When most of you think of going on a cruise, words like fun and relaxation typically come to mind.
However, when LDWF biologists go on a cruise, hard-work and strenuous-activity are better representations of what it’s like.
But because of the important data our biologists receive from these Southeast Area Monitoring and Assessment Program (SEAMAP) surveys, our biologists look forward to their periodic ventures out into the Gulf of Mexico.
We separate our cruises into four surveys – depending on the type of species we are targeting – Icthyoplankton, Shrimp/Groundfish, Bottom Longline and Vertical Line.
By using this strategy, we are able to sample marine species through all their life stages from larvae to adults.
NOAA Fisheries organized all four surveys, which are standardized across the Gulf so that each state’s fisheries division is sampling their respective areas the same way.
Louisiana SEAMAP is coordinated by LDWF biologist Chloe Dean.
“This data is used by the NOAA Fisheries Southeast Fisheries Science Center (SEFSC) to conduct stock assessments that predict present populations and future harvest levels,” Dean said. “LDWF fishery managers use this data for stock assessments, setting seasons and making fishery management recommendations.”
The stock assessment process is called the South East Data Assessment and Review (SEDAR). Stock assessment analysis is very intense and takes an entire team from across the Gulf to conduct one.
The survey cruises typically last between three and seven days. Four to six biologists and volunteers participate in the Icthyoplankton, Bottom Longline and Vertical Line surveys while nine participate in the Shrimp/Groundfish survey.
The data derived becomes part of our fisheries independent sampling – data we acquire without the assistance of commercial and recreational fishermen. The fishery independent data helps negate any fishing bias because our sampling isn’t bound by seasons and bag limits, giving us a fuller glimpse of what’s actually happening in our fisheries.
So here’s a breakdown of the four surveys starting at the bottom of the food chain and moving up.
Icthyoplankton
Before we go any further, we’ll let you know that Icthyoplankton is fish larvae and eggs.
LDWF conducts bi-annual cruises in the spring and fall to receive information on the occurrence, abundance and geographical distribution of the larvae and eggs. The cruises are done in conjunction with other states at the same time of year and using the same equipment, giving a good snapshot of what species are where in the Gulf.
Sampling is conducted using 60-centimeter bongo nets and one by two meter neuston nets, to catch samples of plankton.
The larvae and eggs of bluefin tuna are currently the biggest target, however the larvae and eggs of king mackerel and Spanish mackerel along with various other reef fish also find their way into the nets.
The samples are field processed, preserved and transferred to the National Marine Fisheries Service Pascagoula Laboratory.
Plankton surveys give us an indication of what fish are entering the fishery in the upcoming seasons.
Shrimp/Groundfish
Many small fish and shrimp feed on larvae and eggs, and that’s where the Shrimp/Groundfish survey picks up.
This trawling survey is done twice a year in the summer and fall and utilizes a 42-foot semi-balloon auto-trawl.
All of the Gulf of Mexico states participate in this study, essentially providing a sample of the entire Gulf with a floor of 40 fathoms or fewer.
Shrimp, bait fish, small crabs, vertebrates and small fish including juvenile sport fish that live along the bottom are caught in the net and examined to assess the health of the populations.
Species are identified, counted, measured, weighed and recorded. Then, the data is submitted to the SEAMAP data management system.
The groundfish survey gives scientists a better indication on future recruitment (fish becoming mature) and annual population trends.
Bottom Longline
The next survey is the bottom longline survey, which targets adult fish and sharks three times per year in the spring, summer and fall.
Stations of study are generated in coordination with NMFS and are proportionally allocated by longitude and depth based on the width of the continental shelf. Most of the work is done on mud flats, so many pelagic fish are studied in this survey.
When we say longline, we mean it! The line is a mile long and has 100 hooks on it! Once baited, it is dropped into the water and soaked for an hour before retrieval.
Vertical Line
Finally, the fourth and final survey is the vertical line survey, which is conducted monthly from May to October to collect information on the spatial and temporal distribution of commercial and recreational reef species. These samples are done near platforms, rigs, natural bottom structures and natural and artificial reefs.
The sampling is done through three different lines with 10 hooks on each. Each line has a different size hook.
Biologists may have to pull up a line by hand with as many as 10 adult-sized sport fish on it, making this survey one for the physically fit.
“The bottom longline and vertical line surveys give a snapshot of present day adults in the fishery,” Dean said. “Besides measuring and weighing these fish, parts such as otoliths and gonads are brought back to the LDWF labs for further analysis. All of the data is essential in constructing stock assessments.”
Red snapper, grouper, amberjack and triggerfish are the primary objects of this study.
