Abundance and distribution of paralarval cephalopods in relation to mesoscale hydrographic features in the northeastern Gulf of Mexico

Abstract

Paralarval cephalopods were collected and identified from 1m² and 4 m² MOCNESS (Multiple Opening and Closing Net Environmental Sensing System) and 15' IKMT (Isaacs Kidd Midwater Trawl) trawls taken in 1996 and 1997 in the northeastern Gulf of Mexico. Additional specimens were collected from 1m² MOCNESS tows taken during a 1997 Student Training and Research cruise, as well as from meter net tows done as part of 1998 and 1999 'NEGOM' (Northeastern Gulf of Mexico) Chemical Oceanography and Hydrography cruises. The intent of this research was to determine if mesoscale oceanographic circulation was correlated with the distribution and abundance of paralarval cephalopods. Results were also compared to prey and predator distributions to determine if biological correlations exist. Five families of cephalopods (Enoploteuthidae, Ommastrephidae, Pyroteuthidae, Onychoteuthidae, and Cranchiidae) dominated the catches. Paralarvae reached greatest numerical abundance in the upper 130 m of the water column, but greater mantle length of some of the more abundant taxa was often correlated with increasing depth of capture indicating ontogenetic descent. Paralarval cephalopods showed a positive correlation with zooplankton biomass; this biomass was assumed to be a proxy for potential prey. In addition, paralarvae were less abundant in Loop Current eddies (anticyclones) than in associated cyclones, though overall abundance was higher overall during the August 1997 cruise than during the October 1996 cruise. Seabirds and sperm whales were concentrated within the cyclonic mesoscale features during both cruises, potentially responding to a greater potential to capture cephalopod and other prey.