Jorge A. López-Rocha

USE OF LENGTH-FREQUENCY ANALYSIS FOR GROWTH ESTIMATION OF THE CALIFORNIA TWO-SPOTTED OCTOPUS OCTOPUS BIMACULATUS VERRIL 1883 OF THE GULF OF CALIFORNIA

ABSTRACT Indirect methods such as length—frequency analysis have not been recommended for growth estimation in octopus (length is not a good measure of size for soft-bodied organisms; size is not a good indicator of age because of the high interindividual variability in growth rates and an asymptotic growth is often assumed). However, these methods are still applied in various places where octopus fisheries exist because they are low cost and easy to apply in most fisheries where there are no financial resources or scientific capacity to use direct methods. The purpose of this study was to investigate whether length—frequency analysis is an appropriate method for determining the growth pattern of Octopus bimaculatus from the Gulf of California. We tested the widely used methods ELEFAN I and NSLCA, and a modal progression analysis with a multimodel approach. The results showed that the growth pattern of O. bimaculatus was reasonably described using these analyses. First, the suitability of using mantle length as a measure of size was confirmed through a significant length—weight relationship. A length—age key was also generated in terms of probability to take into account the variability in growth rates, and with the multimodel approach it was not necessary to assume asymptotic growth. Population size structure is the most readily obtained and probably the most commonly used or only available information in a large number of fisheries. Therefore, the usefulness of length—frequency analyses should not be underestimated when direct methods are available.

Spatial Analysis of the Abundance and Catchability of the Red Octopus Octopus maya (Voss and Solís-Ramírez, 1966) on the Continental Shelf of the Yucatan Peninsula, Mexico

ABSTRACT The red octopus Octopus maya is an endemic species of the continental shelf of the Yucatan Peninsula, Mexico and supports the largest octopus fishery in the American continent. Little is, however, known about its spatial dynamics. The study of the space-time variation of catchability is a key element in the stock assessment, because it allows behavioral aspects of the resource and qualities of the various exploitation strategies to be clarified, which are essential for the fishery management. The objective was to analyze the spatio-temporal variations of the abundance and catchability of the octopus O. maya on the continental shelf of the Yucatan Peninsula, Mexico. During the fishing season of 2012 (August–December), fishery landings from the small-scale fleet in 13 ports of the Yucatan Peninsula, were analyzed to obtain data on catch, effort and fishing zone for O. maya. During the closed season of 2013 (January–July) fishing hauls were performed across a network of stations along the coast of the Yucatan Peninsula. Spatio-temporal variations in mean catch per unit effort (CPUE) in terms of number of organisms per hour of effective fishing were analyzed. Catchability and its variation with size, time, and zone were estimated through a model based on the Leslie transition matrix and frequency distributions of mantle length. The results showed significant changes in the distribution of O. maya. During the fishing season, the greatest abundances were found along the coast of Campeche (western zone), whereas, during the closed season the highest abundances were recorded along the coast of Yucatan (eastern zone). Trends of decreasing and increasing catchability were observed with respect to size according to the different zones. A high catchability was presented for small sizes along the coast of Campeche during the fishing season. The results indicate the need to investigate possible management measures differentiated by region (west-east) to ensure the fishery sustainability.

Analysis of the spatial and seasonal variation in catchability of red grouper, Epinephelus morio (Valenciennes, 1828), in the Campeche Bank before overfishing (1973-1977)

La pesqueria de mero Epinephelus morio en el Banco de Campeche, frente a la costa norte de la Peninsula de Yucatan, esta sobreexplotada. Las principales causas son la elevada presion de pesca en zonas de agregacion reproductiva y en zonas de crianza de juveniles. Se realizo un analisis de la variacion espacio-temporal de la capturabilidad, usando datos de 1973 a 1977, con el objetivo de detectar las zonas de mayor vulnerabilidad del mero segun su estado de desarrollo (juveniles, preadultos y adultos). Los resultados mostraron que durante la epoca de reproduccion (enero-marzo) la capturabilidad de los adultos fue mayor en la parte oriental del Banco de Campeche. Se encontraron centros de alta capturabilidad en juveniles durante todas las estaciones del ano en las regiones cercanas a Celestun, Dzilam de Bravo, Rio Lagartos y el Cuyo. Se recomienda la creacion de zonas de restriccion de pesca en dichas areas con el objetivo de reducir la mortalidad por pesca para permitir la recuperacion de la poblacion.

MORTALITY ESTIMATES OF THE INTERTIDAL PURPLE SNAIL PLICOPURPURA PANSA IN THE BAJA CALIFORNIA PENINSULA, MEXICO

Abstract The intertidal purple snail Plicopurpura pansa was intensively exploited for “Tyrian Purple,” leading to declining populations and prohibition by the Mexican government of commercial exploitation. A probable cause for the decline is the difficulty of the snails to reattach themselves fast enough before being washed away by the high impact waves during high tides after being removed from the rocks to obtain ‘ink.’ To assess this hypothesis, six experiments were conducted at two rocky beaches in the Baja California Peninsula. Total mortality rates were estimated by a recapture probability model. Mortality rates ranged from 6.34 y−1 to 14.23 y−1 at Playa Cerritos and 5.04 y−1 to 7.79 y−1 at Punta Perico. Male mortality rate values were lower than females. These rates show high vulnerability of purple snail after being removed from rocks. For management and conservation of snail populations, it is not sufficient to handle the snails with care and to “milk” them only periodically. Detachment from the rocks seems to be the main reason for high mortality and should be prohibited.

Natural mortality estimates throughout the life history of the sea cucumber Isostichopus Badionotus (Holothuroidea: Aspidochirotida)

The Natural Mortality coefficient (M) is a key parameter for stock assessments. The need to establish age-specific natural mortality coefficients is widely recognized because M decreases rapidly over the early stages of the life cycle until it reaches a stable M value around the age-at-maturity. The aim of this study was to estimate M during the life cycle of the sea cucumber Isostichopus badionotus, a species under heavy fishing exploitation in the Caribbean Sea and the Gulf of Mexico. Coefficients M at age were estimated using two models: The Gnomonic Interval Model (GIM) and the Chen & Watanabe model. Two different scenarios were simulated considering early and late age-at-maturity. Estimated M values using the GIM model for the early maturity scenario were 2.15 to 2.35 year−1 (interquartile range) for the juvenile stage and 0.39 to 0.43 year−1 for the adult stage; for the late maturity scenario were 0.65 to 0.71 year−1 for the juvenile stage and 0.68 to 0.74 year−1 for the adult stage. The Chen & Watanabe model M estimates for juvenile stage were between 0.85 and 2.23 year−1 and 0.39 and 2.23 year−1 for the early and late maturity scenarios respectively; for adult stage were between 0.97 and 0.21 year−1 and 0.62 and 0.43 year−1 respectively. The GIM estimated high natural mortality rates during larval stages. These estimates provided a higher level of certainty for the population models to more effectively manage a fishery and improve stock assessments.

Morphometric Relationship, Growth Parameters, and Natural Mortality as Estimated Primary Inputs for Fishery Management in Newfishing Areas for Bivalve Molluscs (Bivalvia: Veneridae)

ABSTRACT The exploitation of bivalve molluscs in new fishing areas generally begins with scarce or no biological and fishery information to support management measures. The objective of this study was to estimate the morphometric relationships, growth parameters, and natural mortality in recently exploited populations of Megapitaria aurantiaca, Megapitaria squalida, and Dosinia ponderosa, to generate information on the population dynamics that could support management and conservation measures. The length–weight relationship and the relationships between the length, height, and width of the shells were calculated, which were used to estimate the morphometric size at first maturity. The parameters of the von Bertalanffy growth model were calculated through a modal progression analysis and the natural mortality was estimated depending on age. The morphometric relationships were allometric in all cases. The morphometric length at first maturity for M. aurantiaca is 67.60–77.20 mm, M. squalida is 35.40–40.32 mm, and D. ponderosa is 103.44 mm, which corresponds to ages between 0.68 and 5.97 y. The species exhibited a moderate growth (k = 0.421–0.448 y-1). Natural mortality for the adult phase oscillated between 0.71 and 1.45 y-1 and between 1.26 and 1.97 y-1 during the juvenile phase. These estimates constitute basic inputs for fishery management and conservation of the species.

Key constraints and problems affecting the inland fishery value chain in central Mexico

Abstract Anthropogenic activities have been the major cause of watershed deterioration in many parts of the world, negatively impacting inland fisheries. In Mexico, freshwater fishing represents a source of protein, income, and employment for rural communities; however, in the national fisheries statistics they only account for 3% of the total production, and increases have not taken place since the 1990s. Demand is higher than supply because the national market can only provide 50% of consumption, and these fisheries are currently passing through a complex situation that prevents an increase in production levels and fishers’ incomes. This study examined the main production constraints and problems that prevent production from increasing to satisfy national demand. We considered value chain analysis and fish catch dynamic approaches. Fieldwork was conducted in 2 periods during 2011 and 2012 in 4 riparian communities near Lake Chapala and Lake Yuriria. The methodological approach considered socioeconomic factors and temporal variability of catch volume in both lakes. Results showed that production constraints are the result of watershed and fisheries mismanagement. Catch levels were strongly related to the environmental conditions of the lakes, which have shown instability and decline that affect fishers’ livelihoods. In addition, illegal, unreported, and unregulated (IUU) fishing and the ineffectiveness of institutions to rule the actions of all actors who intervene in the management and use of these resources allow destructive strategies toward the fisheries. Finally, inland fisheries management is not considered part of watershed management policies, resulting in ill-adapted water allocation policies that affect fisheries production levels.

Growth and mortality of the king angelfish, Holacanthus passer (Actinopterygii: Perciformes: Pomacanthidae), in the central Gulf of California, Mexico

Background. The king angelfi sh, Holacanthus passer Valenciennes, 1846, is one of the principal species captured in the Gulf of California, Mexico, for the purpose of the aquarium trade. Although the species has been exploited for more than 40 years, studies have not yet been undertaken to understand the population parameters required for adequate management of the fi shery. The objective of this work was to describe for the fi rst time the growth and mortality of this species. The information provided in this study contributes to the generation of knowledge necessary to establish sustainable management practices. Materials and methods. The growth curve of the species was determined by applying a modal progression analysis of the sample length frequency distribution to determine the number of cohorts present through the multinomial statistic based on a probability function. Once the cohorts were identifi ed, the von Bertalanffy growth model was adjusted using a maximum likelihood function. To estimate the natural mortality rate and natural mortality-at-age, empirical methods were used. Were also estimated the size and age at fi rst maturity (Lm, tm), the maximum age (tmax), the fi shing mortality (F), the total mortality (Z), and the exploitation rate (E). Results. In total, 794 king angelfi sh were measured and weighed, including 659 juveniles and 135 adults. The total length of the fi sh ranged from 3 to 29 cm, and the weight was within 2–797 g. The potential weight–length relation was signifi cant (r2 = 0.94; P > 0.01), showing a negative allometric curve with the parameters: a = 0.108 and b = 2.618. The parameters of the von Bertalanffy growth equation were: L∞ = 37.894 cm, k = 0.127 year –1, t0 = – 0.658 years. The natural mortality rate was estimated to be 0.315 year–1. The following values were estimated for: Lm = 21.835 cm, tm = 6.10 years, tmax = 20.01 years, Z = 1.19 year –1, F = 0.88 year–1, and E = 0.74. Conclusion. Estimates of natural mortality could be linked to management measures such as catch quotas.