Scuba diving, snorkeling, island tours and whale watching in La Paz, Mexico with Baja Connections

Marine Life Calendar

The Sea of Cortez is known for it's big animals. Supporting these larger animals is the backbone of our marine ecosystem, the coral reef. The Sea of Cortez is home to over 50 species of corals, over 900 species of fish and many other creatures, both big and small. The waters of La Paz are just a small area of the Sea of Cortez but they are home to many of these species. There are unique marine life behaviours that can be observed here and nowhere else. Continue reading to learn more or click on the links to skip to each section.

Coral Reefs

Fish Life

Mobula Rays

California Sea Lions

Whale Sharks

Coral Reefs

Although La Paz is not known for its coral reefs there are at least 39 species of stony coral and 21 species of soft corals found here. Living in among these corals are numerous species of invertebrates and fish all contributing the reef system as a whole. One of the dominant coral species here in La Paz is a stony coral found in the genus Pocillopora. Mound shaped with thick, short branches it creates large colonies which act as a home for a number of different species.There are species of coral on all of the dive sites in La Paz but two main reefs, the island of San Rafaelito and Suwanee Reef. These two dive sites have impressive coral gardens and plenty of macro species. These two reefs could be classified as patch or barrier reefs but our type of reef is a little different than your typical tropical reef. Although the dominant species is a stony coral it does not really contribute to the reef's physical substrate. One of the main components of the substrate, or rock, is mollusc shells. Corals tend to thrive here in micro-environments where the conditions for coral growth are present. Up-welling plays a major part, bringing cold, nutrient and oxygen rich water from the deep in contact with these reefs. Currents bring in a constant supply of food and most of the coral growth is concentrated on small islands and points of land. While our coral reefs are not extensive they are robust, with the reef at San Rafaelito displaying almost 100% cover of pocillopora and large black coral species (Antipathes galapagensis) present in the deeper reefs and shipwrecks of La Paz.

Creature Spotting and Macro Life

Most invertebrates are very small or highly camouflaged to escape predation. Finding them usually requires a little study beforehand, learning their habits and their preferred habitat. The most beneficial thing a diver can do to improve their creature spotting is to slow down. The slower you go the more chance you will have to spot these creatures. It's also a good idea to learn about their habitats. A large number of species are symbiotic with one species of coral, sponge or other invertebrate. They are easy to find because you just look for their host which is typically much bigger and easier to find.

Unfortunately the Sea of Cortez does not have any good invertebrate identification books, there is "Sea of Cortez Marine Animals: A guide to common fishes and invertebrates" but it only has a few invertebrate species. Another place to try is; they have a number of invertebrate species described as well as some birds and mammals. If you're scientifically inclined you can use The Gulf of California Invertebrate Database, it allows you to search using taxonomy and is quite extensive.

There are countless other examples of symbiosis among the marine species here in La Paz and there are far too many invertebrate species to describe here, over 3000 just in Baja Sur, represented by 16 different phyla (taxonomy groups). In short, if you are into macro you won't be disappointed.

Why are coral reefs important?    

Besides man, corals are the only species with the ability to permanently alter the surface of the earth, creating large chains of islands and shaping the coastline. In many areas coral reefs protect the coastline from the open ocean, providing a habitat for mangroves and sea grass beds to thrive. Countless people directly rely on them for their livelihood, both in tourism and fisheries. Globally we rely on them for their photosynthetic activities, carried out by their symbiotic algae. The by-products of this photosynthesis serve as a vital input of food into the tropical/sub-tropical marine food-chain, and assist in recycling the nutrients. Coral reefs provide home and shelter to over 25% of fish in the ocean and up to two million marine species. They are also a nursery for the juvenile forms of many marine creatures. Corals are found throughout the world, in temperate, tropic and arctic waters, able to thrive in all zones of a coastline, from the inter-tidal area down to over 3000m/9800 ft.
What is coral?

A "coral head" is a colony made up of individual organisms. All of the individuals are in the sessile (not-mobile) polyp stage of their life cycle and are typically clones of one individual, the ancestral polyp. This individual is the result of coral spawning, a sexual means of reproduction in corals which happens just once a year. The first stage of the life cycle is a free swimming medusa very similar to a jellyfish. They drift until they come in contact with an available surface and than attach themselves and transform into their polyp stage. This ancestral polyp will than clone itself by either division or budding and form a large colony of individuals. This colony is what is termed a "coral head". There are over 2,500 different species of coral worldwide and all have adapted special ways to survive in a nutrient poor environment where space is highly limited.

A typical individual coral polyp is made up of three layers of cells, a thin mesoglea bordered by the exo and gastroderm. The body is cup shaped with a central opening (mouth) which leads into the gut cavity. This mouth is ringed with tentacles that extend into the water column and using nematocysts the polyp can catch prey that is floating by, mostly in the form of zooplankton, microscopic animals.

Corals can be further divided into two major groupings, Hermatypic (hard) corals, which produce stony skeletons and have zooxanthellae (algae) in their tissues and Ahermatypic (soft) corals, which have soft bodies and no zooxanthellae.


To understand how corals live you need to understand symbiosis, defined as the close physical interrelationship between two different species. There are three types of symbiosis; parasitism, commensalism and mutualism. All types of symbiosis are present in the marine environment and in the case of corals their survival depends on it. If we look at a colony of Pocillopora we can see examples of all three types of symbiosis. The coral exists because of a relationship between the coral and a specific species of algae which lives in its tissues, zooxanthellae. This microscopic plant acts like any other plant, absorbing CO2 and releasing oxygen as a byproduct. The coral, like any other animal, needs oxygen to breath and utilizes the oxygen produced by the algae in turn providing it with CO2. The waste products of photosynthesis, glucose, glycerol, and amino acids are utilized by the coral for food and to create its skeleton which is Calcium Carbonate. Up to 90 percent of the organic material photo-synthetically produced by the zooxanthellae is transferred to the host coral tissue. This efficient relationship, known as mutualism has allowed corals to become so successful.

The small fish and invertebrates that live outside the coral colony use its branches and fissures to hide from predators, either darting out to feed and returning for protection or simply feeding off the detritus that builds up in the cracks and crevices of the coral host. These species use the host as a home, taking advantage of the host but not creating any harmful effects. This relationship, known as commensalism, is where one species benefits from the relationship while there is no impact to the other. While it can be argued that the small fish and invertebrates keep their host colony clean and therefore benefit the coral host it is still a good example.

Burrowed into the coral branches you can find worm snails, marine molluscs belonging to the family Vermetidae. Unlike most marine creatures these worm snails do not start off their life as pelagic larvae. Born from the female they simply crawl until they come in contact with a coral host, attach themselves and secrete a tubular shell which eventually gets enclosed by the growing coral. The end of the shell remains open and the worm snail uses a modified part of its foot called the operculum to block the opening when threatened. From this shell the worm snail secretes mucus nets to trap floating plankton and reels them in once they are full. In this relationship the host coral is affected in two ways, firstly the worm snail takes up valuable space. Corals photosynthesize and their success partly depends on the amount of surface area exposed to sunlight, space which is taken up by the worm snail. While at first glance they do seem small and insignificant but when they exist in great numbers they have been shown to limit coral growth. Secondly the worm snail's mucus contains toxins which deter coral growth and are feeding on the same prey that the corals are. This direct competition for food sources and twormsnailhe harmful effects of the mucus impact the coral host in a negative way, an example of parasitism.  

There are countless other examples of symbiosis among the marine species here in La Paz and there are far too many invertebrate species to describe here, over 3000 just in Baja Sur, represented by 16 different phyla (taxonomy groups). In short, if you are into macro you won't be disappointed.

Fish Life in the Sea of Cortez

Known as the "aquarium of the world", the Sea of Cortez hosts a large variety of fish life. There are over 900 recorded species of fish with about 10% of those being endemic, found here and nowhere else.If there is one consistent thing about diving in La Paz it is the large amount of fish life at our dive sites. Those who have dove in the Indo-pacific and the Caribbean may recognize a lot of the fish species they encounter but the schools and individuals are much larger and display some different behaviour you may not be used to. La Paz is also home to many fish species you will not see anywhere else. About 10 percent of the Gulf of California fish fauna is endemic—80 of the 821 bony fish and 4 out of the 90 cartilaginous fish species are only found in the Sea of Cortez. These include the totoaba, Gulf weakfish, big-eye croaker, Cortez cling-fish, Sonora blenny, white-tip smoothhound, Cortez stingray, Cortez skate, Gulf grunion, delta silverside, leopard grouper, saw-tail grouper, Cortez damselfish, Gulf signal blenny, slow goby, Guaymas goby, and short-jaw mudsucker, among others. Endemic mammals include the vaquita porpoise, and the Gulf fishing bat.

While diving here in La Paz you will encounter many species of fish, for identification purposes it is best to use characteristics such as size and color and to also look at behavior as well. There are only a few identification books for fishes in the Sea of Cortez, one being a volume of the REEF series of New World Publications, "Reef Fish Identification Baja to Panama". The other is "Sea of Cortez Marine Animals: A guide to common fishes and invertebrates". The first mentioned is far superior but only contains information on the fish species. The authors have separated the species into groups based on visual characteristics and behaviors; although there is no relation to taxonomy in these groupings they are useful for identification purposes. A good online resource is; they have a huge amount of information on fish species in the Sea of Cortez.

There are far too many fish species to list here but the one guaranteed thing about diving in La Paz is the huge amount of fish life in these waters. It is common to see large schools of fish on every dive site and mini schools of fish like balloonfish, puffers, cornetfish and moorish idols. There are plenty of fish for macro lovers with over 60 species of goby, blennies and jawfish and countless chances to observe cleaning stations and other relationships.

Mobula Rays

Coming soon.

California Sea lions

The Los Islotes sea lion colony is located at the northern tip of the islands and is used year round by the sea lions. These small rocky islands are a resting area where they can sun themselves, sleep and relax when they are not hunting. Mothers give birth to their pups here in the spring/summer and mating typically happens a few weeks afterwards. Los Islotes is also a superb dive site with many species of fish and birds to observe and a large canyon like swim-through. Both divers and snorkelers can enjoy this beautiful area. Sea lions are also often seen at other dive sites and while we are in transit and are just as easy to interact with.

If you've never snorkeled or dove with sea lions you are in for a treat, younger sea lions are very playful and it is common for them to tug on your fins, swim in crazy circles around you and even bark at you underwater. The larger males however, are a little lazier as you can see in this video clip.

Day trips to the sea lion colony are available year round, for both snorkeling and scuba diving activities. Check out our snorkel tours page or diving tours page for more information.

The California Sea Lion Zalophus californianus

California sea lions are known for their intelligence, playfulness, and noisy barking. Their color ranges from chocolate brown in males to a lighter, golden brown in females. Males reach 850 pounds (390 kg) and seven feet (2.1 m) in length. Females grow to 220 pounds (110 kg) and up to six feet (1.8 m) in length. They have a "dog-like" face, and at around five years of age, males develop a bony bump on top of their skull called a sagittal crest. The top of a male's head often gets lighter in color with age. These members of the otariid, or walking seal, family have external ear flaps and large flippers that they use to "walk" on land. The trained "seals" in zoos and aquariums are usually California sea lions.


California sea lions are found from Vancouver Island, British Columbia to the southern tip of Baja California in Mexico. They breed mainly on offshore islands, ranging from southern California's Channel Islands south to Mexico, although a few pups have been born on Año Nuevo and the Farallon Islands in central California. There is a distinct population of California sea lions at the Galapagos Islands. A third population in the Sea of Japan became extinct, probably during World War II.

Most pups are born in June or July and weigh 13 to 20 pounds (6 to 9 kg). They nurse for at least five to six months and sometimes over a year. Mothers recognize pups on crowded rookeries through smell and vocalizations. Pups also learn to recognize the smell and vocalizations of their mothers. Breeding takes place a few weeks after birth. Males patrol territories and bark almost continuously during the breeding season.


California sea lions are very social animals, and groups often rest closely packed together at favored haul-out sites on land or float together on the ocean's surface in "rafts." They are sometimes seen "porpoising," or jumping out of the water, presumably to speed up their swimming. Sea lions have also been seen "surfing" breaking waves. California sea lions are opportunistic eaters, feeding on squid, octopus, herring, rockfish, mackerel, and small sharks. In turn, sea lions are preyed upon by Orcas (killer whales) and great white sharks (don't worry; there are no great whites in La Paz).


Their population is growing steadily, and California sea lions can be seen in many coastal spots such as the Monterey Coast Guard jetty and PIER 39 in San Francisco. The current population is approximately 238,000.

 Whale Sharks

The whale shark is a filter feeder, one of three species of shark who feed in this similar method, the other two being the basking shark and the mega-mouth shark. Not to be confused with whales, the whale shark was simply named that because of its large size. It is actually a shark, in the same order as Wobbegong sharks and Nurse Sharks. The whale shark is the largest fish species on planet earth and originated about 60 million years ago. The largest confirmed whale shark was 12.65 meters long and weighed 21.5 tons although there have been unconfirmed sightings of whale sharks up to 21 meters long.

Like sharks, and most other fish, a lateral line runs down the length of the body, this lateral line is a system of sense organs and is used by the whale shark to detect movements and vibrations in the surrounding water. The whale shark also has three distinct ridges along its side; the lateral line is located in a depression between the 2nd and 3rd ridges. The pectoral fins are quite large and there are two dorsal fins, the first being significantly larger than the second. Juveniles and adults have different tail fin shapes; the top part of the tail fin is larger than the bottom in juveniles while in adults they are nearly the same. The skin of the whale shark can be quite thick, up to 10cm (3.9 in) and is covered in a pattern of dots and lines which are unique to each individual. This skin pattern is thought to aid in protection against radiation from the sun as the whale shark spends a significant amount of time near the surface.

The whale shark is mostly found in tropical and warmer oceans and lives a pelagic lifestyle, with seasonal feeding aggregations in many parts of the world. Mexico is lucky to have three of these sites in its waters, Isla Holbox, Isla Mujeres and the bay of La Paz. In all three sites whale sharks gather to feed on plankton blooms, large concentrations of microscopic life including crustaceans and algae. These organisms are invisible to the human eye but occur in such large numbers that they become a viable food source.

To capture this small prey the whale shark utilizes one of two feeding methods; Ram filtration or active suction feeding. Whale sharks have very large mouths (1.5m) with 300-350 rows of tiny vestigial teeth and 10 filter pads, which are modified gill rakers. As the water passes across these filter pads food is separated and swallowed while water is expelled through the gills. This filtering system can get clogged from time to time and it is common to see whale sharks "coughing" to clear it.

Ram filtration is the most commonly observed method of feeding here in La Paz. This method is simply the whale shark swimming horizontally with its mouth open and filtering large amounts of water. Whale sharks will feed in this manner when the concentration of plankton is lower and distributed over a larger area.

Active suction feeding typically occurs when there are more solitary patches of dense plankton, in this case the whale shark is vertical and opens and closes its mouth to suction water in, filter the food and expel it out of the gills. You are very lucky if you get to observe this feeding method as the whale shark is not moving anywhere and allows you to get very close. .

Studies have shown that the planktonic life consumed by whale sharks in La Paz is dominated by copepods. Copepods are very small animals, typically 1-2mm in length and exist in every type of aquatic environment, including places such as a simple rain puddle. In the ocean environment copepods exist in vast numbers and when the right conditions are present can multiply rapidly and create what's known as a plankton bloom. These blooms can last just a few days or months depending on the environmental conditions. Whale sharks also feed on schools of spawning fish and their gametes, squid and a number of different species of planktonic life.

The sex of a whale shark can be determined by the presence of claspers, which are only present in males. These claspers develop from the inner rim of the pelvic fins and are used during sexual reproduction. No one has ever observed whale shark mating or birth and it is still unknown how and where these animals reproduce. The smallest confirmed whale shark ever caught was in the Philippines and measured 38cm/15in. Pregnant females have been found to have over 300 pups which tells us whale sharks are ovoviviparous, meaning they bear live young.

For some more information about whale sharks or to see how you can get involved in their conservation check out these sites.


Wildbook for whale sharks


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