Evidence for temperature-dependent shifts in spawning times of anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)

Abstract

We analyzed four decades of presence–absence data from a fishery-independent survey to characterize the long-term phenology of river herring (alewife, Alosa pseudoharengus; and blueback herring, Alosa aestivalis) spawning migrations in their southern distribution. We used logistic generalized additive models to characterize the average ingress, peak, and egress timing of spawning. In the 2010s, alewife arrived to spawning habitat 16 days earlier and egressed 27 days earlier (peak 12 days earlier) relative to the 1970s. Blueback herring arrived 5 days earlier and egressed 23 days earlier (peak 13 days earlier) in the 2010s relative to the 1980s. The changes in ingress and egress timing have shortened the occurrence in spawning systems by 11 days for alewife over four decades and 18 days for blueback herring over three decades. We found that the rate of vernal warming was faster during 2001–2016 relative to 1973–1988 and is the most parsimonious explanation for changes in spawning phenology. The influence of a shortened spawning season on river herring population dynamics warrants further investigation.

Daily Patterns of River Herring (Alosa spp.) Spawning Migrations: Environmental Drivers and Variation among Coastal Streams in Massachusetts

“…Previous analyses of run counts in these same 12 coastal streams found that river herring run durations have not shifted substantially over recent decades (R. M. Dalton, Duke University and M. D. Staudinger, U.S. Geological Survey, unpublished data). In those analyses, run initiation was best predicted by a combination of winter variables prior to the spring run, while the median and end (Lombardo et al 2019).…”

“…There is mounting evidence that climate change is altering the timing of migration and spawning cycles of anadromous fishes by shifting distributions, restricting suitable habitat, or shortening the window of time (i.e., phenophase) in which ideal conditions for those activities take place (Nye et al 2009; Peer and Miller 2014; Lynch et al 2015; Lombardo et al 2019; Nack et al 2019; Staudinger et al 2019). In addition, many anadromous fishes are subjected to overfishing, bycatch in marine fisheries, degradation and destruction of freshwater spawning habitat by human activities, and the obstruction of spawning migration by dams and culverts (Hall et al 2012; ASMFC 2017).…”

“…In recent decades, climate change has resulted in water temperatures reaching these thresholds earlier in the year (Friedland et al 2015; Henderson et al 2017). Thus, warming temperatures could help to explain river herring migrations starting earlier in the spring as well as the considerable interannual variation in migration patterns (Huntington et al 2003; Ellis and Vokoun 2009; Lombardo et al 2019). For example, river herring migrations in the Albemarle Sound watershed, North Carolina, started 16 d earlier in the 2010s compared to the 1970s (Lombardo et al 2019).…”

“…However, unlike interannual migration patterns, the environmental drivers of within‐season patterns are less clear. Fluctuations in the rate of seasonal warming and daily variability in temperature and precipitation are becoming increasingly variable in many systems (USGCRP 2018; Lombardo et al 2019). This could affect the dynamics of upstream pulses of movement exhibited by adult river herring, which are characterized by peaks and troughs of high and low abundance throughout the season (Nelson et al 2020).…”

“…For river herring, previous behavioral experiments (Collins 1952) and counts of adults migrating upstream (Saila et al 1972; Richkus 1974; Ogburn et al 2017; Rosset et al 2017) suggested a correlation between daily movement and water temperature but found conflicting or inconclusive results for the influence of river flow and lunar cycle. Given the interannual and interpopulation variability in environmental regimes and run dynamics (Ogburn et al 2017; Rosset et al 2017; Lombardo et al 2019), a multi‐year, regional examination of river herring migration patterns is needed to disentangle the variety of possible drivers of river herring migrations and aid in optimizing monitoring efforts, population models, and management strategies. Understanding the interannual drivers of spawning migrations has been useful for the management of other anadromous fish stocks in setting seasonal closures and time‐of‐year restrictions (Keefer et al 2008; Peer and Miller 2014).…”