Inefficient predators and prey injuries in a population of giant stickleback

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Abstract
I describe predator-induced injuries in a lake population of large-bodied Gasterosteus aculeatus from the Queen Charlotte Islands, British Columbia. Injuries, which included structural damage (fractured dorsal and pelvic spines) and skin lacerations (scars, abrasions, and punctures), were observed on 13.4% of the population. Bill imprints ("aviscars") from avian piscivores, including Podiceps grisegena and Gavia immer, occurred on one-third of the injured fish. Mean aviscar width (4.2 mm) was low in winter and higher in midsummer correlating with seasonal differences in the presence of avian taxa. One-half of the injured fish had fractured spines without any associated skin damage; sources of these injuries could not be verified although they probably resulted from avian piscivores and resident salmonids. Rate of spine regeneration, determined on artifically marked fish, was 1.09 mm over 26 months. Age of injuries, assessed by condition and regrowth of spines, included recent attacks (ca. 1 month or less, 6.3%) and old attacks (1–3 years, 40%). Thirty percent of skin injuries are undetectable after 1 year. Injuries were absent on juvenile fish (< 50 mm) but were common on adults, reaching an incidence of 32% on sub-samples of the largest fish (> 82 mm). These data are consistent with theoretical predictions of increased manipulation inefficiencies among gape-limited predators and can account in part for the evolution of large body size in this population. Mark–recapture studies on 12 272 adult stickleback (> 70 mm) showed that the probability of incurring a predator injury as an adult fish (0.09/year) is largely a consequence of total length of time in the population; this finding amplifies size-dependent trends in injury frequencies.