Geostatistical Modeling of Blacktip Shark Hotspots and Essential Habitat in the Gulf of Mexico

Shark conservation has moved to the forefront of conservation issues for many people.  Blacktip sharks (Carcharhinus limbatus) are one of the most important commercial shark species in the Gulf of Mexico (GOM).  Identification of essential habitat (EFH) is fundamental for conserving natural resources like sharks.  However, most current methods for identifying EFH have substantial limitations.  To address these shortcomings, we created a new method for identifying EFH for blacktip sharks using  federal and state fishery-independent datasets.  Because shark catch data was highly zero inflated, a 2 stage delta lognormal modeling process was used to create kriged layers.  From these layers, hotspots (>1 std. dev above mean) and coldspots (below the mean) were extracted.  Hotspot and coldspot layers were overlayed to identify patterns in shark distribution and abundance over time and identify areas of hotspot and coldspot persistence.  The resulting composite maps revealed several areas of the GOM with at least a 75% probability of being a hotspot or a greater than 75% probability of being a coldspot.  This method allows the identification of areas most commonly used and avoided by blacktip sharks in the GOM without many of the shortcomings of currently used methods.