Tag Archives: Lateral line

Navigation: It’s Possible in a Featureless Ocean

Navigation is the ability for an organism to travel to a relatively precise target, generally at a considerable distance, without the need for familiar landmarks. It is an extraordinary feat requiring a variety of senses, techniques, and adaptions to allow for successful navigation. 

Humans and Sight

For humans, sight is the most commonly used sense to navigate. Tracing back a thousand years ago to traditional Polynesian cultures, people have been using the stars, specifically fixed stars, for tracking and to stay en route towards their destination. Nowadays, we have technological advances that aid us in navigation, like Google Maps, satellites, and compasses, but celestial bodies remain a constant and dependable asset. In addition to sight, different animal species have evolved specific senses to assist them in the open ocean.

Human Navigation 

Photo: http://www.hokulea.com/education-at-sea/polynesian-navigation/the-star-compass/ 

wayfinding

Photo: https://theconversation.com/how-far-theyll-go-moana-shows-the-power-of-polynesian-celestial-navigation-72375

Dolphins and Hearing

Some animals, such as dolphins, utilize their sense of hearing through a process called echolocation to navigate through the open ocean during times of low visibility. These animals produce high-frequency sound waves that echo back with information such as the direction they are traveling and the location of objects around them.

Echolocation

Photo: http://www.dolphinspotter.karoo.net/factecho.htm

dolphin pic

Photo: https://aqua.org/Experience/Animal-Index/atlantic-bottlenose-dolphin

Crabs and Taste

Crabs, who often live in dark and murky areas, need to be able to navigate to food sources. Crabs use chemoreceptors found on thin, short hairs of their inner antenna, call aesthetascs, which allow them to smell chemicals in the water released by their prey. They not only have a well-developed sense of smell, but have the ability to taste biomolecules in the water using specialized hairs on their mouthparts, pincers, and feet to detect prey. Their acute senses are so crucial to survival, that the majority of their brains are detected to processing scents and tastes!

green crab

Small hair-like appendages of the Green Crab that aid in prey detection by taste. 

Photo: https://wsg.washington.edu/crabteam/about/newsletter/2018-1/

Seabirds and Scent

For some seabirds like the Arctic Tern, the Wandering Albatross, or the Sooty Shearwater, navigation is no joke! Traveling thousands of miles for up to seven years at a time over a featureless blue ocean is quite a feat, requiring some fine-tuned navigational techniques. Studies have shown that many migratory birds use celestial navigation to determine North and Southward orientation, just like humans! But certain hypothesizes suggest that seabirds also use their sense of smell to create scent maps.  In a study where birds had their sense of smell blocked, the test group was less likely to find food sources and their nesting grounds, suggesting that olfactory navigation is a technique adopted by many seabirds!

wandering albatross

The Wandering Albatross has been observed to spend anywhere between 5-7 years at a given time at sea, making them expert navigators. 

Photo:  https://www.hbw.com/ibc/photo/wandering-albatross-diomedea-exulans/old-adult-male-flight-dorsal-view

arctic tern

The Arctic Tern has the longest migration of any animal, traveling from Greenland go Antarctic in a zig-zag route, resulting in over 40,000 miles traveled every year! 

Photo:https://www.npolar.no/en/species/arctic-tern/

Fish and Touch

The lateral line system is an extensive network of canals and sensory receptors that can detect disturbances in the water. The majority of fish species have this lateral line that assists in navigation by sensing pressure changes and providing spatial awareness to avoid underwater obstacles.  Some fish are able to use the lateral line as a type of sonar to feel the movement of water reflect off objects around it, which is especially useful in low visibility areas, such as the deep sea. 

Lateral lines

The lateral line consists of hundreds of superficial neuromasts, or sensory structures of cilia. Many of these neuromasts are embedded in lateral line canals open to their environment through pores that allows them to detect water movements.

Photo: https://www.trails.com/facts_8518_functions-lateral-line-fish.html

Sea Turtles and Magnetoreception

Magnetoreception, the sixth navigational tool illustrated in the video, is an animal’s ability to detect the Earth’s magnetic field in order to determine North and Southward orientation. Many invertebrates like mollusks and insects, as well as vertebrates like birds and sharks,  use this as a natural global positioning system when navigating long migration routes. One example, sea turtles, use magnetoreception as hatchlings when swimming out to the open ocean, and as adults when traveling towards specific feeding, mating, and nesting locations.

Magnetite is found in sea turtles as well as some bird and fish species. This iron mineral can tell animals their position on the globe as well as the direction they are heading. This explains why sea turtles can migrate all around the ocean and find themselves nesting on the same beach as their female ancestors.

compass turtle

Photo:https://www.sciencemag.org/news/2016/06/body-s-hidden-compass-what-it-and-how-does-it-work

Navigation Poles

Photo: https://webstockreview.net/image/field-clipart-campo/1087594.html

The open ocean can be a challenging place to navigate, but the animals that live there utilize their senses to the max in order to find food, avoid underwater obstacles, and be completely aware of their direction of travel.

Sources:

https://www.thoughtco.com/how-do-crabs-find-food-2291888

https://blogs.scientificamerican.com/thoughtomics/terrestrial-hermit-crabs-only-smell-their-favourite-snacks-when-water-is-around/

http://lohmannlab.web.unc.edu/magnetoreception/

https://www.cell.com/current-biology/pdf/S0960-9822(07)00819-6.pdf

https://www.wonderopolis.org/wonder/how-do-dolphins-use-echolocation

https://www.smithsonianmag.com/smart-news/seabirds-use-their-sense-smell-navigate-open-water-180964674/

https://www.ncbi.nlm.nih.gov/pubmed/21392273

Written By: Alyssa Backman, Kyler Mose, and Leanne Murray

Topsmelt: A Funny Kind of Baitfish

Snorkeling in the ocean is one of the most rewarding activities students engage in at CIMI. Jumping into the ocean to snorkel at night is a different experience altogether. Topsmelt earn their CIMI nickname, “giggle fish,” by helping students adjust to darkness through the element of surprise. This species lacks a lateral line, a common sensory system in bony fish used to detect changes in water pressure. Although topsmelt swim well in the daytime, they often smack into the unsuspecting bellies of nervous snorkelers at night, resulting in students giggling with amazement and relief.

Topsmelt (Atherinops affinis) are an elongate schooling fish that join jacksmelt and California grunion in a family commonly known as “silversides”. Topsmelt are also lumped in the colloquial group “baitfish,” because of their physical and behavioral likeness to other silver

schooling fish that are commonly used as bait by fishermen. It has been argued that topsmelt are split into as many as five subspecies, but this has been refuted in recent years thanks to genetic analyses. Unlike true smelts however, silversides do not swim in tight balls when they school because they use sight instead of water pressure to sense where other fish move. As their name suggests, topsmelt prefer to live near the top of the water column in order to feed on algae and zooplankton, small animals that drift with the ocean’s currents. Many topsmelt are opportunistic feeders, with some populations in southern Baja California preferring to feed on parasitic Grey Whale lice! They have two peak spawning periods in May and June and often spawn at night during a full or new moon.

This species is one of the most environmentally tolerant fish in the ocean. Topsmelt have been found from British Columbia, Canada through southern Baja California, Mexico in freshwater bays, brackish estuaries, kelp forests, piers, and offshore blue waters. They also thrive in evaporating salt ponds where the salinity is almost three times that of average seawater! Whereas most fish can only live in a narrow temperature range, the waters topsmelt live in range from 8 – 33ºC (46 – 91ºF). Topsmelt defy challenging conditions to reach a modest 14 cm in length and have a lifespan of 6 – 9 years. Their adaptability has made them a major player in eastern Pacific marine food webs.

Topsmelt have many defense mechanisms that protect them from a long list of predators (leopard sharks, cormorants, harbor seals, and many more). First, their slender body shape and forked tail make them an ideal endurance swimmer with the capacity for sprint bursts if distressed. Topsmelt can even be seen leaping from the water around sunrise and sunset when pursued by predators! Countershading, or light camouflage, allows topsmelt to blend into natural light patterns in the ocean. The contrast between darker blue/green dorsal scales and silver ventral scales allows the fish to hide in the ocean itself instead of using a physical barrier. An observer looking at a topsmelt would have difficulty picking out an individual fish from the darker ocean depths or brighter ocean surface because of countershading.

Like other baitfish, topsmelt use schooling behavior to create a large silver ball that distracts and confuses predators. It becomes difficult for a predator to pick out a single animal for a meal when fish swim close together and frequently change directions as a group. Schooling topsmelt take turns rotating between the outside and inside of the ball so that every animal has the same probability of relative safety and exposure. Topsmelt also use their silver scales to reflect light like a mirror back at predators. This behavior can stun predators and make a school of fish appear larger than what they really are—a collection of small animals.

Topsmelt populations are thriving in our changing oceans and are categorized as “Least Concern” on the IUCN Red List. They are not a popular commercial fishery despite a small following of fisherman who prefer to use topsmelt over other baitfish like sardines or anchovies. Their incredible tolerance for temperature and salinity variation distinguishes them from other fish that can only live in a narrow range of environmental conditions. However, the preferred food sources that topsmelt consume and the habitats that topsmelt use to lay eggs and raise their young are not as tolerant. With oceans becoming hotter and more acidic, it is unclear how the topsmelt will be impacted in future years. Topsmelt are also threatened by bioaccumulation, the process of building up toxins through consumption of primary producers. Eventually, the effects of toxins become magnified relative to the animal’s mass and can have negative impact on juvenile development or metabolic functions. The topsmelt’s wide distribution and environmental adaptability make them a key species for scientists to check on habitat healthiness.

To learn more about topsmelt, check out this link below:

http://www.aquariumofpacific.org/onlinelearningcenter/species/topsmelt

To see how topsmelt are different from other popular baitfish, follow this link:

http://data.recfin.org/wiki/index.php/Smelt_and_Baitfish

Written By: Alyssa Bjorkquist

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