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- Title
Assessing the Relationship between Gulls Larus spp. and Pacific Salmon in Central California Using Radiotelemetry.
- Authors
Frechette, Danielle; Osterback, Ann‐Marie K.; Hayes, Sean A.; Moore, Jonathan W.; Shaffer, Scott A.; Pavelka, Mark; Winchell, Clark; Harvey, James T.
- Abstract
Predation by marine birds has resulted in substantial losses to runs of Pacific salmonOncorhynchusspp., in some cases necessitating management action. Recovery of PIT tags on a seabird breeding colony (Año Nuevo Island) indicated that western gullsLarus occidentalisprey upon federally listed Coho SalmonOncorhynchus kisutchand steelheadO. mykissin central California. Whereas salmonid populations in central California have decreased in recent decades, the western gull population on Año Nuevo Island has increased. We observed gullsLarusspp. within estuaries to document predation and used radiotelemetry to examine gull movement in relation to the availability of salmonids. During 2008 and 2009, observed predation events of out-migrating salmonids by gulls were rare; 21 events occurred during 338 h of observations at two estuaries. During the prehatch and chick-rearing phases of breeding, which coincided with migration of salmonids from fresh to salt water, 74% of the detections of radio-tagged western gulls occurred within 25 km of Año Nuevo Island, suggesting that the relative susceptibility of predation by western gulls using Año Nuevo Island decreased with distance from the island. Western gull presence at creek mouths was greatest during daylight hours (91% of detections), while juvenile salmonids were present predominantly at night (65% of detections). The greatest overlap between western gulls and salmonids occurred at dusk, and predation of out-migrating salmonids was likely opportunistic. Deterring gulls from creek mouths when overlap between predator and prey might otherwise occur may buffer out-migrating salmonids from predation. Our results will inform management strategies to most effectively reduce the impacts of gull predation on central California salmonids. Received May 8, 2014; accepted March 11, 2015
- Subjects
CALIFORNIA; GULLS; PACIFIC salmon; RADIO telemetry; PREDATION
- Publication
North American Journal of Fisheries Management, 2015, Vol 35, Issue 4, p775
- ISSN
0275-5947
- Publication type
Article
- DOI
10.1080/02755947.2015.1032450