| Abstract |
The effects of harvesting of callianassid shrimp (Trypaea australiensis) on the abundance and composition of macrobenthic
assemblages in unvegetated sediments of a subtropical coastal embayment in Queensland, Australia were examined using a
combination of sampling and manipulative experiments. First, the abundance and composition of the benthic infauna in an area
regularly used for the collection of shrimp for bait by recreational anglers was compared with multiple reference areas. Second,
a BACI design, with multiple reference areas, was used to examine the short-term effects of harvesting on the benthic
assemblages from an intensive commercialised fishing competition. Third, a large-scale, controlled manipulative experiment,
where shrimp were harvested from 10,000 m2 plots at intensities commensurate with those from recreational and commercial
operators, was done to determine the impacts on different components of the infaunal assemblage.
Only a few benthic taxa showed significant declines in abundance in response to the removal of ghost shrimp from the
unvegetated sediments. There was evidence, however, of more subtle effects with changes in the degree of spatial variation
(patchiness) of several taxa as a result of harvesting. Groups such as capitellid polychaetes, gammarid amphipods and some
bivalves were significantly more patchy in their distribution in areas subjected to harvesting than reference areas, at a scale of
tens of metres. This scale corresponds to the patterns of movement and activity of recreational harvesters working in these areas.
In contrast, patchiness in the abundance of ghost shrimp decreased significantly under harvesting at scales of hundreds of
metres, in response to harvesters focussing their efforts on areas with greater numbers of burrow entrances, leading to a more
even distribution of the animals. Controlled experimental harvesting caused declines in the abundance of soldier crabs (Mictyris
longicarpus), polychaetes and amphipods and an increase in the spatial patchiness of polychaetes. Populations of ghost shrimp
were, however, resilient to harvesting over extended periods of time. In conclusion, harvesting of ghost shrimp for bait by
recreational and commercial fishers causes significant but localised impacts on a limited range of benthic fauna in unvegetated
sediments, including changes in the degree of spatial patchiness in their distribution. |
