Alberto G. Murta

Structural and functional trends indicate fishing pressure on marine fish assemblages

pressure on marine fish assemblages Sofia Henriques*, Miguel P. Pais, Rita P. Vasconcelos, Alberto Murta, Manuela Azevedo, Maria J. Costa and Henrique N. Cabral Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal; Instituto Português do Mar e da Atmosfera, Av. de Bras ılia, 1449-006 Lisboa, Portugal; and Departamento de Biologia Animal, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal

Discrimination of snipefish Macroramphosus species and boarfish Capros aper morphotypes through multivariate analysis of body shape

The existence of two species of the genus Macroramphosus Lacepède 1803, has been discussed based on morphometric characters, diet composition and depth distribution. Another species, the boarfish Capros aper (Linnaeus 1758), caugth along the Portuguese coast, shows two different morphotypes, one type with smaller eyes and a deeper body than the other, occurring with intermediate forms. In both snipefish and boarfish no sexual dimorphism was found with respect to shape and length relationships. However, females in both genera were on average bigger than males. A multidimensional scaling analysis was performed using Procrustes distances, in order to check if shape geometry was effective in distinguishing the species of snipefish as well as the morphotypes of boarfish. A multivariate discriminant analysis using morphometric characters of snipefish and boarfish was carried out to validate the visual criteria for a distinction of species and morphotypes, respectively. Morphometric characters revealed a great discriminatory power to distinguish morphotypes. Both snipefish and boarfish are very abundant in Portuguese waters, showing two well-defined morphologies and intermediate forms. This study suggests that there may be two different species in each genus and that further studies on these fish should be carried out to investigate if there is reproductive isolation between the morphotypes of boarfish and to validate the species of snipefish.

Issues on Dynamic Cognitive Map modelling of purse-seine fishing skippers behavior

This paper focus on obtaining a qualitative dynamic model based on real world data taken from a real world qualitative system: the day to day behavior of purse seine fishing fleet skippers. The model is based on a dynamic cognitive mapping approach (rule based fuzzy cognitive maps - RB-FCM) where several developments had to be made in order to obtain a workable system. Most changes were due to timing issues, which are essential in the study of system dynamics but have traditionally been avoided in most dynamic cognitive maps modelling approaches.

Sampling for Interdisciplinary Analysis

Abstract Sampling design is the first step to be taken in order to achieve the aims proposed in a multidisciplinary study. When no previous information is available, preliminary sampling is strongly advised. Prospective power analysis should be considered in any sampling design if null hypothesis testing is applied. Variation on a spatial and temporal scale must be considered. Sampling in the spawning season allows to identify the spawning grounds and to target relatively homogeneous spawning populations. Applying different stock identification techniques on the same specimen reduces sampling error when interpreting results. Sampling logistics and the flow of the material are key points in these studies. The underlying structure of the data collected should be recognized as early as possible. In the joint analysis of the data, it is useful to compare the confidence intervals of effect size estimates from the different approaches and to apply statistical techniques for classification.

LONG RANGE DEPENDENCE AND THE DYNAMICS OF EXPLOITED FISH POPULATIONS

Long range dependence or long memory is a feature of many processes in the natural world, which provides important insights on the underlying mechanisms that generate the observed data. The usual tools available to characterize the phenomenon are mostly based on second-order correlations. However, the long memory effects may not be evident at the level of second-order correlations and may require a deeper analysis of the nature of the stochastic processes.After a short review of the notions and tools used to characterize long range dependence, we analyze data related to the abundance of exploited fish populations which provides an example of higher order long range dependence. In particular, we find that fish population time series were thought to have short term memory only because previous studies used averages over species instead of modeling each species individually.

Fuzzy modeling and simulation of purse-seine fishing skippers behavior

This paper focus on the modeling of a qualitative real world dynamic system: the day to day behavior of purse seine fishing fleet skippers. The model is based on a dynamic cognitive mapping approach (rule based fuzzy cognitive maps - RB-FCM) where several developments had to be made in order to obtain a workable system. The model is intended to be used to test the effectiveness of different biological management scenarios, such as catch restrictions, marine closed areas, seasonal fishing bans, etc.

Image Analysis as a Tool to Age Estimations in Fishes: An Approach Using Blue Whiting on ImageJ

Otoliths are the fish bones that allow it to hear sounds and achieve balance. The otolith grows in size as fish grows; ring bands are formed in the otoliths’ surface registering periods of rapid and slow growth, opaque bands appear alternating with translucent bands. Age classification was made considering the number of translucent rings in the otolith; one translucent ring was equivalent to one year. The modeling of fish species abundance on the majority of fisheries assessment use age based models. The task of ring counting and ageing is time consuming and may introduce errors that can have a strong impact in stock assessment results. Thus, accurate and precise age estimates are crucial for the effective management and understanding of fisheries resources because recruitment dynamics, growth and mortality estimates relies on these data. The main goal of this study is to produce automatic reading procedures to help researchers, ageing blue whiting fish, minimize ring error count and improve accuracy and precision on age estimation.

TSP with Multiple Time-Windows and Selective Cities

We address a special TSP in which the set of cities is partitioned into two subsets: mandatory cities and selective cities. All mandatory cities should be visited once within one of the corresponding predefined multiple time windows. A subset of the selective cities, whose cardinality depends on the tour completion time, should be visited within one of the associated multiple time windows. The objective is to plan a tour, not exceeding a predefined number of days, that minimizes a linear combination of the total traveled distance as well as the total waiting time. We present a mixed integer linear programming (MILP) model for the problem and propose a heuristic approach to solve it. Computational experiments address two real world problems that arise in different practical contexts.