Fishery Management Methods: Are Sustainable Fisheries Possible?
A PFC White Paper
The Pacific Fisheries Coalition (PFC), with support from the PEW Charitable Trusts, the Harold K. L. Castle Foundation, and the Marisla Foundation represents a unique collaboration between conservationists and fishermen who find common ground in their desire to promote the conservation and responsible use of living marine resources in Hawai`i and the Central and Western Pacific.
This white paper was drafted by Bob Endreson, President of the Hawai`i Fishermen's Foundation, William Aila, Hawaiian fisherman and Harbor Master of the Wai`anae Small Boat Harbor and Linda Paul, Executive Director for Aquatics, Hawai`i Audubon Society, with the assistance of the Division of Aquatic Resources.
Fishery Management Methods
A Case Study: the Bottom Fishery
Bottom fishing in and around the main Hawaiian Islands is a long tradition, one that was fading with the decline of some fish species such as onaga and ehu. Although some fishermen contended there are just as many fish as there once was, others admitted they had to fish more to catch less and the fish are smaller. Scientists and fishery managers felt action was necessary to prevent further decline in the bottomfish stocks in the main Hawaiian Islands.
Fishermen who harvest bottomfish include full-time commercial operators and part time recreational and subsistence operations. Approximately 1,000 vessels report they sell a portion of their catch during the year. The non-reported catch (including recreational catch) is thought to equal the reported catch.
The Management Framework
Overfishing and loss of habitat are the primary causes for the decline in Hawaii's fisheries. In 1995, the State Division of Aquatic Resources (DAR) formed a broad-based Fishermen's Advisory Panel (Panel) to help develop a comprehensive management plan for the depleted bottomfish fishery around the main Hawaiian islands. The Panel recognized the need to control fishing effort and raise the spawning potential ratios of the stocks at risk.
Under the provisions contained in Hawai`i's Bottomfish Fishery Management Plan (FMP) a Bottomfish Plan Team performs an annual review of the fisheries and status of the stocks each year. It's a complicated science, but based on the best information available to the team members, the Plan Team must determine the size of the bottomfish stocks in the main Hawaiian Islands. Some of these indicators include Catch Per Unit of Effort (CPUE): each hook placed in the water equals one unit of effort. If it takes more and more hooks to catch the same amount of fish the catch per unit of effort is going down and this indicates that there are fewer fish out there to catch. How do they determine how many hooks it takes to catch one fish? Fishermen help provide this important information by maintaining logbooks and turning in catch reports. In the mid 1990s the CPUE for onaga and ehu fell below 50% of what is was in 1986.
Maximum Sustainable Yield (MSY) is the largest annual catch of a particular species that fishermen can take continuously without over fishing it. The problem with MSY as an indicator of the health of the fishery is that we never know what MSY is until we have over fished the stock. Then it is an uphill battle to get back to where we were before the stock was over fished. Optimum Sustainable Yield (OSY), as it is now defined in the federal Sustainable Fisheries Act, is MSY minus a precautionary fudge factor to protect the stock from over fishing.
Other indicators include the Spawning Potential Ratio (SPR), which measures the percentage of sexually mature individuals in the total catch. The SPR uses catch rates and size-frequencies to calculate a number that compares the estimated spawning biomass of the current year's fish population to an estimate of the virgin spawning biomass. When SPR drops below 0.20 the stock is considered to be in trouble. Simply put, the fishery managers don't just rely on one factor to determine if a fishery is stressed. Fisheries biology may never be an exact science, but it's the best we have to help manage our fish stocks.
The Advisory Panel recommended and the State has adopted strict gear restrictions for those fishermen targeting bottomfish. The use of nets, traps, trawls, and longlines for bottom fishing is prohibited. The possession of such gear on boats with bottomfish is also prohibited. These restrictions are very important because the use of these types of gears would greatly increase effort in the fishery and make recovery of the stocks that much more difficult.
Non-commercial bag limits is another management measure that is included in the bottomfish plan. There is a noncommercial bag limit of five (5) onaga or ehu, or a combined total of five for both. This limit allows recreational anglers to catch enough fish for subsistence use while others can obtain a commercial bottomfish fishing license if they want to catch more for commercial sale. Since one of the responsibilities of a commercial license holder is to keep a log book and file catch reports this rule helps data collection as well.
It is critical that accurate logbooks and catch reports be kept and filed by fishermen to prevent a decline in stocks and harvest. Logbooks record the day and area fished, the number of traps, fishing lines, hooks per line, net length, hours fished per method and area, and number and pounds of the various species of fish caught. Commercial fishers are required to keep a logbook and file a timely catch report, but recreational fishers should do so voluntarily. It is in their long term interest as well that fish stocks remain abundant. Without basic logbook data fisheries management is only guess work.
The bottomfish FMP also includes a vessel identification system. All vessels fishing for bottomfish must have a special vessel identification number so they can be identified from a distance while on the open ocean. The numbers must be displayed on both sides of the vessel, either near the top of the gunwales or on the superstructure and must be no less than six (6) inches high and three (3) inches wide in size.
The State has also designated certain Bottomfish Restricted Fishing Areas that comprise 20% of important habitat for spawning onaga and ehu. No bottom fishing is allowed in these areas. This measure was based on a recommendation from the Advisory Panel, which recognized that a network of fish nursery areas (no-fishing-zones) was needed around all the high islands (Hawai`i, Maui, Lana`i, Moloka`i, O`ahu, Kauai) that would be permanently off limits to fishing in order to replenish the stocks and preserve the resource for future generations. The 20% set aside is subject to a five year review.
Management Methods Not Used in the Bottomfish FMP
Seasonal closures are used to protect a specific spawning area, spawning season or critical life stage of the fish. It was not used in the Bottomfish FMP because no-fishing areas must be closed for years to be effective and the benefits of the closures can be quickly lost when fishing resumes and may lead to extra fishing effort when they are opened again.
Size limits have limited effectiveness due to discard mortality. Fish often die when caught in deep water because of injuries associated with depth changes and even when handled carefully, a certain percentage die because of the way they are hooked. When fishing levels are high, accidental mortality would be enough to dissipate any benefits of a size limit. In addition, the big mature fish that are kept are the reproductive factories of the oceans. One 8-10 year old female can generally reproduce as many eggs as 200-300 2-4 year olds. That's what makes over fishing these bigger fish so destructive. These fish are more aggressive and therefore caught by fishermen first. As the big fish disappear, so does the species' ability to quickly replenish itself.
Limited entry schemes, which require a data base, reduce or restrict the number of participants. It was not utilized as a management method in the Bottomfish FMP because there is no statutory authority for it and because bottomfish are harvested in Hawaii in small quantities by a large number of local fishermen, most of whom are fishing as recreational fishermen.
Stock Enhancement and Artificial Reefs
Hatchery programs and stock enhancement programs release young fish into the wild to build up local populations. Hatcheries must incorporate genetic material from wild stocks on a regular basis to avoid interbreeding problems. Although these programs sound like promising methods for rebuilding fish populations, they are expensive and have not generally proven effective for increasing overall abundance. While stock enhancement is not realistic for bottomfish, opakapaka and ehu may have some aquaculture potential. Hawaii has had some success with seeding certain coastal areas with hatchery-reared moi (threadfin) and mullet.
Artificial reefs provide cover from predators and substrate for food and, if properly placed, may increase total biomass; although so me are concerned that they may be acting like fish aggregation devices. Before placing any artificial reef structures, it is very important to examine a prospective area carefully; what may seem like a barren wasteland may in fact be a productive bottomfish nursery area. Derelict vessels and concrete fish habitats have been placed at selected locations on Wai`anae, Maunalua Bay and Waikiki reefs on O`ahu.
Sustainable Fisheries: are they possible?
There are very, very few sustainable fisheries. In unexploited populations of top predators such as ulua, opakapaka, onaga and ehu, the much greater fecundity of larger individuals determines that a relatively few large individuals can provide a substantial portion of the genetic input to the next generation. However, fishermen tend to target the larger fish and after a while only the small individuals remain. In heavily fished populations, nearly all the genetic input is from smaller fish, who in turn produce small fish that reproduce early. Once reproduction starts fish put their energy into producing eggs and sperm and their growth rate slows down. Eventually large individuals disappear from the population and the biomass of the entire fishery is reduced. Because of this fisheries management is evolving into an approach that sets a maximum and a minimum size. The minimum size is that which permits at least one spawning to occur before harvesting is allowed. The maximum size is that which allows the largest females with the most eggs and genetically most robust to survive and reproduce season after season. Gear restrictions protect the pre-reproductive fish; no-take nursery areas protect the largest females. Quotas and bag limits can be used if the intermediate size classes need some protection.
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