ICES CM2007/K:19 Theme Session Monkfish across the world: common problems and commons solutions Aspects of the biology and fishery of Lophius gastrophysus Miranda-Ribeiro, 1915 (Lophiiformes, Lophiidae) in southeastern Brazil Maria de Fátima Moraes Valentim, Marcelo Vianna and Erica Pellegrini Caramaschi Universidade Federal do Rio de Janeiro, Instituto de Biologia. Avenida Pau Brasil, 21941- 590, Ilha do Fundão, Rio de Janeiro, Brasil. E-mail: [email protected] ABSTRACT Historically, Lophius gastrophysus has been considered a bycatch of the trawler fleet, but it was intensively exploited between 2000 and 2002 because of its high value in the international fish market, resulting in a reduction in the catch during that period. On account of this, a management program for fishery in Brazilian waters was developed to promote sustainable use of such resource. In 2005, measures for commercial exploitation of L. gastrophysus were established through a normative instrument edited by the government. However, the biological basis of this regulatory tool was derived from research on other species of Lophius in the Atlantic Ocean. In order to provide information to guide future changes in legislation and to generate basic biological data on L. gastrophysus ; specimens of this species landed by the trawler fleet of the state of Rio de Janeiro were studied. L. gastrophysus spawning took place primarily between spring and summer. Fishes with size less than the one at the first sexual maturation estimated for females (50 cm) were considered juvenile. The most important category in the diet was fish, which showed the highest IAi. Trawl fishery takes place at a depth of 50 to 130 m, where double-rig nets with a net opening of about 24 m are used. Trips in the sea last about 12 days, making six trawls per day. Data obtained showed that specimens caught by the trawling fleets were mainly of the "small" commercial category, that is, juveniles, which congregate in shallower areas. CPUE values were higher between the end of spring and beginning of summer, coinciding with the reproductive peak of the species. Steps to implement and enforce effective measures, to reduce bycatch of L. gastrophysus by trawler fleet must be taken, to guarantee sustainable fishery for this species in Brazilian waters. Key-words: Biology, fishery, Lophius gastrophysus , management, southeastern Brazil, 1 INTRODUCTION The lack of knowledge on the availability of fishing resources on the external continental shelf and slope, associated to the high costs and risks when operating in such areas caused industrial fishery concentration in the internal part of the continental shelf in the southeastern and southern regions of the Brazilian coast up to the end of the 90s, in spite of the serious overfishing tendencies detected in the main demersal resources (e.g. Haimovici, 1998). This fact promoted a new direction in favour of the resources that had not been exploited before, thus focusing on the external continental shelf, as well as in the slope, in the same concentrated way, which potential sustainability is still unknown (Perez et al ., 2001). In 1998, the Agriculture Department, as well as the Cattle Raising and Supply Departments instituted an ocean-fishery program for national companies to be able to acquire foreign vessels through leasing, in an attempt to improve the knowledge of potential fishing resources for a rational occupation of the Brazilian Exclusive Economic Zone (EEZ). This program was implemented in the southern region in 2000, when the leased vessels began to operate at depths of 200 to 900 m using bow nets, gillnets and trawl nets (Perez et al ., 2001). In the subsequent years, besides these vessels acting in the capture of Lophius gastrophysus , the national vessels headed for deeper areas, causing a greater increase in the fishing effort, due to the high commercial value in the international market (Perez et al ., 2001; 2002). In this context, in less than five years L. gastrophysus moved from a subfishing condition to an overfishing threat, as depletion of stocks start to occur , fishing power tends to increase in order to face reduction of captures and to keep the yield. Historically, L. gastrophysus had been registered as a bycatch component of trawler fishery in the southeastern region of the Brazilian coast (Vianna & Almeida 2005). According to the project, Living Resources in the Exclusive Economic Zone (REVIZEE), no potentially important stocks were identified for Brazil. Even the ones considered as promising, as L. gastrophysus , responded to the increase of the fishing effort. To try to avoid a fast depletion of the stock of L. gastrophysus , a fishery management process of the species was implemented. Monitoring of the fishing activity and recommendations of the scientific and government sectors were also carried out. Brazil also agreed to implement the Conduct Code for responsible fishing (FAO, 1995). Management measures were established for commercial exploitation of L. gastrophysus through a government normative instrument (Brazil-MMA, IN - Nº 23, of July 4, 2005), a series of approaches and procedures were also established, such as: vessels nationality (Brazilian); maximum number of vessels 2 allowed (nine); fishing method (bottom gillnet); nets maximum limit to be transported by vessels (a thousand nets); gillnet mesh (280 mm between opposite knots); submersion time for nets (no more than 120 hours); minimum depth allowed (250 m); maximum annual limit allowed for capture (1500 tons gutted weight). However, to give support to this normative instruction, biological data from other species of Lophius in the Atlantic Ocean were used, due to the lack of information on L. gastrophysus at that time. Therefore, studies on such species are essential to help future changes in the legislation and to generate information on L. gastrophysus for a better management and sustainable approach on the fishery activity. Therefore, studies to enable an assessment for local population sustainability and to support effective management of fisheries are essential. In order to emphasize reproduction, feeding and fishery aspects, studies on L. gastrophysus , landed by the commercial trawler fleets of the Rio de Janeiro state, are being carried out. MATERIALS AND METHODS Reproductive and feeding biology During April/2004 and March/2006 454 individuals of L. gastrophysus caught by commercial fishing trawlers and landed in the fishing port of Niteroi, in Rio de Janeiro State were acquired. For each individual, the following data were registered: total length (Lt-cm), total weight (Wt-g), liver weight, sex, maturity stage and ovaries weight. The mean size at first sexual maturity (L 50 ) was obtained for females, using King (1995) modified logistic curve. The gonadosomatic and hepatosomatic index (GSI and HSI) were estimated for females. Spawning period was estimated through the temporal frequency analysis of the maturity stages and variation of the GSI and HSI mean values. The frequency of occurrence method (Hyslop, 1980) and weight percentage were applied to characterize the diet. They were combined in the Alimentary index (IAi) proposed by Kawakami and Vazzoler (1980). Fishery and yield In order to assess how commercial trawler fleets operate on L. gastrophysus , 47 interviews were carried out with different vessel skippers from March/2004 to February/2006, in the fishing port of Niteroi, in Rio de Janeiro state. An overall count number, of 13.926 of L. gastrophysus individuals, was recorded. Fishes were landed gutted in two commercial categories: small (under 1.0 kg) and large (over 1.0 kg). Size structure analyses of L. 3 gastrophysus were carried out by grouping frequency distribution of individuals in the two commercial categories. The number of size classes was stipulated according to the Sturges formula (k= 1+log 2 n; where k= number of classes, n= number of individuals analyzed). Each class interval was defined according to the Siegel formula (Ci = λ/nc; where ci= classes intervals, nc= number of classes, λ= variation in amplitude of the length. Seasonal abundance was estimated by analysis of the catch per unit effort (CPUE). The records for weight (kg) of the total catch per landing of L. gastrophysus were divided by the number of landings for the two study periods. In order to assess recruitment, the estimated value of L50, obtained for females, was calculated. Such value is considered an estimate of the length at which 50% of the population samples begin their sexual maturity. RESULTS Reproductive and feeding biology Size variation in amplitude of the individuals analyzed from 8.9 to 76.0 cm (mean 48.2 ±SD13.2 cm). The mean size at first maturity for females was recorded 50 cm (Figure 1). The period of maximum reproductive activity was registered between August and January, which corresponds to early spring and mid-summer seasons. Unlike the values observed for GSI, lower values of HSI were obtained during this period (Figure 2). Maximum GSI value for females was 12.5%. We identified 40 food items, grouped into four categories: fish, molluscs, crustaceans, and others. Fish was the principal category in the diet (Figure 3), with 25 identified species distributed in 20 families. Among the identified species, flying gurnards Dactylopterus volitans, argentine hake , Merluccius hubbsi and rough scad Trachurus lathami showed the highest IAi rate. Fishery and yield Variation in amplitude of L. gastrophysus measured in the fishing port was from 15.6 to 83.0 cm (mean 40.6 ±SD 11.0 cm). Overall sampling measurement presented 5.911 (42.4%) for small and 8.015 (57.6%) for large commercial categories (Figure 4), where only 20.6% of the individuals presented a higher mean size at first sexual maturity estimated for females (L 50 =50.0 cm), that is, they were adults (Figure 1) . Seasonality and percentage frequency of occurrence of juveniles and adults is shown in Figure 5. A slight increase on adults landing was observed in spring and summer months on the two-year study.