Environmental Considerations for the Management of the Bivalve Fisheries of Bahía Magdalena (Mexico), a Coastal Lagoon at the Southern End of the California Current

This study presents an overview of bivalve assemblages in Bahia Magdalena (BM, México) and the possible impact of environmental variability on these populations, constantly stressed by fishing. This lagoon is responsible for a high proportion of harvest of regional bivalves. First, we list the bivalve species reported in public biogeographic databases. Based on eight commercially exploited species, we described the composition of the bivalve assemblage and its biological characteristics, the history of fishery, and environmental variability in the marine area adjacent to the lagoon (1970–2019) and the habitat of bivalves (2002–2020). Sources of data were public databases and published literature. The enlisted species (n = 184) belong to six orders, and most are small and infaunal, but the structure of the assemblage is unknown. The fisheries began at different times and focused on the most valuable resources. Almost all harvest of bivalves had wide variations because of intensive fishing and a weak regulation frame. After 2015, the main resources were the Pacific wing-oyster (a new resource since 2017) and the geoduck clam due to the declining abundance of other resources (e.g., pen shells, Pacific calico scallop). There was a warming trend in the region since the 1970's, but the strongest El Niño-Southern Oscillation (ENSO) phases caused the most notable changes before 2013; after that year, a combination of large-scale phenomena increased the temperature significantly. The trend of chlorophyll-a abundance negatively correlated with temperature, but there was an almost constant supply of particulate organic matter in the interior of Bahia Magdalena (BM). After 2015, the quality of lagoon water gradually deteriorated, and in 2017 and 2019, harmful algal blooms developed, but the impact was not fully assessed. The challenges faced by the fishery are multiple (institutional weakness and regional warming); however, permanent monitoring programs of environmental conditions and critical biological variables should be implemented to design scenarios that allow fishery sustainability.

Aspectos reproductivos de Mugil curema (Perciformes: Mugilidae) en dos zonas de Baja California Sur, México

La liseta Mugil curema está entre las principales especies que explota la pesquería artesanal en la costa mexicana del Océano Pacífico. Abordar aspectos reproductivos de las especies por zona de pesca reducirá el sesgo en la evaluación del estado de sus poblaciones. El objetivo del presente estudio fue describir el ciclo reproductivo y estimar algunos parámetros biológicos de la liseta en dos sitios de pesca de la costa de Baja California Sur. Mensualmente, se muestreo la captura de Bahía de La Paz (BLP) y Bahía Magdalena (BM), durante 2010-2013. Se analizó histológicamente la maduración gonadal y se describió el ciclo reproductivo. Se estimaron, el índice gonadosomático (IGS), factor de condición (FC), índice hepatosomático (IHS), la relación peso-longitud y longitud promedio de madurez sexual (L50%). La longitud total de los peces varió entre 244 y 455 mm. Las hembras fueron más abundantes, grandes y pesadas que los machos en ambos sitios de pesca. Se identificó un patrón reproductivo con dos máximos anuales en BLP (marzo-junio y octubre-noviembre) y uno en BM (abril-agosto). Se identificó un patrón similar del IGS, FC e IHS por sexos en ambos sitios. La liseta mostró alometría negativa en crecimiento, rasgos de desovador total, desarrollo gonadal sincrónico por grupos y la L50% superior en hembras que en machos. Se recomienda reajustar la veda temporal por sitio de pesca y con base en la L50% ser precautorios en el tamaño de la luz de malla de las redes de pesca.

Distribution patterns of the warrior swimming crab, Callinectes bellicosus, fishery in Bahía Magdalena, Baja California Sur, Mexico

Spatial and temporal distribution patterns of the warrior swimming crab Callinectes bellicosus fishery in the Mexican Pacific were investigated. Geo-referenced commercial trap capture data derived from 44 trips in the Bahia Magdalena were analysed. Three fishing zones (Z1, inner; Z2, middle; Z3, mouth of the bay) and two climate seasons (warm, July-December; and cold, January-June) were defined previously. There were 1099 traps in Z1, 715 in Z2 and 2111 in Z3; in the warm season, 2091 traps were checked, whereas 1834 were checked in the cold season. The average number of individuals per trap (CPUE) varied by sex, zone and season, however, male crabs always predominated. During the warm season, large males (CW > 115 mm) exhibited the greatest value of CPUE. On average, the males represented 77% during the warm season and 84% during the cold season. The average size of the males (125 ± 0.843 mm CW) was significantly higher than the average size of females (121 ± 1.140 mm CW). The catch was composed of large mature males but females were absent in Z1; in comparison, both large mature males and females, in addition to ovigerous females, composed the catch at the mouth of the bay (Z3). Crab abundance was notably reduced in the cold season, especially for female crabs. The temporal behaviour of the warrior swimming crab in Bahia Magdalena is similar to that reported from the coastal lagoons of the Gulf of California; however, the low presence of females throughout the year could be related to their preferred environmental conditions, which include deeper areas with more current circulation, like those that occur at the mouth of the bay. These data corroborate the necessity to interpret with caution the crab population dynamics solely based on results derived from fishing with traps in coastal lagoons.