César Meiners-Mandujano

Shark species are among the most vulnerable marine fishes facing impacts from fisheries. To ensure the international fin trade does not threaten their populations, several species have been listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Appendix II. However, the lack of data on fin‐to‐body weight ratios makes it difficult to accurately estimate the biomass of harvested sharks based on their traded fins and weakens CITES enforcement. This study determines species‐specific fin‐to‐body weight ratios for shark species caught by the artisanal fishery in the southern Gulf of Mexico. Wet fin weights of primary fins from 479 individuals, belonging to 19 species and six families, indicated that Carcharhinus leucas (43.6%), C. plumbeus (18.8%), C. obscurus (15.0%) and Sphyrna lewini (6.6%) were the most significant large‐bodied species involved in the international shark fin trade from the southern Gulf of Mexico. The species‐specific mean wet fin weight to total body weight ratios ranged from 1.22% to 3.44%, while wet fin weight to trunk weight ratios varied between 1.40% and 5.73%. Furthermore, the dry fin weight‐to‐trunk weight ratios oscillated from 0.52% to 1.71%, and the dry fin weight‐to‐trunk weight ratios ranged from 0.58% to 2.86%. The mean dry‐to‐wet fin conversion factor was estimated at 42.9%. Alopias superciliosus , C. altimus , C. leucas , C. obscurus , C. plumbeus and Isurus paucus exhibited the highest fin‐to‐body weight ratios. Our findings provided a practical tool for assessing shark population exploitation based on shark fin trade volumes, contributing to CITES enforcement and management strategies.

The length–weight relationships (LWR) of eleven demersal elasmobranch species captured in the southern Gulf of Mexico were estimated and assessed to provide previously absent somatometric conversion factors. A total of 8852 specimens representing eight families and eleven species caught as bycatch in the Mexican shrimp trawl fishery were analyzed. The following species were covered: Hypanus americanus (Hildebrand et Schroeder, 1928); Gymnura lessae Yokota et Carvalho, 2017; Narcine bancroftii (Griffith et Smith, 1834); Dipturus olseni (Bigelow et Schroeder, 1951); Rostroraja texana (Chandler, 1921); Pseudobatos lentiginosus (Garman, 1880); Rhinoptera bonasus (Mitchill, 1815); Sphyrna tiburo (Linnaeus, 1758); Squatina dumeril Lesueur, 1818; Mustelus canis (Mitchill, 1815); Mustelus norrisi Springer, 1939. The values of the allometric growth parameter b ranged from 2.5 to 3.2, consistent with the expected range. The somatometric growth exhibited negative allometry in fifteen estimations, isometry in six, and positive allometry in two. The LWR differed by sex in five of the six species examined under this criterion, with females consistently exhibiting greater size and weight than males. This study provides the first published LWR for Narcine bancroftii, Dipturus olseni, Rostroraja texana, and Pseudobatos lentiginosus, along with novel LWR estimates for Hypanus americanus, Gymnura lessae, Rhinoptera bonasus, Squatina dumeril, and Mustelus canis in the Gulf of Mexico. It also presents new maximum lengths for R. texana and P. lentiginosus.

Elasmobranch species are susceptible to anthropogenic stressors such as fishing activities, particularly the bycatch in bottom-trawl fisheries. Understanding the diversity, segregation, and population structure of species at risk of capture is critical for enhancing their conservation. This study evaluated the species composition and population structure dynamics of susceptible elasmobranch species caught as bycatch in the Mexican shrimp trawl fishery in the southern Gulf of Mexico. Data were collected by examining bycatch from 55 fishing trips conducted between 2013 and 2017 during closed and commercial fishing seasons. We analyzed the species composition, length, sex ratio, and maturity stages of susceptible species across zones, sampling seasons, and depth. Six dominant species (Rostroraja texana, Gymnura lessae, Narcine bancroftii, Pseudobatos lentiginosus, Squatina dumeril, Hypanus americanus) accounted for >98% of all captures and were found in all fishing zones, seasons, and depths. These species were caught in a range of sizes, from newborns to mature individuals, and showed both inter- and intraspecific segregation patterns across fishing zones, seasons, and depths. The elasmobranch composition and population structure in bycatch are influenced by ontogenetic segregation and bathymetric distribution of the species. Current Mexican shrimp trawl fishery regulations benefit the majority of elasmobranchs by providing comprehensive spatiotemporal protection and selective exclusion mechanisms. However, small-sized ray species and juveniles of larger species continue to face fishing pressure. The preset study highlights the southern Gulf of Mexico as an important reproductive area for demersal elasmobranchs and unravels their complex segregation behavior, leading to the identification of potential risk zones and seasons. The impacts of bycatch on the most susceptible elasmobranchs may be mitigated through improvements in trawl fishing technology and the implementation of additional temporal bans in specific trawling areas, enhancing species-specific conservation efforts.

In terms of fish dynamic population, reproduction is a process related with corporal size of each population member, which is tied with the spawning time and number of eggs produced. In order to relate the size of female little tuny (Euthynnus alletteratus), located in the southwest Gulf of Mexico, and its contribution in reproductive process, cycle and reproductive characteristics were analyzed by different size groups. Biological data were obtained by the artisanal fishing fleet of Antón Lizardo Veracruz community (Mexico). A total of 480 fish were caught from December 2009 to November 2012. Size structure, gonadosomatic index and duration and intensity spawning index (IDI) were determined. The gonadosomatic index showed a decrease in the population after April and July. Nevertheless, these months and the fraction of spawning female may vary depending on size groups. According with the IDI, the individuals with the highest contribution in reproductive process belong to sizes from 44 to 56 cm. Therefore, in order to guarantee the conservation of this species, it is imperative to mainly direct the management measures towards the females from these sizes.

The number of studies of reproductive biology for Atlantic bluefin tuna carried out in the Gulf of Mexico is significantly lower than those undertaken in the Mediterranean Sea. Four spawning areas have been found for the eastern Atlantic bluefin tuna stock in the Mediterranean Sea, so it is not implausible that there is more than one spawning area in the Gulf of Mexico for the western Atlantic bluefin tuna stock. The individuals used in this study were caught as bycatch by the Mexican surface longline fleet between January and April 2015. A total of 63 individuals ranging between 192 and 293 cm L_F (mean = 238 ± 22.52 cm) were measured. Gonads from 46 fish (31 females and 15 males) were collected for histological examination. All the individuals were classified as mature; 25 were reproductively active (in spawning capable and spawning stages). The histological analysis indicates spawning activity in Mexican waters (the southern Gulf of Mexico). Spawning occurred in March and April, when the sea surface temperature was 25.57 °C ± 0.69 in March and 27.03 °C ± 0.69 in April. Information on the location of the spawning areas is necessary for a correct management of species. The present study provides the first histological evidence of reproductive activity in Mexican waters, and indicates a wider spawning area, beyond just the northern zone, potentially encompassing the entire Gulf of Mexico.

In this study, the variation of seasonal and inter-annual density and diversity of the copepod community in the Parque Nacional Sistema Arrecifal Veracruzano (PNSAV) was analysed. Samples were collected under nortes, rainy and dry weather conditions in 2011, as well as under nortes and dry weather conditions in 2012 and 2013 in four transects. Surface trawls with 330-μm conical nets were made. The temperature, salinity and dissolved oxygen were measured in situ. The values obtained were 23.07 ± 0.53 to 29.29 ± 0.27°C for temperature, 33.43 ± 0.49 to 35.91 ± 0.09 for salinity, and 2.52 ± 0.08 to 6.56 ± 0.08 mg l⁻¹ for dissolved oxygen. The copepods collected belonged to 19 families, 28 genera and 62 species. Copepods represented between 69.74% and 76.79% of the abundance of crustaceans present in zooplankton. The highest number of copepods occurred under nortes weather conditions in 2011 with 401,885 ± 28,092 copepods/100 m³ of the species Temora stylifera. In 2012, 256,325 ± 76,872 copepods/100 m³ of the species Paracalanus aculeatus were obtained and in 2013, 311,526 ± 76,872 copepods/100 m³ of the species T. turbinata. The highest specific richness was found in the southern zone with 28 species. In 2013 the highest density was found in the northern zone with 100,323 ± 28,888 copepods/100 m³. The highest diversity was found under dry weather conditions in 2011 with 3.71 bits/individual. In the 3 years of study, 24 species were dominant; 12 of these, appeared in the 3 years of sampling: T. stylifera, T. turbinata, Labidocera scotti, P. aculeatus, O. latus, Pontellopsis villosa, Centropages velificatus, Parvocalanus crassirostris, Corycaeus speciosus, Undinula vulgaris, Oithona plumifera, and Farranula gracilis. Canonical correlation analysis showed the formation of five groups explained by the neritic or oceanic affinity of the species and their tolerance to changes in salinity or temperature.

The aim of this study was to describe the reproductive dynamic ofEuthynnus alletteratusin the southwest Gulf of Mexico. The annual variation of the volume fraction occupied by gametes and tissues in gonads were related with main body indexes, such as the gonadosomatic index (I_G), the hepatosomatic index (I_H), and the nutrition index (I_N), and compared with the sea surface temperature. A total of 951E. alletteratusindividuals were sampled, where a sex ratio of 1:1 and a size interval strongly skewed towards organisms with a fork length (L_F) of 36–40 cm were observed. TheI_Gshowed an increase from March to September with maximum values in April and July. Two clearly defined peaks were observed, and they were consistent with the histological analysis, where the percentage of ripe gametes predominated from April to September. The optimum thermal window for reproductive activity was from 24 to 28 °C. The size of first sex maturity was 34.35 cm ofL_Ffor males and 34.60 (L_F) for females, without significant difference between sexes.