Aquatic News: October 2019

October has been another eventful month in our watery world. If you're an aquarium keeper, it turns out you could be the key to saving several species of freshwater fish. Florida has been hit with its second red tide of this year. We have the good news that dolphins are living in the Potomac River, and the bad news that whales are living in the Great Pacific Garbage Patch.

A new initiative to save fish from extinction

Freshwater fish are a highly diverse group, but they are also the most threatened of the vertebrates. Many species go extinct before conservation efforts can even begin.

A recently published study by Dr Jose Valdez, of Aarhus University, and Kapil Mandrekar, of SUNY College of Environmental Science and Forestry, has shown that aquarium hobbyists can play an important role in freshwater fish conservation.

In some cases, dedicated hobbyists are actually more knowledgeable on certain species than the scientific community due to their hands on experience with the fish. In fact, some species that have not yet been scientifically described are already well-known to hobbyists. When these hobbyists are able to share their knowledge, they can make a real difference and have already helped discover new species and save others from extinction. Some have even provided individuals from their own aquariums to conservation efforts.

The largest organisation coordinating such conservation programmes is the CARES (Conservation, Awareness, Recognition, Encouragement, and Support) preservation programme. It encourages hobbyists to keep the most endangered (or even extinct in the wild) freshwater fish species to ensure their survival. In many cases, these species would have been otherwise overlooked by conservation efforts.

Valdez and Mandrekar found that CARES listed almost 600 freshwater fish species, over 80 of which are unknown by the scientific community. There are also more than 30 species included that are already extinct in the wild.

As it turns out, many of these species are only still here because of hobbyists breeding them in their aquariums. With that in mind, collaboration between scientists and aquarium hobbyists could prove to be a real turning point for the effective conservation of freshwater fish.

Further reading

Deadly red tide returns to Florida

Example of a red tide, this one in La Jolla, California

A new red tide began in Florida in early October. Samples of water taken off the shore of Collier County showed high concentrations of Karenia brevis, the toxic algae responsible for this nasty phenomenon. It also kills marine life and can cause respiratory problems in humans, both of which have been recorded in the affected area.

The locations currently affected include Barefoot Beach, Naples Bay, and around the Gordon River. The species most affected by the toxicity so far has been mullet (of the family Mugilidae).

The last red tide in this area cleared up just eight months ago and, at 15 months in duration, it was the longest lasting red tide in decades. It began in November 2017 and ended in February of this year. Thousands of fish, turtles, and marine mammals were killed and all three of Florida's coasts were affected.

This current red tide is, so far, only affecting the southwestern coast. It is not known how long it will last or how far it will spread as these things are difficult to accurately predict. Hopefully, it won't be as long, or as destructive, as the previous red tide.

Further reading

Dolphins have returned to the Potomac

Dolphins were once common in the Potomac River in the 1800s but, by the 1960s, it was so badly polluted that they could no longer survive there. So they moved on.

This kickstarted 50 years of cleanup efforts that have finally paid off as there are now around 1,000 bottlenose dolphins (of the genus Tursiops) living in the river. Even better, one dolphin was seen giving birth there back in August. The fact that dolphins are now choosing to reproduce and raise their young in the Potomac is a really good sign for the improving health of the river. Long may it continue.

Further reading

Whales are living in the Great Pacific Garbage Patch

The Great Pacific Garbage Patch is the largest accumulation of ocean plastic in the world. It is located between Hawaii and California, where ocean currents to form the North Pacific subtropical gyre. There is a shocking 80,000 tonnes (or 88,000 US tons) of plastic in this patch.

A survey of the area has found that there are, in fact, whales and dolphins living there, some with calves. This could prove to be very dangerous for them.

As you are probably aware, ocean plastic is a significant issue for marine life. There are more and more reports in the news of whales washing up dead after accidentally swallowing plastic waste. For example, in Indonesia, a sperm whale (Physeter macrocephalus) recently washed ashore with a whopping 115 drinking cups, 25 plastic bags, plastic bottles, two flip-flops, and thousands of pieces of string in its stomach. It's an issue of great concern.

The most common debris found in the Great Pacific Garbage Patch is ghost nets, which is fishing gear that has been discarded or lost. They can drift for years, trapping marine life. Whales and dolphins can easily become ensnared in these nets and their calves are especially vulnerable.

The findings of this survey should be a real wake-up call to clean up the area. It needs to be made safer for the whales and dolphins living there and efforts must be made to protect marine life as a whole. If we don't act soon, we will simply continue to see reports of dead whales on the news for the foreseeable future.

Further reading

The Weird and Wonderful: Endothermic Fishes

There are certain things about the animal kingdom that we are taught are absolutes. Birds fly. Reptiles have scales. Fish are cold-blooded. But, if you're anything like me, it's the exceptions to these rules that you'll find the most fascinating. Which is why I'd like to take some time to talk about endothermy, where heat is generated and maintained from within, in fishes.

The vast majority of fish species are ectothermic, which means their body temperature is largely controlled by the environment around them. As a result, their internal temperature can vary greatly and they don't have much physiological control over this. But, despite how it sounds, it's actually an advantage.

Water acts as a heat sink and tends to drain heat from anything it is in contact with, including living organisms. Due to a fish's gills, its blood is constantly in near direct contact with this heat-draining environment. With that in mind, it makes sense that a fish would not have the means to use its metabolism to warm up internally. It would be a massive waste of the fish's energy. It is far more efficient to rely on external factors instead.

But that's not the case for all fishes. Some have physiological mechanisms that enable them to be at least partially endothermic.

Tunas, swordfishes, and certain species of shark, such as the salmon shark (Lamna ditropis), are able to maintain body temperatures warmer than the surrounding water. They generate heat with their powerful swimming muscles, which they can then use to stay warm. For example, bluefin tuna (Thunnus thynnus) is able to maintain muscle temperatures of between 27 and 32°C (82 to 91°F) in waters of around 7 to 25°C (45 to 80°F).

Atlantic sailfish (Istiophorus albicans) mid-leap

Large, predatory billfishes, such as marlins, swordfishes, sailfishes, and spearfishes, are able to use the heat that they generate from swimming to warm their brain and eyes. This serves them well when they are hunting as it allows them to function efficiently and effectively in the deeper waters where they catch their prey.

Many sharks, including the great white (Carcharodon carcharias) and shortfin mako (Isurus oxyrinchus), also have a large vein that helps to warm the central nervous system (CNS). It does so by transporting blood from the swimming muscles to the spinal chord, keeping the nervous system in good working order at a functional temperature. This, again, serves them well when hunting in deeper waters where the temperature is lower.

Great white shark (Carcharodon carcharias)

The only truly endothermic fish that we currently know of, as in one that is fully warm-blooded, is the opah (of the family Lampridae), of which there are two living species. It can maintain its body temperature above the surrounding water temperature. They are found in tropical to temperate waters and swim at depths between 50 and 500 m. They are able to generate heat by constantly flapping their pectoral fins and retain this heat within their layers of fat, which acts as insulation.

An opah, of the species Lampris guttatus, in a rather unfortunate position

However, in 2015, it was discovered that opah also possess a rete mirabile, a specialised system of arteries and veins, within their gill tissue. This rete mirabile is found in several warm-blooded vertebrates and it allows for countercurrent heat exchange, where warm blood is carried from the heart and, in the case of the opah, warms the veins in the gills, which are carrying colder blood. In the reverse, the gills are also able to be cooled by contact with the surrounding water.

So, as you can see, what we think of as fact doesn't always line up with what is actually true. Not all fish are cold-blooded, and those that defy the norm each have their own way of warming the blood. Each method has been developed over time to suit the individual species, their lifestyle, and the habitat they live in. And, though each method is different, they are all effective in their own right.

The diversity of fishes is truly remarkable, as is the diversity of the animal kingdom as a whole. Life is so much stranger than we could ever possibly imagine. I will be covering more Weird and Wonderful creatures on the blog in the future, focusing on nature's oddballs and all the animals that dare to be different!

Species Spotlight: Vaquita

The oceans and seas are filled with a stunning variety of creatures that are unlike anything you will see on land. Every individual species is interesting in its own way and I intend to highlight what makes each one stand out with my Species Spotlight. In this instance, we'll be looking at the vaquita (Phocoena sinus), a magnificent marine mammal and one of the world's most endangered animals.

Vaquita (Phocoena sinus)

Description

The vaquita, meaning "little cow," is a species of porpoise and, as such, belongs to the family Phocoenidae. It is the smallest of all the cetaceans, measuring an average of just 1.37 m (4.5 ft) in length. On top of that, they are not particularly heavy, weighing just 54 kg (120 lb), which is a similar weight as your average 12-year-old human.

They are easily distinguishable from dolphins and other porpoises by the iconic dark markings around their eyes and mouth. The rest of their body is grey, dark on the back and fading to white on the underside. This is a typical example of countershading, allowing the vaquita to blend in with their surroundings both from above and below. They have a smaller skull and shorter rostrum (or beak) than other porpoises, which gives their face a very distinct appearance.

Habitat

The vaquita is the only porpoise species that is found in warm waters, though they are able to tolerate significant changes in temperature. They live in shallow lagoons in the northern section of the Gulf of California, the marginal sea that separates the Baja California Peninsula from mainland Mexico.

Northern-most area of the Gulf of California, where vaquitas can be found

They rarely venture any deeper than 30 m (100 ft) but their general depth range is between 11 and 50 m (36 to 160 ft). They are not often found in the open sea and generally stick to the coastline, between 11 and 25 km (6.8 and 16 miles) from the shore. They prefer murkier water as it has a high nutrient content, which attracts more prey.

Diet

Vaquitas are non-selective predators. They forage around the lagoons within their natural habitat and will eat fish, crustaceans, octopus, and squid. They're really not picky; though, based on the stomach contents of deceased individuals that have been recovered, some of their favourite prey items appear to be grunts, croakers, and sea trout.

A school of grunts (family: Haemulidae), a favourite meal of vaquitas

Vaquitas hunt alone, searching along relatively shallow waters within the lagoons. Like many other cetaceans, they use echolocation, emitting high-pitched sounds that bounce off their surroundings and allow them to navigate. It is thought that they may also use this echolocation to locate their prey, following distinctive sounds to find a particular fish with astounding accuracy.

Reproduction

Vaquitas are less social than other porpoises and are typically solitary animals. Or, at least, they are until the mating season hits in late spring or early summer. During that time, they come together and can become quite competitive when it comes to finding a partner.

The females are larger than the males, with the former being around 1.41 m (4.6 ft) in length and the latter 1.35 m (4.4 ft). In terms of their life cycle, vaquitas are estimated to live for about 20 years and mature between the ages of 3 and 6, at which point they are able to reproduce.

Statue of vaquita mother and calf at San Juan de Aragón Zoo, Mexico City

The gestation period of a vaquita is between 10 and 11 months, so they usually calf in March. The calf will typically weigh around 8 kg (17 lb) at birth and measure just 71 to 78 cm (28 to 31 inches) in length. They are nursed for around 6 to 8 months until they are able to fend for themselves and, at that point, will begin to live independently. The amount of time between calves, when the female is able to reproduce again, is usually around 1 to 2 years.

Biggest Threats

The vaquita is currently the most endangered cetacean in the world and has been listed as critically endangered on the IUCN Red List of Threatened Species since 1996. In 2018, it was believed that there were only between 6 and 22 of the porpoises left. The latest estimate, from July 2019, has concluded that there are now only 9 vaquita porpoises remaining.

The biggest threat to the species comes from illegal gillnet fishing of totoaba (Totoaba macdonaldi), where the vaquita is often caught and killed as accidental bycatch. A gillnet ban was put in place in 2015 but it made no difference and the vaquita population continued to decline at a rate of almost 50% each year.

Fish caught in a gillnet

Poaching is also a major concern, with fishermen going out at night to avoid the consequences of illegally catching protected species. It is believed that some fishermen even kill vaquitas deliberately as they are seen as competition in hunting for fish. It is difficult to estimate the extent to which these issues have impacted the vaquita population but they have, without a doubt, contributed to the species' decline.

It has now become necessary to implement a captive breeding programme and protective housing for vaquitas in order to save the species. However, their ability to survive and reproduce in captivity is uncertain and, so far, all attempts have failed. Unfortunately, it may already be too late for this little porpoise.

My sketch of a vaquita (photographs are hard to come by)

To end on a brighter note, the remaining vaquita do appear healthy and are able to breed. But, to ensure these beautiful and fascinating creatures are able to survive (and, better yet, thrive), we must seriously intensify our efforts to protect them and their habitat, and to crack down on illegal fishing activities.