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Dolphins with scars on their dorsal fins, mouth lines and bodies were studied using underwater images to detect possible interactions with fisheries and fishing gear in the Maui Nui area. . – Photo by the National Marine Sanctuary Foundation
Using imagery of the dorsal fin, buccal line and underwater body, a first for this type of study, the researchers found that the impacts of fishing activity on Maui Nui dolphins may be a more widespread problem than initially thought.
Researchers at the Pacific Whale Foundation conducted a study using new methods to assess the impact of local fishing interactions on dolphin populations in Maui, Molokai, Lanai and Kahoolawe.
“Dolphins play a key role in maintaining healthy oceans, which are necessary to regulate the global climate, and act as early indicators of unhealthy oceans,” Pacific Whale Foundation chief scientist and principal investigator Jens Currie said on Friday. “Understanding how sensitive dolphin populations are to human activities is necessary to enable appropriate conservation efforts. “
Currie co-authored a recent study with Abigail Machernis, Stephanie Stack, Grace Olson, and Florence Sullivan.
This study used long-term historical data from the nonprofit foundation on bottlenose and spotted dolphins, collected over a 24-year period, from 1996 to 2020.
Certain interactions with fishing gear can result in serious injury or mortality from entanglement or ingestion of gear, causing dolphin populations to decline. – Photo by the National Marine Sanctuary Foundation
“Studies like this, which aim to determine the extent of a particular threat, in this case interactions with fisheries, will help us determine where priority action is needed to conserve Hawaii’s dolphins,” said Currie.
Each image in the association’s photo ID catalog was also examined to identify dolphins with scars on dorsal fins, mouthlines and bodies that may indicate past interactions with fisheries and fishing gear in the area. the Maui Nui area.
The aim was to determine whether underwater body images, in addition to traditionally used dorsal fin and mouthline images, increased the discovery rates of fishing-related evidence.
Most population tracks are based on images of dorsal fins above water, which limits scar detections to the dorsal fin and a small area of the body surrounding it, Currie explained.
This new approach involves combining individual assessments of dolphins’ dorsal fins, mouth lines and body into a single assessment, which has increased scar detection rates to between 40 and 50 percent, he said.
“The use of underwater images provided us with a complete view of the dolphin’s body to look for evidence of interactions with fishing”, he added. “Without the images of the underwater body, we assume that the scars detected on the dorsal fins are indicative of the entire body, which we found was not and leads to an underestimation of scar detections. related to fishing. “
Machernis, a foundation research biologist and lead author of the article, looked at data collected from 255 bottlenose dolphins and 374 spotted dolphins.
“Using this new technique, we found that 27% of bottlenose dolphins and 13% of pantropical spotted dolphins in Maui showed signs of previous interactions with fishing,” he added. Currie told The Maui News.
The analysis of underwater photos was “A game changer”, Machernis said in a press release.
“Most of the research papers that look at interactions between fisheries focus on dorsal fins and we wanted to use all the data we collected to examine as many dolphin bodies as possible to look for evidence of gear-related scars. fishing. “ she said. “We strongly recommend that researchers interested in examining the threat of fishing interactions to dolphins make a concerted effort in the field to collect pictures of the mouth line and body above the water. , in addition to the underwater images. “
Around the world, interactions with fisheries resulting in fatal or non-fatal consequences are a major concern in cetacean conservation.
According to the foundation, the extent of the problem is difficult to assess because most entanglements are never observed. However, the International Whaling Commission has reported that more than 300,000 whales and dolphins die each year due to entanglement in marine debris, which can have a “Devastating and long-term impact on conservation” on populations already threatened.
The number of deaths in Hawaii is specifically “Very difficult to estimate with precision” Currie said, because most whales and dolphins that die at sea will sink to the bottom and never be recovered; very few end up stranded on the beaches.
Yet the Hawaiian Islands National Humpback Whale Marine Sanctuary, working with community partners, responded to 21 reports of humpback whale entanglements in 2018 across Hawaii, he noted.
“These responses concerned humpback whales still entangled in gear and do not represent whales and dolphins that become entangled and die at sea,” he said.
Past and ongoing research confirms that direct interactions between cetaceans and fishing gear typically occur when animals unwittingly swim in gear, become entangled or become entangled, or when animals intentionally attempt to remove fish caught in. gear, a behavior known as depredation, and become addicted and / or entangled as a result.
According to the foundation, certain interactions with fishing gear can result in serious injury or death from entanglement or from ingestion of gear.
These types of interactions occur on a global scale and are “Likely to increase” because of the potential for continued human activity in these habitats, Machernis said.
“Avoiding the initial interactions will be the biggest mitigating factor”, said Currie. “In view of this, additional outreach efforts that highlight best practices for avoiding interactions with dolphins while fishing and recommend appropriate actions to be taken if a dolphin is interacting with active gear is needed. “
Some examples to help reduce the risk include queuing up if dolphins appear in the area while fishing or changing locations if the dolphins are interested in the bait.
Foundation researchers concluded that the level of impact of fishing interactions on cetaceans is “Of great concern” and there is a major need to identify which species interact with which fisheries and the places where these interactions occur so that officials can work with fishermen to find sustainable solutions.
The organization recently published an article citing a declining population trend.
“Further research is needed to determine whether the observed rates of interactions with fishing are impacting Maui’s dolphin populations, given that the scars seen on otherwise healthy animals are the result of interactions not lethal with fishing gear, ”he added. said Currie. “We recently co-authored an article reporting a decline in Maui’s bottlenose dolphin population. These two articles together emphasize that we need to determine whether this is a fatal or non-fatal threat and better understand how our activities affect dolphins.
All Pacific Whale Foundation publications are available free at PacificWhale.org/research/publications.
To learn more or make a contribution to support the foundation’s dolphin research, visit PacificWhale.org/pacific-whale-foundation/.
* Dakota Grossman can be contacted at [email protected].
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