incidentally catches Pacific Sleeper Sharks.</p> <p>Received March 19, 2015; accepted December 7, 2015 Published online May 16, 2016</p

Evidence that Marine Temperatures Influence Growth and Maturation of Western Alaskan Chinook Salmon

<p>Chinook Salmon <i>Oncorhynchus tshawytscha</i> from western Alaska have experienced recent declines in abundance, size, and age at maturity. Declines have led to hardships for the region’s subsistence and commercial salmon harvesters, prompting calls to better understand factors affecting the life history of these populations. Western Alaskan Chinook Salmon are thought to spend their entire marine residency in the Bering Sea. The Bering Sea ecosystem demonstrates high interannual variability that is largely driven by the annual extent of sea ice. However, warming is expected to supersede interannual variability in the next several decades as a consequence of climate change. We investigated the influence of sea surface temperatures (SSTs) on the life history of western Alaskan Chinook Salmon by using information from two regional populations subject to long-term monitoring. We found strong correlations between early marine growth and SSTs. Warmer SSTs appeared to lead to a younger age at maturity, largely through the vector of augmented growth. However, we also present evidence that warmer SSTs may additionally decrease the average age of male recruits through reduced growth thresholds for early male maturation. Our results suggest that the anticipated warming of the Bering Sea will lead to higher early marine growth and a younger average age of maturation for western Alaskan Chinook Salmon.</p> <p>Received March 30, 2017; accepted July 4, 2017 </p

Bootstrap histogram of regression slopes based on pup to adult female ratios versus mark-recapture natality estimates.

<p>This figure shows that the regression slopes were strongly centered around zero with no correlative trend.</p