Sustainable Fisheries and Fishing Communities
The Center carries out extensive activities to monitor U.S. fisheries throughout the Pacific Islands Region, assess the status of exploited fish stocks, and provide scientific advice to fishery managers. Fish catch and fishing effort are monitored by Center staff in collaboration with local government partners in American Samoa, CNMI, Guam and Hawaii through the Western Pacific Fisheries Information Network. Research is conducted on fish life history and biology; mitigation of fishery interactions with protected species; fish population dynamics and stock assessment; economics and human dimensions of fisheries; and more. Substantial collaborative research on pelagic stocks is carried out through the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean. Monitoring information and stock assessments support the development and implementation of domestic fishery management plans for insular and pelagic fisheries through the Western Pacific Fishery Management Council. They also contribute to international management of fisheries for tunas, billfishes and other highly migratory pelagic fish through the Western and Central Pacific Fisheries Commission and the Inter-American Tropical Tuna Commission. During 2010, progress was noted in several areas:
Biological Studies Support Improved Bottomfish Stock Assessment
Knowledge of biological processes like growth, longevity and maturation is essential to reliable fish stock assessments. The Center has given priority to improving biological information for Hawaii bottomfish and in 2010 made notable advances for two important species, opakapaka and hapu'upu'u. Both are in the so-called 'Deep-7' group of bottomfish species targeted by commercial and recreational vessels in the main Hawaiian Islands under strict federal and State of Hawaii regulations. For many years, a fishery for bottomfish also operated in the remote Northwestern Hawaiian Islands. That area is now part of the Papahānaumokuākea Marine National Monument, and the bottomfish fishery there ended on January 1, 2010.
Recent research on opakapaka, or pink snapper, has improved knowledge of the species’ age and growth. In previous studies, scientists counted daily growth increments on otoliths (ear bones) to accurately determine ages of smaller opakapaka, but ages of large fish remained elusive. Using bomb radiocarbon dating and lead-radium dating, PIFSC researchers have extended the range of age determinations to include large specimens. The bomb radiocarbon method is based on a dated radiocarbon marker in growth bands of otoliths; the marker results from a pulse of radiocarbon produced through atmospheric testing of thermonuclear devices during the 1950s and 1960s. Accordingly, bomb radiocarbon dating currently allows accurate ageing of opakapaka up to about 53 years. The lead-radium dating method, based on the decay of radioisotopes, is less accurate but can be applied to fish up to 100 years old. Both methods have provided firm evidence that opakapaka have a lifespan of 40+ years, more than double the longevity previously assumed. Augmented by additional samples, these results will be combined with other reliable opakapaka age determinations to develop an improved age and growth model for stock assessment. Results will be prepared for publication in a peer-reviewed journal. Following the opakapaka research, both lead-radium and bomb radiocarbon dating will be used to study age and growth of two other bottomfish species, ehu (squirrelfish snapper) and hapu'upu'u (Hawaiian grouper).
For the hapu'upu'u, recent studies have advanced our understanding of the species’ sexual development and maturation. PIFSC scientists extracted gonads from more than 600 hapu'upu'u caught during research cruises or provided to the Center by cooperating commercial fishermen. The specimens were collected on reefs and banks of the Northwestern Hawaiian Islands from the late 1970s to the present and during all seasons of the year. Tissue samples from the gonads were studied under a microscope to determine the gender and state of maturity of the fish. Both males and females were identified among large adult specimens. But among immature and small specimens, only female or bisexual fish were found; there were no males. The data strongly indicate that hapu'upu'u in the Northwestern Hawaiian Islands begin their life as females and that after reaching maturity, some females become males (biologists refer to such organisms as "protogynous hermaphrodites"). Among adults, there are more than 5 females to each male. Data on size of females and condition of their ovaries showed that the proportion of mature females increases with size, reaching 50% for fish of about 58 cm body length; this is an estimate of average size at first sexual maturity. At an average body length of about 90 cm, at least some mature female hapu'upu'u transition to mature males. Data on gonadal state and reproductive activity showed no change in the size of testes with time, but the average size of ovaries in relation to fish body weight changed seasonally, indicating a spawning period of February–June for the fish studied. The results of this research, limited to hapu'upu'u in the Northwestern Hawaiian Islands, were recently published in the peer-reviewed journal Fishery Bulletin. Further studies are needed to determine whether fish in main Hawaiian Islands exhibit the same characteristics. A full understanding of hapu'upu'u reproductive biology across the entire archipelago is essential for reliable stock assessment and fishery management.
New Assessment Research Shows Decline of Striped Marlin in the North Pacific
In the North Pacific, striped marlin is a valued catch of several commercial pelagic longline fleets and recreational troll fisheries. Assessments of the North Pacific striped marlin stock are carried out by the Billfish Working Group of the International Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) whose members include Canada, China, Mexico, Japan, Republic of Korea, Taiwan and the U.S. Within the working group, scientists have assembled the best available fishery data from the multinational fleets, reviewed current biological information on billfish species, and assessed changes in stock size and productivity under different assumptions about stock dynamics, taking into account information uncertainties. However, a full assessment has been problematic because the group has not yet adopted biological reference points for determining striped marlin stock status, such as those based on maximum sustainable yield (MSY); MSY-related reference points are currently used in management of Pacific tuna stocks. In addition, the group has lacked a comprehensive analytical framework to evaluate the full range of alternative assumptions that can affect the stock assessment and determination of stock status. In 2010, PIFSC members of the working group established such a framework. Then they used it to study uncertainties in the striped marlin stock assessment and evaluated the stock status in terms of MSY-based reference points.
A key uncertainty in the assessment concerned the resilience of the stock as measured by its ability to generate a sufficient number of young fish, or recruits, when the adult spawning stock is reduced to low levels; a more resilient stock is able to sustain a higher level of harvest and rebuild more quickly. The ISC working group had identified 2 possible stock-recruitment scenarios, which they considered equally plausible. The first scenario assumed that the annual number of recruits was dependent on size of the spawning stock as described by a Beverton-Holt model with moderate resilience: when the spawning stock was reduced to 20% of its maximum average level, it was assumed to produce 30% fewer recruits than it would at maximum stock size. Under the second scenario, the stock was assumed to be highly resilient, with recruitment fluctuating randomly around a constant level, independent of spawning stock.
Under each stock-recruitment scenario, the PIFSC team generated 40-year time series (1965-2004) of spawning stock size and associated recruitment, using the Stock Synthesis statistical model (SS2) on which ISC striped marlin stock assessments are based. Then to determine the status of the striped marlin stock, they used the two sets of SS2 output data as input to a Bayesian age-structured production model, SRFIT, which calculated MSY-based biological reference points. In this post-hoc analysis, the production model was applied in 4 different configurations, taking into account uncertainties in various aspects of model structure and other technical matters. Each candidate model was run under each of the 2 stock-recruitment scenarios, producing 8 alternative determinations of stock status relative to the MSY-based reference points. Instead of assuming a single one of the candidates was correct and basing the stock status determination on that premise, the PIFSC scientists took a more sophisticated approach. For each stock-recruitment scenario, they combined results on stock status from the candidate models using Bayesian model averaging. Then they derived the most probable overall results by simply averaging over the two stock-recruitment scenarios, taking into account the equal plausibility of each scenario. Further analysis showed that conclusions on stock status, and most other post-hoc results, were not sensitive to the scenario plausibility assumptions.
The scenario-averaged results revealed an interesting history of spawning stock biomass. Abundance of the spawning stock declined threefold from 1950 to the late 1960s, followed by a brief but temporary return to the high levels of the early 1950s. Since the early 1970s, though, the stock has steadily declined to very low levels. Spawning stock biomass for 2004, the most recent year for which comprehensive Pacific-wide data were available, was estimated at only 36% of the average stock level needed to support maximum sustainable yield. Moreover, scenario averages of relative fishing mortality showed that fishing mortality has exceeded the MSY level for decades and as of 2004 was almost 3 times higher than the MSY level; overfishing is clearly occurring. These conclusions take into consideration the best available data, a broad range of uncertainties, and a weighing of reasonable beliefs about the underlying model.
This research on the North Pacific striped marlin stock assessment was published in the Canadian Journal of Fisheries and Aquatic Sciences in 2010.
Compliance with Bigeye Tuna Catch Limit Ensured by Careful Catch Monitoring
In the western and central Pacific Ocean (WCPO), bigeye tuna are harvested by international fleets of open-ocean vessels using longline gear or purse seines, and coastal island fleets using various small-scale gear. Although the impact of individual fleets varies widely, the aggregate impact of all fleets on the bigeye stock is great. Catch data used to monitor the harvest and assess fishery impacts are collected by the Central and Western Pacific Fisheries Commission. On the advice of its Scientific Committee, the Commission has determined that overfishing of the bigeye stock is occurring — the aggregate fishing mortality exceeds the level that would produce MSY. Accordingly, the Commission enacted conservation measures to reduce fishing mortality in the form of bigeye tuna annual catch limits and other measures. For the U.S. longline fleet, based primarily in Hawaii, the WCPO bigeye catch limit in 2010 was 3763 metric tons. To ensure the U.S. did not exceed the limit, PIFSC scientists carefully monitored the catch by U.S. longline vessels throughout the year. By analyzing data from the current fishing season, historical data, and other information they estimated the date when the U.S. longline fleet’s bigeye tuna catch in the WCPO would reach the established catch limit. They updated the estimates frequently and issued forecasts to NMFS fishery managers and the public on NOAA websites. Given this information, NMFS was able to issue timely regulations to curtail WCPO catches of bigeye tuna by U.S. longliners on November 22, 2010, enabling the U.S. to comply with the WCPFC conservation measures.
Center Hosts Workshop on Economics of Catch Shares
In early 2010, PIFSC hosted a national workshop on the economics of catch shares in response to NOAA’s recent policy to encourage use of catch shares as a fishery management tool to end overfishing and rebuild fisheries and fishing communities. Currently, no catch share programs have been established in the Pacific Islands Region. The objective of the workshop was to explore potential roles, goals, limitations, and design characteristics of management programs based on catch shares (such as individual fishing quotas, individual tradable quotas, and other schemes) in the context of Pacific Island Region fisheries. Held at the Hawaii Imin International Conference Center on the University of Hawaii’s Manoa campus, the workshop featured 20 invited speakers including leading economists and social scientists from the U.S., Canada and New Zealand. Participants included researchers from PIFSC, government fisheries managers, and experts from the Western Pacific Fishery Management Council, the NOAA Fisheries Pacific Islands Regional Office, and the University of Hawaii. Workshop discussions allowed participants from the Pacific Islands Region to express their concerns and requirements for catch share programs in a setting where the invited guests could suggest possible alternatives to meet those needs. A report of the workshop proceedings will be issued soon.