Rogelio González-Armas

Billfish rostra potentially have several functions; however, their role in feeding is unequivocal in some species. Recent work linked morphological variation in rostral micro‐teeth to differences in feeding behavior in two billfish species, the striped marlin (Kajikia audax) and the sailfish (Istiophorus platypterus). Here, we present the rostral micro‐tooth morphology for a third billfish species, the blue marlin (Makaira nigricans), for which the use of the rostrum in feeding behavior is still undocumented from systematic observations in the wild. We measured the micro‐teeth on rostrum tips of blue marlin, striped marlin, and sailfish using a micro–computed tomography approach and compared the tooth morphology among the three species. This was done after an analysis of video‐recorded hunting behavior of striped marlin and sailfish revealed that both species strike prey predominantly with the first third of the rostrum, which provided the justification to focus our analysis on the rostrum tips. In blue marlin, intact micro‐teeth were longer compared to striped marlin but not to sailfish. Blue marlin had a higher fraction of broken teeth than both striped marlin and sailfish, and broken teeth were distributed more evenly on the rostrum. Micro‐tooth regrowth was equally low in both marlin species but higher in sailfish. Based on the differences and similarities in the micro‐tooth morphology between the billfish species, we discuss potential feeding‐related rostrum use in blue marlin. We put forward the hypothesis that blue marlin might use their rostra in high‐speed dashes as observed in striped marlin, rather than in the high‐precision rostral strikes described for sailfish, possibly focusing on larger prey organisms.

We examined the reproductive behavior (courtship and mating), seasonality and its distribution in three Mobula species, spinetail, bentfin, and Munk’s devil rays (M. mobular, M. thurstoni, and M. munkiana) in the southwestern Gulf of California, Mexico, using boat surveys (with drone and in-water observations) (n = 69 survey days), spotter planes (n = 428 flights), and citizen science observations (n = 31). We examined whether (1) reproductive grounds existed within the area for any of these species, (2) whether reproductive behavior followed seasonal patterns, and (3) if this behavior was similar among all mobula rays. We observed reproductive behavior in 221 events in 2017 and 2021–2022, for M. mobular (n = 10), M. thurstoni (n = 3), and M. munkiana (n = 208) dispersed along 312 km of the eastern Baja California Peninsula between 4 m and 6.3 km away from the coast. Most events (n = 209) occurred in the La Ventana and Ensenada de Muertos areas. Courtship was observed for M. mobular and M. thurstoni and a copulation attempt for M. munkiana, with reproductive behavior following a seasonal pattern occurring from March to August, with a peak during May (81.9% of the events). Mobula munkiana displayed previously undescribed behaviors, such as the “piggyback leaps” as a pre-copulatory position and the “courtship vortex”, where 122 individuals were observed circling in a clockwise direction for 5 h with courtship groups joining and leaving the main vortex formation. This study highlights the areas of La Ventana and Ensenada de Muertos as critical habitats for reproductive behavior of two endangered and one vulnerable devil ray species.

The trophic ecology of the Pelagic Thresher shark (Alopias pelagicus) was evaluated based on chemical ecology using stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in the vertebrae and muscles. Individuals were caught between August 2013 and October 2019 on both the coasts of Baja California Sur, Mexico. In Bahía Tortugas, the mean vertebrae (n = 35) values were 12.72 ± 1.06‰ (δ¹⁵N) and −14.79 ± 0.61‰ (δ¹³C), while in muscles (n = 32) these values were 16.63 ± 0.76‰ (δ¹⁵N) and −17.18 ± 0.39‰ (δ¹³C). In Santa Rosalía, the mean vertebrae (n = 125) isotopic values were 14.4 ± 1.59‰ (δ¹⁵N) and −14.18 ± 0.51‰ (δ¹³C), while in muscles (n = 43), these values were 18.08 ± 0.96‰ (δ¹⁵N) and −16.43 ± 0.34‰ (δ¹³C). These results show higher δ¹⁵N values in Santa Rosalía as an effect of baseline isotopic differences between the two regions, whereas the δ¹³C values were lower in Bahía Tortugas, suggesting offshore ecological behavior (p < 0.05). In Santa Rosalía, there were significant differences by sex for δ¹⁵N in muscle, whereas the δ¹³C showed ontogenetic shifts, indicating that neonates feed in coastal areas more commonly than juveniles or adults (p < 0.05). Neither sex nor ontogenetic differences were observed in Bahía Tortugas (p > 0.05), suggesting a high overlap between their isotopic niches. Therefore, Alopias pelagicus uses the same ecological niche throughout its life, and there is consistency between sexes. The mean trophic position for both tissues and regions was 4.5, which corresponds to a tertiary predator, without any differences between stages or sex. Due to their higher energetic needs, juveniles and females showed the greatest isotopic niche amplitude; thus, their ecological niche is the widest.

This study aimed to characterize their Spatio-temporal distribution of hydrological variables and plankton during neap tides in Bahía Magdalena, a subtropical lagoon south of the California Current. We compare data from surface and bottom waters of stations located inside the lagoon with those near the bay's mouth and between surface and bottom. The availability of nutrients and the chlorophyll-a are associated primarily with the intense upwelling activity in spring. Due to direct marine influence, this relationship was more significant at the inlet than inside the lagoon, especially at the bottom. During the intense upwellings marine influence is maintained even during neap tides. The wind probably causes the homogeneous distribution in most variables within the bay's surface; this may also contribute to the re-suspension of nutrients due to vertical water column mixing. Abiotic variables were not linearly related with zooplankton biovolume and the density of diatoms and dinoflagellates. Phytoplankton was composed mainly by the micro fraction and diatoms during spring and nanoplankton in the warmest season of the year; however, the strong upwellings at the spring's end caused a HAB composed for diatoms. Chlorophyll-a concentration and diatoms were more abundant inside the lagoon and could explain the lower nutrient concentration of that zone. Zooplankton biovolume seasonality differed from other years, with higher values during winter and a significant decreasing trend throughout the year, resulting from the phytoplankton variability. Upwelling and wind variability explains the high biological productivity observed over most of the year.

Fine‐scale movement patterns are driven by both biotic (hunting, physiological needs) and abiotic (environmental conditions) factors. The energy balance governs all movement‐related strategic decisions. Marine environments can be better understood by considering the vertical component. From 24 acoustic trackings of 10 white sharks in Guadalupe Island, this study linked, for the first time, horizontal and vertical movement data and inferred six different behavioral states along with movement states, through the use of hidden Markov models, which allowed to draw a comprehensive picture of white shark behavior. Traveling was the most frequent state of behavior for white sharks, carried out mainly at night and twilight. In contrast, area‐restricted searching was the least used, occurring primarily in daylight hours. Time of day, distance to shore, total shark length, and, to a lesser extent, tide phase affected behavioral states. Chumming activity reversed, in the short term and in a nonpermanent way, the behavioral pattern to a general diel vertical pattern.

Cabo Pulmo National Park was established in 1995 and has since seen a large increase in fish biomass. An unoccupied aerial vehicle (UAV) was used to survey shallow coastal habitat in which lemon sharks (Negaprion brevirostris), bull sharks (Carcharhinus leucas) and Pacific nurse sharks (Ginglymostoma unami) were recorded. Sharks were more common in the afternoon, potentially using warmer shallow areas to behaviourally thermoregulate. This study highlights UAV surveying to be a viable tool for species identification, a limitation of previous terrestrial surveys conducted in the area.