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Micro-elemental analysis of statoliths as a tool for tracking tributary origins of sea lampreyCollaborators Executive SummaryDuring 2004, collections of larval, parasitic, and adult lamprey were made from numerous tributaries of Lake Huron, as well as the open lake, by our partners (US Fish and Wildlife Service and Canadian Department of Fisheries and Oceans). Larvae (n = 15 per stream) from ~30 Lake Huron streams have been processed using laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Our preliminary results, which were presented in a poster at the annual American Fisheries Society meeting in Anchorage, AK, suggest that site discrimination will be possible for many streams, based upon statolith micro-elemental composition, but not for others. Further analysis, however, is needed to determine which sites can be discriminated. Similar larval, parasitic, and adult sea lamprey collections were made by the USFWS and DFO during 2005, which will be analyzed during FY06. Scientific RationaleThe analysis of otolith micro-elemental composition has been a valuable tool for differentiating between local spawning populations, and identifying origins of recruits to the fishery. Building on two pilot investigations conducted in lakes Champlain and Huron, we will determine whether trace elements incorporated into sea lamprey statoliths during larval stream residence can be used to discriminate among local populations in Lake Huron. Assuming discrimination is possible, we will begin to identify origins of parasites and spawners in Lake Huron, focusing on tributaries (e.g., St. Marys River) important to US and Canadian agencies. We also will develop predictive relationships between water and statolith chemistry, which eventually could help eliminate the need to sample larvae annually to develop stream-specific signatures. By using statolith elemental “signatures” as a natural environmental tag, we aim to provide an alternative means to identify spawning origins of spawners and parasites, which currently can only be acquired using labor-intensive tagging studies that yield low tag returns. Beyond helping assess whether recent sea lamprey control efforts (e.g., St. Marys River) have been successful, an ability to identify natal origins would pave the way for studies aimed at understanding attributes (e.g., stream-specific growth rates, sex ratios, and movement) that promote survival to parasitic and spawning stages, as well as help better target streams for control measures. BackgroundOf the numerous anthropogenic perturbations experienced by the Laurentian
Great Lakes during the past century, arguably the most costly, from both
ecological and economic standpoints, has been invasion of the sea lamprey
(Petromyzon marinus). By parasitizing large-bodied native fishes,
sea lampreys have greatly altered the ecology of the Laurentian Great
Lakes, as well as other coolwater systems within the surrounding basin
(e.g., Lake Champlain). Of primary importance has been the reduction of
native salmonines, including lake trout (Salvelinus namaycush)
and lake whitefish (Coregonus clupeaformis), which underwent dramatic
declines during the 1940s and 1950s (Smith and Tibbles 1980). In fact,
sea lamprey predation played a major role in causing the extirpation of
lake trout in lakes Ontario, Erie, Huron, and Michigan (Cornelius et al.
1995, Elrod et al. 1995, Eshenroder et al. 1995, Holey et al. 1995). Herein, we propose to continue development of a rather novel technological approach, statolith microchemistry, as a tool to determine which local spawning tributaries contribute to parasitic- and spawning-stage sea lamprey populations in Lake Huron. First, we seek to provide a definitive answer as to whether statolith elemental concentrations can be used as a tool to identify sources of sea lamprey in Lake Huron, which no study has currently done. Given the geographical scope of our study and technologies available in Fryer’s laboratory, we are confident in our ability to do this. Second, assuming that statolith microchemistry holds up to its potential, we will seek to quantify the relative contribution of parasites and spawners from spawning tributaries important to Great Lakes management agencies, including the St. Marys River. This river is of specific interest because historically it has been the primary source of sea lamprey production in the Great Lakes (Young et al. 1996). In addition, a major control effort, consisting of the application of granular Bayluscide, trapping of adult sea lamprey, and release of sterile males (GLFC 2001), has recently been undertaken in the St. Marys River. Although preliminary data suggest that the larval population has been reduced by as much as 45% in this river after initial (1999) application of Bayluscide, a true assessment of whether the St. Marys River control effort has changed the relative contribution of adult spawners and parasites in Lake Huron remains unknown. We fully expect that estimation of relative contributions from other Lake Huron tributaries, including difficult-to-sample large rivers (e.g., Spanish and Mississagi; M. Steeves, DFO, pers. comm.), will be possible as well. Finally, taking advantage of the stability of water chemistry in Lake Huron tributaries (see below), we will attempt to quantify relationships between water and statolith chemistry in hopes of eliminating any future need for annual larval sampling from spawning tributaries. Ultimately, this would reduce the expense associated with using this technology for estimation of tributary contributions of sea lamprey to the open lake. Inductively Coupled Plasma Mass Spectrometer (ICPMS) 2005 AccomplishmentsBelow, we describe our accomplishments for each of the three primary objectives. PROJECT OBJECTIVES: 1. Determine whether statolith elemental signatures differ among larvae produced in different L. Huron streams. Larval sea lamprey Collections To develop characteristic statolith elemental signatures for Lake Huron streams, larvae were collected from numerous Lake Huron tributaries (Figure 1) by the US Fish and Wildlife Service (Marquette and Ludington stations) and the Department of Fisheries and Oceans (Sault Ste. Marie). Similar collections in tributaries surrounding both Lake Michigan and Huron have already begun for 2005. Importantly, these collections will allow us to explore inter-annual variability in stream signatures, as well as fill in gaps in sampling because not all Lake Huron streams were sampled during 2004. We currently have analyzed larval sea lamprey from 30 streams surrounding Lake Huron and Lake Michigan (Ford River, St. Mary's River, Silver Creek, Mississagi River, Hessel Creek, Tawas River and Trout Creek) (n = 15 per stream). We fully expect that all samples, from both 2004 and 2005, will be processed and analyzed by January 2006. Preliminary Results Preliminary results from the seven streams (see Figure 1) processed thus far are encouraging. In total, 8 of 13 elements analyzed were above detection limits (i.e., concentrations in statoliths were sufficiently high to be reliably detected by our ICPMS). More importantly, we found several elements (rubidium, manganese, strontium, and zinc) were valuable for discriminating among streams (Table 1; Figure 2). Using these 8 elements, we could reliably discriminate most streams; 6 of 7 streams could be discriminated (using Linear Discriminant Function Analysis, LDFA) with ? 85% accuracy, whereas the seventh stream (Mississagi River) could only be discriminated from other with 50% accuracy (Table 2). As we increase the number of streams analyzed at any given time, it is likely that other elements will become valuable for discrimination purposes. Further, as we increase sample sizes for each stream-ideal sample sizes will be determined objectively, using a rigorous bootstrapping analysis to look at how sample sizes within streams influence characteristic elemental signatures-we are hopeful that our discrimination abilities will increase (e.g., we will be able to discriminate the Mississagi River from others as well).
Figure 1: Locations of sample sites, with processed and analyzed sites highlighted. Unlabeled locations not yet processed. 2. Quantify relative contributions of parasitic and spawning lamprey from important production tributaries. We will address this objective once the preliminary work on the larvae has been completed, since without results from our first objective, we will have no basis for determining the origins of parasites and spawners. However, to this point, we have secured both parasites and spawners from Lake Huron from both commercial fishing operations and agent trapping efforts (the USFWS, DFO, and USGS were instrumental in securing these collections). We also will receive parasites and spawners from Lake Huron, as well as Lake Michigan, during 2005. The Lake Michigan adults and parasites will prove invaluable to (hopeful) future efforts to conduct a similar study in Lake Michigan (per some discussions with Chuck Krueger). One assumption we are making is that storage method has no effect on elemental composition of statoliths, given that larvae are stored in ethanol and adults/parasites are stored frozen. To explore the effects of storage method on statolith elemental composition, we analyzed larvae (n = 14 stored frozen; n = 15stored in 95% ethanol) collected from Browns Bayou in the Big Manistee River. Briefly, we found no significant differences between frozen and ethanol preserved fish for magnesium, manganese, zinc, barium, lead or strontium (two-sample t-tests; all p > 0.05). We did, however, a significant, difference between storage methods for rubidium. Importantly, however, the difference, although statistically significant, was small (ethanol mean + 1 SD = 2.10+0.49 ppm; ethanol mean + 1 SD = 2.76+0.62 ppm) relative to the variation in rubidium that has been documented across Lake Huron and Lake Michigan streams (range in Rb across the seven streams processed thus far is 2.47 to 7.09 ppm). Thus, we are optimistic that any biases associated with storage method will be negligible. We will further assess the robustness of these results by performing a similar suite of analyses on larvae collected in Lake Champlain this summer. 3. Develop relationships to predict statolith elemental chemistry from water chemistry. This objective will be met first with some preliminary work on Lake Champlain, followed by comparative work on Lake Huron. Water and sediment samples from Lake Champlain will be collected by Carrol Hand during the week of June 13-18, brought back and analyzed at the lab in Windsor. Specifically, Carrol will sample all 22 sea lamprey producing streams in Lake Champlain for both water chemistry and sediments. Additional collections in these same streams will be made again during fall 2005 and spring 2006 (after snowmelt) to assess inter-annual variability in signatures. Collections of water chemistry and sediment samples around Lake Huron also will be made during summer 2005, which will supplement collections being made by other agencies (USGS). Ultimately, we will compare our water and sediment chemistry results to sea lamprey statolith micro-elemental composition to develop partition coefficients. Figure 2. Canonical analysis of sea lamprey larvae (only Roots 1 and 2 presented, which explained a combined 78% of the variation in the data). See Table 1 for an explanation of elemental concentrations, and Figure 1 for an explanation of stream acronyms. Table 1. Correlation of elemental concentrations with Linear Discriminant Function Analysis axes (roots). Elements most highly correlated with each axis are highlighted in gray, and indicate their importance in discrimination. For example, Manganese (Mn) and Rubidium (Rb) were most important for explaining variation along Root 1 (horizontal axis; positive coefficients indicate that Mn and Rb increase from left to right along Root 1; see Figure 2). Root 2 was positively correlated with Strontium (Sr), indicating that individuals at the top of Figure 2 were higher in Sr than those at the bottom (see Figure 2). The percentage of variation that each axis (root) explained is provided in the bottom row.
Table 2: Classification matrix for larvae processed at seven Lake Huron/Michigan sampling locations. Our ability to discriminate among individuals (larvae) from different streams was quite good. With the exception of Mississagi River (MISR) individuals, we could discriminate among streams with > 85% accuracy. In the case of the Mississagi River, individuals were misclassified as Hessel Creek (HESC) individuals in half the cases (5 of 10). Individuals classified correctly are highlighted in gray. See Figure 1 for stream acronym definitions.
ReferencesCornelius, F.C., K.M. Muth, and R. Kenyon. 1995. Lake trout rehabilitation
in Lake Erie: a case history. Journal of Great Lakes Research 21(sup1):65-82. last updated: 2006-04-12 mbl |
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