Abundance of King Mackerel Larvae from SEAMAP Fall Plankton Survey (1986 to 2006) Bongo Net Collections

Since 1982, Southeast Area Monitoring and Assessment Program (SEAMAP) plankton surveys have been conducted by the National Marine Fisheries Service in cooperation with the states of Florida, Alabama, Mississippi, and Louisiana. The SEAMAP Spring Plankton Survey began in 1982 while the SEAMAP Fall Plankton Survey began in 1985. A SEAMAP Winter Plankton Survey took place in 1983, 1984, 1993, 1996, 2004, 2008, 2009, and 2011. Plankton sampling is carried out during these surveys at predetermined SEAMAP stations arranged in a fixed, systematic grid pattern across the entire Gulf of Mexico. Most but not all SEAMAP stations (designated by a unique SEAMAP number) are located at ~56 km or 0.5-degree intervals along this grid. Some SEAMAP stations are located at less than 56 km intervals especially along the continental shelf edge, while others have been moved to avoid obstructions, navigational hazards, or shallow water. Most SEAMAP plankton samples are taken during either dedicated plankton or shrimp/groundfish surveys, but over the years additional samples were taken using SEAMAP gear and collection methods at locations other than designated SEAMAP stations and/or outside established SEAMAP surveys, e.g. during Louisiana seasonal trawl surveys, SEAMAP Squid/Butterfish survey; and other serendipitous or special projects. Although other plankton sampling gear types and mesh sizes have been used throughout the SEAMAP time series, the standard sampling gear and methodology used to collect plankton samples during SEAMAP surveys are bongo and/or neuston nets. A 61 cm (outside diameter) bongo net fitted with 0.335 mm mesh netting is fished in an oblique tow path from a maximum depth of 200 m or to 2-5 m off the bottom at station depths less than 200 m. A single or double, 2x1 m pipe frame neuston net fitted with 0.950 mm mesh netting is the other standard gear employed and it is towed at the surface with the frame half-submerged for 10 minutes. Maximum bongo tow depth is calculated using the amount of wire paid out and the wire angle at the `targeted? maximum tow depth, or observed and recorded in real time throughout the tow. A mechanical flowmeter is mounted off-center in the mouth of each bongo net to record the volume of water filtered. During surveys in the early part of the time series a flowmeter was placed in only one side of the bongo gear. Water volume filtered during bongo net tows ranges from ~20 to 600 m3 but is typically 30 to 40 m3 at the shallowest stations and 300 to 400 m3 at the deepest stations. Samples are taken upon arrival on station regardless of time of day. Samples are routinely preserved in 5 to 10 % formalin and later transferred after 48 hours to 95 % ethanol for long-term storage. During some surveys, selected samples are preserved initially in 95 % ethanol and later transferred to fresh ethanol. Essential elements of SEAMAP plankton survey activities include sample processing (sorting and identification), specimen archival and re-examination of selected taxa. Since the inception of the SEAMAP program most plankton samples have been sorted for fish eggs and larvae, and specimens have been initially identified (mostly to the family level) at the Sea Fisheries Institute, Plankton Sorting and Identification Center (MIR ZSIOP), in Gdynia and Szczecin, Poland under a Joint Studies Agreement between the NMFS and the Sea Fisheries Institute. During the period 1989 to 2002 plankton samples collected by the Louisiana Department of Wildlife and Fisheries were processed by Louisiana state biologists following SEFSC/SEAMAP protocols in use at MIR ZSIOP. Vials of eggs and identified larvae, plankton displacement volumes, total egg counts; and counts and body length measurements of identified larvae are sent to the SEAMAP Archive at the Fish and Wildlife Research Institute, Florida Fish and Wildlife Commission, St. Petersburg, FL. At the SEAMAP Archive data are entered into the SEAMAP database and specimens are curated and loaned to researchers upon request. Data files containing specimen identifications and lengths are sent to the NMFS Mississippi Laboratories where these data are combined with field collection data, edited and maintained in the SEAMAP database.

Ichthyoplankton catch data from SEAMAP resource surveys in the Gulf of Mexico are used to map the distribution, abundance and occurrence of larval king mackerel. Data is limited to samples collected with 61 cm bongo nets fitted with 0.333 mm mesh nets during Fall Plankton surveys from 1986 to 2006. Abundance (number of larvae per 10 square meters of sea surface) is summarized by 0.5 degree longitude by latitude blocks in which samples have been collected.

SEAMAP is a State/Federal/university program for collection, management and dissemination of fishery-independent data and information in the southeastern United States. Resource surveys began in the Gulf of Mexico in 1982. These surveys currently include Winter, Summer, and Fall Shrimp/Groundfish Surveys; Winter, Spring, and Fall Plankton Surveys; a Reeffish Survey; a Vertical Longline Survey; and an Inshore Bottom Longline Survey. These surveys collect a variety of biological and environmental information. All SEAMAP data are available upon request. For information concerning SEAMAP, please contact Jeff Rester of the Gulf States Marine Fisheries Commission at (228) 875-5912 or via e-mail at jrester@gsmfc.org.