| Resumo: |
This study analyses the recreational and artisanal fisheries in San Blas Bay and their relationship with the dynamic of the temporal and spatial variability of the coastal fish assemblage. In addition some biological characteristics of two main target species are assessed. San Blas Bay is part of a natural reserve located in the southern part of Buenos Aires province, which has a great value in terms of tourism, ecology and productivity. According to different sampling methodologies used in this thesis 11 species of chondrychthes, 26 species of bony fish, and a hagfish (Class Petromizontida) were recorded, with a predominance of species belonging to Buenos Aires biogeographic province. To evaluate the fish assemblage seasonal pattern, every three months were performed samplings with bottom gill nets at three different sites within south Anegada Bay during two consecutive years. In the integrative analysis of fish assemblage six ABUNDANTS species were registered (Mustelus schmitti, Cynoscion guatucupa, Odontesthes argentinensis, Myliobatis goodei, Micropogonias furnieri and Squatina guggenheim), any species were considered as OCCASIONAL, three as CONSTANTS (Brevoortia aurea, Callorhinchus callorynchus and Stromateus brasiliensis) and twelve were classified as RARE. The seasonal analysis of species richness, the CPUE and others assemblage indices showed a clear pattern of seasonal variation, which emphasizes that during spring and summer (warm months) the species diversity and catch per unit effort were larger than during autumn and winter (cold month). This pattern of inter-annual variation was also supported by cluster and ordination analysis, in which the sampling stations included in warmer months are joined as a separated distinct group with respect of these stations belonging to the colder months. The recreational fisheries in San Blas Bay take places in a pebble-gravel and sands beaches where fishing is directed to gvariada h fishes. Also in this area fishing tournament take place during the summer. Moreover, a recreational fishery has been developed on the bridge located at the entrance to San Blas Bay and its targets species were marine silversides and flounders. In turn, a boat fishery is concentrated over the "variada" fishes. In any case the recreational activity shows a noticeable seasonal pattern being concentrated during spring and summer months. The roving creel census technique was used to characterize the coastline recreational fisheries. The sampling program included a pilot survey to define spatial and temporal sampling strata. A total of 507 interviews based on 63 working days were conducted between november 2008 and april 2009 (season I), whereas 856 interviews were performed based on working 108 days between june and april 2010 (season II). A semistructured questionnaire was designed to acquire both fisheries and socio-economic information. Beaches anglers were mostly male between 40 and 60 years old coming from 13 different province of the country. They believed that San Blas Bay is the best recreational fishing place in Argentinean coastal waters. The whitemouth croaker was targeted as the favorite species followed by the category gwithout catch preferences h. The minimum sizeable catches to keep fish were selected between 30 and 40 centimeters but 21 percent of anglers noted the need for a specificic minimum length by species. In addition, most anglers would catch as much fish as possible during a fishing day. It was found a seasonal pattern in the qualification of fishing days, being October, November and December considered as the best months and the summer months as the worst. Despite the CPUE was the largest during late spring, the fishing effort during both seasons showed a monthly growing tendency to reach a peak in January and after that decreased to be minimum during autumn and winter months. As was observed in other recreational fisheries, the fishing effort during weekend days was higher than during week days, with the exception of summer-holydays months. This fact was related to the anglers time availability and therefore another variables (not only fishing quality) are important to decide the right moment for fishing ( grecreational angler h profile). In contrast, during November and December a "angler extractive" profile predominated being the catch of fish the main motivation to visit San Blas Bay. These anglers exhibited the highest value of their fishing tackle and participated in more boat fishing trips. In terms of catch, the stripped weakfish and withemouth croaker were the most prevalent target species, accounting both by more than 60 percent of monthly total harvest in weight. In both seasons, catch were greatest in December. It was estimated an annual total harvest of 193 ton during the first season and 235 ton during the second one. The two Sciaenidae were caught above their length at first maturity (TL50), while the smoothhound lengths catch were below their TL50 and therefore a mandatory catch and release was suggested. The fishing effort in the bridge was very low compared to that observed in the beaches. The CPUE was higher during spring and catch were focused on O. argentinensis, which exceed 85% in every month. Annually, the boat fishing in San Blas bay take places between October and April. More fishing trips were detected proportionally in November and December and the largest number of fishing trips occur in January. The CPUE estimated varied between 6.8 and 8.1 fish per angler and the catches included stripped weakfish, whitemouth croaker, smoothhound and rays. The artisanal fishery worked under a plan agreed with the enforcement authority between 2002 and 2007 and after then was banned. The artisanal fishery season occurs between October and middle December every years using seven bottom gill nets of 105 mm between opposite knots per boat. The San Blas fleet was composed by 16 small vessels employing local people for whom this fishery represented the mainstay of the family economy. Fish landing analysis allowed to define this fishery as monospecific based on smoothhound captures and without interfering with recreational fishery. The smoothhound artisanal catches were mostly adults, representing in average 164 tons per season. This figure was equivalent to only 2% of the catch recorded at national level. These results support the fact that fishing prohibition after year 2007 is not considered as justified. The experimental catch analysis of this species allowed to identify a seasonal pattern in which the largest smoothhound occurred in the warm months and cold months were characterized by presence of smaller smoothhound. Cluster analysis of sampling sites based on species length of this species showed that spring-summer sites should be considered as a separate group respect of those sites belonging to autumn-winter. It was also during spring and summer when pregnant females were found. Females reach arger total lengths than males and L50 were estimated as 56.3 and 54.3 cm total lenghts respectively. In terms of CPUE, the highest values were found in spring, followed by summer, autumn and finally winter. Based on these results, we proposed a life cycle of smoothhound population that includes the arrival of adults to give birth in the Bay during spring, after mating followed by a new summer-autumn migration remaining juveniles in the area until next year. Such model implies that San Blas area represent a valuable reproductive and nursery area. The silversides O. argentinensis was also a main target species in recreational fisheries being in the past an alternative target species for the artisanal fishery as well. The application of geometric morphometric techniques and genetics analysis did not show difference in the two morphotypes recognizeed at a glance by some fishermen in the area. Using a monthly sampling program during an annual cycle it was determined that 32 mm gill net was the most efficient one in terms of catch number of commercial size fish. However, this net keeps 20% of juvenile smoothhound as by-catch. On the other hand, analysis of monthly average GSI (gonadosomatic index) indicated a spawning season extending from september to november with a peak in october when the temperature was below 20 ‹ C. This species behaves in the study area as a total spawner leaving on average about 9380 eggs per female per year. The reproductive strategy was modified for populations at higher latitudes and would have adjusted according to the temperate conditions of San Blas Bay. It was found that females were more numerous and reach greater lengths than males (44 vs. 40 cm) being the TL50 estimated as 27 and 28 cm respectively. These lengths were higher than those recorded in southern Brazil and could be related to environmental conditions. Age and growth studies using scales indicated that the growth did not differ between sexes ranging the population age between 1 and 7 years. The parameters of von Bertalanffy models were: L ‡ = 404 mm, k = 0.48 and to = 0.55. These values were within the range expected for the genera. We found an average natural mortality of 0.65 and an optimal length of 28 cm. It highlighted the paucity of specimens less than 27 cm of total lengths in the sampling areas. The 32 mm floating gill nets used for silverside artisanal fishery impacts only on fish with 4 or more years. At this age O. argentinensis exceeded the critical size and the length at first maturity and therefore fishery practices accomplished with a precautionary approach. If this fishery would be enabled again, it is necessary to restrict fishing permits to local residents, and regulate fishing methods to minimize juvenile smoothhound by-catch. Finally, it was concluded that there is a direct relationship between the annual dynamics of the fish assemblage and fishing effort and CPUE of recreational fishing, and also between the life cycle of smoothhound and artisanal fishing season. Management measures and a general framework are proposed to draw a sustainable management of fishery resources.
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