Adult spotted seatrout are being collected in lower Tampa Bay to
evaluate the effect of the 2005 red tide event on the population.
Scientists and local anglers have documented a decrease in
the spotted seatrout population in lower Tampa Bay following the
red tide event in 2005 (Article: 2005
Red Tide Impacts on Fish Spawning in Tampa Bay) .
Although it is known that
spotted seatrout were killed and/or displaced by the red tide, the
time it takes for the population to recover is not known. By
comparing catches and the biological condition of spotted seatrout
before and after the red tide event, biologists can document the
The gill net survey is a small component of a comprehensive
research plan examining spotted seatrout in Tampa Bay (Article: Spotted
Seatrout Research in Tampa Bay-An Overview). The gill net
survey originally began in 2000 and extended through 2003, covering
a variety of areas in lower Tampa Bay.
Research mullet skiff. With the engine mounted towards the front
of the boat, these vessels are designed specifically for deploying
nets over the stern.
Gill net strike. The net is set from the back of a research skiff.
After the net is fully deployed, it soaks for five minutes before
Net retrieval. The gill net is pulled into the boat and captured
fish are removed from the mesh.
Adult spotted seatrout were targeted
for capture and sacrificed to collect data on age, reproductive
condition, and health.
spotted seatrout are immediately placed on ice for
further study. Other species are released alive and
Based on these three years of data (2000-2003) scientists gained
a much better understanding of the population in Tampa Bay
(demographics and reproductive biology) during normal conditions.
After the major red tide event in 2005, the gill net survey was
reinstated to collect fish and compare data between pre- and
post-red tide periods. Although the original gill net survey
encompassed a much broader geographic region, the post-red tide
survey focused on a smaller area that has been heavily monitored
through a variety of studies. From these studies and from the
original gill net survey, biologists knew this area traditionally
supported a healthy spotted seatrout population.
Following the 2005 red tide, catches by
both biologists and recreational anglers in this area dramatically
declined. It was apparent that the red tide had either killed or
displaced the once healthy spotted seatrout population but the
extent of the damage, as well as how quickly the fish would
rebound, remained unknown. It is necessary to capture fish after
the red tide event to evaluate if the recovering population is made
up of fish that survived the red tide, or fish that were born after
the red tide event.
This can be accomplished if the ages of the fish in the
recovering population are known. In order to determine age,
spotted seatrout must be sacrificed, as age is determined by
counting the rings within their otoliths, or earstones,
to Aging Fish: What Are Otoliths? and The
Otolith Sectioning Process). However, in an effort to kill as
few fish as possible and to learn everything possible from the fish
that are sacrificed, multiple types of data are collected from each
fish. This data contributes not only to our understanding of
the spotted seatrout recovery but to a number of different studies
being conducted at the Fish and Wildlife Research Institute such
as: trophic interactions (gut contents), fish health (gill arch and
internal organs), and genetic stock structure (fin clip).
Spotted seatrout are measured, weighed, and the circled organs
are used to determine various conditions. Further detail on the
fish health analyses can be found in the article: Fish and
Wildlife Health Program Summary.
Although the catches of spotted seatrout in 2006
and 2007 are still below pre-red tide levels, the numbers are
increasing, indicating the population is on the road to recovery.
Spotted seatrout mature at a relatively small size and age, with
most fish spawning at age one, and approximately 11.8-15.7 inches
long (Article: Spotted Seatrout (Cynoscion
nebulosus) Species Account). Because spotted seatrout
reproduce at an early age and produce hundreds of thousands of
eggs, they are expected to be fairly resilient and capable of
recovering in the near future.