| Popis: |
River herring (Alosa spp.) are anadromous fish that spawn in freshwater rivers and lakes in North America from Florida to Nova Scotia, CA. They have been listed as a species of conservation concern due to dramatic stock declines observed in the 1970’s. Stocks have failed to show significant signs of recovery despite over a decade of harvest restrictions throughout their range. Bycatch in commercial fisheries and reduced access to spawning habitat due to anthropogenic barriers to migration, such as dams and tide gates, have been identified as major causes of the decline in herring populations. Physical barriers to migration can prevent or delay anadromous fish from reaching their spawning grounds which can cause reduced spawning stock biomass reaching spawning habitat, reduction in reproductive output by decreasing the duration of time spent on the spawning grounds, and increased mortality. In this dissertation, I used telemetry to study river herring movement behavior around a tide gate and road-stream crossing culverts on the Herring River in Wellfleet, MA. I also used videography and stable isotope analyses to investigate the predator-prey relationships of multiple predator taxa of river herring throughout the system, particularly at anthropogenic barriers to movement. I found that the tide gate disproportionately prevented later arriving river herring from passing upstream (16%) than fish arriving earlier in the year (78%) and delayed those that did pass by ~7 d. Specific movement patterns of river herring and predatory striped bass (Morone saxatilis) around the tide gate suggest that the presence of the striped bass may contribute to the reduced herring passage success late in the season. I also found that a series of even easily passable culverts, such as those found on the Herring River, can delay herring migrations by >100%. Furthermore, snapping turtles (Chelydra serpentina) used culverts to ambush river herring, preventing and delaying passage more than the culvert itself. Removal or remediation of these barriers would likely improve river herring reproductive success. Future fish passage studies should investigate the potential for predator-prey interactions at anthropogenic barriers to fish passage and not just passage as a function of physical characteristics of the barrier. |
