Biological patterns of the Brazilian sardine in the purse seine fishery off Brazil
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1
Centro Interdisciplinar de Investigação Marinha e Ambiental. Terminal de Cruzeiros do Porto de Leixões, Avenida General Norton de Matos S/N, 4550-208, Portugal
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2
Laboratório de Ecossistemas Aquáticos e Pesqueiros, Departamento de Oceanografia, Universidade do Vale do Itajaí, R. Uruguai 458, Centro 88302-901, Brazil
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3
Faculdade de Ciências da Saúde da Universidade Fernando Pessoa. Rua Carlos da Maia 296 4200-150, Portugal
Size at first maturity and fishing areas of the Brazilian sardine showed important shifts during the last 20 years. Although changes in biological parameters are widely discussed, the determination of the size at first maturity (L50) requires the correct definition of maturity stages. The classification of gonadal maturity of the Brazilian sardine Sardinella brasiliensis is divided into 5 stages: [0] Juvenile; [I] Immature; [II] Maturation; [III] Mature and [IV] Spawning. After spawning, gonads returns to stage II, when it will be able to start a new reproductive cycle after gonadal rest. However, during the macroscopic analysis, it is difficult to differentiate young individuals who are in the beginning of their first reproductive cycle, from those who have already spawned and are able to start a new cycle after gonadal rest. All individuals are therefore classified in the stage II, being necessary the creation of a tool to reclassify this stage. This study analyzed size at maturity variability under the null hypothesis that S. brasiliensis increased size at maturity throughout time against the alternative hypothesis that vessels became more capitalized allowing the exploration of more productive fishing areas to catch sardines with distinct biological properties.
Biological and fishery information (capture and geographic position of catch) was obtained during interviews with the captain at landings of industrial purse seine vessels in the main Brazilian fishing port between 1997 and 2019. During landings, 300 individuals were measured (total length, Lt) and weight (body weight, Bw) and one sample of 60 individuals was separated for further analysis. In the laboratory, Lt and Bw were taken. After dissection, sex and maturity stage was assigned. In order to develop this tool, gonad weight (Wgon), Gonad-somatic Index (GSI) and condition factor (K) of males and females of stage II sampled between 1997 and 2019 were analyzed. Logarithmic values of these variables were adjusted to a linear model and the subsequent analysis of the residuals was conducted. After reclassification, the proportion of mature individual was fit again to a logistic model using least of squares iterative method with resampling to determine L50. After expanding each biological sample to the respective biometry, size distributions were constructed for latitudinal and bathymetrical extracts, within the study area (-22oS RJ and -29oS SC). The association among quantitative variables obtained from fishery (latitude, longitude, depth, year and month of capture) and biological data (Lt, Bw, Wgon, GSI, K and residuals of length x weight relationship) was analyzed in a principal component analysis for mixed data (PCAmix) to verify the homogeneity of biological data through time and space. Dispersion ellipses using standard deviation of point scores were calculated for sardines captured off each State (i.e. SC, PR, SP and RJ). Four other qualitative variables were used: method of conservation onboard (i.e. ice and refrigerated brine), season of capture, sex and maturity stage. The homogeneity of size at first maturity was analyzed by fitting binomial generalized additive models (GAMs) to all records of Lt and GM data from each sex separately to determine whether any modes in size at maturity could be distinguished performed.
Analysis of the residuals distinguished two groups: one corresponding to the young sardines that will reproduce for the first time, and another composed of individuals able to start a new cycle after gonadal rest. After the reclassification, the proportion of mature individuals per length class adjusted to a logistic model showed a better fit for the logistic model. Analysis of dispersion ellipses fitted over PCAmix scores showed the presence of two groups: (1) RJ and (2) SP, PR and SC. GAM also showed a non-linear profile. This tendency was corroborated by the non-linear profile of model parameters. Sardines with higher Bw, GSI, K and Res were placed in Group 2. Indicators of a better fit condition, such as Bw and Res were associated the presence of juveniles in the south portion of study area during the winter. First time maturing individuals were found between SC and PR during spring. Gonads development occurs in parallel to a migratory movement to the north portion of study area to spawn during the summer. Sardines in gonadal rest were observed in northern part of study area in RJ. Group 1 was better described by Lat, Year. Latitude, year and state showed a strong association with the conservation of fish onboard. When both numerical and categorical variables were compared Res was highly associated with k, showing a weak relationship with other variables.
The new tool created not only increased model explanation but also enhanced our understanding of S. brasiliensis life cycle. This pattern resembles a one population picture. On the other hand, maturity stages observed in each State evidenced an opposed pattern. Juveniles occurred at different months and females achieved size at first maturity in a different length class in the two identified groups, being larger in Group 1. Using the developed technique, the sum of the squares decreased significantly giving a more realistic estimate of the global L50 and could serve as a new reference point for the species, since the minimum catch size in the current legislation is limited by the L50. Individuals of Group 1 postpone size at maturity to a larger size possibly as function of their development in waters more often enriched by upwelling event of the South Atlantic Central Water. Limiting the size of first capture under the size of first maturity may possibly be the reason for species collapse since fishing effort remained constant.
Acknowledgements
Sincere thanks to the industrial fish processing industries whose partnership made this study possible. The Coordination for the Improvement of Higher Education Personnel (CAPES) for the granting of a PhD scholarship, the National Research Council (CNPq) under the Projeto Sardinha: Apoio Técnico-Científico ao Plano de Gestão para o Uso Sustentável da Sardinha-Verdadeira no Sudeste do Brasil and the Brazilian Fund for Biodiversity (FUNBIO) for financial support.
Keywords:
Reclassification,
size at first maturity,
population structure,
Sardinella brasiliensis,
Maturity stages
Conference:
XVI European Congress of Ichthyology, Lausanne, Switzerland, 2 Sep - 6 Sep, 2019.
Presentation Type:
Oral
Topic:
ECOLOGY AND LIFE CYCLES
Citation:
Schroeder
R,
Petermann
A,
Correia
AT and
Schwingel
PR
(2019). Biological patterns of the Brazilian sardine in the purse seine fishery off Brazil.
Front. Mar. Sci.
Conference Abstract:
XVI European Congress of Ichthyology.
doi: 10.3389/conf.fmars.2019.07.00008
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Received:
13 Jun 2019;
Published Online:
14 Aug 2019.
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Correspondence:
Mr. Rafael Schroeder, Centro Interdisciplinar de Investigação Marinha e Ambiental. Terminal de Cruzeiros do Porto de Leixões, Avenida General Norton de Matos S/N, 4550-208, Matosinhos, Portugal, schroederichthys@gmail.com