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Juvenile Reef Fish Study

General Info

Many species of fish caught in the Gulf of Mexico spend the early part of their lives in seagrass beds in the bay.  The most important of these species include gag grouper, lane snapper and gray (mangrove) snapper.  The grouper spawn in the late winter and juveniles arrive in the bay in late spring.  The snapper are early summer spawners and their offspring arrive in the middle of summer.  When the juveniles arrive in the grassbeds, they are less than ½ inch long and use the grass as both a place to hide to avoid larger fish and a place to hunt for food (usually small shrimp).  By using a small trawl to collect juvenile grouper and snapper in the grassbeds, we can evaluate the size of each year’s production and predict how many grouper or snapper will be available to fishermen a few years in the future when the juveniles grow into adults.  This predictive capability helps fishery managers adjust the regulations to avoid shortages of these species in the future.  The number of fish produced each year fluctuates widely; we have seen 20 times the number of snapper and grouper in one year compared to the number the year before or after.  Our sampling method uses short tows of less than one minute and all fish are quickly measured and released alive to minimize our impact on the resource.  Between 95 and 98% of the grouper and snapper we collect survive.

Methodology

Methodology followed for the Juvenile Reef fish study

1. Tie a knot at the end of the net
2. Throw the net in the water near the buoy
3. Drive for 50m at 2 Knots
4. Pull the net back to the boat
5. Measure the distance from the boat to the buoy with the laser rangefinder
6. Put the sample in a tray
7. Go through sea grass to find snapper and grouper
8. Measure snapper, grouper and flounder and throw them back into the water
9. Get water temperature and salinity with the YSI-30