Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks Sphyrna lewini in a nursery habitat

Nursery habitat use and growth rates of juvenile scalloped hammerhead sharks Sphyrna lewini were measured in a Hawai'i nursery (Kane'ohe Bay, O'ahu) using a 28 mo tag-and-recapture study augmented by experimental determination of the relative age of neonate sharks. An estimated 7700 ( +/- 2240 SD) hammerhead sharks are born in Kane'ohe Bay each year. Neonates are born in the summer between May and September and had low retention (from 0.07 to 0.15, as a fraction of neonate population size) within the bay from Age 0 to Age 1.A primary cause of low retention appears to be mortality from starvation. Most juvenile sharks recaptured after short periods of time at liberty ( < 60 d) showed weight loss. There was also a significant negative relationship between shark weight and umbilical wound condition. Sharks with healed wounds had lower average body weights than sharks with open wounds, indicating that many sharks lose weight in the first few weeks after birth. Shark condition factor (body weight x length(-3)) was also significantly lower during late summer and early fall. Despite this apparent lack of foraging success, growth rates and size distribution of recaptured sharks indicated that juvenile S. lewini utilize Kane'ohe Bay for up to 1 yr. During their residency, sharks move throughout the nursery and there is no discernible ontogenetic shift in habitat use. These findings confirmed recent hypotheses that Kane'ohe Bay may be more important in providing protection from predators than in providing a plentiful source of food for juvenile S. lewini.