La Entrada
Having sailed northward overnight from Cabo San Lucas, the MV Sea Bird entered La Entrada today. As the sun came up, at least six small pods of common dolphins approached the Sea Bird, each bow-riding for a few minutes and giving everyone close-up views of their elegant patterning and playful character. An hour later, red patches in the water and vigorous surface feeding from red-necked phalaropes and pelicans lured us to an unusual spectacle - dense shoals of the extraordinary pelagic red crab, Pleuroncodes planipes, sometimes known as 'rock lobsters' or 'lobster krill'. These crabs are part of a group known as squat lobsters (the family Galatheidae) and feed for extended periods in the plankton. Our shoals, numbering tens of thousands of animals, were intermixed with even denser shoals ofkrill and may have been feeding on them. As the crabs were picked off by the birds, we could see the energy-flow through a food chain before our eyes. We collected some of the Pleuroncodes in a plankton trawl and everyone was able to observe them in hand.
A large rorqual whale appeared off the bow a few minutes later, apparently partaking in this planktonic feast and adding a second top predator to the food chain. The animal was elusive, showing little of itself at the surface, but the collective was that it was probably a fin whale. While following this whale, we passed more flocks of the phalaropes and learned of the peculiar polyandrous breeding system of these tundra-nesting shorebirds. The males establish nesting sites early in the year, before the females arrive, then advertise them to the females. Females select the most desirable nesting sites and display to the males, moving from one nest to the next and often mating serially with a large number of males. The need for females, rather than males, to advertise their genetic fitness has led to a reversal of the more commonsexual dimorphism such that the females are now the more brilliantly colored and showy sex.
In the afternoon, the Sea Bird sailed around the northern end of Isla Santa Margarita and into Magdalena Bay where we anchored and spent several minutes watching an inquisitive grey whale that approached close to the ship. From here people took Zodiacs out to the island and spent the afternoon exploring dunes and sand beaches. The strand lines on the Magalena Bay side were thick with stranded masses of the pelagic red crabs, while the lower shore was decorated with the projecting sand tubes of filter-feeding polychaete worms. A Pacific loon and eared grebes fed close to the shore, and one party sighted a peregrine in pursuit of sandpipers. On the Pacific side, the shoreline sported an amazing abundance of bleached sand dollar tests, mixed with countless snail and bivalve shells. The interveningdune systems were a photographic feast, strongly sculpted by the sand and stabilized only in irregular elevated mounds where succulent ice plants and other species have established a root-hold. Storm-washed flotsam provided hours or curiosity and included skeletons of turtles and pelicans and whale vertebrae. The dunes also retain some striking shell middens, many probably dating back several centuries. These middens were created by the Guayacura Indians who gathered some of the important food species - the large Dosinia clams and murex snails - and discarded the shells in mounds that persist to this day, scoured and polished by the ever-blowing sand.
Having sailed northward overnight from Cabo San Lucas, the MV Sea Bird entered La Entrada today. As the sun came up, at least six small pods of common dolphins approached the Sea Bird, each bow-riding for a few minutes and giving everyone close-up views of their elegant patterning and playful character. An hour later, red patches in the water and vigorous surface feeding from red-necked phalaropes and pelicans lured us to an unusual spectacle - dense shoals of the extraordinary pelagic red crab, Pleuroncodes planipes, sometimes known as 'rock lobsters' or 'lobster krill'. These crabs are part of a group known as squat lobsters (the family Galatheidae) and feed for extended periods in the plankton. Our shoals, numbering tens of thousands of animals, were intermixed with even denser shoals ofkrill and may have been feeding on them. As the crabs were picked off by the birds, we could see the energy-flow through a food chain before our eyes. We collected some of the Pleuroncodes in a plankton trawl and everyone was able to observe them in hand.
A large rorqual whale appeared off the bow a few minutes later, apparently partaking in this planktonic feast and adding a second top predator to the food chain. The animal was elusive, showing little of itself at the surface, but the collective was that it was probably a fin whale. While following this whale, we passed more flocks of the phalaropes and learned of the peculiar polyandrous breeding system of these tundra-nesting shorebirds. The males establish nesting sites early in the year, before the females arrive, then advertise them to the females. Females select the most desirable nesting sites and display to the males, moving from one nest to the next and often mating serially with a large number of males. The need for females, rather than males, to advertise their genetic fitness has led to a reversal of the more commonsexual dimorphism such that the females are now the more brilliantly colored and showy sex.
In the afternoon, the Sea Bird sailed around the northern end of Isla Santa Margarita and into Magdalena Bay where we anchored and spent several minutes watching an inquisitive grey whale that approached close to the ship. From here people took Zodiacs out to the island and spent the afternoon exploring dunes and sand beaches. The strand lines on the Magalena Bay side were thick with stranded masses of the pelagic red crabs, while the lower shore was decorated with the projecting sand tubes of filter-feeding polychaete worms. A Pacific loon and eared grebes fed close to the shore, and one party sighted a peregrine in pursuit of sandpipers. On the Pacific side, the shoreline sported an amazing abundance of bleached sand dollar tests, mixed with countless snail and bivalve shells. The interveningdune systems were a photographic feast, strongly sculpted by the sand and stabilized only in irregular elevated mounds where succulent ice plants and other species have established a root-hold. Storm-washed flotsam provided hours or curiosity and included skeletons of turtles and pelicans and whale vertebrae. The dunes also retain some striking shell middens, many probably dating back several centuries. These middens were created by the Guayacura Indians who gathered some of the important food species - the large Dosinia clams and murex snails - and discarded the shells in mounds that persist to this day, scoured and polished by the ever-blowing sand.
