Biomass and fishing potential yield of demersal resources from the outer shelf and upper slope of southern Brazil

Abstract

ABSTRACT. The relative abundance and fishing potential of the commercially valuable fishes and cephalopods with marketable size was assessed using two seasonal bottom trawl surveys performed in 2001 and 2002 on the outer shelf and upper slope (100-600 m depth) off the coast of southern Brazil. These surveys were part of REVIZEE, a national program designed to assess the fishery potential within the Economic Exclusive Zone. Of the 228 fish and cephalopod species caught during the surveys, only 27 species and genera were considered to be of commercial interest. Commercial-sized individuals of these species made up 52.3% of the total catch. The total biomass was estimated to be 167,193 ton (± 22%) and 165,460 ton (± 25%) in the winter-spring and summer-autumn surveys, respectively. The most abundant species were the Argentine short-fin squid Illex argentinus, a species with highly variable recruitment, followed by the Argentine hake Merluccius hubbsi, the gulf-hake Urophycis mystacea, and the monkfish Lophius gastrophysus. The latter three were intensively fished prior to the surveys, as well as the beardfish Polymixia lowei and silvery John dory Zenopsis conchifera, both relatively abundant but with a very low market value. The potential yield of the demersal fish species, not considering Illex argentinus, estimated with the Gulland equation for a mean natural mortality of M = 0.31, was 20,460 ton. When considering only Merluccius hubbsi, Urophycis mystacea, and Lophius gastrophysus, the potential yield decreased to 6,625 ton. The surveys showed that the fishery potential of the outer shelf and upper slope was substantially lower than that of the inner shelf. Therefore, this environment should be carefully monitored to avoid overfishing and fast depletion.

Surveying while fishing in the slope areas off Brazil: direct assessment of fish stock abundance from data recorded during commercial trawl fishing operations

“…Biomass estimates obtained in this study for the three stocks exceeded those obtained in the same area and years by scientific trawl surveys under REVIZEE Program (Haimovici et al, 2009). Such difference was 14-18 times larger in the case of the hake stock (Table 6).…”

“…Whereas these patterns in principle refute the proposed hypothesis, an in-depth analysis of basic differences in the data analyzed and methods employed may address at more complex conclusions. Firstly, this study did not assume that trawl nets operated with full efficiency (X1 = 1) as opposed to the previous fishing survey estimates (Haimovici et al, 2009). Instead efficiency coefficients were estimated for each species and employed during sample density calculation, as generally recommended in bottom trawl surveys, to account for the differential vulnerability of the studied organisms to the 'sampling' procedure (Gunderson, 1993).…”

“…To that end, only trawls conducted in 2000, 2001 and 2002 were included for biomass estimation analysis, which corresponded to the period when the foreign trawl fleet was fully focused in fishing slope finfish species (Perez et al, 2009b). Selecting that period was also crucial because it also matched the area and period covered by bottom trawl surveys of the Program REVIZEE (Haimovici et al, 2009) (Fig. 1).…”

“…Initiatives for managing slope trawling in Brazil date back to 2006, and were focused on the implementation of measures aiming to control the impacts of the growing national fleet and preserve productivity of the new exploited stocks. These measures were based on three components: a) stock biomass estimations obtained in 2001/2002 at the main fishing grounds (Haimovici et al, 2009), b) Maximum Sustainable Yield (MSY) calculations based on lifehistory parameters (Perez, 2006), and c) the establishment of effort limitations for the national slope trawl fishery (Perez & Pezzuto, 2006;Perez et al, 2009b). The former resulted from a 10-year Governmentfunded fishing survey REVIZEE Program that ended in 2006, not to be resumed ever since (MMA, 2006).…”

Pathways for sustainable industrial fisheries in southeastern and southern Brazil

“…In contrast, fishing authorities launched between 2000 and 2008 an on-going oil subsidy policy, which further supported both managed and unmanaged emerging fishing operations, and sponsored the assessment and development of deep-sea fishing poten- tialities as an alternative for the overcapitalized coastal fleet (Abdallah & Sumaila, 2007). The latter not only proved unpromising, but also added new components to the "chaotic" scenario of fishing development and management (Haimovici et al, 2009;Perez et al, 2009). Attempts to change licensing system and prohibit the capture of certain endangered species were implemented after 2011, but these turned out to be highly debated and little effective management actions (Pezzuto & Mastella-Benincá, 2015).…”