Population synchrony of a native fish across three Laurentian Great Lakes: evaluating the effects of dispersal and climate

Abstract

Climate and dispersal are the two most commonly cited mechanisms to explain spatial synchrony among time series of animal populations, and climate is typically most important for fishes. Using data from 1978-2006, we quantified the spatial synchrony in recruitment and population catch-per-unit-effort (CPUE) for bloater (Coregonus hoyi) populations across lakes Superior, Michigan, and Huron. In this natural field experiment, climate was highly synchronous across lakes but the likelihood of dispersal between lakes differed. When data from all lakes were pooled, modified correlograms revealed spatial synchrony to occur up to 800 km for long-term (data not detrended) trends and up to 600 km for short-term (data detrended by the annual rate of change) trends. This large spatial synchrony more than doubles the scale previously observed in freshwater fish populations, and exceeds the scale found in most marine or estuarine populations. When analyzing the data separately for within- and between-lake pairs, spatial synchrony was always observed within lakes, up to 400 or 600 km. Conversely, between-lake synchrony did not occur among short-term trends, and for long-term trends, the scale of synchrony was highly variable. For recruit CPUE, synchrony occurred up to 600 km between both lakes Michigan and Huron (where dispersal was most likely) and lakes Michigan and Superior (where dispersal was least likely), but failed to occur between lakes Huron and Superior (where dispersal likelihood was intermediate). When considering the scale of putative bloater dispersal and genetic information from previous studies, we concluded that dispersal was likely underlying within-lake synchrony but climate was more likely underlying between-lake synchrony. The broad scale of synchrony in Great Lakes bloater populations increases their probability of extirpation, a timely message for fishery managers given current low levels of bloater abundance.

Patterns of asynchrony for phytoplankton fluctuations from reservoir mainstream to a tributary bay in a giant dendritic reservoir (Three Gorges Reservoir, China)

“…One commonly cited mechanism explaining synchrony is the Moran effect, whereby spatially autocorrelated climate synchronizes disparate populations that have a similar density-dependent structure (Bunnell et al 2010). The central idea of the Moran effect is that natural communities would be synchronized if they were subjected to regional drivers (Ranta et al 1997;Hudson and Cattadori 1999;Ripa 2000).…”

“…We thus argue that regional environmental drivers were not preponderant in controlling phytoplankton phenology in the giant dendritic reservoir, although seasonal fluctuations of phytoplankton was often regarded as one of the important cyclic events in aquatic ecosystems, and was even emphasized as an important sign of regional climatic change. Dispersal among populations can reduce the size of relatively large populations and increase relatively small ones, and is often treated as an alternative explanation for synchrony (Paradis et al 1999;Goldwyn and Hastings 2008;Bunnell et al 2010). Compared to fish and other aquatic vertebrates, phytoplankton is largely an obligate passive disperser (Shurin et al 2009) and the incidence of dispersal is related to habitat type (lotic vs. lentic).…”

Contemporary life history characteristics of Lake Superior deepwater ciscoes

“…Cisco, typically considered a shallow-water form, was found in relatively high abundance in our deepwater sets and is currently an important component of the Deepwater Cisco community (Pratt, 2012), so we included it in our assessment. While researchers have recently addressed the ecology of deepwater ciscoes in Lake Superior Jensen et al, 2006;Gorman and Todd, 2007;Schmidt et al, 2009;Stockwell et al, 2010;Gorman, 2012), and the biology and life history of Bloater in other Great Lakes (Bunnell et al, 2006;Bunnell et al, 2009;Bunnell et al, 2010), with the exception of Cisco (Yule et al, 2008;Stockwell et al, 2009), very little or no recent biological information exists on the life history characteristics of Lake Superior's ciscoes. The most recent comprehensive examinations of Bloater (Dryer and Beil, 1968), Kiyi (Koelz, 1929), and Shortjaw Cisco (Van Oosten, 1937) from Lake Superior are many decades old.…”

Energy Density of Bloaters in the Upper Great Lakes

“…We did not test for differences between sites within a given lake because we were interested in the broad-scale variation in bloater energy content across lakes. Furthermore, bloater populations in the three upper Great lakes have broad synchrony in population dynamics, both within and across lakes (Bunnell et al 2010). We chose to analyze the data separately for 2008 and 2009 owing to differences in sites sampled during each year.…”

“…The population dynamics of bloaters in these systems are highly variable, with years of consistently strong recruitment followed by years of relatively weak recruitment (Bunnell et al 2010). In each system, recruitment of bloaters appears to be trending upward in recent years (Bunnell et al 2010). Whether this recruitment success will reach the high levels that were obtained in the 1980s may, in part, depend on the energy content of the fish, which is often associated with fitness.…”