Distribution and habitat partitioning of immature bull sharks (Carcharhinus leucas) in a southwest Florida estuary

The distribution and salinity preference of immature bull sharks (Garcharhinus leucas) were examined based on the results of longline surveys in three adjacent estuarine habitats in southwest Florida: the Caloosahatchee River, San Carlos Bay, and Pine Island Sound. Mean sizes were significantly different between each of these areas indicating the occurrence of size-based habitat partitioning. Neonate and young-of-the-year animals occurred in the Caloosahatchee River and juveniles older than 1 year occurred in the adjacent embayments. Habitat partitioning may reduce intraspecific predation risk and increase survival of young animals. Classification tree analysis showed that both temperature and salinity were important factors in determining the occurrence and catch per unit effort (CPUE) of immature C. leucas. The CPUE of < 1 year old C leucas was highest at temperatures over 29 degrees C and in areas with salinities between 7 parts per thousand and 17.5 parts per thousand. Although they are able to osmoregulate in salinities from fresh to fully marine, young C. leucas may have a salinity preference. Reasons for this preference are unknown, but need to be further investigated.