FWRI freshwater fisheries scientists in Melbourne conducted a
study to determine the effect of cast-net fishing on habitat and
sport fish species in the St. Johns River.
What Effect Does the
Cast-Net Fishery for the Exotic Brown Hoplo (Hoplosternum
littorale) Have on Native Recreational Fisheries?
Cast-netters on the St. Johns River.
hoplo, an exotic armored catfish, has become abundant enough to
support a cast-net fishery on the upper St. Johns River.
Recreational anglers using the river expressed concern that
cast-netters were illegally harvesting sport fish, overharvesting
native catfish species, and destroying habitat and spawning areas.
To address these concerns and gain additional insight about this
fishery, FWRI freshwater fisheries scientists in Melbourne
conducted a study in the reach of the St. Johns River between State
Road 520 and State Road 46. The study included creel surveys and
fish population electroshocking.
Access-point creel survey results from January to April 2003
revealed cast-netters were the dominant user group (38%) in the
upper St. Johns River, and brown hoplo was the main species
harvested (95% of this group's total harvest). Cast-netters were
found to be in possession of illegally caught sport fish in only
two instances (98% compliance). Previous FWC law enforcement
activity targeting cast-netters in this area revealed a 94%
compliance rate, which is extremely high for any resource user
group. The survey revealed that, while they were the dominant user
group, cast-netters accounted for only about 20% of the harvest of
native catfish species. With so little illegal harvest of sport
fish and nominal harvest of native catfish, there appeared to
be little evidence to suggest the cast-net fishery for armored
catfish was adversely affecting the traditional recreational
Electroshocking, a common sampling method for freshwater fishes,
uses electricity to momentarily stun fish. When done properly,
electroshocking allows fish to be collected, measured, and released
back to the water unharmed. Electrofishing catch-per-unit effort
data have regularly been collected from this section of river since
1991. These data show no noticeable declines in sport fish
populations. In some cases, when compared to earlier years, the
numbers of sport fish of harvestable size appeared to have actually
Finally, concerns about physical damage to habitat and spawning
areas due to cast-netting activity are difficult to quantify due to
the variability of a dynamic system like a river. However, because
the brown hoplo is an air gulper and seems to prefer low-oxygen
backwater habitats, interspecific competition (competition between
different species) is probably minimal. They do not spawn on the
bottom like native fishes. Instead, brown hoplo construct floating
bubble nests that are not subjected to the debilitating effects of
silty substrates found in backwater areas. Sport fish are unlikely
to spawn or even inhabit these areas, and biologists suspect that
cast-netting in these areas is not likely to damage habitat that
can be used by sport fish.