Population structure of shrimp discarded as bycatch from the <i>Penaeus subtilis</i> (Decapoda) fishery on the Amazon Continental Shelf

The industrial fishing of the southern brown shrimp (<i>Penaeus subtilis</i>) has, since the 1960s, considered several shrimp species to be bycatch that are discarded without any use. This extractive fishing activity has a profound impact on the aquatic ecosystem since it removes from the environment an important set of little-studied invertebrate species found in the Amazon coastal area, an inconspicuous region with great species diversity. This research aims to describe the population structure, sex ratio and spatial distribution of the shrimp species captured as bycatch on the Amazon Continental Shelf (ACS). Sampling was conducted during 124 trawls, with 430.30 h of observation. A total of 17 shrimp morphotypes distributed in six families and eight genera were captured as bycatch. The most abundant species was <i>Rimapenaeus similis</i>, with 3788 individuals captured (44.34%), followed by <i>Xiphopenaeus</i> spp. (25.9%), while <i>Penaeus subtilis</i> (19.7%), the target species of industrial fishing, appeared in third place only. The other species contributed approximately 10% of the total shrimp caught. The species population structure was described and the sex ratio was determined as mostly 1:1. In general, juveniles and adults were collected, between 0.8°S and 4.95°N latitude at depths varying from 35 to 85 m, in different substrates. To our knowledge, this is the first study describing the population structure of non-commercial shrimp species, such as <i>R. similis</i>, in the region and to report the unsustainability of fishing as it is practised today, since the fleet subtracts 17 morphotypes of which the target species is only the third most abundant while discarding all others. The results obtained provide basic data about shrimp biology and ecology in a vast equatorial region, where these shrimp are resources intensively exploited by the fishing industry, and can serve as a baseline for elaborating future management policies for the fisheries operating in the region.