The deep-water rose shrimp in the Ionian Sea: a spatio-temporal analysis of zero-inflated abundance data

In the ecological field, the sampling of abundance data is often characterized by the zero inflation of population distributions. Constrained zero-inflated GAM’s (COZIGAM) are obtained assuming that the probability of non-zero inflation and the mean non-zero-inflated population abundance are linearly related. Models of this class have been applied to a spatio-temporal case study concerning the deep-water rose shrimp, Parapenaeus longirostris (Lucas, 1846). Abundance data were collected during 16 experimental trawl surveys conducted from 1995 to 2010 in the Ionian Sea. The sampling design adopted was random-stratified by depth, with proportional allocation of hauls to the area of each depth range and geographical sector. Density index (N/km2) and length (mm) were considered for each haul identified by time, depth, geographic coordinates and geographical sector.