Protecting Deepwater Fish Populations in Hawaii

by Katie Huang

Starting in 1998, specific types of marine protected areas (MPAs) called bottomfish restricted fishing areas (BRFAs) were implemented throughout Hawaii to address conservation concerns over deep-sea species. Although much research has been conducted on how MPAs benefit shallow reef fish populations, less is known about how protection affects deepwater ecosystems. Sackett et al. (2014) studied four BRFAs of differing ages to determine whether relative abundance, mean length, and species richness of seven commonly exploited species varied when compared to unprotected regions. The authors took video surveys along the deep sea floor in both types of areas and counted the number and type of fish in each. They found that mean fish length increased for at least one species in nearly all BRFAs and that reserve effects were stronger in the more established MPAs. The oldest BRFA had higher percentages of mature fish than outside the area as well as potential spillover effects. The authors suggest that while further research should be conducted on the effectiveness of BRFAs, precautionary MPAs should be established in the meantime to protect deepwater populations.

Sackett et al. studied four BRFAs in the Main Hawaiian Islands that varied in how long they had been in effect. At 14 years, Ni’ihau was the oldest, while two others, Penguin Bank and Makapu’u, were classified as intermediately aged because they included both old and newly protected areas. Pailolo Channel was the youngest, having been instituted in 2007 briefly before the study began. In each of the BRFAs and in unprotected paired locations from May 2007 to June 2011, the authors set a baited stereo-video camera system approximately three meters above the seafloor and recorded 45 minute video segments. They then identified the different species observed and calculated relative abundance by counting the maximum number of each species observed in a single video frame. To determine whether populations had grown larger over time, they also classified fish lengths using the video footage. Biodiversity was measured by observing the number of seven commonly exploited species, known as the Deep 7, found in a single video. The authors ran seven models against these measures to determine whether factors such as type of habitat had significant effects on fish abundance, size structure, and species richness. They also compared the proportions of mature fish inside and outside of BRFAs by categorizing individuals as mature or juvenile based on their length.

Of the seven models, one consistently ranked best among the BRFAs and species. Among its explaining factors were protection, habitat, and the interaction between protection and sampling year. However, all of the models were negatively influenced by small sample sizes, which reduced the amount of analyses that could be run. Ni’ihau, the oldest BRFA, observed no significant effects for relative abundance data for all of the models, potentially due to the relatively fewer amount of areas where fish were found. Three of the Deep 7 species were found to be significantly larger than the fish outside the BRFA, and there were more mature fish inside for all but one species. They also found that there was greater species abundance in areas adjacent to Ni’ihau, suggesting the existence of spillover effects. Penguin Bank, one of the intermediate BRFAs, had a greater relative abundance for one species and larger mean lengths for four species. There were also more mature fish for three species in comparison with outside the BRFA. Maturity results were more mixed in Makapu’u, the other intermediate BRFA, but protection was an important factor for both areas in influencing fish abundance and length. In Pailolo Channel, the youngest BRFA, two species were larger inside the protected area and one also had higher species abundance, but maturity results were varied. The two intermediate BRFAs had more significant positive effects than Pailolo Channel, which is consistent with research that finds that MPA effects take about five years to appear within the population. In comparison, Ni’ihau had benefits not observed in the younger BRFAs such as higher proportions of mature fish and the potential spillover effects, suggesting that more established MPAs are more effective at protecting target populations. Overall, the authors found that mean fish length and sometimes abundance increased for at least one of the Deep 7 species in nearly all of the BRFAs, indicating that they are indeed effective in aiding the recovery of deepwater fish. However, they suggest that more research be conducted in order to better understand deepwater ecosystems, as there are many factors that can influence BRFA effectiveness. In the meantime, they advocate that a network of precautionary MPAs be established in order to prevent further exploitation.

Sackett D.K., Drazen J.C., Moriwake V.N., Kelley C.D., Schumacher B.D., Misa W.F.X.E., 2014. Marine protected areas for deepwater fish populations: an evaluation of their effects in Hawai’i. Marine Biology 161, 411–425. Full paper at:


1 thought on “Protecting Deepwater Fish Populations in Hawaii

  1. Katie,
    Very nice article! And thank you for highlighting our work in your blog. We have continued to monitor BRFAs and recently found that spillover has likely begun to develop in the most recent years for a number of these deepwater species.


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