RESUMO
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.
Assuntos
Conservação dos Recursos Naturais , Ecossistema , Cadeia Alimentar , Tubarões/fisiologia , Animais , México , Oceano Pacífico , Comportamento Predatório , Tubarões/classificaçãoRESUMO
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⯵g/g wet weight) followed by kidney (0.12⯱â¯0.02⯵g/g), liver (0.11⯱â¯0.01⯵g/g), and gonads (0.04⯱â¯0.00⯵g/g). The maximum of Se was found in the kidney (5.60⯱â¯0.40⯵g/g) and the minimum in muscle (0.60⯱â¯0.01⯵g/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 (<80â¯cm FL) did not exhibit biomagnification, in contrast with larger fish (>90â¯cm FL: 100% for Hg; 65% for Se). These results appear to be related to different feeding habits and availability of prey.