Sociometric analysis of the role of penaeids in the continental shelf food web off Veracruz, Mexico based on by-catch

Continental shelf macrofauna are impacted by trawling and associated by-catch activities. These activities have been predicted to change the macrofaunal community structure and the resulting food web. Four food webs (three seasonal and one pooled) were constructed using shrimp by-catch samples from 21 surveys from 1991 to 1994. Network sociometric analyses were performed on the webs in order to explore structural characteristics focusing on the role of penaeids. The number of nodes varied from 43 to 73. The out-degree centrality value for the combined web was the highest. For the penaeid node, the windy season centrality was the highest (47%) and the rainy season the lowest (11%). The number of cutpoints by season was: windy four, dry two, and three for the combined web. Using the lambda sets analysis; penaeid is a key node for the structural cohesion of the trophic network. The rainy season food web is the most homogeneous and penaeid is an important node such that its elimination would cause a major structural and functional disruption to the network. These modeling exercises suggest over-fishing by trawlers would impact the continental shelf community structure and thus significantly change the existing trophic relationships.