Extreme Predation on Atlantic Herring (Clupea harengus) Eggs by Waterbirds in an Anthropogenic Wharf Spawning Habitat

Spawning and hatching is integral to population growth. Southern Gulf of St. Lawrence spring-spawning Clupea harengus (Atlantic Herring) are a key forage fish in the region; however, contemporary knowledge on spawning habitat is lacking. Since 2022, there have been multiple anecdotal reports by fishers (i.e., commercial fishers) that the population has begun to spawn on wharfs. In 2025, we solicited both fisher and public observations of spawning events to facilitate a dedicated study on spawning habitat of spring-spawning Atlantic Herring in the region. The first spawning event reported by a fisher in 2025 occurred on a wharf in Cap-Pele, NB, Canada, providing the unique opportunity to evaluate egg incubation and survival at an anthropogenic wharf habitat. Our observations revealed intensive predation by waterbirds, including Larus delawarensis (Ring-billed Gull), Larus smithsonianus (American Herring Gull), Melanitta americana (Black Scoter), and Somateria mollissima (Common Eider), over the course of several days and found the vast majority of eggs were consumed by waterbirds within 5 days of spawning. As a result, no notable amount of eggs survived long enough to hatch; thus, the spawn event likely yielded no viable progeny. Under continuing climate change and anthropogenic development, it is plausible that Atlantic Herring may more frequently utilize suboptimal spawning habitat such as at wharfs, which have poor structural complexity and are particularly vulnerable to predators. Our observations highlight the drawbacks of spawning in such habitats, where progeny of entire spawning events can be subject to substantial predation mortality and thus not contribute to the population.