Birds do it, bees do it, and all the fishes in the sea do it. All creatures arrive on this planet somehow, with some reproducing asexually, and others creating new life only after complicated courting and mating rituals. Others are somewhere in the middle. For us divers, few things are quite as fascinating as witnessing courtship and mating behavior underwater. Here, we’ll take a look at some of the ways fish and other marine animals play the game of love.
Reproduction in Fishes Varies
Our oceans are filled with an endless variety of fish, and though all fish have certain things in common, their reproductive strategies are wonderfully varied. In most cases, male and female fishes aggregate at specific spawning grounds. Once female fish release eggs, male fish hover over the eggs, releasing clouds of semen to fertilize them. After mating, many mature fish go back to life as usual and live to reproduce again. Some fish, particularly migratory salmon, grow to maturity, head to their spawning grounds to reproduce, and die shortly after spawning has been completed.
In some cases, fish vocalize and dance to attract mates, much in the same way birds and other higher animals do. Sergeant fishes and Garibaldis are two species with fascinating mating rituals; males first create snug nests in algae, then work hard to attract female attention. The fish woo one another for an extended period of time, after which the female lays her eggs in the nest and the male fertilizes them. Afterward, the male essentially shuns his partner, chasing her away from the nest and guarding it until the eggs hatch. In some cases, males mate with multiple partners, ensuring their offspring are hardy and varied. Should you encounter a male sergeant fish or garibaldi guarding his nest, keep a respectful distance – you could be nipped if you get too close!
Male jawfish utilize a similar strategy with one important difference: once the eggs have been fertilized, the jawfish stores them inside his mouth until they hatch. Certain jawfish species even allow their fry to live inside their mouths after hatching – a real rarity in the fish world since most young fish are left to their own devices from the moment they’re born or hatch, and since many species will eat their own young fairly indiscriminately.
Male sea horses and sea dragons also take on the task of storing eggs after fertilization. These fish have specialized pouches that keep the eggs safe until they hatch; once fry emerge from eggs, they make their way out of the pouch into the marine environment. Though this looks a lot like live birth, it is not; however, it’s fascinating nonetheless.
Other fish including guppies, some sharks, rays, and skates utilize more complicated methods, mating when the female is ready. This type of internal fertilization sometimes leads to the animals releasing fertilized eggs which develop outside the body; in some cases, pups develop inside the female, who gives live birth at a later date. Even in cases of internal fertilization, there is variety. Certain female sharks simply store the male’s semen, waiting to fertilize eggs until conditions are right.
Mates and Mating Cycles
Just as reproductive methods vary, so do mating cycles. While some species rely on lunar and tidal cycles to provide cues to mate, many species mate on a day to day basis, with mass fertilization occurring as eggs and sperm are released into the water column. For many reef fish, the aim is to spawn at the right time for certain tides and currents to carry their fertilized eggs away in hopes of populating another area.
Most marine animals are polygamous, with multiple mates. Surprisingly, a few species, including coelacanths, are monogamous, mating only with a certain partner and replacing that partner only if he or she dies. Still other marine species, including nudibranchs, are androgynous, possessing both male and female organs and having the capacity for mating with any other member of the same species.
There are many different factors governing the success of mating cycles. Variables include the availability of a compatible partner, favorable tides and currents, appropriate temperature, food availability, and the ability to mate in a safe, stress-free environment.
Turtles are experts at cyclical mating. These animals are slow to develop, reaching sexual maturity around age fifteen, and mating on a regular basis until at least age fifty. Marine turtles prefer isolated beaches, traveling thousands of miles in order to reach nesting grounds. Not only do they prefer to use specific areas, they come together during certain seasons, coming from all over with uncanny precision, guided by the moon and stars, the earth’s magnetic field, and other sensory input.
Once the turtles aggregate and have mated, the females look for good nesting sites beyond the high-tide mark. Using their flippers, they carefully dig deep pits approximately twice the width of their shells. After digging the pits, the turtles remain in place until after they have laid their eggs. This process can take anywhere from a few hours to a few days; however, once the egg laying begins, it doesn’t stop until all eggs have been deposited in the nest. Each female lays approximately 100 eggs in close succession to one another. After the eggs have been laid, the turtle covers them carefully, then makes her way back to the sea.
Turtles will leave their nests without covering their eggs if disturbed, which is one reason nesting beaches are closed to the public during mating season.
Approximately a month after eggs are laid, young turtles emerge and make their way to the ocean. During the long march to the sea, birds and other animals often feast on the young; in many places, humans intervene, protecting the baby turtles to ensure they make it into the water safely. While we try hard not to disrupt the natural order of things, it’s important to note that even though endangered turtles may lay 5,000 eggs or more during a lifetime, only a few offspring survive to adulthood.
These are just a few of the many stories the ocean has to tell about how marine species reproduce, but they’re among the most interesting. Knowing which strategies different creatures employ can increase our chances of stumbling upon fascinating behaviors while diving, so keep learning, and keep looking. The more you know, the greater your odds of witnessing new life in the making.
Comments
Informative and entertaining.