Assessing Cause and Effect with Data in Hawaii’s Aquarium Fishery

Swarms of butterflyfishes, tangs, and other reef fishes appeared throughout Hawaii. (Image: Pauline Fiene)

Swarms of butterflyfishes, tangs, and other reef fishes appeared throughout Hawaii. (Image: Pauline Fiene)

Yesterday I reported on the 2015 commercial northern shrimp fishery moratorium in New England, an event where ocean warming, rather than poor fishery management, is likely responsible for fishery collapse. Today, I want to take a look at Hawaii, where anti-aquarium fishery advocates have argued that El Niño, not fishery management, is responsible for an exceptionally large fish recruitment event this past summer. Both of these situations show that, while adaptive fishery management is essential, larger forces having nothing to do with fishing effort can ultimately have the most significant effects of all on fisheries.

Conjecture about Causes 

In the current issue of Coral Magazine, which should be arriving in people’s mailbox right around now, I take a follow-up look at a piece I wrote in late August about a far larger than usual number of young fishes showing up on Hawaii’s reefs. Following this exceptional spawning and recruitment event, there was (and continues to be) a lot of conjecture and speculation about what caused it. While the spawning event was not restricted to fishes targeted in the aquarium fishery, it will not surprise readers familiar with my work to learn that the extremes on both sides of the debate over Hawaii’s aquarium fishery sought to use the event to bolster their case.

Some advocates of the aquarium fishery claimed the exceptionally high recruitment of young fishes onto Hawaii’s reefs was a direct result of the Fish Replenishment Areas (FRA), which were established along the Kona coast of the Big Island in response to concerns over the aquarium fishery. The FRAs are areas where no aquarium fishing is allowed, and they currently represent more than 30% of the coastline in the West Hawaii Fishery Management Area (WHFMA). The WHFMA is Hawaii’s single largest aquarium fishery. Some fishery advocates claimed the recruitment event proved fishery management was working and that the fishery was clearly sustainable.

Some anti-aquarium fishery advocates took a different tact, not wanting to conceded fishery sustainability, nor that the FRAs are having the positive effect that has been shown recently in the scientific literature. They emphatically stated the recruitment event had nothing to do with the FRAs and was instead tied to El Niño. They further stated that even with spikes in recruitment secondary to other El Niño events, iconic yellow tang (Zebrasoma flavescens) are still less abundant in West Hawaii owing to poor fishery management and overfishing for the aquarium trade.

As is so often the case in the heated debate over Hawaii’s controversial aquarium fishery, the truth is somewhere in between the extremes. As for the claims that FRAs were responsible for the high recruitment, there is no data so far presented to support that claim. Dr. William Walsh, an aquatic biologist with Hawaii’s Department of Land and Natural Resources’ (DLNR) Division of Aquatic Resources (DAR), says, “There’s a lot of interconnectedness of potential factors which might produce highly successful recruitment.”

Dr. Walsh points to a plethora of favorable biological and oceanographic conditions such as sufficient food and breeding population size, low predation and disease, and currents that move larval fishes to good settlement sites. Might the FRAs have played a role? Sure. But no scientist is saying they are the reason for the recruitment event.

Remarkable Recruitment Not Linked to El Niño 

Running Three-Month Mean ONI Values Show Hawaii was not experiencing an El Nino event.

Running Three-Month Mean ONI Values Show Hawaii was not experiencing an El Nino event.

When it comes to claiming El Niño caused the extraordinarily high recruitment, as the leading anti-aquarium fishery group in Hawaii claimed, the extant data show a different story. For the Fishes stated on the group’s Facebook page, “Supporters of the AQ trade, including scientists, want people to think this summer’s large numbers of baby fish are a result of Hawaii’s no-take AQ areas. Nothing could be further from the truth. It’s an El Nino event.”

But this assertion does not square with the available data. The Oceanic Niño Index (ONI), a primary indices used to monitor the El Nino-Southern Oscillation (ENSO), shows Hawaii is not currently experiencing an El Niño event. The ONI is calculated by averaging sea surface temperature anomalies in an area of the east-central equatorial Pacific Ocean. Also, a 3-month time average is calculated in order to better isolate variability closely related to the ENSO phenomenon. Dr. Walsh points to the running 3-month mean ONI values. “For all of 2013 and most of the spring of 2014,” he says, “water temperatures in the analysis area have been cooler than normal.”

There is a general consensus that a weak El Niño may develop this autumn and continue into early 2015. The likelihood is pegged at around 60-65 percent, but this is months after the large numbers of recruits settled onto Hawaii’s reefs.

“Claiming that an El Niño is the sole or primary reason for this spring-summer’s robust recruitment doesn’t have much basis in fact,” says Dr. Walsh.

Yellow Tang Abundance and El Niño

Anti-aquarium fishery advocates used the recruitment event as an opportunity to once again make a claim about yellow tang abundance that is not supported by the data. In addition to erroneously attributing this summer’s remarkable recruitment to an El Niño event, For the Fishes also states that the most recent El Niño events did not increase yellow tang populations. “Most importantly,” the group states, “yellow tangs are less abundant despite those huge prior boosts.” For the Fishes cites El Niño events in 2002 and 2009, but as Dr. Walsh points out, these were both weak El Niño years. He also adds that there were weak El Niño events in 2004-05 and 2006-07.

Based on recent research (Fox et al 2012), Dr. Walsh says correlation between recruitment totals and ONI is not as straightforward as one might think. In one study, Dr. Walsh and his colleagues found that, when combined, the five species studied (Zebrasoma flavescens, Ctenochaetus strigosus, Acanthurus nigrofuscus, Chaetodon multicinctusand Thalassoma duperrey) “showed no statistically significant correlation between recruitment totals and the Oceanic Niño Index.” When the species were examined individually, however, yellow tang did show “a significant positive correlation between recruitment and the presence of El Niño.” He acknowledges this finding is counter to others’ descriptions of decreased larval supply during warmer periods.

“It’s by no means clear that an El Niño should be expected to enhance coral reef fish recruitment,” concludes Dr. Walsh, but at the same time, yellow tang have appeared to benefit from El Niño events. Why? “El Niño events are known to influence regional trade winds and cyclonic activity,” explains Dr. Walsh, “which can influence ocean currents and thus recruitment dynamics.” The exact mechanism remains unknown, but it’s possible ocean currents resulting from El Niño events may be having a significant effect on recruitment dynamics for yellow tang.

Are Yellow Tang Really Less Abundant?

Overall Change in Yellow Tang Abundance in FRAs, Marine Protected Areas (MPAs) and Open Areas Where Aquarium Fishing is Allowed

Overall Change in Yellow Tang Abundance in FRAs, Marine Protected Areas (MPAs) and Open Areas Where Aquarium Fishing is Allowed

For the Fishes asserts that even with El Niño “boosts” in 2002 and 2009 (clearly seen in the figure shown here), “yellow tangs are less abundant despite those huge prior boosts.” The message is clear: the yellow tang fishery is unsustainable and nobody should be touting this summer’s phenomenal recruitment to assuage fears of fishery unsustainability.

Largely because of the controversy surrounding the fishery, fishery managers and biologists like Dr. Walsh have the data to be able to assess For the Fishes’ claim. So is it true? Are yellow tangs now less abundant despite previously strong El Niño-driven recruitment years?

“This is definitely not the case,” says Dr. Walsh. The data show yellow tang populations have increased by 10 percent in marine protected areas (MPAs) and 65 percent in the FRAs between 1999 and 2013. While open areas in the fishery do have fewer yellow tang, Dr. Walsh says there has been no significant decrease of yellow tang in these areas over the same time period. While yellow tang remain the driver of the West Hawaii aquarium fishery with the species representing 84 percent of the overall aquarium catch in 2014, yellow tang populations appear to be sustainable.

“In terms of total estimated West Hawaii population of yellow tang in the depth range where the survey sites are located,” says Dr. Walsh, “there has been an overall increase of more than 1.3 million fish.”

Read the full story about this summer’s remarkable recruitment event in the November/December issue of Coral Magazine.


About Ret Talbot

Ret Talbot is a freelance writer who covers fisheries at the intersection of science and sustainability. His work has appeared in publications such as National Geographic, Mongabay, Discover Magazine, Ocean Geographic and Coral Magazine. He lives on the coast of Maine with his wife, scientific illustrator Karen Talbot.
This entry was posted in Global Climate Change, Hawaii, Ornamental Fisheries, Overfishing and tagged , , , , , , . Bookmark the permalink.

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