Shark ecology, the role of the apex predator and current conservation status.

Feeding studies, since traditional stomach content analysis to stable isotopes analyses, provides insights into the trophic relationship among the apex predators and the ecosystems they inhabit. The Pacific Coast of Mexico (PCM) is inhabited by 62 known species (or 12%) of living sharks, which belong to 21 families and 34 genera. We divide the Pacific Coast of Mexico (PCM) into four regions for consideration: (1) the western coast of Baja California (WcBJ), (2) the Gulf of California (GC), (3) the Central Pacific Mexican (CPM), and (4) the Gulf of Tehuantepec (GT). Biodiversity is highest in the GC, with 48 shark species, followed by the WcBJ with 44 species, then the CPM with 28 species and the GT with 26 species. Few large species (>2m in total length) function as top predators in any region, with a greater number of smaller shark species (<1.5m total length). Information about the trophic ecology of different shark species is included to know the ecological role and position of each shark species within a food web to understand the dynamics of marine communities and the impact that each species has on trophic net, which is critical to effective resource conservation and responsible exploitation. The different shark species predate mainly on coastal or oceanic waters. The coastal sharks feed mainly on crustaceans and small fishes; whereas the oceanic species predate mainly on squids and fishes from mesopelagic to epipelagic habits. Also is included a summary of the IUCN Red List category assigned to all shark species from the Mexican Pacific. Thirty-one percent (19 species) of sharks in the Mexican Pacific are considered as threatened (Critically Endangered, Endangered or Vulnerable). Of these, 4.9% (3 species) are Endangered and 26.2% (15 species) are Vulnerable. In addition, since 2012 the fishing of shark and rays has been closed between 1 May and 31 July in the Mexican Pacific as a conservative management measure.

Patterns of mercury and selenium in tissues and stomach contents of the dolphinfish Coryphaena hippurus from the SE Gulf of California, Mexico: Concentrations, biomagnification and dietary intake.

Selenium and mercury were evaluated in tissues and stomachs of the dolphinfish Coryphaena hippurus from two sites in the Southeastern Gulf of California. Hg levels were consistently low and exhibited the following patterns: muscle (0.14 ±â€¯0.01 µg/g wet weight) followed by kidney (0.12 ±â€¯0.02 µg/g), liver (0.11 ±â€¯0.01 µg/g), and gonads (0.04 ±â€¯0.00 µg/g). The maximum of Se was found in the kidney (5.60 ±â€¯0.40 µg/g) and the minimum in muscle (0.60 ±â€¯0.01 µg/g). All the Se:Hg molar ratios were between 3.7 and 697.1, with the minimum in muscle and the highest in gonads. The results indicate a contrasting behavior biomagnification of Hg and Se; smaller fish (<80 cm FL) did not exhibit biomagnification, in contrast with larger fish (>90 cm FL: 100% for Hg; 65% for Se). These results appear to be related to different feeding habits and availability of prey.

Trace metals in target tissues and stomach contents of the top predator sailfish Istiophorus platypterus from the Eastern Pacific: concentrations and contrasting behavior of biomagnification.

Cadmium, lead, copper, and zinc were analyzed in the dorsal muscle, liver, gonad, and stomach contents of 67 sailfish, Istiophorus platypterus, from the Eastern Pacific. Muscle exhibited the following pattern (µg/g wet weight): Zn (15.05 ± 1.24) > Cu (0.461 ± 0.026) > Cd (0.434 ± 0.099) > Pb (0.025 ± 0.001); liver Zn (119.1 ± 7.6) > Cd (95.1 ± 11.0) > Cu (39.7 ± 2.6) > Pb (0.047 ± 0.004); and gonad Zn (96.8 ± 7.8) > Cd (2.16 ± 0.38) > Cu (2.08 ± 0.14) > Pb (0.033 ± 0.003). Significant (p < 0.05) correlations were observed between elements, length, and weight. I. platypterus feed mainly on fishes and cephalopods with variable concentrations (µg/g wet weight) of Cd (0.081-11.41), Pb (0.002-0.057), Cu (0.204-4.35), and Zn (3.23-86.6). Of the four analyzed elements, only Pb was biomagnified (BMF = 1.85). According to the regulatory limits, muscle exhibited Cd concentrations higher than the Official Mexican Standard, WHO, FDA (28 % of samples), and the European Union (40 %) regulations.

Mercury and selenium in tissues and stomach contents of the migratory sailfish, Istiophorus platypterus, from the Eastern Pacific: Concentration, biomagnification, and dietary intake.

Mercury and selenium were assessed in the sailfish, Istiophorus platypterus, from the Eastern Pacific. Sixty-seven individuals were sampled, muscle, liver, kidney, gonads and the prey found in the stomach contents were isolated during fishing 2011-2013 tournaments. Hg exhibited the following pattern (µg g(-1) wet weight): liver (0.57 ± 0.07)>muscle (0.56 ± 0.04)>kidney (0.44 ± 0.08)>gonad (0.14 ± 0.01). The maximum concentration of Se was found in kidneys (14.1 ± 1.9 µg g(-1)), and the minimum in muscles (0.67 ± 0.03 µg g(-1)). High Se:Hg ratios were found for muscle (4.1 ± 0.3), kidney (132.4 ± 12.1), liver (54.0 ± 4.4) and gonads (88.2 ± 7.9); Hg:Se molar ratios were several orders of magnitude lower (muscle<0.4 and liver, kidney and gonad<0.03). Sailfish feed mainly on fishes and cephalopods with low Hg levels (<0.13 µg g(-1)), these results indicate biomagnification of Hg and Se. The muscle of I. platypterus should be consumed (according the provisional tolerable weekly intake) by people cautiously so as not to exceed the recommended intake of 215 g per week.

Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks.

Selenium and mercury were evaluated in muscle, liver, kidney, brain, and the stomach contents of juvenile scalloped hammerhead shark Sphyrna lewini. Se:Hg molar ratios were calculated. The average Hg levels in muscle ranged from 0.12 to 1.17 µg/g (wet weight); Hg was <0.39 µg/g in liver and kidneys and <0.19 µg/g in brain. The lowest value of Se was found in muscle (0.4 µg/g) and the highest in kidney (26.7 µg/g). An excess of Se over Hg was found, with Se:Hg molar ratios >1. Correlations were found for Hg in muscle with size, age, and weight, and also for Hg in liver with size, age, and weight. Hg in muscle was significantly positive correlated to Hg in brain as well as Hg in liver was correlated to Hg in kidney. The highest Hg in preys was for carangid fishes; scombrid and carangid fishes contributed with the highest Se levels. Results suggest that more than 98 % of the total Hg and 62 % of Se end up in muscle and might be affected by factors, such as geographical area, age, size, and feeding habits. The muscle of S. lewini should be consumed by people cautiously so as not to exceed the recommended intake per week.