4. Discussion
4.1. Shallow and warm bias
Capture records show that most lionfish were reported from relatively warm waters (mean 26.5 °C) less than 35 m, corresponding closely with recommended recreational SCUBA diving limits and reflecting that most captures likely were reported by divers. Exceptions include those lionfish reported off North Carolina where populations utilize deep sea offshore wrecks (Kimball et al., 2004). It is difficult to ascertain if this shallow, warm water, bias is representative of the overall population, as lionfish can inhabit depths down to bottom water temperature limitations of about 10 °C (Kimball et al., 2004). In our RSM, neither depth nor temperature were shown as highly influential in the spread of lionfish larvae into new areas; however due to the origins of most USGS records being from the diving community, depth limitations could not be fully explored. We also acknowledge that temperature and depth are likely correlated. However, these two parameters had little influence (low weight values of .02) on spread of lionfish through the RSM. For that reason, any correlation is not considered to be detrimental to the study. Additionally, over the last 25 years, awareness of the lionfish invasion has increased dramatically and likely has resulted in increased sampling intensity in the affected areas, possibility introducing spatial bias to the USGS records invasion sequence upon which our model is based.
The distribution map shows suitable habitat throughout the Caribbean Sea, Gulf of Mexico, and the eastern shore of the United States north to Cape Hatteras, North Carolina (Fig. 1A). This northern most limit corresponds to major benthic structure and habitat changes and was also found the likely northernmost limit for lionfish by Kimball et al. (2004) and other tropical fauna by Briggs (1974). Additionally, the Gulf Stream is deflected offshore from the coast in this area, resulting in cooler coastal winter water temperatures.