Accurate fishery-independent methods for assessing the abundance of marine fish stocks are important tools for proper pelagic fisheries management. The review and improvement of standardized sampling methods used in fisheries-independent sampling, and the establishment of improved models of abundance and population dynamics utilizing novel statistical techniques for fisheries management will further improve our understanding of the way in which marine fish stocks vary spatially and temporally. One of the most important and longest running surveys of fisheries-independent data in the Southeastern United States is the spring ichthyoplankton survey conducted through the Southeast Area Mapping and Assessment Program (SEAMAP). These surveys of highly migratory pelagic fish larvae and eggs in the exclusive economic zone of the USA in the Gulf of Mexico have been conducted annually during spring spawning periods (March to June) since 1982 by the National Oceanic and Atmospheric Administration (NOAA) National Marine Fisheries Service (NMFS). A primary focus of this survey is collecting the data used in a larval abundance index of bluefin tuna (Thunnus thynnus) for "tuning" population estimates for the western Atlantic stock of this species using virtual population analysis (VPA). As with many other forms of fishery independent data, there is statistical overdispersion of larval fish and high variability in catch rates related to non-static environmental conditions. This variability in catch rates, along with zero-inflated estimates of abundance, i.e. characterized by high numbers of stations with low or zero catches, present problems in deriving accurate and reliable stock assessments for western Atlantic bluefin tuna. The research presented here was conducted in an effort to improve the decision support system used in managing bluefin tuna in the western Atlantic, by improving catch rates of their larvae during spring ichthyoplankton cruises. A major focus of which was to overcome challenges related to reducing the variance of the larval index of abundance. The research presented here, explored the influence of sampling design and oceanographic conditions on an assemblage of commercially important taxa within the Gulf of Mexico. Such studies are necessary to evaluate differences in habitat utilization within a specific complex or among assemblages of closely related taxa. The spatial and temporal patterns of larval bluefin tuna (Thunnus thynnus) were analyzed in relation to mesoscale patterns of circulation, types of sampling gear used during fishery independent surveys, and in the context of common oceanographic variables associated with the spawning habitat of this iconic pelagic predator. Collaterally the relationship between the above factors on spatial and temporal patterns of the larvae of seven congeneric species of marine fish, whose larvae commonly occur with bluefin tuna, during the spring spawning season in the Gulf of Mexico (Auxis spp., Euthynnus alleteratus Corphaena spp., Katsuwonus pelamis, other Thunnus spp.: Thunnus albacares and Thunnus atlanticus, Istiophoridae, and Xiphias gladius) was investigated. The historical distribution of abundance in these eight taxa of larval epipelagic fish were analyzed in the context of mesoscale and large scale circulation features in the Gulf of Mexico between 1994 and 2008. Characterization of these features was conducted using concurrent, synoptic satellite altimeter, sea surface temperature (SST), and ocean color (OC) observations. Larval abundance among mesocale features was examined for the eight pelagic fish taxa using permutational multivariate analysis of variance (PERMANOVA). All but one taxon, T. thynnus, showed differences in occurrence across features. Additionally only two taxa (X. gladius and Istiophoridae) did not show highest abundances in "Common Waters" of the Gulf of Mexico. The abundance of the eight taxa, when examined in aggregate or as an assemblage, differed significantly between circulation features. However, distributions of individual taxa among circulation features differed for only the other Thunnus spp. taxa, which incorporates Thunnus albacares and atlanticus. The results from this study indicated that for most of the individual taxa studied, and Thunnus thynnus in particular the distribution of spawning habitat in the Gulf of Mexico is not associated with specific patterns in circulation. To analyze the impact of sampling gear on larval epipelagic abundance, the collection methods of the eight taxa during spring surveys, including a new net sampling methodology tested in surveys between 2009 and 2011, were compared. This new sampling methodology consisted of a 1x2 m frame fitted with a 0.505 mm mesh net, towed in a yo-yo fashion between the surface and 10m depth, referred to as the S-10 net. Sampling effectiveness between gears was compared by examining the abundance and length of the eight taxa of larval fish. A PERMANOVA of net type and time of sampling (day/night) on abundance and mean body length (BL) indicated that net type was a significant factor in assessing abundance and BL for all taxa. Highest mean assemblage and individual taxa abundance for seven of the eight taxa were in S-10 samples. Depth discrete sampling of the upper 50 m indicated that highest abundances for all scombrid taxa were found in the upper 30 m and provided justification for the improved sampling efficiency of the S-10 net. These results indicate that distributions of these epipelagic fish are not truly neustonic and that sampling effectiveness for them strongly depends on depth range fished by the net. Finally, the results of two research cruises using the new sampling methodology (S-10 net) during the spring of 2010 and 2011 were investigated to explore larval fish assemblages. Canonical analysis of principal coordinates (CAP) was used to evaluate the horizontal distribution of eight taxa of epipelagic larval fish and to relate these distributions to a total of eight variables observed through in-situ and remotely obtained data. Larval assemblages were established for the CAP via unweighted pair group method with arithmetic mean (UPGMA) hierarchical clustering utilizing similarity profile analysis (SIMPROF) tests for stopping rules. Further refinement to five common assemblage groups was obtained using indicator species values (INDVALS) and percent composition of taxa abundance within groups. Total model accuracy was 54%, with highest classification success for the assemblage group characterized by T. thynnus and the other Thunnus spp. (64%), and lowest classification success for negative stations (22%). Changes in the assemblage of these larval fish were partially explained by the seasonal progression in day-length, and related changes in sea surface temperature. Depth, chlorophyll a concentration, salinity, and optical clarity were also important. Five assemblages of larval fish were identified, characterized by differences in the relative abundance of the five taxa of scombrids, and the Coryphaena spp. taxa, and indicated a high degree of shared spawning habitat. The differences in habitat utilization by these taxa is highly influenced by seasonal changes in sea surface temperature, and large scale differences in depth and water masses in the Gulf of Mexico. This results in a gradual shift from groups with smaller and more abundant coastally influenced taxa with protracted spawning seasons to the larger sub-tropical, more pelagic species across a large expanse of shared spawning habitat. This dissertation research provides a context to the historical assessment of abundance, evidence for the association of specific taxa with particular oceanographic conditions, and improved assessment capabilities for epipelagic larval fish. As this research shows the spawning habitat of these taxa in the Gulf of Mexico are largely shared, and the influence of environmental variables only partly addressed the spatial and temporal variance attributed to larval abundance in the Gulf of Mexico. The improved methods used in this study will be useful to researchers studying the factors impacting larval recruitment and survival of highly migratory species, and comprehensive ecosystem based resource management. The results will improve fisheries-independent sampling and management for highly migratory species, and provides new methods for evaluating larval fish assemblages within the framework of oceanographic conditions for large marine ecosystems.

Utilizando-se materiais coletados durante qua-tro cruzeiros oceanográficos com o N/Oc .\"Prof. W. Besnard\", na região Sudeste do Brasil, compreendida entre Cabo Frio (RJ) e Florianópolis (SC), de janeiro de 1980 a março de 1982, foram realizados estudos quali quantitativos so-bre ocorrências de larvas de peixes, relacionando-as com fatores abióticos. Problemas concernentes aos processos de amostragem tambem foram verificadas. Realizaram-se dois tipos de arrastos: arrasto oblíquo com a rede Bongo usando-se malhagens de 0,333 mm (fina) e de 0,505 mm (regular), e arrasto horizontal de superfície com a rede de Neuston, de 0,333 mm de malhagem. Em cada estação oceanográfica, alem das amostras biologicas, efetuaram-se as medições de temperatura e coleta de água para determinação de salinidade. Um total de 35.090 larvas foram analisadas, incluíndo as coletas das redes fina e regular da Bongo e a rede de Neuston. Dentre estas, 61 grupos diferentes foram separados, chegando a níveis específicos em alguns casos.- Dois gêneros e quatro especies foram identificados pela primeira vez na região: Saurida spp, Hygophum spp, Trachinocephalus myops, Synodus foetens Bregmaceros can-tori e Maurolicus muelleri. As famílias predominantes foram Clupeidae, Engraulidae, Myctophidae e Gonostomatidae. De uma maneira geral, a região Sudeste apresentou grande riqueza em taxa, mas com o predomínio de poucos grupos, em termos de abundância. Análises da relação entre larvas de peixes e fatores abióticos revelaram a existência de padrões de ocorrência e distribuição próprios para cada espécie, dentro de uma determinada faixa de variaçao de temperatura e de salinidade. Estudos realizados durante uma estação fixa de 36 horas em Cabo Frio, mostraram uma situação típica da estrutura oceanográfica da região, notando-se mudanças de massas de água no local, devido ao fenômeno da ressurgiê-cia. Este fator, associado ao horário de coleta, deve ter exercido influência de maneira complexa sobre o componen-te biológico, induzindo mudanças na ocorrência de diferentes tipos de larvas. Dois transectos, um ao largo de Cabo Frio e ou-tro ao largo de paranaguá, foram analisados com o intuito de obter-se informações a respeito da ocorrência e distribuição de larvas de acordo com a distância da costa. Os dados hidrográficos comprovam a existincia de diferentes massas de água compondo a estrutura oceanográfica daregião, que por sua vez influenciam a ocorrência e distribuição de larvas. A família Gerreidae teve a maior abundância associada à massa costeira. Sardinella brasiliensis, Harenguia jaguna e Engraulis anchoita foram de distribuição tipicamente nerítica, assim como as famílias Sciaenidae, Bleniidae, Ophidiidae, Carangidae e Cynoglossidae. Por ou-tro lado, Myctophidae, Gonostomatidae, Paralepedidae e Scombridae ocorreram preferencialmente na região ocêanica, que sofre influência da Corrente do Brasil. Análise do material coletado com a rede de Neuston comprovam a importância deste tipo de amostragem su-perficial para os estudos relacionados com o ictioplâncton, uma vez que esta rede captura uma porcentagem da população que é subamostrada pela rede Bongo. Observou-se a tendência de estratificação na camada superficial, principalmete de formas jovens, como no caso de Sardinella brasiliensis. Um aspecto especialmente notável foi o caso das fa-mílias Mugilidae e Mullidae em que a captura se deu significativamente em maior número no arrasto de superfície do que no arrasto oblíquo. Comparando-se os materiais coletados com as re-des finas e regular da Bongo, pôde-se verificar dois pro-blemas relacionados com a seletividade: o entupimento da rede e o escape de larvas menores através da malhagem. Ecomparando-se os materiais coletados durante os períodos diurno e noturno, pôde-se verificar o outro problema importante de seletividade, que é a fuga da boca da rede de larvas maiores. As nossas amostragens parecem nao ter sido afetadas pelo problema de entupimento, como mostram as análises do volume de água filtrada. Já o escape de lar-vas menores foi constatado em vários grupos, tendo sido de terminado para três especies o tamanho a partir do qual este problema começa a se tornar evidente: 7,5 mm para Sardinella brasiliensis e 6,5 mm para Harengula jaguana e Engraulis anchoita. A fuga da boca da rede ocorreu em lar-vas maiores durante o dia, concluindo-se que este problema varia conforme a especie, o padrão de migração vertical e o desenvolvimento do sistema visual. / Four oceanographic cruises have heen carried out off the southeastern Brazilian coast from Cabo Frio (23ºS) to Florianópolis (27°S) during the period from January 1980 to March 1982 by the R/V\" Prof. W. Besnard ,\". Fish larvae taken during these cruises were analysed and influences of abiotic factors on their occurrence were discussed.Problems regarding the sampling process were also discussed. Two kinds of sampling gears were used: Bongo nets fitted with a 0.505 mm and 0.333 mm mesh nets for oblique tow and Neuston net with a 0.333 mesh net for surface horizontal tow. At each sampling station, hydrographic data were sampled in addition to biological data. Total of 35,090 larvae were analysed. Sixty one groups were classified and some dominant ones were identified to spec1es level. Larvae belonging to two genera and four species were identified for the first time in the region under observation, i. e. Saurida spp., Hygophum spp., Synodus foetens, Trachinocephalus myops, Bregmaceros cantori and Maurolicus muelleri. The most abundant families were clupeidae, Engraulidae, Myctophidae and Gonostomatidae. In general, the ichthyoplankton from the southeastern Brazilian coast showed a large variety of larvae, but just few groups were outstandingly abundant. Analysing the relations between occurrence of fish larvae and hydrographic parameters, we found specific distri-bution patterns for each species. At the fixed station off Cabo Frio (22°59\'S; 042º05\'7W), 36 hour observations have been done and biological and hydrographic data have been collected every two hours. A change in the local oceanographic structure during the survey period has been observed along with wind induced coastal upwelling. A change of the oceanographic conditions associated with sampling time, may have influenced the occurrence of fish larvae. In order to obtain information on the distribution patterns of fish larvae in relation to distance from the coast, the samples collected on two transects off Cabo Frio and paranaguá were analysed. The presence of four different water masses in this region was confirmed and the occurrence and distribution of larvae seems to have close relationship with those water masses. Larvae of the family Gerreidae were more abundant in the coas tal water mass and those of Sardinella braziliensis, Harengula jaguana and Engraulis anchoita showed typical neritic distribution. Larvae belonging to the families Sciaenidae, Blenniidae, Ophídiidae, Carangidae and Cynoglossidae also showed the same distribution pattern. On the other hand, larvae belonging to the families Myctophidae, Gonostomatidae, Paralepedidae and Scombridae occurred mainly in the oceanic region where the influence of the Brazil Current is eminent. The ichthyoplankton collected at surface layer with Neuston net showed quite different types and size composition of fish larvae, In comparison with those taken with Bongo nets. Clear tendency of stratification in size composition at the surface layer was observed on some species (e.g. S.braziliensis). Larvae belonging to the families Mugilidae and Mullidae seems to be more concentrated at the surface layer, since they were more frequently sampled with the Neuston neto Three problems related to selectivity of plankton net (clogging, extrusion and avoidance) can be studied compar1ng the materials collected with the Bongo ets fitted with different mesh size nets and sampled at different times of the day. As shown in Figs. 23 and 24, there is no evidence of clogging of the fine mesh net during this survey. On the other hand, the extrusion of smaller larvae was confirmed for many groups and it was observed at sizes smaller than 7.5 mm, 6.5 mm, and 6.5 mm, respectively for S.brasiliensis, H.jaguana and E. anchoita. The avoidance was more remarkeble during the day time for larger larvae, but this problem varies depending on spec1es, migration pattern, and development stage of the visual system of each larvae

Utilizando-se materiais coletados durante qua-tro cruzeiros oceanográficos com o N/Oc .\"Prof. W. Besnard\", na região Sudeste do Brasil, compreendida entre Cabo Frio (RJ) e Florianópolis (SC), de janeiro de 1980 a março de 1982, foram realizados estudos quali quantitativos so-bre ocorrências de larvas de peixes, relacionando-as com fatores abióticos. Problemas concernentes aos processos de amostragem tambem foram verificadas. Realizaram-se dois tipos de arrastos: arrasto oblíquo com a rede Bongo usando-se malhagens de 0,333 mm (fina) e de 0,505 mm (regular), e arrasto horizontal de superfície com a rede de Neuston, de 0,333 mm de malhagem. Em cada estação oceanográfica, alem das amostras biologicas, efetuaram-se as medições de temperatura e coleta de água para determinação de salinidade. Um total de 35.090 larvas foram analisadas, incluíndo as coletas das redes fina e regular da Bongo e a rede de Neuston. Dentre estas, 61 grupos diferentes foram separados, chegando a níveis específicos em alguns casos.- Dois gêneros e quatro especies foram identificados pela primeira vez na região: Saurida spp, Hygophum spp, Trachinocephalus myops, Synodus foetens Bregmaceros can-tori e Maurolicus muelleri. As famílias predominantes foram Clupeidae, Engraulidae, Myctophidae e Gonostomatidae. De uma maneira geral, a região Sudeste apresentou grande riqueza em taxa, mas com o predomínio de poucos grupos, em termos de abundância. Análises da relação entre larvas de peixes e fatores abióticos revelaram a existência de padrões de ocorrência e distribuição próprios para cada espécie, dentro de uma determinada faixa de variaçao de temperatura e de salinidade. Estudos realizados durante uma estação fixa de 36 horas em Cabo Frio, mostraram uma situação típica da estrutura oceanográfica da região, notando-se mudanças de massas de água no local, devido ao fenômeno da ressurgiê-cia. Este fator, associado ao horário de coleta, deve ter exercido influência de maneira complexa sobre o componen-te biológico, induzindo mudanças na ocorrência de diferentes tipos de larvas. Dois transectos, um ao largo de Cabo Frio e ou-tro ao largo de paranaguá, foram analisados com o intuito de obter-se informações a respeito da ocorrência e distribuição de larvas de acordo com a distância da costa. Os dados hidrográficos comprovam a existincia de diferentes massas de água compondo a estrutura oceanográfica daregião, que por sua vez influenciam a ocorrência e distribuição de larvas. A família Gerreidae teve a maior abundância associada à massa costeira. Sardinella brasiliensis, Harenguia jaguna e Engraulis anchoita foram de distribuição tipicamente nerítica, assim como as famílias Sciaenidae, Bleniidae, Ophidiidae, Carangidae e Cynoglossidae. Por ou-tro lado, Myctophidae, Gonostomatidae, Paralepedidae e Scombridae ocorreram preferencialmente na região ocêanica, que sofre influência da Corrente do Brasil. Análise do material coletado com a rede de Neuston comprovam a importância deste tipo de amostragem su-perficial para os estudos relacionados com o ictioplâncton, uma vez que esta rede captura uma porcentagem da população que é subamostrada pela rede Bongo. Observou-se a tendência de estratificação na camada superficial, principalmete de formas jovens, como no caso de Sardinella brasiliensis. Um aspecto especialmente notável foi o caso das fa-mílias Mugilidae e Mullidae em que a captura se deu significativamente em maior número no arrasto de superfície do que no arrasto oblíquo. Comparando-se os materiais coletados com as re-des finas e regular da Bongo, pôde-se verificar dois pro-blemas relacionados com a seletividade: o entupimento da rede e o escape de larvas menores através da malhagem. Ecomparando-se os materiais coletados durante os períodos diurno e noturno, pôde-se verificar o outro problema importante de seletividade, que é a fuga da boca da rede de larvas maiores. As nossas amostragens parecem nao ter sido afetadas pelo problema de entupimento, como mostram as análises do volume de água filtrada. Já o escape de lar-vas menores foi constatado em vários grupos, tendo sido de terminado para três especies o tamanho a partir do qual este problema começa a se tornar evidente: 7,5 mm para Sardinella brasiliensis e 6,5 mm para Harengula jaguana e Engraulis anchoita. A fuga da boca da rede ocorreu em lar-vas maiores durante o dia, concluindo-se que este problema varia conforme a especie, o padrão de migração vertical e o desenvolvimento do sistema visual. / Four oceanographic cruises have heen carried out off the southeastern Brazilian coast from Cabo Frio (23ºS) to Florianópolis (27°S) during the period from January 1980 to March 1982 by the R/V\" Prof. W. Besnard ,\". Fish larvae taken during these cruises were analysed and influences of abiotic factors on their occurrence were discussed.Problems regarding the sampling process were also discussed. Two kinds of sampling gears were used: Bongo nets fitted with a 0.505 mm and 0.333 mm mesh nets for oblique tow and Neuston net with a 0.333 mesh net for surface horizontal tow. At each sampling station, hydrographic data were sampled in addition to biological data. Total of 35,090 larvae were analysed. Sixty one groups were classified and some dominant ones were identified to spec1es level. Larvae belonging to two genera and four species were identified for the first time in the region under observation, i. e. Saurida spp., Hygophum spp., Synodus foetens, Trachinocephalus myops, Bregmaceros cantori and Maurolicus muelleri. The most abundant families were clupeidae, Engraulidae, Myctophidae and Gonostomatidae. In general, the ichthyoplankton from the southeastern Brazilian coast showed a large variety of larvae, but just few groups were outstandingly abundant. Analysing the relations between occurrence of fish larvae and hydrographic parameters, we found specific distri-bution patterns for each species. At the fixed station off Cabo Frio (22°59\'S; 042º05\'7W), 36 hour observations have been done and biological and hydrographic data have been collected every two hours. A change in the local oceanographic structure during the survey period has been observed along with wind induced coastal upwelling. A change of the oceanographic conditions associated with sampling time, may have influenced the occurrence of fish larvae. In order to obtain information on the distribution patterns of fish larvae in relation to distance from the coast, the samples collected on two transects off Cabo Frio and paranaguá were analysed. The presence of four different water masses in this region was confirmed and the occurrence and distribution of larvae seems to have close relationship with those water masses. Larvae of the family Gerreidae were more abundant in the coas tal water mass and those of Sardinella braziliensis, Harengula jaguana and Engraulis anchoita showed typical neritic distribution. Larvae belonging to the families Sciaenidae, Blenniidae, Ophídiidae, Carangidae and Cynoglossidae also showed the same distribution pattern. On the other hand, larvae belonging to the families Myctophidae, Gonostomatidae, Paralepedidae and Scombridae occurred mainly in the oceanic region where the influence of the Brazil Current is eminent. The ichthyoplankton collected at surface layer with Neuston net showed quite different types and size composition of fish larvae, In comparison with those taken with Bongo nets. Clear tendency of stratification in size composition at the surface layer was observed on some species (e.g. S.braziliensis). Larvae belonging to the families Mugilidae and Mullidae seems to be more concentrated at the surface layer, since they were more frequently sampled with the Neuston neto Three problems related to selectivity of plankton net (clogging, extrusion and avoidance) can be studied compar1ng the materials collected with the Bongo ets fitted with different mesh size nets and sampled at different times of the day. As shown in Figs. 23 and 24, there is no evidence of clogging of the fine mesh net during this survey. On the other hand, the extrusion of smaller larvae was confirmed for many groups and it was observed at sizes smaller than 7.5 mm, 6.5 mm, and 6.5 mm, respectively for S.brasiliensis, H.jaguana and E. anchoita. The avoidance was more remarkeble during the day time for larger larvae, but this problem varies depending on spec1es, migration pattern, and development stage of the visual system of each larvae