A LACK OF CRACKS: SPAWNING HABITAT DEGRADATION AND CLIMATE CHANGE THREATENS COREGONINE POPULATIONS

Like many cold water fishes, conservation concerns for whitefishes (subfamily Coregoninae) continue to increase across their global range. We describe results from Lake Ontario that suggest spawning habitat degradation and changing winter conditions are likely impeding population growth. Cisco, Coregonus artedi, and Lake Whitefish, Coregonus clupeaformis, experience sporadic year-class success while abundances have declined for centuries. Spawning historically occurred lake-wide but is now confined to northern regions where ice forms most consistently. Egg deposition patterns indicate spawning (December) is targeted over shallow areas (2 – 5 m), where hard substrates with limited interstices (rock, dressenid mussels, dead shells) are still available. Habitats with interstices are rare due to centuries of sedimentation from land use, eutrophication, and now shells embedding interstices. Many eggs are dispersed by waves into deeper, soft sediments, but emergence traps find larvae only hatch from shallow, hard substrates. When we added clean rock to a degraded spawning site, egg incubation success increased 40 times relative to control sites. We suggest sedimentation has slowly reduced coregonine reproductive success by affecting the amount, quality, and distribution of habitats that can incubate eggs over winter. Shallow-deposited eggs require early forming ice to protect them, but ice cover has, and continues to, decline. Spawning habitat remediation may be needed in Lake Ontario and similar ecosystems, to conserve or restore lithophilic-spawning fish populations.

Primary Presenter: Brian Weidel, USGS (bweidel@usgs.gov)

Authors:

Brian Weidel, USGS  (bweidel@usgs.gov)

Taylor Brown, Cornell University  (tab289@cornell.edu)

Alexander Gatch, USGS  (agatch@usgs.gov)

Ryan Walquist, USGS  (rwalquist@usgs.gov)

Nicholas Sard, SUNY Oswego  (nicholas.sard@oswego.edu)

Dimitry Gorsky, USFWS  (dimitry_gorsky@fws.gov)