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Group‐hunting animals have been shown to engage their prey in long pursuits (kms) to increase capture success, but the evidence for this is limited to a few terrestrial species. This predation strategy may be effective in the open‐ocean, where group‐hunts are characterised by large predator–prey size ratios and there are few places for prey to hide.However, recording the attack rates, capture rates and capture success probabilities of grouping predators during long‐distance pursuits through the open ocean, remains a significant challenge.Here we use a combination of underwater and aerial video to assess the attack and capture behaviour of striped marlin, Kajikia audax, in relation to the movement of their schooling prey ('stationary' and 'mobile' movement states) during group hunts.We found that the attack rate was higher when the prey school was 'stationary' and, during these times, individual marlin could make longer sequences of uninterrupted attacks on the prey school, effectively monopolising the prey resource for short periods over conspecifics.When the prey school was 'mobile', the attack pattern changed and individual marlin alternated their attacks on the prey school more frequently. Capture success probability (likelihood of capture per attack) was not affected by prey movement state. However, attacks on 'mobile' schools resulted in more prey fish becoming isolated from the school, and these isolated prey were easily captured—not by the attacker but by conspecifics swimming nearby.The likelihood of a prey becoming isolated from a 'mobile' school was predicted by prey school speed, with a 0.1 m s−1 increase leading to an 18.01% increase in the chance of isolation.Altogether this meant the capture rate at the group level was highest when the prey school was 'mobile' rather than 'stationary' because the predators that were pursuing the 'mobile' prey school had an increased availability of isolated and easy to capture prey.This mechanism provides evidence for a by‐product mutualism selecting for conspecific group formation and we discuss our findings in consideration of the social structure of the hunting group and the type of prey. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The shovelnose guitarfish Pseudobatos productus is a major species in batoid catch on the north-western coasts of Mexico. Our goal was to describe the reproductive biology of this species, including morphometric and histological analysis of the gonads. Sampling was carried out on artisanal fishing camps near Bahía Tortugas, Baja California Sur, Mexico. A total of 147 organisms were collected, with a size of 58.9 to 162 cm of total length (TL). The size of first maturity (L50%) was 111.3 cm TL for females, and 102.2 cm TL for males. The sex ratio was 1.42 females per male, but 1:1 for embryos. Positive correlations were found between TL and the number of oocytes, the diameter of oocytes, the uterus height, the oviducal gland height, the oviducal gland width, and the clasper length. We describe four histological zones in the oviducal gland of females, with no sperm storage. Mature testicle lobes showed distinct spermatogenesis stages, ranging from spermatogonia to mature sperm cells. [ABSTRACT FROM AUTHOR]

The white shark Carcharodon carcharias has been present in the Mediterranean Sea since 3.2 million years ago. Nevertheless, the current population shows a low genetic variability suggesting an endangered small population, on which there is scarce information regarding ecotoxicology or trophic ecology. Given that white shark's sightings are rare in the Mediterranean and the possibility of obtaining samples is highly limited, the aim of this research was to provide general information regarding the concentration of trace elements and stable isotopes (δ15N and δ13C). Laboratory analyses were performed on 18 and 12 subsamples from two different white sharks' vertebrae obtained from two adult specimens caught in 1987, in Favignana Island, Italy. Perforations were made along the vertebrae to describe both trace elements and stable isotopes at different life stages. A total of 38 trace elements were analysed, in which the highest concentrations were found in Fe, Sr, U, Pb, and Zn. The fluctuations of these elements during the ontogeny of both individuals could have been related to changes in diet and environment, although the specific origin remains unknown. Regarding stable isotopes, the vertebrae from the male showed an isotopic range from 9.6‰ to 10.8‰ (δ15N) and from −16.5‰ to −13.0‰ (δ13C) with a mean ± SD value of 10.3 ± 0.4‰ for δ15N and −14.6 ± 1.3‰ for δ13C; whereas the female vertebrae had an isotopic range from 9.8‰ to 11.1‰ (δ15N) and from −16.9‰ to −15.0‰ (δ13C), with a mean ± SD value of 10.8 ± 0.6‰ for δ15N and −15.8 ± 0.8‰ for δ13C. There were no significant δ15N differences (U = 6, p = 0.07346) between the two individuals. However, there were just significant differences in δ13C (t = −1.8, p = 0.049256), which could suggest sexual segregation in terms of habitat use and feeding habits. [ABSTRACT FROM AUTHOR]

The shovelnose guitarfish Pseudobatos productus is a major species in batoid catch on the north-western coasts of Mexico. Our goal was to describe the reproductive biology of this species, including morphometric and histological analysis of the gonads. Sampling was carried out on artisanal fishing camps near Bahía Tortugas, Baja California Sur, Mexico. A total of 147 organisms were collected, with a size of 58.9 to 162 cm of total length (TL). The size of first maturity (L50%) was 111.3 cm TL for females, and 102.2 cm TL for males. The sex ratio was 1.42 females per male, but 1:1 for embryos. Positive correlations were found between TL and the number of oocytes, the diameter of oocytes, the uterus height, the oviducal gland height, the oviducal gland width, and the clasper length. We describe four histological zones in the oviducal gland of females, with no sperm storage. Mature testicle lobes showed distinct spermatogenesis stages, ranging from spermatogonia to mature sperm cells. [ABSTRACT FROM AUTHOR]

Rationale: The jumbo squid Dosidicus gigas is a fishery resource of considerable economic and ecological importance in the Mexican Pacific. Studies on its habitat preferences are needed to understand recent fluctuations in the abundance and availability of the species. Stable isotope analysis allows us to infer ecological aspects such as spatial distribution and trophic preferences. Methods: We used an isotope ratio mass spectrometer, automated for carbonate analysis, and coupled to an elemental analyzer, to determine the isotopic composition of statoliths (δ18O and δ13C values) and beaks (δ13C and δ15N values) from 219 individuals caught over two fishing seasons (2007 and 2009) off the coast of Santa Rosalía, in the central Gulf of California. We used these isotopic ratios to assess variation in spatial and trophic preferences by sex, size, and fishing season. Results: In the 2009 group, we observed significant differences in statolith δ13C values and beak δ13C and δ15N values between males and females. Between size groups, we observed significant differences in statolith δ18O and δ13C values in 2007 and in beak δ13C and δ15N values during both seasons. Both seasons were characterized by high overlap in δ18O and δ13C values between sexes and in 2009 between size groups. We observed low trophic overlap between sexes in 2009 and between size groups during both seasons. Conclusions: The isotopic ratios from statoliths and beaks indicate that D. gigas has changed its spatial and trophic preferences, a shift that is probably related to changes in the species' diet. This intraspecific variation in preferences could be related to characteristics such as size, which may influence squid distribution preferences. [ABSTRACT FROM AUTHOR]

Reproductive characteristics of the Pacific angel shark, Squatina californica, were evaluated from 420 specimens obtained from the artisanal fishery in La Paz Bay, Gulf of California, Mexico. Females (99 cm, 6000 g) were larger than males (95 cm, 5000 g) in terms of both total length (LT) and body mass (MT). The overall sex ratio was significantly different from the expected 1:1, suggesting sexual segregation of mature individuals in La Paz Bay. Males had developed reproductive organs and calcified claspers from 72 cm LT; the median size at maturity (LT50) was 75·6 cm. In females, only the left ovary was functional and mature ovarian follicles were present from 77 cm LT; the estimated LT50 was 77·7 cm. For the 10 gravid females sampled, uterine fecundity was between two and 10 embryos. Mature, non-gravid females with small and large ovarian follicles appeared simultaneously with gravid females with follicles that did not exceed 1·9 cm diameter. [ABSTRACT FROM AUTHOR]

RATIONALE: Individual foraging behavior is an important variable of predators commonly studied at the population level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods. METHODS: We determined the isotopic composition (δ13C and δ15N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values. RESULTS: There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ15N values of S. zygaena vertebrae, with lower values in the first group of samples. CONCLUSIONS: Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology. [ABSTRACT FROM AUTHOR]

Despite being one of the most abundant and highly exploited species in the Mexican Pacific Ocean, information on the biology of the silky shark, Carcharhinus falciformis is limited. The objective of the present study was to describe the reproductive biology of this species, based on 262 sharks (117 females and 145 males) caught from September 2004 to May 2006 in the Gulf of Tehuantepec, Mexico. The size of females ranged from 70 to 229 cm total length (TL); males measured from 69 to 220 cm TL. Female reproductive organ measurements showed that between 175 and 190 cm TL there was an increase in oviducal gland width (19–45 mm), as well as in uterus size (20–220 mm width). Mature males over 180 cm had calcified claspers, well-developed testes (184–282 mm) and presence of sperm in the seminal vesicles. The estimated length of males at first maturity was 180 cm, and that of females was 190 cm. Ovarian fecundity varied from 4 to 11 oocytes, and uterine fecundity varied from 2 to 14 embryos. We infer that mating occurs between May and June. We did not find sperm storage in the oviducal glands. Birth size was observed to be between 60 and 69 cm TL. No defined gestation period was observed. [ABSTRACT FROM PUBLISHER]

Dolphinfish (Mahimahi) are a high-demand resource for sport and coastal fisheries, mainly in the Pacific Ocean. Due to their economic and ecological importance, studies of their biology are very important to understand their function in ecosystems. We used stable isotope and stomach content analyses to determine the most important prey of the common dolphinfish, as well as the trophic level of this species in two areas of the southern Gulf of California. Stomach contents of 445 specimens were analysed. Using both techniques, we found that the most important prey for dolphinfish in the southern Gulf of California were three invertebrate species followed by fish. This contrasts with results from other authors who found that this species was mainly piscivorous in other locations. Stomach content analysis indicated differences in prey biomass by area, season and size class. The isotopic analysis did not show significant differences between seasons or sexes. Both stomach contents and stable isotope analyses showed that although this predator consumed a wide prey spectrum, only a few prey items made up the bulk of the diet, which resulted in a low SD in δ15N values and low Levin's index values. We conclude that this fish is an opportunistic predator that may consume a wide prey spectrum, but that it mainly consumes prey that are abundant in the area, such as crustaceans and cephalopods in the Gulf of California. [ABSTRACT FROM PUBLISHER]

The reproductive biology of the pelagic thresher shark Alopias pelagicus, was analysed based on 241 individuals (101 males and 140 females). Samples were collected from April 2005 to February 2006, from the artisanal fishery in Manta, Ecuador. Males ranged from 68 to 183 cm precaudal length (PL); females ranged from 70 to 180 cm PL. In embryos, sexual proportion was 1F:1M; while in adults the proportion was 1.4F:1M, which suggests sexual segregation in maturing individuals. We showed differences in the development of reproductive structures according to the reproductive condition, and in males the size at maturity occurs at 144.3 cm PL and in females at 151.4 cm PL. We recorded 33 pregnant females that presented one embryo in each uterus in different developmental stages. The results of this study provide information on reproduction of the species that will help to establish an appropriate fisheries management. [ABSTRACT FROM PUBLISHER]

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The once-abundant silky shark population has declined drastically in recent years, caused by extensive by-catch in the tuna purse-seine and longline fishery in the eastern Pacific Ocean. As no information is available for this area on age, growth or population characteristics of this species, age and growth of the silky shark Carcharhinus falciformis in waters off the west coast of Baja California Sur were examined based on counts of growth rings on longitudinal sections of the vertebra. From August 2000 to October 2002, sharks were sampled monthly in the fishing camps at Punta Lobos and Punta Belcher. In total, 252 sharks were sampled, mainly between June and November. Total length (TL) of females was 88-230 cm and males 142-260 cm. The relationship of the vertebra radius to the total length was linear ( r = 0.94), indicating the use of vertebrae for age estimates and growth description in this species. It was assumed that growth marks have an annual periodicity and that the opaque band is formed during the period from summer to autumn. Estimated ages for sampled females were 2-16 years and 3-14 years for males. No significant differences between genders in size or age were detected. Estimated parameters of the von Bertalanffy growth model for genders combined were L = 240 cm TL, k = 0.14 per year, and t = −2.98 years. According to the growth model, the silky shark averages 20 cm growth after the first year of life, with a growth rate of 16 cm per year between the 2nd and 4th year, 10 cm per year from the 5th to 7th year, about 6 cm per year in the 8th to 10th years, and only 3 cm per year or less after age 11. Females and males were found to reach sexual maturity between 7 and 8 years. [ABSTRACT FROM AUTHOR]

The objective of this study was to establish the trophic niche of the silky shark and to determine the ecological role of this predator in the ecosystem close to Baja California. The trophic spectrum was analyzed from samples taken during summer and autumn (2000–2002) from the fishing camps of Punta Lobos and Punta Belcher on the western coast of Baja California Sur. A total of 263 stomach contents were analyzed (143 with food; 120 empty). The index of relative importance (IRI) showed that at Punta Lobos, silky sharks fed mainly on red crabs Pleuroncodes planipes (%IRI = 83%), whereas at Punta Belcher the main food item was the jumbo squid Dosidicus gigas (%IRI = 41%), followed by chub mackerel Scomber japonicus (%IRI = 33%). According to the Levin Index (Bi), the trophic niche breadth in silky sharks is low (Bi = <0.6), which means that silky sharks are specialist predators because they mainly consume three prey types: red crab, chub mackerel, and jumbo squid. The Shannon-Wiener Index indicated that all trophic categories at Punta Belcher (0.85–1.22) had lower diversity than at Punta Lobos (0.50–1.6), because the silky shark feeds more on tropical prey found close to Punta Lobos. The Morisita-Horn Index (Cλ) showed an overlap in the diet between the two areas analyzed and between sexes (Cλ = >0.6). The juveniles and adult females did not show any overlap. In the caloric analysis of the main prey, the jumbo squid ( D. gigas) contributed the most calories to the silky shark diet (76%). [ABSTRACT FROM AUTHOR]

The objective of the study was to identify key elements of the feeding ecology of the dolphinfish, which is a high tropic predator important for sport and artisanal fishing in the Mexican Pacific. Feeding habits were investigated during the years 2000–2003. This species is seasonal in the southern Gulf of California and probably remains there because of the abundant prey. The contents of 232 dolphinfish stomachs were analyzed, identifying 98 prey species, although only eight of these were well-represented in the diet. The most important prey by weight was the fish Hemiramphus saltator, however by number and frequency of occurrence was the crustacean Hemisquilla californiensis. No differences in the diet were found between males and females, although there was an ontogenic diet shift between seasons. There was no relationship between dolphinfish size and prey size, because dolphinfish fed preferentially on prey with an average size of 4.7 cm. [ABSTRACT FROM AUTHOR]

The article focuses on the torpedo californica, a Pacific electric ray that occurs from the Queen Charlotte Islands, British Columbia to Baja California, Mexico. It states that torpedo californica could produce up to 45 volts power electric charge for self defense and to stun their prey. It mentions that torpedo californica specimen was captured by fishermen by using monofilament gill nets in the fishing camp in El Portugués in Gulf of California in Mexico in July 2007.

The Cortez angelfish Pomacanthus zonipectus is an important species for the aquarium market and knowledge of its reproductive potential is useful to establish strategies for its fishery management. To estimate partial and relative fecundity, samples of P. zonipectus were collected during the breeding season (June—November) off Espíritu Santo Island, Gulf of California, Mexico. After a histological study, mature ovaries that showed no evidence of spawning were selected for analysis. The minimum sample size was calculated with a new methodology based on the von Bertalanffy model and fecundity was calculated using the hydrated oocytes method. The minimum sample size was 0.04 g. Mean partial fecundity was 40,755 oocytes female-1, and relative fecundity was 79.4 oocytes g-1 eviscerated weight (EW) and 201.2 oocytes mm-1 standard length (SL). A positive and significant correlation was observed between partial fecundity and fish size, in both EW and SL (P < 0.05). The relation between partial fecundity and fish size (EW and SL) was expressed by an exponential function. [ABSTRACT FROM AUTHOR]