Population Structure and Stock Identification of Eulachon
Total Page：16
File Type：pdf, Size：1020Kb
Population Structure and Stock Identification of Eulachon (Thaleichthys pacificus), an Anadromous Smelt, in the Pacific Northwest Terry D. Beacham, Douglas E. Hay, Khai D. Le Department of Fisheries and Oceans, Pacific Biological Station, Nanaimo, B.C., Canada V9T 6N7 Received: 25 June 2004 / Accepted: 7 October 2004 / Online publication: 26 May 2005 Abstract Introduction The genetic structure of eulachon (Thaleichthys Eulachons (Thaleichthys pacificus) are an anadro- pacificus) populations was examined in an analysis of mous semelparous smelt (Osmeridae) whose distri- variation of 14 microsatellite loci representing bution is confined to eastern North America between approximately 1900 fish from 9 sites between the northern California and the eastern Bering Sea (Hay Columbia River and Cook Inlet, Alaska. Significant and McCarter, 2000). Within this range they spawn genetic differentiation occurred among the putative only in a limited number of rivers, mainly those that populations. The mean FST for all loci was 0.0046, and have a pronounced spring runoff. Within rivers the there was a significant correlation between popula- duration of the spawning period may be several weeks. tion genetic differentiation (FST) and geographic dis- Spawning usually begins in January or February in tance. Simulated mixed-stock samples comprising southern rivers such as the Columbia River, and ex- populations from different regions suggested that tends into June in northern Alaskan rivers. There is variation at microsatellite loci provided reasonably some unexplained temporal variation within this accurate estimates of stock composition for potential range. For example, the Fraser River population in fishery samples. Marine sampling indicated that southern British Columbia spawns mainly in April, immature eulachons from different rivers, during the later than most northern populations, such as those in 2 to 3 years of prespawning life in offshore marine the Nass and Skeena rivers, which spawn mainly in waters, do not mix thoroughly. For eulachons cap- March. Although the ecologic basis of spawning times tured incidentally in offshore trawl fisheries, there is not clear, it appears that within specific river was a clear geographic cline in relative abundance of drainages, eulachons generally have a characteristic eulachons from different geographic areas. The sam- timing of spawning. During spawning mature fish ple from northern British Columbia was dominated spawn a short distance upriver, with the eggs adhering by northern and central coastal populations of British to a sandy substrate or other debris. The larvae gen- Columbia, the sample from central British Columbia erally hatch within 2 to 4 weeks and then are washed was composed of eulachons from all regions, and the downstream, where they may remain in lower-salin- sample from southern British Columbia was domi- ity estuarine waters for several weeks. They then nated by Columbia River and Fraser River popula- move to nearshore waters, where they remain until tions. These results have implications for the they become sexually mature, which is thought to be management of trawl fisheries and conservation of primarily at 3 years of age (Hay and McCarter, 2000). spawning populations in some rivers where abun- They return to spawn in freshwater, after which they dance is at historically low levels. probably die. Eulachons are very high in oil content (Payne et al., 1999), so much so that dried eulachons Key words: eulachon — microsatellite variation — can be burnt as candles (hence one of the common mixed-stock fisheries — population structure — names of candlefish). The oil is unique among fishes stock identification in that it is solid at room temperatures, and in British Columbia, Canada, eulachons have enormous social Correspondence to: Terry D. Beacham; E-mail: Beachamt@pac. and cultural significance to First Nations (aboriginal) dfo-mpo.gc.ca peoples (Kuhnlein et al., 1982). DOI: 10.1007/s10126-004-4075-0 Volume 7, 363–372 (2005) Ó Springer Science+Business Media, Inc. 2005 363 364 TERRY D. BEACHAM ET AL.: EULACHON POPULATION STRUCTURE Eulachon abundance has varied widely, but distinct demographic units (McLean and Taylor, nearly all eulachon spawning runs have declined 2001). The microsatellite loci surveyed in that anal- from California to southeastern Alaska in the past 20 ysis were characterized by low levels of variation years, especially since the mid 1990s (Hay and (number of alleles ranged from 3 to 10, heterozygosity McCarter, 2000). The cause of these declines remains from 4% to 64%). In Pacific salmon, loci with such a uncertain. Eulachons are caught as bycatch during restricted number of alleles are generally less valu- shrimp fishing, but in most areas the total bycatch is able than more variable loci in detecting population small, so other factors may be important in the de- differentiation (Beacham et al., 2002). crease in abundance. The decline in eulachon abun- Eulachon populations in British Columbia have dance has prompted fishery managers to limit shrimp been a focus of conservation concern for the last 5 fisheries in marine areas adjacent to rivers with poor years, but a fundamental question about eulachon spawning runs. Although abundance has increased in population structure remains uncertain. Specifically, some British Columbia rivers since 2000, in other what is the geographic unit that may be genetically rivers, particularly in the central coastal region of distinct? Are eulachons in the eastern Pacific one British Columbia, levels remain very low. genetic stock, as was indicated by the survey of Effective conservation and management of eu- mtDNA variation, or as with anadromous salmo- lachons require determination of genetic structure of nids, is there a level of genetic differentiation among the exploited populations. In some respects eulachon eulachons that is linked to their spawning in rivers life history is similar to salmonid life history. They or watersheds in the eastern Pacific? return to spawn in freshwater after an extended The objective of the current study was to assess marine residence. It follows that, as with salmonids, the population structure of eulachons within British there may be a potential for the development of Columbia, and evaluate whether they were geneti- genetically distinct populations of eulachons. Pre- cally distinct from more distant populations in the vious analysis of vertebral number had indicated Columbia River and Cook Inlet. If some level of significant differences among eulachons in different genetic differentiation were observed, then we river drainages (Hart and McHugh, 1944). When wanted to evaluate the utility of using microsatellite examined throughout the entire range within British variation for stock identification of mixed-stock Columbia, the timing of spawning of eulachons in samples of eulachons from nearshore marine waters. rivers can differ by more than 3 months. Such vari- ation in spawning time is consistent with the Materials and Methods hypothesis of local adaptation and genetic differ- ences among populations spawning in different Collection of DNA Samples and Laboratory Anal- watersheds. Additionally, trends in eulachon popu- ysis. Putative eulachon populations were geneti- lation abundance vary among rivers. Since 2000 cally characterized with tissue samples obtained abundance in some British Columbia rivers, such as from previously collected frozen adult fish sampled the Nass, Skeena, and Fraser, has increased, while in from freshwater spawning locations (Table 1). Three others, such as the Bella Coola in the central coast, it mixed-stock samples were also collected and ana- has decreased. These observations support the lyzed to determine the origins of eulachons in the hypothesis of population differentiation among samples. The first sample was collected near Nootka eulachon spawning in different rivers. Sound, and the second sample was collected near the If eulachon spawning runs are distinct, this Goose Island Group during trawl surveys on shrimp should be reflected in surveys of genetic variation. In abundance aboard the research vessel W. E. Ricker a previous study that centered on surveying genetic during May 2000 (Figure 1). The final sample was variation at the ND5/6 and 12S/16S regions of the collected from bycatch in research surveys near mitochondrial genome by restriction fragment Chatham Sound during March 2001. DNA was ex- length polymorphism analysis, little genetic differ- tracted from all samples as described by Withler et entiation was observed among spawning eulachons al. (2000). Polymerase chain reaction (PCR) products from the Columbia River in the south to Cook Inlet at 14 microsatellite loci, Tca103, Tca104, Tca111, in central Alaska (McLean et al., 1999). The results of Tca112, Tca113, Tca114, Tca115, Tca117, Tca118, this analysis formed the basis of eulachons in British Tca119. Tca121, Tca122, Tca127,andTca129 (Ka- Columbia and elsewhere being considered as a single ukinen et al., 2004), were size fractionated on dena- stock for assessment and management (Hay and turing polyacrylamide gels, and allele sizes were McCarter, 2000). Subsequent analysis of microsatel- determined with the ABI377 automated DNA se- lite variation revealed more differentiation than that quencer. Allele sizes were determined with Gene- observed with mtDNA, yet it was difficult to define scan 3.1 and Genotyper 2.5 software (PE Biosystems). TERRY D. BEACHAM ET AL.: EULACHON POPULATION STRUCTURE 365