Spinner Dolphin

Human Interactions and Viewing Pressure

Viewing wild marine mammals in Hawaiʻi has been a popular recreational activity for both tourists and residents over the past several decades. We estimate that there are upwards of 70 tour operators that provide dolphin-directed tours focused on Hawaiian spinner dolphins. More than 100 commercial boat tour and kayak tour operations may opportunistically view these animals.

Tours operate out of various harbors along most of the coasts of the main Hawaiian Islands, bringing guests to well-known locations for spinner dolphin viewing. Researchers have observed up to 13 tour boats at a time in some locations, with vessels jockeying for position on a single spinner dolphin group and more than 60 swimmers in the water attempting to closely interact with the dolphins at once. In addition, a number of residents and visitors venture on their own, independent of commercial operators, to view and interact with spinner dolphins. Some operators and various media outlets have encouraged the expectation for close interactions with wild dolphins, and routinely promote close vessel or in-water encounters with the dolphins. This contradicts established wildlife viewing guidelines.

Commercial operators and individuals interested in viewing or closely interacting with Hawaiian spinner dolphins increasingly target the dolphins' essential daytime habitats. Encounters with dolphins in these areas are very common due to the predictability of spinner dolphin behavior. Viewing spinner dolphins in their natural habitat can be an educational and enriching experience if conducted safely and responsibly from a distance. However, closely approaching, swimming with, pursuing, interacting, or attempting to interact with the dolphins could disrupt their daytime behaviors. Some interactions with people in essential daytime habitats may disturb individual dolphins or resting groups, even rising to the level of “take” under the Marine Mammal Protection Act, which is illegal.

Response to disturbance varies among individuals, but ultimately diverts time and energy from fitness-enhancing activities (such as resting and recuperating after an energetically-costly night of foraging for prey). These responses may, over time, result in negative effects to the fitness of individuals or resident populations. For example, lack of consistent, undisturbed resting periods can reduce the amount of energy available for a spinner dolphin to engage effectively in foraging activities at night. Over time, this can result in overall poor body condition, which reduces the dolphin’s ability to fight off disease, protect itself from predators, successfully reproduce, or rear young.

Peer-reviewed scientific literature has documented disturbance responses by individual spinner dolphins, as well as changes to spinner dolphin group behavior patterns over time. Individual dolphin responses include:

• Increased displays such as leaping, spinning, or tail slapping when closely approached by vessels and swimmers.
• Avoidance behaviors, including increased swimming speed and moving away from swimmers and vessels, or leaving the bay completely in response to human pursuit.
• Aggressive behaviors directed at people, including charging or threat displays. 

Researchers have also documented changes to spinner dolphins’ behavior patterns in essential daytime habitats, including changes to patterns associated with aerial behaviors, residence times, and distribution within the habitat. Human-caused disturbances to daily behaviors may be incidents of 'take,' as defined (and prohibited) under the Marine Mammal Protection Act. The chronic nature of these problems in Hawaiʻi and the observed changes to behavioral patterns over time are a cause for concern for this dolphin population.

Marine Debris

Marine debris is a growing concern within the marine environment, as it poses multiple threats to the marine ecosystem. For instance, spinner dolphins may ingest (either directly or through prey items) or become entangled in marine debris. These interactions may cause:

• Drowning
• Debilitation
• Limited predator avoidance
• Internal or external wounds
• Skin lesions or sores
• Blockage of the digestive tract, resulting in starvation that often leads to death
• Reductions in quality of life and/or reproductive capacity
• Impairment of feeding capacity
• Introduction and/or concentration of damaging or toxic compounds to the animal

The severity of the effects of debris interactions on all dolphin populations remains unclear because many deaths likely occur undetected at sea

We do not have sufficient information to determine the severity of the threat of direct ingestion of large debris on spinner dolphin populations. Some data indicates that spinner dolphin prey species are consuming very small plastics. In 2010, researchers analyzed mesopelagic fish in the North Pacific Central Gyre and found that 35 percent of the fish—many of which were lantern fish (spinner dolphins’ main prey)—had ingested plastic. Larger fish generally had more pieces of plastic in their guts than smaller fish. We are particularly concerned about the ability for plastic debris to absorb organic pollutants that may be toxic to the marine organisms that ingest them. These contaminants can bioaccumulate as they move up the food chain to top predators such as spinner dolphins. Scientists have also found high levels of butyltin and organochlorine (chemical compounds found in some plastics) in migrating lantern fish species in the Western North Pacific, which may indicate a cause for concern for predators, such as spinner dolphins.

Human-Made Noise

Humans introduce sound intentionally and unintentionally into the marine environment. This could be from commercial and recreational ocean activities, navigation, oil and gas exploration and acquisition, research, and military activities. Spinner dolphins use sound to communicate, navigate, locate prey, locate predators, and sense their environment, which can be impacted by introduced anthropogenic noise How severely noise exposure affects dolphins and whales depends on factors including:

• Noise source
• Decibel level
• Distance between the source and the animal
• Characteristics of the animal (for example, hearing sensitivity, behavioral context, age, sex, and previous experience with sound source)
• Time of day or season (which affects how sound travels through the water)

In marine mammal populations, noise can seriously disrupt communication, navigational ability, and social patterns.

Disease

Spinner dolphins, like all marine mammals, can be susceptible to widespread disease. Outbreaks in spinner dolphins are not commonly reported, but scientists have previously detected serious diseases, such as toxoplasmosis and cetacean morbillivirus. Although the number of spinner dolphin deaths attributed to these diseases is fairly low (many are thought to be unreported), thousands of other marine mammal species have died from these diseases worldwide.