Population connectivity of red drum in the northern Gulf of Mexico

Stable carbon (delta C-13) and oxygen (delta O-18) isotope ratios in otoliths were used to assess the degree of connectivity between early life and adult habitats of red drum Sciaenops ocellatus in the northern Gulf of Mexico. Young-of-the-year (YOY) red drum were sampled over a 3 yr period from major estuaries along the Texas coast, and otolith delta C-13 and delta O-18 were quantified to determine whether chemical tags in otoliths were region specific. North to south gradients were pronounced for otolith delta C-13 and delta O-18, with values being higher (enriched in the heavier isotope) for YOY red drum from southern estuaries relative to those in the north. Four distinct regional groups of YOY red drum were identified using otolith delta C-13 and delta O-18: North (N), Sabine Lake and East Galveston Bay; North-Central (NC), Christmas Bay and Matagorda Bay; South-Central (SC), Aransas Bay and Redfish Bay; and South (S), Laguna Madre. Overall classification success to these regional nurseries was high for each year examined: 2001 (92%), 2002 (82%) and 2003 (90%). Mixed-stock analysis performed with age-2+ red drum collected in 2003 matched to the 2001 YOY baseline indicated that most of the sub-adult and adult red drum sampled in the S and SC regions were produced from the same areas (82 to 91%), with limited exchange between these regions. Mixing was more pronounced in the northern regions (N, NC), with a large percentage (35 to 42%) of individuals originating from the adjacent region to the south. Overall, the majority of sub-adult and adult red drum was collected within or near the same region occupied during the YOY period, suggestive of natal homing, retention within specific estuarine corridors, or lower survivability of recruits migrating from distant regions.