Western Fisheries Science News, December 2014 | Issue 2.12

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The Great Lakes are one of the world’s most remarkable ecosystems and have historically supported a thriving sport and commercial fishery. However, by the 1960’s the Great Lakes fisheries began a serious decline due to the unintentional introduction of sea lampreys and alewives, a species of Atlantic ocean herring, that invaded the Great Lakes using the Welland Canal to bypass Niagara Falls. The alewives had no predators and out-competed native Great Lakes fish for food. In an effort to rebuild the fishery, 6 million Chinook salmon and 15 million coho salmon were introduced into Lake Michigan from 1966 to 1970 to act as predators on them. The alewife population plummeted and the Chinook salmon stocks increased annually, enabling a highly popular salmon sports fishery to develop. However, in the late 1980s, the salmon population in Lake Michigan began to collapse. Thousands of dead or dying Chinook salmon were found floating near the surface or washed up on beaches. The cause of the mass mortality was determined to be bacterial kidney disease (BKD), an insidious, progressive infection with a protracted course. The bacterium causing BKD is a small rod-shaped bacterium named Renibacterium salmoninarum. Infected fish may take months to show signs of disease. The slow progress of the infection is deceptive and makes it difficult to treat or prevent the spread of the infection. Although BKD is considered an important factor in the decline of Chinook salmon in Lake Michigan, the precise relation between R. salmoninarum infection and fish mortality has been difficult to determine, in part because of a lack of standardized diagnostic tools.

The WFRC has long been recognized as a world leader for its pioneering research to develop both standardized diagnostic tools and improved control methods for BKD in West coast Pacific salmon. Accordingly, WFRC scientists began applying their expertise to solving the BKD problem in the Great Lakes. Since the 1990s, work has focused on developing and validating a suite of rapid, standardized immunological and molecular diagnostic methods for detecting and quantifying R. salmoninarum infections in salmon; examining transmission of R. salmoninarum; and characterizing genetic variation in BKD resistance of Lake Michigan Chinook salmon. Funding and/or collaboration has been provided by the U.S. Geological Survey, the Great Lakes Fishery Trust, the Great Lakes Fishery Commission, the Washington Department of Fish and Wildlife, NOAA, and the Wisconsin Department of Natural Resources. Research results have been reported by consultations with fishery management agencies, presentations at meetings, and numerous peer reviewed publications in scientific journals. A synopsis of the two most recent WFRC publications follows:

Genetic variation in bacterial kidney disease (BKD) susceptibility in Lake Michigan Chinook salmon and its progenitor population from the Puget Sound. Purcell, M.K., et al. 2014. J. Aquat. Anim. Health, 26(1): 9-18.

It is hypothesized that the contemporary population of Chinook salmon from Lake Michigan may have higher resistance due to pathogen-driven selection associated with large fish kills caused by bacterial kidney disease (BKD) that occurred in the late 1980s. One trade-off of selection for higher disease resistance may be a loss of additive genetic variation at that trait, which is essential for evolutionary change. In this article, researchers from the WFRC and NOAA Northwest Fisheries Science Center compared levels of variation in the Lake Michigan stock relative to its progenitor stock from Washington State. Our results found no evidence of a trade-off as the Lake Michigan stock had both higher resistance and a greater level of genetic variation. Major ecological events that alter host-pathogen relationships or the introduction of novel pathogens into naïve fish population may result in large fish kills and associated population declines. It may be tempting for managers to ‘kick-start’ rebuilding of the population with stocking from neighboring unaffected regions. This is particularly true with BKD because the infectious agent is vertically transmitted from mother to offspring and obtaining sufficient numbers of pathogen-free eggs may be difficult. Our results suggest that, when possible, allowing populations to naturally rebound following major disease epizootics can be a sound management approach.

Bench-top validation testing of selected immunological and molecular Renibacteirum salmoninarum diagnostic assays by comparison with quantitative bacteriological culture. Elliott, D.G., et al. 2013. J. Fish. Dis. 36(9): 779-809.

This paper by USGS scientists at the WFRC represents the first thorough evaluation for laboratory validation of the most widely used diagnostic assays for the detection of R. salmoninarum; several of the assays had been developed at the WFRC. Validation is a multi-stage process that establishes the fitness of a diagnostic assay under the conditions in which it will be used. The study compared seven rapid immunological and molecular assays with a quantitative culture method to determine performance characteristics such as sensitivity, specificity and repeatability for each assay. The use of standardized, validated diagnostic assays is crucial in a system such as the Great Lakes basin, where fish stocks are managed by multiple agencies. The paper is expected to serve as a reference guide worldwide for professionals involved in BKD diagnosis and management. Protocols for the validated assays are available on the WFRC website.

Newsletter Authors - Debra Becker and Dr. Diane Elliott

Research

USGS Scientist Provides Research Update on Southwestern Willow Flycatcher Habitat Modeling:  On December 1, Jim Hatten, a Research Biogeographer with the Western Fisheries Research Center, Columbia River Research Laboratory, provided Mark Sogge (USGS Pacific Regional Director) with a progress update (WebEx) on mapping Southwestern Willow Flycatcher (SWFL) breeding habitat. Funded by U.S. Bureau of Reclamation (USBR) and U.S. Fish and Wildlife Service (USFWS), Hatten is using Landsat imagery and a model he published in 2003 to develop detailed rangewide maps of potential SWFL breeding habitat. Breeding exclusively in riparian areas of the southwestern U.S., the SWFL has become an iconic species of southwestern riparian areas. Hatten’s satellite-based maps are the first-ever to cover the entire southwest, at 30-m resolution. The USFWS and USBR intend to use the maps for management purposes, including fulfilling responsibilities related to numerous biological opinions.

Events

USGS Presents at First Nations Fisheries Council:  On December 19th, Western Fisheries Research Center senior scientist James Winton was one of four invited scientists to present information at a meeting hosted by the First Nations Fisheries Council in Vancouver, B.C, Canada. The meeting, titled “Promoting Healthy, Resilient Fish Populations: the Role of Pathogens and Disease”, was the first of a four-part series designed to provide First Nations leaders and fisheries managers with current scientific information about factors affecting the health and abundance of fisheries resources critical to the economy and culture of the First Nations of Western Canada. The talk titled; “Drivers of Emerging Diseases in Populations of Wild Fish” included examples of wild fish affected by diseases from introduced pathogens, or compounded by impacts from the global increase in aquaculture, climate change, introduction of non-native species, alterations in food webs and greater inputs of novel contaminants.