By-catch analysis of Argentinean prawn Artemesia longinaris (Decapoda: Penaeidae) in surrounding area of Patos Lagoon, southern Brazil: effects of different rainfall

Abstract

One of the most problematic fishing methods in terms of by-catch and discarding is prawn-trawling. This paper analyses the incidental catch of an artisanal trawl fleet during two discrete Artemesia longinaris fishery seasons (2002 and 2004). The fishery season of A. longinaris operates monthly and it takes place in the surrounding area of the Barra do Rio Grande. Sampling was carried out during the fishing season (April–December) always on the same artisanal trawl boat. An observer was included on-board to avoid loss of information due to discards made by the fishermen at sea. Fifty species were caught: 38 fish and 12 crustaceans. Discrete fauna abundance and composition were recorded in analysed years, with higher by-catch ratios associated with elevated rainfall and low salinity. The overall discard ratio was 1:5.6, with values ranging from 1:11.3 in 2002 to 1:2.5 in 2004. The most striking differences between both years analysed were observed during autumn (1:75 in 2002 and 1:11.30 in 2004) and winter (1:16 in 2002 and 1:0.97 in 2004), while spring presented similar values (1:8 in 2002 and 1:4 in 2004). The discard ratio estimated in terms of number showed a different pattern, presenting overall values of 1:2.24 in 2002 and 1:0.5 in 2004. Higher estuarine runoff may have increased biomass production in the surrounding area of Patos Lagoon during 2002, sustaining higher abundance of estuarine-related and marine species in the area, as well as higher mean trophic level and abundance of top-predators. Conversely, A. longinaris production was consistently lower, since this marine species does not tolerate marked reductions in salinity. In 2004, salinity was higher, associated with low rainfall and favouring A. longinaris abundance in the area. During this dry year, the target-species was dominant in samples resulting in very low by-catch ratios, especially in winter (1:0.97). The catch was mainly composed of juvenile fish, since fishery is performed in nursery grounds.

Factoring scales of spatial and temporal variation in fish abundance in a subtropical estuary

“…It seems plausible, therefore, that such large-scale phenomenon affecting atmospheric and oceanographic conditions in the South Atlantic with approximately a 2 yr frequency would play a role in the post-spawning success of marine migrant species that use the Patos Lagoon Estuary as a nursery. The current study supports findings from several prior studies that demonstrated the influence of large-scale coupled ocean−atmosphere phenomena in the Pacific Ocean (ENSO) on the estuarine fish assemblage inhabiting the Southwestern Atlantic Coast of Brazil (Garcia et al 2001, 2003a, Dumont & D'Incao 2011. The influence of similar coupled ocean−atmosphere phenomena, such as the SAM, on inter-annual variation of estuarinedependent fishes and other marine taxa in this region and elsewhere deserves further investigation.…”

Evaluation of the Blue Crab Callinectes sapidus Rathbun, 1896 Bycatch in Artisanal Fisheries in Southern Brazil

“…) 26, 14 , where P is the probability of capture, r is the steepness constant of the curve, CW is the carapace width and CW 50 is the average size at first capture. The model was adjusted by the solver tool (Microsoft Excel) to minimize the amount of waste between the cumulative frequency of observed CW and the frequency calculated by the model.…”

Mouth gape determines the response of marine top predators to long-term fishery-induced changes in food web structure

“…The feeding mode of Franciscana dolphins, combined with the ability to locate prey by echolocation, is better suited for turbid water than that of fur seals 17 , 60 , which probably explain why Franciscana dolphins have undergone a more dramatic shift in isotopic niche than the latter. However, it is worth mentioning that the dramatic shift observed in the isotopic niche of Franciscana dolphin may also have been favored by the simultaneously reduction, due to by-catch, in the population size of Atlantic midshipman Porichthys porosissimus 61 , 62 , a fish species which constituted a major prey for the Franciscan dolphin until the 1980s 40 , 41 (see Supplementary Table S2 ).…”