Winter presence and temperature-related diel vertical migration of striped bass (Morone saxatilis) in an extreme high-flow passage in the inner Bay of Fundy

Abstract

During a multiyear fish tracking study, subadult and adult life stages of Shubenacadie River striped bass (Morone saxatilis) were detected throughout winter in the well-mixed, hypertidal waters of the Minas Passage, Bay of Fundy. Thirty-five percent of the striped bass tagged with Vemco V16 transmitters were detected by two Minas Passage receiver arrays. Transmissions were received on 82% of winter days (December to April) and by all receivers spanning the width of the passage. Tagged striped bass were detected largely within the top 20–40 m during the day. The extent of vertical migration to shallower waters at night showed a strong relationship with water temperature; however, there was no diel vertical movement pattern observed at water temperatures <1 °C. Our results demonstrate overwintering of a portion of the Shubenacadie River striped bass population in high-flow inner Bay of Fundy waters, which extends the northern limit of this species’ winter marine range. This study is also the first to describe the relationship between daily vertical migration by striped bass and low water temperatures. Both findings suggest an elevated potential risk of interaction with an in-stream tidal turbine facility in Minas Passage.

Winter and summer differences in probability of fish encounter (spatial overlap) with MHK devices

“…Based on sampling in Minas Basin and other parts of the Bay of Fundy, some species known to be in the area from spring through fall that are also likely to be detected mid-water-column include anadromous species, e.g. alewife (Alosa pseudoharengus), blueback herring (Alosa aestivalis), American shad (Alosa sapidissima), Atlantic salmon (Salmo salar), striped bass (Morone saxatilis), rainbow smelt (Osmerus mordax), sea lamprey (Petromyzon marinus), and Atlantic sturgeon (Acipenser oxyrhynchus); the catadromous American eel (Anguilla rostrata); seasonally present species such as Atlantic mackerel (Scomber scombrus), pollock (Pollachius virens), and blackspotted stickleback (Gasterosteus wheatlandi); and species present year-round in various life stages, including Atlantic herring (Clupea harengus) and threespine stickleback (Gasterosteus aculeatus) [2,3,21,22]. Various shark species may also be present in the summer, the most common being porbeagles (Lamna nasus) and spiny dogfish (Squalus acanthias), which likely follow their migrating fish prey [21].…”

“…The majority of fish in the passage at that time was likely to be herring, whose presence was supported by frequent trails of bubbles seen rising from schools or individuals in the echogram (herring and other clupeids are known to release swim bladder gas through the anal duct [23,24]). Rainbow smelt and sticklebacks were also potentially present in the area based on what is generally known of their life histories [21], and acoustically tagged striped bass have been recorded repeatedly passing through Minas Passage in the winter [3]. The repeated movement of striped bass through Minas Passage indicated they were overwintering rather than migrating, moving more or less with the tidal currents, and it is possible this would be the case for other overwintering species.…”

“…Though typical fish movements may be altered in these areas of fast flow [22], many of the fish species present in Minas Passage in the summer have exhibited nightly migrations upward into the water column in other locations. These species include alewife [34], American shad and blueback herring [35], Atlantic herring [36], and striped bass [3]. Any fish moving into the upper 10 m of water at night would be outside the portion of the analysis region, which would be recorded as lower density.…”

“…Additionally, temperature-related changes in physiology and behaviour alter the likelihood of fish interacting with an MHK device. For example, striped bass were recently found to be present in the passage near year-round, but with reduced diel vertical migration during periods of very low temperatures [3].…”

Changes in Relative Fish Density Around a Deployed Tidal Turbine during on-Water Activities

“…Fish research in such regions usually focuses on areas sheltered from tidal currents or on slack tide periods [12,22] because physically sampling fish, e.g., with nets, in high tidal currents can be both difficult and dangerous. Remote sensing of active acoustic tags with stationary receivers has been used successfully in Minas Basin for several species [14,23,24], but poor receiver efficiency resulted at current speeds >2 m•s −1 , when the risk from turbines would be greatest [25]. Additionally, such studies require many captured fish of the species of interest (that may never even approach a device), adding significantly to the cost, uncertainty, and coordination of conducting the research.…”